fix(clang-tidy): performance fixes applied in tests and CI (#3051)

* Initial fixes

* Whoops

* Finish clang-tidy manual fixes

* Add two missing fixes

* Revert

* Update clang-tidy

* Try to fix unreachable code error

* Move nolint comment

* Apply missing fix

* Don't override clang-tidy config

* Does this fix clang-tidy?

* Make all clang-tidy errors visible

* Add comments about NOLINTs and remove a few

* Fix typo

.clang-tidy

@@ -18,6 +18,7 @@ modernize-use-noexcept,
 modernize-use-emplace,
 modernize-use-override,
 modernize-use-using,
+*performance*,
 readability-container-size-empty,
 readability-make-member-function-const,
 readability-redundant-function-ptr-dereference,

.github/workflows/format.yml

@@ -27,7 +27,7 @@ jobs:
   clang-tidy:
     name: Clang-Tidy
     runs-on: ubuntu-latest
-    container: silkeh/clang:10
+    container: silkeh/clang:12
     steps:
     - uses: actions/checkout@v2
 
@@ -37,10 +37,10 @@ jobs:
     - name: Configure
       run: >
         cmake -S . -B build
-        -DCMAKE_CXX_CLANG_TIDY="$(which clang-tidy);--warnings-as-errors=*"
+        -DCMAKE_CXX_CLANG_TIDY="$(which clang-tidy)"
         -DDOWNLOAD_EIGEN=ON
         -DDOWNLOAD_CATCH=ON
         -DCMAKE_CXX_STANDARD=17
 
     - name: Build
-      run: cmake --build build -j 2
+      run: cmake --build build -j 2 -- --keep-going

include/pybind11/iostream.h

@@ -262,7 +262,7 @@ add_ostream_redirect(module_ m, const std::string &name = "ostream_redirect") {
     return class_<detail::OstreamRedirect>(std::move(m), name.c_str(), module_local())
         .def(init<bool, bool>(), arg("stdout") = true, arg("stderr") = true)
         .def("__enter__", &detail::OstreamRedirect::enter)
-        .def("__exit__", [](detail::OstreamRedirect &self_, args) { self_.exit(); });
+        .def("__exit__", [](detail::OstreamRedirect &self_, const args &) { self_.exit(); });
 }
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

include/pybind11/pybind11.h

@@ -1629,12 +1629,13 @@ struct enum_base {
         auto static_property = handle((PyObject *) get_internals().static_property_type);
 
         m_base.attr("__repr__") = cpp_function(
-            [](object arg) -> str {
+            [](const object &arg) -> str {
                 handle type = type::handle_of(arg);
                 object type_name = type.attr("__name__");
                 return pybind11::str("<{}.{}: {}>").format(type_name, enum_name(arg), int_(arg));
-            }, name("__repr__"), is_method(m_base)
+            },
-        );
+            name("__repr__"),
+            is_method(m_base));
 
         m_base.attr("name") = property(cpp_function(&enum_name, name("name"), is_method(m_base)));
 
@@ -1718,8 +1719,10 @@ struct enum_base {
                 PYBIND11_ENUM_OP_CONV("__ror__",  a |  b);
                 PYBIND11_ENUM_OP_CONV("__xor__",  a ^  b);
                 PYBIND11_ENUM_OP_CONV("__rxor__", a ^  b);
-                m_base.attr("__invert__") = cpp_function(
+                m_base.attr("__invert__")
-                    [](object arg) { return ~(int_(arg)); }, name("__invert__"), is_method(m_base));
+                    = cpp_function([](const object &arg) { return ~(int_(arg)); },
+                                   name("__invert__"),
+                                   is_method(m_base));
             }
         } else {
             PYBIND11_ENUM_OP_STRICT("__eq__",  int_(a).equal(int_(b)), return false);
@@ -1740,10 +1743,10 @@ struct enum_base {
         #undef PYBIND11_ENUM_OP_STRICT
 
         m_base.attr("__getstate__") = cpp_function(
-            [](object arg) { return int_(arg); }, name("__getstate__"), is_method(m_base));
+            [](const object &arg) { return int_(arg); }, name("__getstate__"), is_method(m_base));
 
         m_base.attr("__hash__") = cpp_function(
-            [](object arg) { return int_(arg); }, name("__hash__"), is_method(m_base));
+            [](const object &arg) { return int_(arg); }, name("__hash__"), is_method(m_base));
     }
 
     PYBIND11_NOINLINE void value(char const* name_, object value, const char *doc = nullptr) {

tests/local_bindings.h

@@ -1,4 +1,6 @@
 #pragma once
+#include <utility>
+
 #include "pybind11_tests.h"
 
 /// Simple class used to test py::local:
@@ -54,7 +56,7 @@ py::class_<T> bind_local(Args && ...args) {
 namespace pets {
 class Pet {
 public:
-    Pet(std::string name) : name_(name) {}
+    Pet(std::string name) : name_(std::move(name)) {}
     std::string name_;
     const std::string &name() const { return name_; }
 };

tests/object.h

@@ -81,7 +81,7 @@ public:
     }
 
     /// Move constructor
-    ref(ref &&r) : m_ptr(r.m_ptr) {
+    ref(ref &&r) noexcept : m_ptr(r.m_ptr) {
         r.m_ptr = nullptr;
 
         print_move_created(this, "with pointer", m_ptr); track_move_created((ref_tag*) this);
@@ -96,7 +96,7 @@ public:
     }
 
     /// Move another reference into the current one
-    ref& operator=(ref&& r) {
+    ref &operator=(ref &&r) noexcept {
         print_move_assigned(this, "pointer", r.m_ptr); track_move_assigned((ref_tag*) this);
 
         if (*this == r)

tests/pybind11_cross_module_tests.cpp

@@ -104,6 +104,8 @@ PYBIND11_MODULE(pybind11_cross_module_tests, m) {
     m.def("return_self", [](LocalVec *v) { return v; });
     m.def("return_copy", [](const LocalVec &v) { return LocalVec(v); });
 
+    // Changing this broke things with pygrep. TODO fix
+    // NOLINTNEXTLINE
     class Dog : public pets::Pet { public: Dog(std::string name) : Pet(name) {}; };
     py::class_<pets::Pet>(m, "Pet", py::module_local())
         .def("name", &pets::Pet::name);
@@ -126,6 +128,7 @@ PYBIND11_MODULE(pybind11_cross_module_tests, m) {
     // test_missing_header_message
     // The main module already includes stl.h, but we need to test the error message
     // which appears when this header is missing.
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("missing_header_arg", [](std::vector<float>) { });
     m.def("missing_header_return", []() { return std::vector<float>(); });
 }

tests/test_buffers.cpp

@@ -27,7 +27,7 @@ TEST_SUBMODULE(buffers, m) {
             memcpy(m_data, s.m_data, sizeof(float) * (size_t) (m_rows * m_cols));
         }
 
-        Matrix(Matrix &&s) : m_rows(s.m_rows), m_cols(s.m_cols), m_data(s.m_data) {
+        Matrix(Matrix &&s) noexcept : m_rows(s.m_rows), m_cols(s.m_cols), m_data(s.m_data) {
             print_move_created(this);
             s.m_rows = 0;
             s.m_cols = 0;
@@ -49,7 +49,7 @@ TEST_SUBMODULE(buffers, m) {
             return *this;
         }
 
-        Matrix &operator=(Matrix &&s) {
+        Matrix &operator=(Matrix &&s) noexcept {
             print_move_assigned(this, std::to_string(m_rows) + "x" + std::to_string(m_cols) + " matrix");
             if (&s != this) {
                 delete[] m_data;
@@ -79,6 +79,7 @@ TEST_SUBMODULE(buffers, m) {
     py::class_<Matrix>(m, "Matrix", py::buffer_protocol())
         .def(py::init<py::ssize_t, py::ssize_t>())
         /// Construct from a buffer
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
         .def(py::init([](py::buffer const b) {
             py::buffer_info info = b.request();
             if (info.format != py::format_descriptor<float>::format() || info.ndim != 2)
@@ -89,31 +90,31 @@ TEST_SUBMODULE(buffers, m) {
             return v;
         }))
 
-       .def("rows", &Matrix::rows)
+        .def("rows", &Matrix::rows)
-       .def("cols", &Matrix::cols)
+        .def("cols", &Matrix::cols)
 
         /// Bare bones interface
-       .def("__getitem__", [](const Matrix &m, std::pair<py::ssize_t, py::ssize_t> i) {
+        .def("__getitem__",
-            if (i.first >= m.rows() || i.second >= m.cols())
+             [](const Matrix &m, std::pair<py::ssize_t, py::ssize_t> i) {
-                throw py::index_error();
+                 if (i.first >= m.rows() || i.second >= m.cols())
-            return m(i.first, i.second);
+                     throw py::index_error();
-        })
+                 return m(i.first, i.second);
-       .def("__setitem__", [](Matrix &m, std::pair<py::ssize_t, py::ssize_t> i, float v) {
+             })
-            if (i.first >= m.rows() || i.second >= m.cols())
+        .def("__setitem__",
-                throw py::index_error();
+             [](Matrix &m, std::pair<py::ssize_t, py::ssize_t> i, float v) {
-            m(i.first, i.second) = v;
+                 if (i.first >= m.rows() || i.second >= m.cols())
-        })
+                     throw py::index_error();
-       /// Provide buffer access
+                 m(i.first, i.second) = v;
-       .def_buffer([](Matrix &m) -> py::buffer_info {
+             })
+        /// Provide buffer access
+        .def_buffer([](Matrix &m) -> py::buffer_info {
             return py::buffer_info(
                 m.data(),                               /* Pointer to buffer */
                 { m.rows(), m.cols() },                 /* Buffer dimensions */
                 { sizeof(float) * size_t(m.cols()),     /* Strides (in bytes) for each index */
                   sizeof(float) }
             );
-        })
+        });
-        ;
-
 
     // test_inherited_protocol
     class SquareMatrix : public Matrix {
@@ -208,7 +209,5 @@ TEST_SUBMODULE(buffers, m) {
         })
         ;
 
-    m.def("get_buffer_info", [](py::buffer buffer) {
+    m.def("get_buffer_info", [](const py::buffer &buffer) { return buffer.request(); });
-        return buffer.request();
-    });
 }

tests/test_builtin_casters.cpp

@@ -30,7 +30,11 @@ class type_caster<ConstRefCasted> {
   // cast operator.
   bool load(handle, bool) { return true; }
 
-  operator ConstRefCasted&&() { value = {1}; return std::move(value); }
+  operator ConstRefCasted &&() {
+      value = {1};
+      // NOLINTNEXTLINE(performance-move-const-arg)
+      return std::move(value);
+  }
   operator ConstRefCasted&() { value = {2}; return value; }
   operator ConstRefCasted*() { value = {3}; return &value; }
 
@@ -101,6 +105,7 @@ TEST_SUBMODULE(builtin_casters, m) {
 
     // test_bytes_to_string
     m.def("strlen", [](char *s) { return strlen(s); });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("string_length", [](std::string s) { return s.length(); });
 
 #ifdef PYBIND11_HAS_U8STRING
@@ -146,6 +151,7 @@ TEST_SUBMODULE(builtin_casters, m) {
     m.def("int_passthrough_noconvert", [](int arg) { return arg; }, py::arg{}.noconvert());
 
     // test_tuple
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("pair_passthrough", [](std::pair<bool, std::string> input) {
         return std::make_pair(input.second, input.first);
     }, "Return a pair in reversed order");
@@ -177,10 +183,13 @@ TEST_SUBMODULE(builtin_casters, m) {
 
     // test_none_deferred
     m.def("defer_none_cstring", [](char *) { return false; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("defer_none_cstring", [](py::none) { return true; });
     m.def("defer_none_custom", [](UserType *) { return false; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("defer_none_custom", [](py::none) { return true; });
     m.def("nodefer_none_void", [](void *) { return true; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("nodefer_none_void", [](py::none) { return false; });
 
     // test_void_caster
@@ -231,6 +240,7 @@ TEST_SUBMODULE(builtin_casters, m) {
     }, "copy"_a);
 
     m.def("refwrap_iiw", [](const IncType &w) { return w.value(); });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("refwrap_call_iiw", [](IncType &w, py::function f) {
         py::list l;
         l.append(f(std::ref(w)));

tests/test_callbacks.cpp

@@ -17,8 +17,8 @@ int dummy_function(int i) { return i + 1; }
 
 TEST_SUBMODULE(callbacks, m) {
     // test_callbacks, test_function_signatures
-    m.def("test_callback1", [](py::object func) { return func(); });
+    m.def("test_callback1", [](const py::object &func) { return func(); });
-    m.def("test_callback2", [](py::object func) { return func("Hello", 'x', true, 5); });
+    m.def("test_callback2", [](const py::object &func) { return func("Hello", 'x', true, 5); });
     m.def("test_callback3", [](const std::function<int(int)> &func) {
         return "func(43) = " + std::to_string(func(43)); });
     m.def("test_callback4", []() -> std::function<int(int)> { return [](int i) { return i+1; }; });
@@ -27,51 +27,48 @@ TEST_SUBMODULE(callbacks, m) {
     });
 
     // test_keyword_args_and_generalized_unpacking
-    m.def("test_tuple_unpacking", [](py::function f) {
+    m.def("test_tuple_unpacking", [](const py::function &f) {
         auto t1 = py::make_tuple(2, 3);
         auto t2 = py::make_tuple(5, 6);
         return f("positional", 1, *t1, 4, *t2);
     });
 
-    m.def("test_dict_unpacking", [](py::function f) {
+    m.def("test_dict_unpacking", [](const py::function &f) {
         auto d1 = py::dict("key"_a="value", "a"_a=1);
         auto d2 = py::dict();
         auto d3 = py::dict("b"_a=2);
         return f("positional", 1, **d1, **d2, **d3);
     });
 
-    m.def("test_keyword_args", [](py::function f) {
+    m.def("test_keyword_args", [](const py::function &f) { return f("x"_a = 10, "y"_a = 20); });
-        return f("x"_a=10, "y"_a=20);
-    });
 
-    m.def("test_unpacking_and_keywords1", [](py::function f) {
+    m.def("test_unpacking_and_keywords1", [](const py::function &f) {
         auto args = py::make_tuple(2);
         auto kwargs = py::dict("d"_a=4);
         return f(1, *args, "c"_a=3, **kwargs);
     });
 
-    m.def("test_unpacking_and_keywords2", [](py::function f) {
+    m.def("test_unpacking_and_keywords2", [](const py::function &f) {
         auto kwargs1 = py::dict("a"_a=1);
         auto kwargs2 = py::dict("c"_a=3, "d"_a=4);
         return f("positional", *py::make_tuple(1), 2, *py::make_tuple(3, 4), 5,
                  "key"_a="value", **kwargs1, "b"_a=2, **kwargs2, "e"_a=5);
     });
 
-    m.def("test_unpacking_error1", [](py::function f) {
+    m.def("test_unpacking_error1", [](const py::function &f) {
         auto kwargs = py::dict("x"_a=3);
         return f("x"_a=1, "y"_a=2, **kwargs); // duplicate ** after keyword
     });
 
-    m.def("test_unpacking_error2", [](py::function f) {
+    m.def("test_unpacking_error2", [](const py::function &f) {
         auto kwargs = py::dict("x"_a=3);
         return f(**kwargs, "x"_a=1); // duplicate keyword after **
     });
 
-    m.def("test_arg_conversion_error1", [](py::function f) {
+    m.def("test_arg_conversion_error1",
-        f(234, UnregisteredType(), "kw"_a=567);
+          [](const py::function &f) { f(234, UnregisteredType(), "kw"_a = 567); });
-    });
 
-    m.def("test_arg_conversion_error2", [](py::function f) {
+    m.def("test_arg_conversion_error2", [](const py::function &f) {
         f(234, "expected_name"_a=UnregisteredType(), "kw"_a=567);
     });
 
@@ -80,7 +77,7 @@ TEST_SUBMODULE(callbacks, m) {
         Payload() { print_default_created(this); }
         ~Payload() { print_destroyed(this); }
         Payload(const Payload &) { print_copy_created(this); }
-        Payload(Payload &&) { print_move_created(this); }
+        Payload(Payload &&) noexcept { print_move_created(this); }
     };
     // Export the payload constructor statistics for testing purposes:
     m.def("payload_cstats", &ConstructorStats::get<Payload>);
@@ -127,7 +124,8 @@ TEST_SUBMODULE(callbacks, m) {
         virtual ~AbstractBase() {};  // NOLINT(modernize-use-equals-default)
         virtual unsigned int func() = 0;
     };
-    m.def("func_accepting_func_accepting_base", [](std::function<double(AbstractBase&)>) { });
+    m.def("func_accepting_func_accepting_base",
+          [](const std::function<double(AbstractBase &)> &) {});
 
     struct MovableObject {
         bool valid = true;
@@ -135,8 +133,8 @@ TEST_SUBMODULE(callbacks, m) {
         MovableObject() = default;
         MovableObject(const MovableObject &) = default;
         MovableObject &operator=(const MovableObject &) = default;
-        MovableObject(MovableObject &&o) : valid(o.valid) { o.valid = false; }
+        MovableObject(MovableObject &&o) noexcept : valid(o.valid) { o.valid = false; }
-        MovableObject &operator=(MovableObject &&o) {
+        MovableObject &operator=(MovableObject &&o) noexcept {
             valid = o.valid;
             o.valid = false;
             return *this;
@@ -145,7 +143,7 @@ TEST_SUBMODULE(callbacks, m) {
     py::class_<MovableObject>(m, "MovableObject");
 
     // test_movable_object
-    m.def("callback_with_movable", [](std::function<void(MovableObject &)> f) {
+    m.def("callback_with_movable", [](const std::function<void(MovableObject &)> &f) {
         auto x = MovableObject();
         f(x); // lvalue reference shouldn't move out object
         return x.valid; // must still return `true`
@@ -159,7 +157,7 @@ TEST_SUBMODULE(callbacks, m) {
 
     // test async Python callbacks
     using callback_f = std::function<void(int)>;
-    m.def("test_async_callback", [](callback_f f, py::list work) {
+    m.def("test_async_callback", [](const callback_f &f, const py::list &work) {
         // make detached thread that calls `f` with piece of work after a little delay
         auto start_f = [f](int j) {
             auto invoke_f = [f, j] {
@@ -175,7 +173,7 @@ TEST_SUBMODULE(callbacks, m) {
             start_f(py::cast<int>(i));
     });
 
-    m.def("callback_num_times", [](py::function f, std::size_t num) {
+    m.def("callback_num_times", [](const py::function &f, std::size_t num) {
         for (std::size_t i = 0; i < num; i++) {
             f();
         }

tests/test_class.cpp

@@ -19,6 +19,8 @@
 #include "local_bindings.h"
 #include <pybind11/stl.h>
 
+#include <utility>
+
 #if defined(_MSC_VER)
 #  pragma warning(disable: 4324) // warning C4324: structure was padded due to alignment specifier
 #endif
@@ -129,6 +131,7 @@ TEST_SUBMODULE(class_, m) {
     m.def("return_none", []() -> BaseClass* { return nullptr; });
 
     // test_isinstance
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("check_instances", [](py::list l) {
         return py::make_tuple(
             py::isinstance<py::tuple>(l[0]),
@@ -155,17 +158,13 @@ TEST_SUBMODULE(class_, m) {
             return py::type::of<Invalid>();
     });
 
-    m.def("get_type_of", [](py::object ob) {
+    m.def("get_type_of", [](py::object ob) { return py::type::of(std::move(ob)); });
-        return py::type::of(ob);
-    });
 
     m.def("get_type_classic", [](py::handle h) {
         return h.get_type();
     });
 
-    m.def("as_type", [](py::object ob) {
+    m.def("as_type", [](const py::object &ob) { return py::type(ob); });
-        return py::type(ob);
-    });
 
     // test_mismatched_holder
     struct MismatchBase1 { };
@@ -219,6 +218,7 @@ TEST_SUBMODULE(class_, m) {
     py::implicitly_convertible<UserType, ConvertibleFromUserType>();
 
     m.def("implicitly_convert_argument", [](const ConvertibleFromUserType &r) { return r.i; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("implicitly_convert_variable", [](py::object o) {
         // `o` is `UserType` and `r` is a reference to a temporary created by implicit
         // conversion. This is valid when called inside a bound function because the temp
@@ -397,6 +397,7 @@ TEST_SUBMODULE(class_, m) {
     struct StringWrapper { std::string str; };
     m.def("test_error_after_conversions", [](int) {});
     m.def("test_error_after_conversions",
+          // NOLINTNEXTLINE(performance-unnecessary-value-param)
           [](StringWrapper) -> NotRegistered { return {}; });
     py::class_<StringWrapper>(m, "StringWrapper").def(py::init<std::string>());
     py::implicitly_convertible<std::string, StringWrapper>();
@@ -461,19 +462,20 @@ TEST_SUBMODULE(class_, m) {
     struct OtherDuplicate {};
     struct DuplicateNested {};
     struct OtherDuplicateNested {};
-    m.def("register_duplicate_class_name", [](py::module_ m) {
+
+    m.def("register_duplicate_class_name", [](const py::module_ &m) {
         py::class_<Duplicate>(m, "Duplicate");
         py::class_<OtherDuplicate>(m, "Duplicate");
     });
-    m.def("register_duplicate_class_type", [](py::module_ m) {
+    m.def("register_duplicate_class_type", [](const py::module_ &m) {
         py::class_<OtherDuplicate>(m, "OtherDuplicate");
         py::class_<OtherDuplicate>(m, "YetAnotherDuplicate");
     });
-    m.def("register_duplicate_nested_class_name", [](py::object gt) {
+    m.def("register_duplicate_nested_class_name", [](const py::object &gt) {
         py::class_<DuplicateNested>(gt, "DuplicateNested");
         py::class_<OtherDuplicateNested>(gt, "DuplicateNested");
     });
-    m.def("register_duplicate_nested_class_type", [](py::object gt) {
+    m.def("register_duplicate_nested_class_type", [](const py::object &gt) {
         py::class_<OtherDuplicateNested>(gt, "OtherDuplicateNested");
         py::class_<OtherDuplicateNested>(gt, "YetAnotherDuplicateNested");
     });

tests/test_constants_and_functions.cpp

@@ -34,7 +34,7 @@ py::bytes return_bytes() {
     return std::string(data, 4);
 }
 
-std::string print_bytes(py::bytes bytes) {
+std::string print_bytes(const py::bytes &bytes) {
     std::string ret = "bytes[";
     const auto value = static_cast<std::string>(bytes);
     for (size_t i = 0; i < value.length(); ++i) {
@@ -146,8 +146,13 @@ TEST_SUBMODULE(constants_and_functions, m) {
         LargeCapture capture;  // VS 2015's MSVC is acting up if we create the array here
         m.def("should_raise", [capture](int) { return capture.zeros[9] + 33; }, py::kw_only(), py::arg());
     });
-    m.def("register_with_raising_repr", [](py::module_ m, py::object default_value) {
+    m.def("register_with_raising_repr", [](py::module_ m, const py::object &default_value) {
-        m.def("should_raise", [](int, int, py::object) { return 42; }, "some docstring",
+        m.def(
-              py::arg_v("x", 42), py::arg_v("y", 42, "<the answer>"), py::arg_v("z", default_value));
+            "should_raise",
+            [](int, int, const py::object &) { return 42; },
+            "some docstring",
+            py::arg_v("x", 42),
+            py::arg_v("y", 42, "<the answer>"),
+            py::arg_v("z", default_value));
     });
 }

tests/test_copy_move.cpp

@@ -37,9 +37,16 @@ template <> lacking_move_ctor empty<lacking_move_ctor>::instance_ = {};
 class MoveOnlyInt {
 public:
     MoveOnlyInt() { print_default_created(this); }
-    MoveOnlyInt(int v) : value{std::move(v)} { print_created(this, value); }
+    MoveOnlyInt(int v) : value{v} { print_created(this, value); }
-    MoveOnlyInt(MoveOnlyInt &&m) { print_move_created(this, m.value); std::swap(value, m.value); }
+    MoveOnlyInt(MoveOnlyInt &&m) noexcept {
-    MoveOnlyInt &operator=(MoveOnlyInt &&m) { print_move_assigned(this, m.value); std::swap(value, m.value); return *this; }
+        print_move_created(this, m.value);
+        std::swap(value, m.value);
+    }
+    MoveOnlyInt &operator=(MoveOnlyInt &&m) noexcept {
+        print_move_assigned(this, m.value);
+        std::swap(value, m.value);
+        return *this;
+    }
     MoveOnlyInt(const MoveOnlyInt &) = delete;
     MoveOnlyInt &operator=(const MoveOnlyInt &) = delete;
     ~MoveOnlyInt() { print_destroyed(this); }
@@ -49,9 +56,16 @@ public:
 class MoveOrCopyInt {
 public:
     MoveOrCopyInt() { print_default_created(this); }
-    MoveOrCopyInt(int v) : value{std::move(v)} { print_created(this, value); }
+    MoveOrCopyInt(int v) : value{v} { print_created(this, value); }
-    MoveOrCopyInt(MoveOrCopyInt &&m) { print_move_created(this, m.value); std::swap(value, m.value); }
+    MoveOrCopyInt(MoveOrCopyInt &&m) noexcept {
-    MoveOrCopyInt &operator=(MoveOrCopyInt &&m) { print_move_assigned(this, m.value); std::swap(value, m.value); return *this; }
+        print_move_created(this, m.value);
+        std::swap(value, m.value);
+    }
+    MoveOrCopyInt &operator=(MoveOrCopyInt &&m) noexcept {
+        print_move_assigned(this, m.value);
+        std::swap(value, m.value);
+        return *this;
+    }
     MoveOrCopyInt(const MoveOrCopyInt &c) { print_copy_created(this, c.value); value = c.value; }
     MoveOrCopyInt &operator=(const MoveOrCopyInt &c) { print_copy_assigned(this, c.value); value = c.value; return *this; }
     ~MoveOrCopyInt() { print_destroyed(this); }
@@ -61,7 +75,7 @@ public:
 class CopyOnlyInt {
 public:
     CopyOnlyInt() { print_default_created(this); }
-    CopyOnlyInt(int v) : value{std::move(v)} { print_created(this, value); }
+    CopyOnlyInt(int v) : value{v} { print_created(this, value); }
     CopyOnlyInt(const CopyOnlyInt &c) { print_copy_created(this, c.value); value = c.value; }
     CopyOnlyInt &operator=(const CopyOnlyInt &c) { print_copy_assigned(this, c.value); value = c.value; return *this; }
     ~CopyOnlyInt() { print_destroyed(this); }
@@ -111,6 +125,7 @@ TEST_SUBMODULE(copy_move_policies, m) {
                     py::return_value_policy::move);
 
     // test_move_and_copy_casts
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("move_and_copy_casts", [](py::object o) {
         int r = 0;
         r += py::cast<MoveOrCopyInt>(o).value; /* moves */
@@ -126,7 +141,9 @@ TEST_SUBMODULE(copy_move_policies, m) {
 
     // test_move_and_copy_loads
     m.def("move_only", [](MoveOnlyInt m) { return m.value; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("move_or_copy", [](MoveOrCopyInt m) { return m.value; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("copy_only", [](CopyOnlyInt m) { return m.value; });
     m.def("move_pair", [](std::pair<MoveOnlyInt, MoveOrCopyInt> p) {
         return p.first.value + p.second.value;

tests/test_custom_type_casters.cpp

@@ -67,9 +67,12 @@ public:
     DestructionTester() { print_default_created(this); }
     ~DestructionTester() { print_destroyed(this); }
     DestructionTester(const DestructionTester &) { print_copy_created(this); }
-    DestructionTester(DestructionTester &&) { print_move_created(this); }
+    DestructionTester(DestructionTester &&) noexcept { print_move_created(this); }
     DestructionTester &operator=(const DestructionTester &) { print_copy_assigned(this); return *this; }
-    DestructionTester &operator=(DestructionTester &&) { print_move_assigned(this); return *this; }
+    DestructionTester &operator=(DestructionTester &&) noexcept {
+        print_move_assigned(this);
+        return *this;
+    }
 };
 namespace pybind11 { namespace detail {
 template <> struct type_caster<DestructionTester> {
@@ -94,7 +97,11 @@ TEST_SUBMODULE(custom_type_casters, m) {
     class ArgInspector {
     public:
         ArgInspector1 f(ArgInspector1 a, ArgAlwaysConverts) { return a; }
-        std::string g(ArgInspector1 a, const ArgInspector1 &b, int c, ArgInspector2 *d, ArgAlwaysConverts) {
+        std::string g(const ArgInspector1 &a,
+                      const ArgInspector1 &b,
+                      int c,
+                      ArgInspector2 *d,
+                      ArgAlwaysConverts) {
             return a.arg + "\n" + b.arg + "\n" + std::to_string(c) + "\n" + d->arg;
         }
         static ArgInspector2 h(ArgInspector2 a, ArgAlwaysConverts) { return a; }
@@ -106,8 +113,14 @@ TEST_SUBMODULE(custom_type_casters, m) {
         .def("g", &ArgInspector::g, "a"_a.noconvert(), "b"_a, "c"_a.noconvert()=13, "d"_a=ArgInspector2(), py::arg() = ArgAlwaysConverts())
         .def_static("h", &ArgInspector::h, py::arg{}.noconvert(), py::arg() = ArgAlwaysConverts())
         ;
-    m.def("arg_inspect_func", [](ArgInspector2 a, ArgInspector1 b, ArgAlwaysConverts) { return a.arg + "\n" + b.arg; },
+    m.def(
-            py::arg{}.noconvert(false), py::arg_v(nullptr, ArgInspector1()).noconvert(true), py::arg() = ArgAlwaysConverts());
+        "arg_inspect_func",
+        [](const ArgInspector2 &a, const ArgInspector1 &b, ArgAlwaysConverts) {
+            return a.arg + "\n" + b.arg;
+        },
+        py::arg{}.noconvert(false),
+        py::arg_v(nullptr, ArgInspector1()).noconvert(true),
+        py::arg() = ArgAlwaysConverts());
 
     m.def("floats_preferred", [](double f) { return 0.5 * f; }, "f"_a);
     m.def("floats_only", [](double f) { return 0.5 * f; }, "f"_a.noconvert());

tests/test_eigen.cpp

@@ -54,8 +54,7 @@ void reset_refs() {
 }
 
 // Returns element 2,1 from a matrix (used to test copy/nocopy)
-double get_elem(Eigen::Ref<const Eigen::MatrixXd> m) { return m(2, 1); };
+double get_elem(const Eigen::Ref<const Eigen::MatrixXd> &m) { return m(2, 1); };
-
 
 // Returns a matrix with 10*r + 100*c added to each matrix element (to help test that the matrix
 // reference is referencing rows/columns correctly).
@@ -94,14 +93,16 @@ TEST_SUBMODULE(eigen, m) {
     m.def("double_complex", [](const Eigen::VectorXcf &x) -> Eigen::VectorXcf { return 2.0f * x; });
     m.def("double_threec", [](py::EigenDRef<Eigen::Vector3f> x) { x *= 2; });
     m.def("double_threer", [](py::EigenDRef<Eigen::RowVector3f> x) { x *= 2; });
-    m.def("double_mat_cm", [](Eigen::MatrixXf x) -> Eigen::MatrixXf { return 2.0f * x; });
+    m.def("double_mat_cm", [](const Eigen::MatrixXf &x) -> Eigen::MatrixXf { return 2.0f * x; });
-    m.def("double_mat_rm", [](DenseMatrixR x) -> DenseMatrixR { return 2.0f * x; });
+    m.def("double_mat_rm", [](const DenseMatrixR &x) -> DenseMatrixR { return 2.0f * x; });
 
     // test_eigen_ref_to_python
     // Different ways of passing via Eigen::Ref; the first and second are the Eigen-recommended
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("cholesky1", [](Eigen::Ref<MatrixXdR> x) -> Eigen::MatrixXd { return x.llt().matrixL(); });
     m.def("cholesky2", [](const Eigen::Ref<const MatrixXdR> &x) -> Eigen::MatrixXd { return x.llt().matrixL(); });
     m.def("cholesky3", [](const Eigen::Ref<MatrixXdR> &x) -> Eigen::MatrixXd { return x.llt().matrixL(); });
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("cholesky4", [](Eigen::Ref<const MatrixXdR> x) -> Eigen::MatrixXd { return x.llt().matrixL(); });
 
     // test_eigen_ref_mutators
@@ -247,8 +248,11 @@ TEST_SUBMODULE(eigen, m) {
     m.def("fixed_copy_r", [](const FixedMatrixR &m) -> FixedMatrixR { return m; });
     m.def("fixed_copy_c", [](const FixedMatrixC &m) -> FixedMatrixC { return m; });
     // test_mutator_descriptors
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("fixed_mutator_r", [](Eigen::Ref<FixedMatrixR>) {});
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("fixed_mutator_c", [](Eigen::Ref<FixedMatrixC>) {});
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("fixed_mutator_a", [](py::EigenDRef<FixedMatrixC>) {});
     // test_dense
     m.def("dense_r", [mat]() -> DenseMatrixR { return DenseMatrixR(mat); });
@@ -280,6 +284,7 @@ TEST_SUBMODULE(eigen, m) {
     // that would allow copying (if types or strides don't match) for comparison:
     m.def("get_elem", &get_elem);
     // Now this alternative that calls the tells pybind to fail rather than copy:
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("get_elem_nocopy", [](Eigen::Ref<const Eigen::MatrixXd> m) -> double { return get_elem(m); },
             py::arg{}.noconvert());
     // Also test a row-major-only no-copy const ref:
@@ -295,13 +300,16 @@ TEST_SUBMODULE(eigen, m) {
 
     // test_issue1105
     // Issue #1105: when converting from a numpy two-dimensional (Nx1) or (1xN) value into a dense
-    // eigen Vector or RowVector, the argument would fail to load because the numpy copy would fail:
+    // eigen Vector or RowVector, the argument would fail to load because the numpy copy would
-    // numpy won't broadcast a Nx1 into a 1-dimensional vector.
+    // fail: numpy won't broadcast a Nx1 into a 1-dimensional vector. NOLINTNEXTLINE
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("iss1105_col", [](Eigen::VectorXd) { return true; });
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("iss1105_row", [](Eigen::RowVectorXd) { return true; });
 
     // test_named_arguments
     // Make sure named arguments are working properly:
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("matrix_multiply", [](const py::EigenDRef<const Eigen::MatrixXd> A, const py::EigenDRef<const Eigen::MatrixXd> B)
             -> Eigen::MatrixXd {
         if (A.cols() != B.rows()) throw std::domain_error("Nonconformable matrices!");
@@ -318,6 +326,7 @@ TEST_SUBMODULE(eigen, m) {
     // In case of a failure (the caster's temp array does not live long enough), creating
     // a new array (np.ones(10)) increases the chances that the temp array will be garbage
     // collected and/or that its memory will be overridden with different values.
+    // NOLINTNEXTLINE (performance-unnecessary-value-param)
     m.def("get_elem_direct", [](Eigen::Ref<const Eigen::VectorXd> v) {
         py::module_::import("numpy").attr("ones")(10);
         return v(5);

tests/test_embed/test_interpreter.cpp

@@ -8,16 +8,17 @@
 
 #include <catch.hpp>
 
-#include <thread>
 #include <fstream>
 #include <functional>
+#include <thread>
+#include <utility>
 
 namespace py = pybind11;
 using namespace py::literals;
 
 class Widget {
 public:
-    Widget(std::string message) : message(message) { }
+    Widget(std::string message) : message(std::move(message)) {}
     virtual ~Widget() = default;
 
     std::string the_message() const { return message; }

tests/test_eval.cpp

@@ -9,7 +9,9 @@
 
 
 #include <pybind11/eval.h>
+
 #include "pybind11_tests.h"
+#include <utility>
 
 TEST_SUBMODULE(eval_, m) {
     // test_evals
@@ -67,7 +69,7 @@ TEST_SUBMODULE(eval_, m) {
         int val_out;
         local["call_test2"] = py::cpp_function([&](int value) { val_out = value; });
 
-        auto result = py::eval_file(filename, global, local);
+        auto result = py::eval_file(std::move(filename), global, local);
         return val_out == 43 && result.is_none();
     });
 

tests/test_exceptions.cpp

@@ -8,7 +8,9 @@
 */
 
 #include "test_exceptions.h"
+
 #include "pybind11_tests.h"
+#include <utility>
 
 // A type that should be raised as an exception in Python
 class MyException : public std::exception {
@@ -199,6 +201,8 @@ TEST_SUBMODULE(exceptions, m) {
         throw py::error_already_set();
     });
 
+    // Changing this broke things. Don't know why
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("python_call_in_destructor", [](py::dict d) {
         try {
             PythonCallInDestructor set_dict_in_destructor(d);
@@ -210,21 +214,23 @@ TEST_SUBMODULE(exceptions, m) {
         return false;
     });
 
-    m.def("python_alreadyset_in_destructor", [](py::str s) {
+    m.def("python_alreadyset_in_destructor", [](const py::str &s) {
         PythonAlreadySetInDestructor alreadyset_in_destructor(s);
         return true;
     });
 
     // test_nested_throws
-    m.def("try_catch", [m](py::object exc_type, py::function f, py::args args) {
+    m.def("try_catch",
-        try { f(*args); }
+          [m](const py::object &exc_type, const py::function &f, const py::args &args) {
-        catch (py::error_already_set &ex) {
+              try {
-            if (ex.matches(exc_type))
+                  f(*args);
-                py::print(ex.what());
+              } catch (py::error_already_set &ex) {
-            else
+                  if (ex.matches(exc_type))
-                throw;
+                      py::print(ex.what());
-        }
+                  else
-    });
+                      throw;
+              }
+          });
 
     // Test repr that cannot be displayed
     m.def("simple_bool_passthrough", [](bool x) {return x;});

tests/test_factory_constructors.cpp

@@ -8,10 +8,11 @@
     BSD-style license that can be found in the LICENSE file.
 */
 
-#include "pybind11_tests.h"
 #include "constructor_stats.h"
+#include "pybind11_tests.h"
 #include <cmath>
 #include <new>
+#include <utility>
 
 // Classes for testing python construction via C++ factory function:
 // Not publicly constructible, copyable, or movable:
@@ -35,8 +36,15 @@ class TestFactory2 {
     TestFactory2(int v) : value(std::to_string(v)) { print_created(this, value); }
     TestFactory2(std::string v) : value(std::move(v)) { print_created(this, value); }
 public:
-    TestFactory2(TestFactory2 &&m) { value = std::move(m.value); print_move_created(this); }
+    TestFactory2(TestFactory2 &&m) noexcept {
-    TestFactory2 &operator=(TestFactory2 &&m) { value = std::move(m.value); print_move_assigned(this); return *this; }
+        value = std::move(m.value);
+        print_move_created(this);
+    }
+    TestFactory2 &operator=(TestFactory2 &&m) noexcept {
+        value = std::move(m.value);
+        print_move_assigned(this);
+        return *this;
+    }
     std::string value;
     ~TestFactory2() { print_destroyed(this); }
 };
@@ -48,8 +56,15 @@ protected:
     TestFactory3(int v) : value(std::to_string(v)) { print_created(this, value); }
 public:
     TestFactory3(std::string v) : value(std::move(v)) { print_created(this, value); }
-    TestFactory3(TestFactory3 &&m) { value = std::move(m.value); print_move_created(this); }
+    TestFactory3(TestFactory3 &&m) noexcept {
-    TestFactory3 &operator=(TestFactory3 &&m) { value = std::move(m.value); print_move_assigned(this); return *this; }
+        value = std::move(m.value);
+        print_move_created(this);
+    }
+    TestFactory3 &operator=(TestFactory3 &&m) noexcept {
+        value = std::move(m.value);
+        print_move_assigned(this);
+        return *this;
+    }
     std::string value;
     virtual ~TestFactory3() { print_destroyed(this); }
 };
@@ -73,7 +88,11 @@ protected:
     bool alias = false;
 public:
     TestFactory6(int i) : value{i} { print_created(this, i); }
-    TestFactory6(TestFactory6 &&f) { print_move_created(this); value = f.value; alias = f.alias; }
+    TestFactory6(TestFactory6 &&f) noexcept {
+        print_move_created(this);
+        value = f.value;
+        alias = f.alias;
+    }
     TestFactory6(const TestFactory6 &f) { print_copy_created(this); value = f.value; alias = f.alias; }
     virtual ~TestFactory6() { print_destroyed(this); }
     virtual int get() { return value; }
@@ -85,7 +104,7 @@ public:
     // when an alias is needed:
     PyTF6(TestFactory6 &&base) : TestFactory6(std::move(base)) { alias = true; print_created(this, "move", value); }
     PyTF6(int i) : TestFactory6(i) { alias = true; print_created(this, i); }
-    PyTF6(PyTF6 &&f) : TestFactory6(std::move(f)) { print_move_created(this); }
+    PyTF6(PyTF6 &&f) noexcept : TestFactory6(std::move(f)) { print_move_created(this); }
     PyTF6(const PyTF6 &f) : TestFactory6(f) { print_copy_created(this); }
     PyTF6(std::string s) : TestFactory6((int) s.size()) { alias = true; print_created(this, s); }
     ~PyTF6() override { print_destroyed(this); }
@@ -98,7 +117,11 @@ protected:
     bool alias = false;
 public:
     TestFactory7(int i) : value{i} { print_created(this, i); }
-    TestFactory7(TestFactory7 &&f) { print_move_created(this); value = f.value; alias = f.alias; }
+    TestFactory7(TestFactory7 &&f) noexcept {
+        print_move_created(this);
+        value = f.value;
+        alias = f.alias;
+    }
     TestFactory7(const TestFactory7 &f) { print_copy_created(this); value = f.value; alias = f.alias; }
     virtual ~TestFactory7() { print_destroyed(this); }
     virtual int get() { return value; }
@@ -107,7 +130,7 @@ public:
 class PyTF7 : public TestFactory7 {
 public:
     PyTF7(int i) : TestFactory7(i) { alias = true; print_created(this, i); }
-    PyTF7(PyTF7 &&f) : TestFactory7(std::move(f)) { print_move_created(this); }
+    PyTF7(PyTF7 &&f) noexcept : TestFactory7(std::move(f)) { print_move_created(this); }
     PyTF7(const PyTF7 &f) : TestFactory7(f) { print_copy_created(this); }
     ~PyTF7() override { print_destroyed(this); }
     int get() override { PYBIND11_OVERRIDE(int, TestFactory7, get, /*no args*/); }
@@ -122,7 +145,9 @@ public:
     // Holder:
     static std::unique_ptr<TestFactory1> construct1(int a) { return std::unique_ptr<TestFactory1>(new TestFactory1(a)); }
     // pointer again
-    static TestFactory1 *construct1_string(std::string a) { return new TestFactory1(a); }
+    static TestFactory1 *construct1_string(std::string a) {
+        return new TestFactory1(std::move(a));
+    }
 
     // Moveable type:
     // pointer:
@@ -130,7 +155,7 @@ public:
     // holder:
     static std::unique_ptr<TestFactory2> construct2(int a) { return std::unique_ptr<TestFactory2>(new TestFactory2(a)); }
     // by value moving:
-    static TestFactory2 construct2(std::string a) { return TestFactory2(a); }
+    static TestFactory2 construct2(std::string a) { return TestFactory2(std::move(a)); }
 
     // shared_ptr holder type:
     // pointer:
@@ -173,10 +198,11 @@ TEST_SUBMODULE(factory_constructors, m) {
         ;
     py::class_<TestFactory2>(m, "TestFactory2")
         .def(py::init([](pointer_tag, int v) { return TestFactoryHelper::construct2(v); }))
-        .def(py::init([](unique_ptr_tag, std::string v) { return TestFactoryHelper::construct2(v); }))
+        .def(py::init([](unique_ptr_tag, std::string v) {
+            return TestFactoryHelper::construct2(std::move(v));
+        }))
         .def(py::init([](move_tag) { return TestFactoryHelper::construct2(); }))
-        .def_readwrite("value", &TestFactory2::value)
+        .def_readwrite("value", &TestFactory2::value);
-        ;
 
     // Stateful & reused:
     int c = 1;
@@ -188,7 +214,9 @@ TEST_SUBMODULE(factory_constructors, m) {
         .def(py::init([](pointer_tag, int v) { return TestFactoryHelper::construct3(v); }))
         .def(py::init([](shared_ptr_tag) { return TestFactoryHelper::construct3(); }));
     ignoreOldStyleInitWarnings([&pyTestFactory3]() {
-        pyTestFactory3.def("__init__", [](TestFactory3 &self, std::string v) { new (&self) TestFactory3(v); }); // placement-new ctor
+        pyTestFactory3.def("__init__", [](TestFactory3 &self, std::string v) {
+            new (&self) TestFactory3(std::move(v));
+        }); // placement-new ctor
     });
     pyTestFactory3
         // factories returning a derived type:
@@ -219,52 +247,54 @@ TEST_SUBMODULE(factory_constructors, m) {
     py::class_<TestFactory6, PyTF6>(m, "TestFactory6")
         .def(py::init([](base_tag, int i) { return TestFactory6(i); }))
         .def(py::init([](alias_tag, int i) { return PyTF6(i); }))
-        .def(py::init([](alias_tag, std::string s) { return PyTF6(s); }))
+        .def(py::init([](alias_tag, std::string s) { return PyTF6(std::move(s)); }))
         .def(py::init([](alias_tag, pointer_tag, int i) { return new PyTF6(i); }))
         .def(py::init([](base_tag, pointer_tag, int i) { return new TestFactory6(i); }))
-        .def(py::init([](base_tag, alias_tag, pointer_tag, int i) { return (TestFactory6 *) new PyTF6(i); }))
+        .def(py::init(
+            [](base_tag, alias_tag, pointer_tag, int i) { return (TestFactory6 *) new PyTF6(i); }))
 
         .def("get", &TestFactory6::get)
         .def("has_alias", &TestFactory6::has_alias)
 
-        .def_static("get_cstats", &ConstructorStats::get<TestFactory6>, py::return_value_policy::reference)
+        .def_static(
-        .def_static("get_alias_cstats", &ConstructorStats::get<PyTF6>, py::return_value_policy::reference)
+            "get_cstats", &ConstructorStats::get<TestFactory6>, py::return_value_policy::reference)
-        ;
+        .def_static(
+            "get_alias_cstats", &ConstructorStats::get<PyTF6>, py::return_value_policy::reference);
 
     // test_init_factory_dual
     // Separate alias constructor testing
     py::class_<TestFactory7, PyTF7, std::shared_ptr<TestFactory7>>(m, "TestFactory7")
-        .def(py::init(
+        .def(py::init([](int i) { return TestFactory7(i); }, [](int i) { return PyTF7(i); }))
-            [](int i) { return TestFactory7(i); },
+        .def(py::init([](pointer_tag, int i) { return new TestFactory7(i); },
-            [](int i) { return PyTF7(i); }))
+                      [](pointer_tag, int i) { return new PyTF7(i); }))
-        .def(py::init(
+        .def(py::init([](mixed_tag, int i) { return new TestFactory7(i); },
-            [](pointer_tag, int i) { return new TestFactory7(i); },
+                      [](mixed_tag, int i) { return PyTF7(i); }))
-            [](pointer_tag, int i) { return new PyTF7(i); }))
+        .def(py::init([](mixed_tag, const std::string &s) { return TestFactory7((int) s.size()); },
-        .def(py::init(
+                      [](mixed_tag, const std::string &s) { return new PyTF7((int) s.size()); }))
-            [](mixed_tag, int i) { return new TestFactory7(i); },
+        .def(py::init([](base_tag, pointer_tag, int i) { return new TestFactory7(i); },
-            [](mixed_tag, int i) { return PyTF7(i); }))
+                      [](base_tag, pointer_tag, int i) { return (TestFactory7 *) new PyTF7(i); }))
-        .def(py::init(
+        .def(py::init([](alias_tag, pointer_tag, int i) { return new PyTF7(i); },
-            [](mixed_tag, std::string s) { return TestFactory7((int) s.size()); },
+                      [](alias_tag, pointer_tag, int i) { return new PyTF7(10 * i); }))
-            [](mixed_tag, std::string s) { return new PyTF7((int) s.size()); }))
-        .def(py::init(
-            [](base_tag, pointer_tag, int i) { return new TestFactory7(i); },
-            [](base_tag, pointer_tag, int i) { return (TestFactory7 *) new PyTF7(i); }))
-        .def(py::init(
-            [](alias_tag, pointer_tag, int i) { return new PyTF7(i); },
-            [](alias_tag, pointer_tag, int i) { return new PyTF7(10*i); }))
         .def(py::init(
             [](shared_ptr_tag, base_tag, int i) { return std::make_shared<TestFactory7>(i); },
-            [](shared_ptr_tag, base_tag, int i) { auto *p = new PyTF7(i); return std::shared_ptr<TestFactory7>(p); }))
+            [](shared_ptr_tag, base_tag, int i) {
-        .def(py::init(
+                auto *p = new PyTF7(i);
-            [](shared_ptr_tag, invalid_base_tag, int i) { return std::make_shared<TestFactory7>(i); },
+                return std::shared_ptr<TestFactory7>(p);
-            [](shared_ptr_tag, invalid_base_tag, int i) { return std::make_shared<TestFactory7>(i); })) // <-- invalid alias factory
+            }))
+        .def(py::init([](shared_ptr_tag,
+                         invalid_base_tag,
+                         int i) { return std::make_shared<TestFactory7>(i); },
+                      [](shared_ptr_tag, invalid_base_tag, int i) {
+                          return std::make_shared<TestFactory7>(i);
+                      })) // <-- invalid alias factory
 
         .def("get", &TestFactory7::get)
         .def("has_alias", &TestFactory7::has_alias)
 
-        .def_static("get_cstats", &ConstructorStats::get<TestFactory7>, py::return_value_policy::reference)
+        .def_static(
-        .def_static("get_alias_cstats", &ConstructorStats::get<PyTF7>, py::return_value_policy::reference)
+            "get_cstats", &ConstructorStats::get<TestFactory7>, py::return_value_policy::reference)
-        ;
+        .def_static(
+            "get_alias_cstats", &ConstructorStats::get<PyTF7>, py::return_value_policy::reference);
 
     // test_placement_new_alternative
     // Class with a custom new operator but *without* a placement new operator (issue #948)
@@ -331,12 +361,10 @@ TEST_SUBMODULE(factory_constructors, m) {
     pyNoisyAlloc.def(py::init([](int i, double) { return new NoisyAlloc(i); }));
     // Regular again: requires yet another preallocation
     ignoreOldStyleInitWarnings([&pyNoisyAlloc]() {
-        pyNoisyAlloc.def("__init__", [](NoisyAlloc &a, int i, std::string) { new (&a) NoisyAlloc(i); });
+        pyNoisyAlloc.def(
+            "__init__", [](NoisyAlloc &a, int i, const std::string &) { new (&a) NoisyAlloc(i); });
     });
 
-
-
-
     // static_assert testing (the following def's should all fail with appropriate compilation errors):
 #if 0
     struct BadF1Base {};

tests/test_gil_scoped.cpp

@@ -35,20 +35,15 @@ TEST_SUBMODULE(gil_scoped, m) {
       .def("virtual_func", &VirtClass::virtual_func)
       .def("pure_virtual_func", &VirtClass::pure_virtual_func);
 
-    m.def("test_callback_py_obj",
+  m.def("test_callback_py_obj", [](py::object &func) { func(); });
-          [](py::object func) { func(); });
+  m.def("test_callback_std_func", [](const std::function<void()> &func) { func(); });
-    m.def("test_callback_std_func",
+  m.def("test_callback_virtual_func", [](VirtClass &virt) { virt.virtual_func(); });
-          [](const std::function<void()> &func) { func(); });
+  m.def("test_callback_pure_virtual_func", [](VirtClass &virt) { virt.pure_virtual_func(); });
-    m.def("test_callback_virtual_func",
+  m.def("test_cross_module_gil", []() {
-          [](VirtClass &virt) { virt.virtual_func(); });
+      auto cm = py::module_::import("cross_module_gil_utils");
-    m.def("test_callback_pure_virtual_func",
+      auto gil_acquire
-          [](VirtClass &virt) { virt.pure_virtual_func(); });
+          = reinterpret_cast<void (*)()>(PyLong_AsVoidPtr(cm.attr("gil_acquire_funcaddr").ptr()));
-    m.def("test_cross_module_gil",
+      py::gil_scoped_release gil_release;
-          []() {
+      gil_acquire();
-              auto cm = py::module_::import("cross_module_gil_utils");
+  });
-              auto gil_acquire = reinterpret_cast<void (*)()>(
-                  PyLong_AsVoidPtr(cm.attr("gil_acquire_funcaddr").ptr()));
-              py::gil_scoped_release gil_release;
-              gil_acquire();
-          });
 }

tests/test_iostream.cpp

@@ -17,15 +17,14 @@
 #include <iostream>
 #include <thread>
 
-
+void noisy_function(const std::string &msg, bool flush) {
-void noisy_function(std::string msg, bool flush) {
 
     std::cout << msg;
     if (flush)
         std::cout << std::flush;
 }
 
-void noisy_funct_dual(std::string msg, std::string emsg) {
+void noisy_funct_dual(const std::string &msg, const std::string &emsg) {
     std::cout << msg;
     std::cerr << emsg;
 }
@@ -70,12 +69,12 @@ TEST_SUBMODULE(iostream, m) {
 
     // test_evals
 
-    m.def("captured_output_default", [](std::string msg) {
+    m.def("captured_output_default", [](const std::string &msg) {
         py::scoped_ostream_redirect redir;
         std::cout << msg << std::flush;
     });
 
-    m.def("captured_output", [](std::string msg) {
+    m.def("captured_output", [](const std::string &msg) {
         py::scoped_ostream_redirect redir(std::cout, py::module_::import("sys").attr("stdout"));
         std::cout << msg << std::flush;
     });
@@ -84,7 +83,7 @@ TEST_SUBMODULE(iostream, m) {
             py::call_guard<py::scoped_ostream_redirect>(),
             py::arg("msg"), py::arg("flush")=true);
 
-    m.def("captured_err", [](std::string msg) {
+    m.def("captured_err", [](const std::string &msg) {
         py::scoped_ostream_redirect redir(std::cerr, py::module_::import("sys").attr("stderr"));
         std::cerr << msg << std::flush;
     });
@@ -95,15 +94,11 @@ TEST_SUBMODULE(iostream, m) {
             py::call_guard<py::scoped_ostream_redirect, py::scoped_estream_redirect>(),
             py::arg("msg"), py::arg("emsg"));
 
-    m.def("raw_output", [](std::string msg) {
+    m.def("raw_output", [](const std::string &msg) { std::cout << msg << std::flush; });
-        std::cout << msg << std::flush;
-    });
 
-    m.def("raw_err", [](std::string msg) {
+    m.def("raw_err", [](const std::string &msg) { std::cerr << msg << std::flush; });
-        std::cerr << msg << std::flush;
-    });
 
-    m.def("captured_dual", [](std::string msg, std::string emsg) {
+    m.def("captured_dual", [](const std::string &msg, const std::string &emsg) {
         py::scoped_ostream_redirect redirout(std::cout, py::module_::import("sys").attr("stdout"));
         py::scoped_ostream_redirect redirerr(std::cerr, py::module_::import("sys").attr("stderr"));
         std::cout << msg << std::flush;

tests/test_kwargs_and_defaults.cpp

@@ -11,6 +11,8 @@
 #include "constructor_stats.h"
 #include <pybind11/stl.h>
 
+#include <utility>
+
 TEST_SUBMODULE(kwargs_and_defaults, m) {
     auto kw_func = [](int x, int y) { return "x=" + std::to_string(x) + ", y=" + std::to_string(y); };
 
@@ -37,18 +39,16 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
     m.def("args_function", [](py::args args) -> py::tuple {
         return std::move(args);
     });
-    m.def("args_kwargs_function", [](py::args args, py::kwargs kwargs) {
+    m.def("args_kwargs_function", [](const py::args &args, const py::kwargs &kwargs) {
         return py::make_tuple(args, kwargs);
     });
 
     // test_mixed_args_and_kwargs
-    m.def("mixed_plus_args", [](int i, double j, py::args args) {
+    m.def("mixed_plus_args",
-        return py::make_tuple(i, j, args);
+          [](int i, double j, const py::args &args) { return py::make_tuple(i, j, args); });
-    });
+    m.def("mixed_plus_kwargs",
-    m.def("mixed_plus_kwargs", [](int i, double j, py::kwargs kwargs) {
+          [](int i, double j, const py::kwargs &kwargs) { return py::make_tuple(i, j, kwargs); });
-        return py::make_tuple(i, j, kwargs);
+    auto mixed_plus_both = [](int i, double j, const py::args &args, const py::kwargs &kwargs) {
-    });
-    auto mixed_plus_both = [](int i, double j, py::args args, py::kwargs kwargs) {
         return py::make_tuple(i, j, args, kwargs);
     };
     m.def("mixed_plus_args_kwargs", mixed_plus_both);
@@ -65,6 +65,8 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
     #endif
     m.def("arg_refcount_h", [](py::handle h) { GC_IF_NEEDED; return h.ref_count(); });
     m.def("arg_refcount_h", [](py::handle h, py::handle, py::handle) { GC_IF_NEEDED; return h.ref_count(); });
+    // TODO replace the following nolints as appropiate
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("arg_refcount_o", [](py::object o) { GC_IF_NEEDED; return o.ref_count(); });
     m.def("args_refcount", [](py::args a) {
         GC_IF_NEEDED;
@@ -74,6 +76,7 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
             t[i] = (int) Py_REFCNT(PyTuple_GET_ITEM(a.ptr(), static_cast<py::ssize_t>(i)));
         return t;
     });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("mixed_args_refcount", [](py::object o, py::args a) {
         GC_IF_NEEDED;
         py::tuple t(a.size() + 1);
@@ -103,6 +106,7 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
             py::arg() = 3, "j"_a = 4, py::kw_only(), "k"_a = 5, "z"_a);
     m.def("kw_only_mixed", [](int i, int j) { return py::make_tuple(i, j); },
             "i"_a, py::kw_only(), "j"_a);
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("kw_only_plus_more", [](int i, int j, int k, py::kwargs kwargs) {
             return py::make_tuple(i, j, k, kwargs); },
             py::arg() /* positional */, py::arg("j") = -1 /* both */, py::kw_only(), py::arg("k") /* kw-only */);
@@ -137,6 +141,8 @@ TEST_SUBMODULE(kwargs_and_defaults, m) {
 
     // Make sure a class (not an instance) can be used as a default argument.
     // The return value doesn't matter, only that the module is importable.
-    m.def("class_default_argument", [](py::object a) { return py::repr(a); },
+    m.def(
+        "class_default_argument",
+        [](py::object a) { return py::repr(std::move(a)); },
         "a"_a = py::module_::import("decimal").attr("Decimal"));
 }

tests/test_local_bindings.cpp

@@ -86,6 +86,8 @@ TEST_SUBMODULE(local_bindings, m) {
     m.def("return_self", [](LocalVec *v) { return v; });
     m.def("return_copy", [](const LocalVec &v) { return LocalVec(v); });
 
+    // Reformatting this class broke pygrep checks
+    // NOLINTNEXTLINE
     class Cat : public pets::Pet { public: Cat(std::string name) : Pet(name) {}; };
     py::class_<pets::Pet>(m, "Pet", py::module_local())
         .def("get_name", &pets::Pet::name);

tests/test_methods_and_attributes.cpp

@@ -22,14 +22,18 @@ public:
     ExampleMandA(int value) : value(value) { print_created(this, value); }
     ExampleMandA(const ExampleMandA &e) : value(e.value) { print_copy_created(this); }
     ExampleMandA(std::string&&) {}
-    ExampleMandA(ExampleMandA &&e) : value(e.value) { print_move_created(this); }
+    ExampleMandA(ExampleMandA &&e) noexcept : value(e.value) { print_move_created(this); }
     ~ExampleMandA() { print_destroyed(this); }
 
     std::string toString() const { return "ExampleMandA[value=" + std::to_string(value) + "]"; }
 
     void operator=(const ExampleMandA &e) { print_copy_assigned(this); value = e.value; }
-    void operator=(ExampleMandA &&e) { print_move_assigned(this); value = e.value; }
+    void operator=(ExampleMandA &&e) noexcept {
+        print_move_assigned(this);
+        value = e.value;
+    }
 
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     void add1(ExampleMandA other) { value += other.value; }         // passing by value
     void add2(ExampleMandA &other) { value += other.value; }        // passing by reference
     void add3(const ExampleMandA &other) { value += other.value; }  // passing by const reference
@@ -112,7 +116,7 @@ int none1(const NoneTester &obj) { return obj.answer; }
 int none2(NoneTester *obj) { return obj ? obj->answer : -1; }
 int none3(std::shared_ptr<NoneTester> &obj) { return obj ? obj->answer : -1; }
 int none4(std::shared_ptr<NoneTester> *obj) { return obj && *obj ? (*obj)->answer : -1; }
-int none5(std::shared_ptr<NoneTester> obj) { return obj ? obj->answer : -1; }
+int none5(const std::shared_ptr<NoneTester> &obj) { return obj ? obj->answer : -1; }
 
 struct StrIssue {
     int val = -1;
@@ -226,36 +230,41 @@ TEST_SUBMODULE(methods_and_attributes, m) {
         .def(py::init<>())
         .def_readonly("def_readonly", &TestProperties::value)
         .def_readwrite("def_readwrite", &TestProperties::value)
-        .def_property("def_writeonly", nullptr,
+        .def_property("def_writeonly", nullptr, [](TestProperties &s, int v) { s.value = v; })
-                      [](TestProperties& s,int v) { s.value = v; } )
         .def_property("def_property_writeonly", nullptr, &TestProperties::set)
         .def_property_readonly("def_property_readonly", &TestProperties::get)
         .def_property("def_property", &TestProperties::get, &TestProperties::set)
         .def_property("def_property_impossible", nullptr, nullptr)
         .def_readonly_static("def_readonly_static", &TestProperties::static_value)
         .def_readwrite_static("def_readwrite_static", &TestProperties::static_value)
-        .def_property_static("def_writeonly_static", nullptr,
+        .def_property_static("def_writeonly_static",
-                             [](py::object, int v) { TestProperties::static_value = v; })
+                             nullptr,
-        .def_property_readonly_static("def_property_readonly_static",
+                             [](const py::object &, int v) { TestProperties::static_value = v; })
-                                      [](py::object) { return TestProperties::static_get(); })
+        .def_property_readonly_static(
-        .def_property_static("def_property_writeonly_static", nullptr,
+            "def_property_readonly_static",
-                             [](py::object, int v) { return TestProperties::static_set(v); })
+            [](const py::object &) { return TestProperties::static_get(); })
-        .def_property_static("def_property_static",
+        .def_property_static(
-                             [](py::object) { return TestProperties::static_get(); },
+            "def_property_writeonly_static",
-                             [](py::object, int v) { TestProperties::static_set(v); })
+            nullptr,
-        .def_property_static("static_cls",
+            [](const py::object &, int v) { return TestProperties::static_set(v); })
-                             [](py::object cls) { return cls; },
+        .def_property_static(
-                             [](py::object cls, py::function f) { f(cls); });
+            "def_property_static",
+            [](const py::object &) { return TestProperties::static_get(); },
+            [](const py::object &, int v) { TestProperties::static_set(v); })
+        .def_property_static(
+            "static_cls",
+            [](py::object cls) { return cls; },
+            [](const py::object &cls, const py::function &f) { f(cls); });
 
     py::class_<TestPropertiesOverride, TestProperties>(m, "TestPropertiesOverride")
         .def(py::init<>())
         .def_readonly("def_readonly", &TestPropertiesOverride::value)
         .def_readonly_static("def_readonly_static", &TestPropertiesOverride::static_value);
 
-    auto static_get1 = [](py::object) -> const UserType & { return TestPropRVP::sv1; };
+    auto static_get1 = [](const py::object &) -> const UserType & { return TestPropRVP::sv1; };
-    auto static_get2 = [](py::object) -> const UserType & { return TestPropRVP::sv2; };
+    auto static_get2 = [](const py::object &) -> const UserType & { return TestPropRVP::sv2; };
-    auto static_set1 = [](py::object, int v) { TestPropRVP::sv1.set(v); };
+    auto static_set1 = [](const py::object &, int v) { TestPropRVP::sv1.set(v); };
-    auto static_set2 = [](py::object, int v) { TestPropRVP::sv2.set(v); };
+    auto static_set2 = [](const py::object &, int v) { TestPropRVP::sv2.set(v); };
     auto rvp_copy = py::return_value_policy::copy;
 
     // test_property_return_value_policies
@@ -266,24 +275,30 @@ TEST_SUBMODULE(methods_and_attributes, m) {
         .def_property_readonly("ro_func", py::cpp_function(&TestPropRVP::get2, rvp_copy))
         .def_property("rw_ref", &TestPropRVP::get1, &TestPropRVP::set1)
         .def_property("rw_copy", &TestPropRVP::get2, &TestPropRVP::set2, rvp_copy)
-        .def_property("rw_func", py::cpp_function(&TestPropRVP::get2, rvp_copy), &TestPropRVP::set2)
+        .def_property(
+            "rw_func", py::cpp_function(&TestPropRVP::get2, rvp_copy), &TestPropRVP::set2)
         .def_property_readonly_static("static_ro_ref", static_get1)
         .def_property_readonly_static("static_ro_copy", static_get2, rvp_copy)
         .def_property_readonly_static("static_ro_func", py::cpp_function(static_get2, rvp_copy))
         .def_property_static("static_rw_ref", static_get1, static_set1)
         .def_property_static("static_rw_copy", static_get2, static_set2, rvp_copy)
-        .def_property_static("static_rw_func", py::cpp_function(static_get2, rvp_copy), static_set2)
+        .def_property_static(
+            "static_rw_func", py::cpp_function(static_get2, rvp_copy), static_set2)
         // test_property_rvalue_policy
         .def_property_readonly("rvalue", &TestPropRVP::get_rvalue)
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
         .def_property_readonly_static("static_rvalue", [](py::object) { return UserType(1); });
 
     // test_metaclass_override
     struct MetaclassOverride { };
     py::class_<MetaclassOverride>(m, "MetaclassOverride", py::metaclass((PyObject *) &PyType_Type))
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
         .def_property_readonly_static("readonly", [](py::object) { return 1; });
 
     // test_overload_ordering
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("overload_order", [](std::string) { return 1; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("overload_order", [](std::string) { return 2; });
     m.def("overload_order", [](int) { return 3; });
     m.def("overload_order", [](int) { return 4; }, py::prepend{});

tests/test_multiple_inheritance.cpp

@@ -141,6 +141,7 @@ TEST_SUBMODULE(multiple_inheritance, m) {
         .def(py::init<int, int>());
 
     m.def("bar_base2a", [](Base2a *b) { return b->bar(); });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("bar_base2a_sharedptr", [](std::shared_ptr<Base2a> b) { return b->bar(); });
 
     // test_mi_unaligned_base

tests/test_numpy_array.cpp

@@ -13,6 +13,7 @@
 #include <pybind11/stl.h>
 
 #include <cstdint>
+#include <utility>
 
 // Size / dtype checks.
 struct DtypeCheck {
@@ -192,7 +193,7 @@ TEST_SUBMODULE(numpy_array, sm) {
     sm.def("scalar_int", []() { return py::array(py::dtype("i"), {}, {}, &data_i); });
 
     // test_wrap
-    sm.def("wrap", [](py::array a) {
+    sm.def("wrap", [](const py::array &a) {
         return py::array(
             a.dtype(),
             {a.shape(), a.shape() + a.ndim()},
@@ -222,8 +223,10 @@ TEST_SUBMODULE(numpy_array, sm) {
 
     // test_isinstance
     sm.def("isinstance_untyped", [](py::object yes, py::object no) {
-        return py::isinstance<py::array>(yes) && !py::isinstance<py::array>(no);
+        return py::isinstance<py::array>(std::move(yes))
+               && !py::isinstance<py::array>(std::move(no));
     });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("isinstance_typed", [](py::object o) {
         return py::isinstance<py::array_t<double>>(o) && !py::isinstance<py::array_t<int>>(o);
     });
@@ -236,7 +239,7 @@ TEST_SUBMODULE(numpy_array, sm) {
             "array_t<double>"_a=py::array_t<double>()
         );
     });
-    sm.def("converting_constructors", [](py::object o) {
+    sm.def("converting_constructors", [](const py::object &o) {
         return py::dict(
             "array"_a=py::array(o),
             "array_t<int32>"_a=py::array_t<std::int32_t>(o),
@@ -245,39 +248,59 @@ TEST_SUBMODULE(numpy_array, sm) {
     });
 
     // test_overload_resolution
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded", [](py::array_t<double>) { return "double"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded", [](py::array_t<float>) { return "float"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded", [](py::array_t<int>) { return "int"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded", [](py::array_t<unsigned short>) { return "unsigned short"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded", [](py::array_t<long long>) { return "long long"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded", [](py::array_t<std::complex<double>>) { return "double complex"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded", [](py::array_t<std::complex<float>>) { return "float complex"; });
 
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded2", [](py::array_t<std::complex<double>>) { return "double complex"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded2", [](py::array_t<double>) { return "double"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded2", [](py::array_t<std::complex<float>>) { return "float complex"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded2", [](py::array_t<float>) { return "float"; });
 
     // [workaround(intel)] ICC 20/21 breaks with py::arg().stuff, using py::arg{}.stuff works.
 
     // Only accept the exact types:
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded3", [](py::array_t<int>) { return "int"; }, py::arg{}.noconvert());
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded3", [](py::array_t<double>) { return "double"; }, py::arg{}.noconvert());
 
     // Make sure we don't do unsafe coercion (e.g. float to int) when not using forcecast, but
     // rather that float gets converted via the safe (conversion to double) overload:
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded4", [](py::array_t<long long, 0>) { return "long long"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded4", [](py::array_t<double, 0>) { return "double"; });
 
     // But we do allow conversion to int if forcecast is enabled (but only if no overload matches
     // without conversion)
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded5", [](py::array_t<unsigned int>) { return "unsigned int"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("overloaded5", [](py::array_t<double>) { return "double"; });
 
     // test_greedy_string_overload
     // Issue 685: ndarray shouldn't go to std::string overload
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("issue685", [](std::string) { return "string"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("issue685", [](py::array) { return "array"; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("issue685", [](py::object) { return "other"; });
 
     // test_array_unchecked_fixed_dims
@@ -306,7 +329,7 @@ TEST_SUBMODULE(numpy_array, sm) {
             r(i, j, k) = start++;
         return a;
     });
-    sm.def("proxy_squared_L2_norm", [](py::array_t<double> a) {
+    sm.def("proxy_squared_L2_norm", [](const py::array_t<double> &a) {
         auto r = a.unchecked<1>();
         double sumsq = 0;
         for (py::ssize_t i = 0; i < r.shape(0); i++)
@@ -396,51 +419,78 @@ TEST_SUBMODULE(numpy_array, sm) {
         return a;
     });
 
-    sm.def("index_using_ellipsis", [](py::array a) {
+    sm.def("index_using_ellipsis",
-        return a[py::make_tuple(0, py::ellipsis(), 0)];
+           [](const py::array &a) { return a[py::make_tuple(0, py::ellipsis(), 0)]; });
-    });
 
     // test_argument_conversions
-    sm.def("accept_double",
+    sm.def(
-           [](py::array_t<double, 0>) {},
+        "accept_double",
-           py::arg("a"));
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
-    sm.def("accept_double_forcecast",
+        [](py::array_t<double, 0>) {},
-           [](py::array_t<double, py::array::forcecast>) {},
+        py::arg("a"));
-           py::arg("a"));
+    sm.def(
-    sm.def("accept_double_c_style",
+        "accept_double_forcecast",
-           [](py::array_t<double, py::array::c_style>) {},
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
-           py::arg("a"));
+        [](py::array_t<double, py::array::forcecast>) {},
-    sm.def("accept_double_c_style_forcecast",
+        py::arg("a"));
-           [](py::array_t<double, py::array::forcecast | py::array::c_style>) {},
+    sm.def(
-           py::arg("a"));
+        "accept_double_c_style",
-    sm.def("accept_double_f_style",
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
-           [](py::array_t<double, py::array::f_style>) {},
+        [](py::array_t<double, py::array::c_style>) {},
-           py::arg("a"));
+        py::arg("a"));
-    sm.def("accept_double_f_style_forcecast",
+    sm.def(
-           [](py::array_t<double, py::array::forcecast | py::array::f_style>) {},
+        "accept_double_c_style_forcecast",
-           py::arg("a"));
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
-    sm.def("accept_double_noconvert",
+        [](py::array_t<double, py::array::forcecast | py::array::c_style>) {},
-           [](py::array_t<double, 0>) {},
+        py::arg("a"));
-           "a"_a.noconvert());
+    sm.def(
-    sm.def("accept_double_forcecast_noconvert",
+        "accept_double_f_style",
-           [](py::array_t<double, py::array::forcecast>) {},
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
-           "a"_a.noconvert());
+        [](py::array_t<double, py::array::f_style>) {},
-    sm.def("accept_double_c_style_noconvert",
+        py::arg("a"));
-           [](py::array_t<double, py::array::c_style>) {},
+    sm.def(
-           "a"_a.noconvert());
+        "accept_double_f_style_forcecast",
-    sm.def("accept_double_c_style_forcecast_noconvert",
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
-           [](py::array_t<double, py::array::forcecast | py::array::c_style>) {},
+        [](py::array_t<double, py::array::forcecast | py::array::f_style>) {},
-           "a"_a.noconvert());
+        py::arg("a"));
-    sm.def("accept_double_f_style_noconvert",
+    sm.def(
-           [](py::array_t<double, py::array::f_style>) {},
+        "accept_double_noconvert",
-           "a"_a.noconvert());
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
-    sm.def("accept_double_f_style_forcecast_noconvert",
+        [](py::array_t<double, 0>) {},
-           [](py::array_t<double, py::array::forcecast | py::array::f_style>) {},
+        "a"_a.noconvert());
-           "a"_a.noconvert());
+    sm.def(
+        "accept_double_forcecast_noconvert",
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
+        [](py::array_t<double, py::array::forcecast>) {},
+        "a"_a.noconvert());
+    sm.def(
+        "accept_double_c_style_noconvert",
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
+        [](py::array_t<double, py::array::c_style>) {},
+        "a"_a.noconvert());
+    sm.def(
+        "accept_double_c_style_forcecast_noconvert",
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
+        [](py::array_t<double, py::array::forcecast | py::array::c_style>) {},
+        "a"_a.noconvert());
+    sm.def(
+        "accept_double_f_style_noconvert",
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
+        [](py::array_t<double, py::array::f_style>) {},
+        "a"_a.noconvert());
+    sm.def(
+        "accept_double_f_style_forcecast_noconvert",
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
+        [](py::array_t<double, py::array::forcecast | py::array::f_style>) {},
+        "a"_a.noconvert());
 
     // Check that types returns correct npy format descriptor
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("test_fmt_desc_float", [](py::array_t<float>) {});
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("test_fmt_desc_double", [](py::array_t<double>) {});
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("test_fmt_desc_const_float", [](py::array_t<const float>) {});
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     sm.def("test_fmt_desc_const_double", [](py::array_t<const double>) {});
 }

tests/test_numpy_dtypes.cpp

@@ -266,10 +266,11 @@ TEST_SUBMODULE(numpy_dtypes, m) {
         .def_readwrite("uint_", &SimpleStruct::uint_)
         .def_readwrite("float_", &SimpleStruct::float_)
         .def_readwrite("ldbl_", &SimpleStruct::ldbl_)
-        .def("astuple", [](const SimpleStruct& self) {
+        .def("astuple",
-            return py::make_tuple(self.bool_, self.uint_, self.float_, self.ldbl_);
+             [](const SimpleStruct &self) {
-        })
+                 return py::make_tuple(self.bool_, self.uint_, self.float_, self.ldbl_);
-        .def_static("fromtuple", [](const py::tuple tup) {
+             })
+        .def_static("fromtuple", [](const py::tuple &tup) {
             if (py::len(tup) != 4) {
                 throw py::cast_error("Invalid size");
             }

tests/test_numpy_vectorize.cpp

@@ -11,6 +11,8 @@
 #include "pybind11_tests.h"
 #include <pybind11/numpy.h>
 
+#include <utility>
+
 double my_func(int x, float y, double z) {
     py::print("my_func(x:int={}, y:float={:.0f}, z:float={:.0f})"_s.format(x, y, z));
     return (float) x*y*z;
@@ -25,11 +27,10 @@ TEST_SUBMODULE(numpy_vectorize, m) {
     m.def("vectorized_func", py::vectorize(my_func));
 
     // Vectorize a lambda function with a capture object (e.g. to exclude some arguments from the vectorization)
-    m.def("vectorized_func2",
+    m.def("vectorized_func2", [](py::array_t<int> x, py::array_t<float> y, float z) {
-        [](py::array_t<int> x, py::array_t<float> y, float z) {
+        return py::vectorize([z](int x, float y) { return my_func(x, y, z); })(std::move(x),
-            return py::vectorize([z](int x, float y) { return my_func(x, y, z); })(x, y);
+                                                                               std::move(y));
-        }
+    });
-    );
 
     // Vectorize a complex-valued function
     m.def("vectorized_func3", py::vectorize(
@@ -38,8 +39,12 @@ TEST_SUBMODULE(numpy_vectorize, m) {
 
     // test_type_selection
     // NumPy function which only accepts specific data types
+    // Alot of these no lints could be replaced with const refs, and probably should at some point.
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("selective_func", [](py::array_t<int, py::array::c_style>) { return "Int branch taken."; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("selective_func", [](py::array_t<float, py::array::c_style>) { return "Float branch taken."; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("selective_func", [](py::array_t<std::complex<float>, py::array::c_style>) { return "Complex float branch taken."; });
 
 
@@ -53,11 +58,16 @@ TEST_SUBMODULE(numpy_vectorize, m) {
     py::class_<NonPODClass>(m, "NonPODClass")
         .def(py::init<int>())
         .def_readwrite("value", &NonPODClass::value);
-    m.def("vec_passthrough", py::vectorize(
+    m.def("vec_passthrough",
-        [](double *a, double b, py::array_t<double> c, const int &d, int &e, NonPODClass f, const double g) {
+          py::vectorize([](double *a,
-            return *a + b + c.at(0) + d + e + f.value + g;
+                           double b,
-        }
+                           // Changing this broke things
-    ));
+                           // NOLINTNEXTLINE(performance-unnecessary-value-param)
+                           py::array_t<double> c,
+                           const int &d,
+                           int &e,
+                           NonPODClass f,
+                           const double g) { return *a + b + c.at(0) + d + e + f.value + g; }));
 
     // test_method_vectorization
     struct VectorizeTestClass {
@@ -78,16 +88,20 @@ TEST_SUBMODULE(numpy_vectorize, m) {
         .value("f_trivial", py::detail::broadcast_trivial::f_trivial)
         .value("c_trivial", py::detail::broadcast_trivial::c_trivial)
         .value("non_trivial", py::detail::broadcast_trivial::non_trivial);
-    m.def("vectorized_is_trivial", [](
+    m.def("vectorized_is_trivial",
-                py::array_t<int, py::array::forcecast> arg1,
+          [](
-                py::array_t<float, py::array::forcecast> arg2,
+              // NOLINTNEXTLINE(performance-unnecessary-value-param)
-                py::array_t<double, py::array::forcecast> arg3
+              py::array_t<int, py::array::forcecast> arg1,
-                ) {
+              // NOLINTNEXTLINE(performance-unnecessary-value-param)
-        py::ssize_t ndim;
+              py::array_t<float, py::array::forcecast> arg2,
-        std::vector<py::ssize_t> shape;
+              // NOLINTNEXTLINE(performance-unnecessary-value-param)
-        std::array<py::buffer_info, 3> buffers {{ arg1.request(), arg2.request(), arg3.request() }};
+              py::array_t<double, py::array::forcecast> arg3) {
-        return py::detail::broadcast(buffers, ndim, shape);
+              py::ssize_t ndim;
-    });
+              std::vector<py::ssize_t> shape;
+              std::array<py::buffer_info, 3> buffers{
+                  {arg1.request(), arg2.request(), arg3.request()}};
+              return py::detail::broadcast(buffers, ndim, shape);
+          });
 
     m.def("add_to", py::vectorize([](NonPODClass& x, int a) { x.value += a; }));
 }

tests/test_opaque_types.cpp

@@ -44,7 +44,7 @@ TEST_SUBMODULE(opaque_types, m) {
     m.def("print_opaque_list", [](const StringList &l) {
         std::string ret = "Opaque list: [";
         bool first = true;
-        for (auto entry : l) {
+        for (const auto &entry : l) {
             if (!first)
                 ret += ", ";
             ret += entry;

tests/test_operator_overloading.cpp

@@ -16,9 +16,18 @@ class Vector2 {
 public:
     Vector2(float x, float y) : x(x), y(y) { print_created(this, toString()); }
     Vector2(const Vector2 &v) : x(v.x), y(v.y) { print_copy_created(this); }
-    Vector2(Vector2 &&v) : x(v.x), y(v.y) { print_move_created(this); v.x = v.y = 0; }
+    Vector2(Vector2 &&v) noexcept : x(v.x), y(v.y) {
+        print_move_created(this);
+        v.x = v.y = 0;
+    }
     Vector2 &operator=(const Vector2 &v) { x = v.x; y = v.y; print_copy_assigned(this); return *this; }
-    Vector2 &operator=(Vector2 &&v) { x = v.x; y = v.y; v.x = v.y = 0; print_move_assigned(this); return *this; }
+    Vector2 &operator=(Vector2 &&v) noexcept {
+        x   = v.x;
+        y   = v.y;
+        v.x = v.y = 0;
+        print_move_assigned(this);
+        return *this;
+    }
     ~Vector2() { print_destroyed(this); }
 
     std::string toString() const { return "[" + std::to_string(x) + ", " + std::to_string(y) + "]"; }

tests/test_pickling.cpp

@@ -46,17 +46,16 @@ TEST_SUBMODULE(pickling, m) {
             return py::make_tuple(p.value(), p.extra1(), p.extra2());
         });
     ignoreOldStyleInitWarnings([&pyPickleable]() {
-        pyPickleable
+        pyPickleable.def("__setstate__", [](Pickleable &p, const py::tuple &t) {
-            .def("__setstate__", [](Pickleable &p, py::tuple t) {
+            if (t.size() != 3)
-                if (t.size() != 3)
+                throw std::runtime_error("Invalid state!");
-                    throw std::runtime_error("Invalid state!");
+            /* Invoke the constructor (need to use in-place version) */
-                /* Invoke the constructor (need to use in-place version) */
+            new (&p) Pickleable(t[0].cast<std::string>());
-                new (&p) Pickleable(t[0].cast<std::string>());
 
-                /* Assign any additional state */
+            /* Assign any additional state */
-                p.setExtra1(t[1].cast<int>());
+            p.setExtra1(t[1].cast<int>());
-                p.setExtra2(t[2].cast<int>());
+            p.setExtra2(t[2].cast<int>());
-            });
+        });
     });
 
     py::class_<PickleableNew, Pickleable>(m, "PickleableNew")
@@ -65,7 +64,7 @@ TEST_SUBMODULE(pickling, m) {
             [](const PickleableNew &p) {
                 return py::make_tuple(p.value(), p.extra1(), p.extra2());
             },
-            [](py::tuple t) {
+            [](const py::tuple &t) {
                 if (t.size() != 3)
                     throw std::runtime_error("Invalid state!");
                 auto p = PickleableNew(t[0].cast<std::string>());
@@ -73,8 +72,7 @@ TEST_SUBMODULE(pickling, m) {
                 p.setExtra1(t[1].cast<int>());
                 p.setExtra2(t[2].cast<int>());
                 return p;
-            }
+            }));
-        ));
 
 #if !defined(PYPY_VERSION)
     // test_roundtrip_with_dict
@@ -92,35 +90,33 @@ TEST_SUBMODULE(pickling, m) {
     };
 
     py::class_<PickleableWithDict> pyPickleableWithDict(m, "PickleableWithDict", py::dynamic_attr());
-    pyPickleableWithDict
+    pyPickleableWithDict.def(py::init<std::string>())
-        .def(py::init<std::string>())
         .def_readwrite("value", &PickleableWithDict::value)
         .def_readwrite("extra", &PickleableWithDict::extra)
-        .def("__getstate__", [](py::object self) {
+        .def("__getstate__", [](const py::object &self) {
             /* Also include __dict__ in state */
             return py::make_tuple(self.attr("value"), self.attr("extra"), self.attr("__dict__"));
         });
     ignoreOldStyleInitWarnings([&pyPickleableWithDict]() {
-        pyPickleableWithDict
+        pyPickleableWithDict.def("__setstate__", [](const py::object &self, const py::tuple &t) {
-            .def("__setstate__", [](py::object self, py::tuple t) {
+            if (t.size() != 3)
-                if (t.size() != 3)
+                throw std::runtime_error("Invalid state!");
-                    throw std::runtime_error("Invalid state!");
+            /* Cast and construct */
-                /* Cast and construct */
+            auto &p = self.cast<PickleableWithDict &>();
-                auto& p = self.cast<PickleableWithDict&>();
+            new (&p) PickleableWithDict(t[0].cast<std::string>());
-                new (&p) PickleableWithDict(t[0].cast<std::string>());
 
-                /* Assign C++ state */
+            /* Assign C++ state */
-                p.extra = t[1].cast<int>();
+            p.extra = t[1].cast<int>();
 
-                /* Assign Python state */
+            /* Assign Python state */
-                self.attr("__dict__") = t[2];
+            self.attr("__dict__") = t[2];
-            });
+        });
     });
 
     py::class_<PickleableWithDictNew, PickleableWithDict>(m, "PickleableWithDictNew")
         .def(py::init<std::string>())
         .def(py::pickle(
-            [](py::object self) {
+            [](const py::object &self) {
                 return py::make_tuple(self.attr("value"), self.attr("extra"), self.attr("__dict__"));
             },
             [](const py::tuple &t) {
@@ -132,7 +128,6 @@ TEST_SUBMODULE(pickling, m) {
 
                 auto py_state = t[2].cast<py::dict>();
                 return std::make_pair(cpp_state, py_state);
-            }
+            }));
-        ));
 #endif
 }

tests/test_pytypes.cpp

@@ -7,6 +7,8 @@
     BSD-style license that can be found in the LICENSE file.
 */
 
+#include <utility>
+
 #include "pybind11_tests.h"
 
 
@@ -27,16 +29,14 @@ TEST_SUBMODULE(pytypes, m) {
         list.insert(2, "inserted-2");
         return list;
     });
-    m.def("print_list", [](py::list list) {
+    m.def("print_list", [](const py::list &list) {
         int index = 0;
         for (auto item : list)
             py::print("list item {}: {}"_s.format(index++, item));
     });
     // test_none
     m.def("get_none", []{return py::none();});
-    m.def("print_none", [](py::none none) {
+    m.def("print_none", [](const py::none &none) { py::print("none: {}"_s.format(none)); });
-        py::print("none: {}"_s.format(none));
-    });
 
     // test_set
     m.def("get_set", []() {
@@ -46,20 +46,17 @@ TEST_SUBMODULE(pytypes, m) {
         set.add(std::string("key3"));
         return set;
     });
-    m.def("print_set", [](py::set set) {
+    m.def("print_set", [](const py::set &set) {
         for (auto item : set)
             py::print("key:", item);
     });
-    m.def("set_contains", [](py::set set, py::object key) {
+    m.def("set_contains",
-        return set.contains(key);
+          [](const py::set &set, const py::object &key) { return set.contains(key); });
-    });
+    m.def("set_contains", [](const py::set &set, const char *key) { return set.contains(key); });
-    m.def("set_contains", [](py::set set, const char* key) {
-        return set.contains(key);
-    });
 
     // test_dict
     m.def("get_dict", []() { return py::dict("key"_a="value"); });
-    m.def("print_dict", [](py::dict dict) {
+    m.def("print_dict", [](const py::dict &dict) {
         for (auto item : dict)
             py::print("key: {}, value={}"_s.format(item.first, item.second));
     });
@@ -68,12 +65,10 @@ TEST_SUBMODULE(pytypes, m) {
         auto d2 = py::dict("z"_a=3, **d1);
         return d2;
     });
-    m.def("dict_contains", [](py::dict dict, py::object val) {
+    m.def("dict_contains",
-        return dict.contains(val);
+          [](const py::dict &dict, py::object val) { return dict.contains(val); });
-    });
+    m.def("dict_contains",
-    m.def("dict_contains", [](py::dict dict, const char* val) {
+          [](const py::dict &dict, const char *val) { return dict.contains(val); });
-        return dict.contains(val);
-    });
 
     // test_str
     m.def("str_from_string", []() { return py::str(std::string("baz")); });
@@ -137,7 +132,7 @@ TEST_SUBMODULE(pytypes, m) {
     });
 
     // test_accessors
-    m.def("accessor_api", [](py::object o) {
+    m.def("accessor_api", [](const py::object &o) {
         auto d = py::dict();
 
         d["basic_attr"] = o.attr("basic_attr");
@@ -178,7 +173,7 @@ TEST_SUBMODULE(pytypes, m) {
         return d;
     });
 
-    m.def("tuple_accessor", [](py::tuple existing_t) {
+    m.def("tuple_accessor", [](const py::tuple &existing_t) {
         try {
             existing_t[0] = 1;
         } catch (const py::error_already_set &) {
@@ -226,7 +221,7 @@ TEST_SUBMODULE(pytypes, m) {
         );
     });
 
-    m.def("converting_constructors", [](py::dict d) {
+    m.def("converting_constructors", [](const py::dict &d) {
         return py::dict(
             "bytes"_a=py::bytes(d["bytes"]),
             "bytearray"_a=py::bytearray(d["bytearray"]),
@@ -242,6 +237,7 @@ TEST_SUBMODULE(pytypes, m) {
         );
     });
 
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("cast_functions", [](py::dict d) {
         // When converting between Python types, obj.cast<T>() should be the same as T(obj)
         return py::dict(
@@ -259,8 +255,10 @@ TEST_SUBMODULE(pytypes, m) {
         );
     });
 
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("convert_to_pybind11_str", [](py::object o) { return py::str(o); });
 
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("nonconverting_constructor", [](std::string type, py::object value, bool move) -> py::object {
         if (type == "bytes") {
             return move ? py::bytes(std::move(value)) : py::bytes(value);
@@ -333,8 +331,9 @@ TEST_SUBMODULE(pytypes, m) {
 
     m.def("print_failure", []() { py::print(42, UnregisteredType()); });
 
-    m.def("hash_function", [](py::object obj) { return py::hash(obj); });
+    m.def("hash_function", [](py::object obj) { return py::hash(std::move(obj)); });
 
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("test_number_protocol", [](py::object a, py::object b) {
         py::list l;
         l.append(a.equal(b));
@@ -355,6 +354,7 @@ TEST_SUBMODULE(pytypes, m) {
         return l;
     });
 
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("test_list_slicing", [](py::list a) {
         return a[py::slice(0, -1, 2)];
     });
@@ -369,10 +369,12 @@ TEST_SUBMODULE(pytypes, m) {
         return is_this_none;
     });
 
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("test_memoryview_object", [](py::buffer b) {
         return py::memoryview(b);
     });
 
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("test_memoryview_buffer_info", [](py::buffer b) {
         return py::memoryview(b.request());
     });
@@ -425,20 +427,22 @@ TEST_SUBMODULE(pytypes, m) {
     m.attr("PYBIND11_STR_LEGACY_PERMISSIVE") = true;
 #endif
 
-    m.def("isinstance_pybind11_bytes", [](py::object o) { return py::isinstance<py::bytes>(o); });
+    m.def("isinstance_pybind11_bytes",
-    m.def("isinstance_pybind11_str", [](py::object o) { return py::isinstance<py::str>(o); });
+          [](py::object o) { return py::isinstance<py::bytes>(std::move(o)); });
+    m.def("isinstance_pybind11_str",
+          [](py::object o) { return py::isinstance<py::str>(std::move(o)); });
 
-    m.def("pass_to_pybind11_bytes", [](py::bytes b) { return py::len(b); });
+    m.def("pass_to_pybind11_bytes", [](py::bytes b) { return py::len(std::move(b)); });
-    m.def("pass_to_pybind11_str", [](py::str s) { return py::len(s); });
+    m.def("pass_to_pybind11_str", [](py::str s) { return py::len(std::move(s)); });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("pass_to_std_string", [](std::string s) { return s.size(); });
 
     // test_weakref
     m.def("weakref_from_handle",
           [](py::handle h) { return py::weakref(h); });
     m.def("weakref_from_handle_and_function",
-          [](py::handle h, py::function f) { return py::weakref(h, f); });
+          [](py::handle h, py::function f) { return py::weakref(h, std::move(f)); });
-    m.def("weakref_from_object",
+    m.def("weakref_from_object", [](const py::object &o) { return py::weakref(o); });
-          [](py::object o) { return py::weakref(o); });
     m.def("weakref_from_object_and_function",
-          [](py::object o, py::function f) { return py::weakref(o, f); });
+          [](py::object o, py::function f) { return py::weakref(std::move(o), std::move(f)); });
 }

tests/test_sequences_and_iterators.cpp

@@ -14,6 +14,7 @@
 #include <pybind11/stl.h>
 
 #include <algorithm>
+#include <utility>
 
 template<typename T>
 class NonZeroIterator {
@@ -80,18 +81,17 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
       int start,stop,step;
       int size;
     };
-    py::class_<Sliceable>(m,"Sliceable")
+    py::class_<Sliceable>(m, "Sliceable")
         .def(py::init<int>())
-        .def("__getitem__",[](const Sliceable &s, py::slice slice) {
+        .def("__getitem__", [](const Sliceable &s, const py::slice &slice) {
-          py::ssize_t start, stop, step, slicelength;
+            py::ssize_t start, stop, step, slicelength;
-          if (!slice.compute(s.size, &start, &stop, &step, &slicelength))
+            if (!slice.compute(s.size, &start, &stop, &step, &slicelength))
-              throw py::error_already_set();
+                throw py::error_already_set();
-          int istart = static_cast<int>(start);
+            int istart = static_cast<int>(start);
-          int istop =  static_cast<int>(stop);
+            int istop  = static_cast<int>(stop);
-          int istep =  static_cast<int>(step);
+            int istep  = static_cast<int>(step);
-          return std::make_tuple(istart,istop,istep);
+            return std::make_tuple(istart, istop, istep);
-        })
+        });
-        ;
 
     // test_sequence
     class Sequence {
@@ -111,7 +111,7 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
             m_data = new float[m_size];
             memcpy(m_data, s.m_data, sizeof(float)*m_size);
         }
-        Sequence(Sequence &&s) : m_size(s.m_size), m_data(s.m_data) {
+        Sequence(Sequence &&s) noexcept : m_size(s.m_size), m_data(s.m_data) {
             print_move_created(this);
             s.m_size = 0;
             s.m_data = nullptr;
@@ -130,7 +130,7 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
             return *this;
         }
 
-        Sequence &operator=(Sequence &&s) {
+        Sequence &operator=(Sequence &&s) noexcept {
             if (&s != this) {
                 delete[] m_data;
                 m_size = s.m_size;
@@ -179,43 +179,54 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
     };
     py::class_<Sequence>(m, "Sequence")
         .def(py::init<size_t>())
-        .def(py::init<const std::vector<float>&>())
+        .def(py::init<const std::vector<float> &>())
         /// Bare bones interface
-        .def("__getitem__", [](const Sequence &s, size_t i) {
+        .def("__getitem__",
-            if (i >= s.size()) throw py::index_error();
+             [](const Sequence &s, size_t i) {
-            return s[i];
+                 if (i >= s.size())
-        })
+                     throw py::index_error();
-        .def("__setitem__", [](Sequence &s, size_t i, float v) {
+                 return s[i];
-            if (i >= s.size()) throw py::index_error();
+             })
-            s[i] = v;
+        .def("__setitem__",
-        })
+             [](Sequence &s, size_t i, float v) {
+                 if (i >= s.size())
+                     throw py::index_error();
+                 s[i] = v;
+             })
         .def("__len__", &Sequence::size)
         /// Optional sequence protocol operations
-        .def("__iter__", [](const Sequence &s) { return py::make_iterator(s.begin(), s.end()); },
+        .def(
-                         py::keep_alive<0, 1>() /* Essential: keep object alive while iterator exists */)
+            "__iter__",
+            [](const Sequence &s) { return py::make_iterator(s.begin(), s.end()); },
+            py::keep_alive<0, 1>() /* Essential: keep object alive while iterator exists */)
         .def("__contains__", [](const Sequence &s, float v) { return s.contains(v); })
         .def("__reversed__", [](const Sequence &s) -> Sequence { return s.reversed(); })
         /// Slicing protocol (optional)
-        .def("__getitem__", [](const Sequence &s, py::slice slice) -> Sequence* {
+        .def("__getitem__",
-            size_t start, stop, step, slicelength;
+             [](const Sequence &s, const py::slice &slice) -> Sequence * {
-            if (!slice.compute(s.size(), &start, &stop, &step, &slicelength))
+                 size_t start, stop, step, slicelength;
-                throw py::error_already_set();
+                 if (!slice.compute(s.size(), &start, &stop, &step, &slicelength))
-            auto *seq = new Sequence(slicelength);
+                     throw py::error_already_set();
-            for (size_t i = 0; i < slicelength; ++i) {
+                 auto *seq = new Sequence(slicelength);
-                (*seq)[i] = s[start]; start += step;
+                 for (size_t i = 0; i < slicelength; ++i) {
-            }
+                     (*seq)[i] = s[start];
-            return seq;
+                     start += step;
-        })
+                 }
-        .def("__setitem__", [](Sequence &s, py::slice slice, const Sequence &value) {
+                 return seq;
-            size_t start, stop, step, slicelength;
+             })
-            if (!slice.compute(s.size(), &start, &stop, &step, &slicelength))
+        .def("__setitem__",
-                throw py::error_already_set();
+             [](Sequence &s, const py::slice &slice, const Sequence &value) {
-            if (slicelength != value.size())
+                 size_t start, stop, step, slicelength;
-                throw std::runtime_error("Left and right hand size of slice assignment have different sizes!");
+                 if (!slice.compute(s.size(), &start, &stop, &step, &slicelength))
-            for (size_t i = 0; i < slicelength; ++i) {
+                     throw py::error_already_set();
-                s[start] = value[i]; start += step;
+                 if (slicelength != value.size())
-            }
+                     throw std::runtime_error(
-        })
+                         "Left and right hand size of slice assignment have different sizes!");
+                 for (size_t i = 0; i < slicelength; ++i) {
+                     s[start] = value[i];
+                     start += step;
+                 }
+             })
         /// Comparisons
         .def(py::self == py::self)
         .def(py::self != py::self)
@@ -231,8 +242,8 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
         StringMap(std::unordered_map<std::string, std::string> init)
             : map(std::move(init)) {}
 
-        void set(std::string key, std::string val) { map[key] = val; }
+        void set(const std::string &key, std::string val) { map[key] = std::move(val); }
-        std::string get(std::string key) const { return map.at(key); }
+        std::string get(const std::string &key) const { return map.at(key); }
         size_t size() const { return map.size(); }
     private:
         std::unordered_map<std::string, std::string> map;
@@ -243,19 +254,24 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
     py::class_<StringMap>(m, "StringMap")
         .def(py::init<>())
         .def(py::init<std::unordered_map<std::string, std::string>>())
-        .def("__getitem__", [](const StringMap &map, std::string key) {
+        .def("__getitem__",
-                try { return map.get(key); }
+             [](const StringMap &map, const std::string &key) {
-                catch (const std::out_of_range&) {
+                 try {
-                    throw py::key_error("key '" + key + "' does not exist");
+                     return map.get(key);
-                }
+                 } catch (const std::out_of_range &) {
-        })
+                     throw py::key_error("key '" + key + "' does not exist");
+                 }
+             })
         .def("__setitem__", &StringMap::set)
         .def("__len__", &StringMap::size)
-        .def("__iter__", [](const StringMap &map) { return py::make_key_iterator(map.begin(), map.end()); },
+        .def(
-                py::keep_alive<0, 1>())
+            "__iter__",
-        .def("items", [](const StringMap &map) { return py::make_iterator(map.begin(), map.end()); },
+            [](const StringMap &map) { return py::make_key_iterator(map.begin(), map.end()); },
-                py::keep_alive<0, 1>())
+            py::keep_alive<0, 1>())
-        ;
+        .def(
+            "items",
+            [](const StringMap &map) { return py::make_iterator(map.begin(), map.end()); },
+            py::keep_alive<0, 1>());
 
     // test_generalized_iterators
     class IntPairs {
@@ -304,7 +320,7 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
 #endif
 
     // test_python_iterator_in_cpp
-    m.def("object_to_list", [](py::object o) {
+    m.def("object_to_list", [](const py::object &o) {
         auto l = py::list();
         for (auto item : o) {
             l.append(item);
@@ -322,22 +338,22 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
     });
 
     // test_sequence_length: check that Python sequences can be converted to py::sequence.
-    m.def("sequence_length", [](py::sequence seq) { return seq.size(); });
+    m.def("sequence_length", [](const py::sequence &seq) { return seq.size(); });
 
     // Make sure that py::iterator works with std algorithms
-    m.def("count_none", [](py::object o) {
+    m.def("count_none", [](const py::object &o) {
         return std::count_if(o.begin(), o.end(), [](py::handle h) { return h.is_none(); });
     });
 
-    m.def("find_none", [](py::object o) {
+    m.def("find_none", [](const py::object &o) {
         auto it = std::find_if(o.begin(), o.end(), [](py::handle h) { return h.is_none(); });
         return it->is_none();
     });
 
-    m.def("count_nonzeros", [](py::dict d) {
+    m.def("count_nonzeros", [](const py::dict &d) {
-       return std::count_if(d.begin(), d.end(), [](std::pair<py::handle, py::handle> p) {
+        return std::count_if(d.begin(), d.end(), [](std::pair<py::handle, py::handle> p) {
-           return p.second.cast<int>() != 0;
+            return p.second.cast<int>() != 0;
-       });
+        });
     });
 
     m.def("tuple_iterator", &test_random_access_iterator<py::tuple>);

tests/test_smart_ptr.cpp

@@ -170,7 +170,7 @@ struct SharedPtrRef {
     struct A {
         A() { print_created(this); }
         A(const A &) { print_copy_created(this); }
-        A(A &&) { print_move_created(this); }
+        A(A &&) noexcept { print_move_created(this); }
         ~A() { print_destroyed(this); }
     };
 
@@ -183,7 +183,7 @@ struct SharedFromThisRef {
     struct B : std::enable_shared_from_this<B> {
         B() { print_created(this); }
         B(const B &) : std::enable_shared_from_this<B>() { print_copy_created(this); }
-        B(B &&) : std::enable_shared_from_this<B>() { print_move_created(this); }
+        B(B &&) noexcept : std::enable_shared_from_this<B>() { print_move_created(this); }
         ~B() { print_destroyed(this); }
     };
 
@@ -209,7 +209,9 @@ struct C {
 struct TypeForHolderWithAddressOf {
     TypeForHolderWithAddressOf() { print_created(this); }
     TypeForHolderWithAddressOf(const TypeForHolderWithAddressOf &) { print_copy_created(this); }
-    TypeForHolderWithAddressOf(TypeForHolderWithAddressOf &&) { print_move_created(this); }
+    TypeForHolderWithAddressOf(TypeForHolderWithAddressOf &&) noexcept {
+        print_move_created(this);
+    }
     ~TypeForHolderWithAddressOf() { print_destroyed(this); }
     std::string toString() const {
         return "TypeForHolderWithAddressOf[" + std::to_string(value) + "]";
@@ -245,7 +247,7 @@ struct ElementA : ElementBase {
 };
 
 struct ElementList {
-    void add(std::shared_ptr<ElementBase> e) { l.push_back(e); }
+    void add(const std::shared_ptr<ElementBase> &e) { l.push_back(e); }
     std::vector<std::shared_ptr<ElementBase>> l;
 };
 
@@ -308,6 +310,7 @@ TEST_SUBMODULE(smart_ptr, m) {
     m.def("make_myobject2_1", []() { return new MyObject2(6); });
     m.def("make_myobject2_2", []() { return std::make_shared<MyObject2>(7); });
     m.def("print_myobject2_1", [](const MyObject2 *obj) { py::print(obj->toString()); });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("print_myobject2_2", [](std::shared_ptr<MyObject2> obj) { py::print(obj->toString()); });
     m.def("print_myobject2_3", [](const std::shared_ptr<MyObject2> &obj) { py::print(obj->toString()); });
     m.def("print_myobject2_4", [](const std::shared_ptr<MyObject2> *obj) { py::print((*obj)->toString()); });
@@ -317,6 +320,7 @@ TEST_SUBMODULE(smart_ptr, m) {
     m.def("make_myobject3_1", []() { return new MyObject3(8); });
     m.def("make_myobject3_2", []() { return std::make_shared<MyObject3>(9); });
     m.def("print_myobject3_1", [](const MyObject3 *obj) { py::print(obj->toString()); });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("print_myobject3_2", [](std::shared_ptr<MyObject3> obj) { py::print(obj->toString()); });
     m.def("print_myobject3_3", [](const std::shared_ptr<MyObject3> &obj) { py::print(obj->toString()); });
     m.def("print_myobject3_4", [](const std::shared_ptr<MyObject3> *obj) { py::print((*obj)->toString()); });
@@ -358,12 +362,15 @@ TEST_SUBMODULE(smart_ptr, m) {
     py::class_<SharedPtrRef, std::unique_ptr<SharedPtrRef>>(m, "SharedPtrRef")
         .def(py::init<>())
         .def_readonly("ref", &SharedPtrRef::value)
-        .def_property_readonly("copy", [](const SharedPtrRef &s) { return s.value; },
+        .def_property_readonly(
-                               py::return_value_policy::copy)
+            "copy", [](const SharedPtrRef &s) { return s.value; }, py::return_value_policy::copy)
         .def_readonly("holder_ref", &SharedPtrRef::shared)
-        .def_property_readonly("holder_copy", [](const SharedPtrRef &s) { return s.shared; },
+        .def_property_readonly(
-                               py::return_value_policy::copy)
+            "holder_copy",
+            [](const SharedPtrRef &s) { return s.shared; },
+            py::return_value_policy::copy)
         .def("set_ref", [](SharedPtrRef &, const A &) { return true; })
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
         .def("set_holder", [](SharedPtrRef &, std::shared_ptr<A>) { return true; });
 
     // test_shared_ptr_from_this_and_references
@@ -372,13 +379,19 @@ TEST_SUBMODULE(smart_ptr, m) {
     py::class_<SharedFromThisRef, std::unique_ptr<SharedFromThisRef>>(m, "SharedFromThisRef")
         .def(py::init<>())
         .def_readonly("bad_wp", &SharedFromThisRef::value)
-        .def_property_readonly("ref", [](const SharedFromThisRef &s) -> const B & { return *s.shared; })
+        .def_property_readonly("ref",
-        .def_property_readonly("copy", [](const SharedFromThisRef &s) { return s.value; },
+                               [](const SharedFromThisRef &s) -> const B & { return *s.shared; })
-                               py::return_value_policy::copy)
+        .def_property_readonly(
+            "copy",
+            [](const SharedFromThisRef &s) { return s.value; },
+            py::return_value_policy::copy)
         .def_readonly("holder_ref", &SharedFromThisRef::shared)
-        .def_property_readonly("holder_copy", [](const SharedFromThisRef &s) { return s.shared; },
+        .def_property_readonly(
-                               py::return_value_policy::copy)
+            "holder_copy",
+            [](const SharedFromThisRef &s) { return s.shared; },
+            py::return_value_policy::copy)
         .def("set_ref", [](SharedFromThisRef &, const B &) { return true; })
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
         .def("set_holder", [](SharedFromThisRef &, std::shared_ptr<B>) { return true; });
 
     // Issue #865: shared_from_this doesn't work with virtual inheritance
@@ -396,10 +409,14 @@ TEST_SUBMODULE(smart_ptr, m) {
     py::class_<TypeForHolderWithAddressOf, HolderWithAddressOf>(m, "TypeForHolderWithAddressOf")
         .def_static("make", []() { return HolderWithAddressOf(new TypeForHolderWithAddressOf); })
         .def("get", [](const HolderWithAddressOf &self) { return self.get(); })
-        .def("print_object_1", [](const TypeForHolderWithAddressOf *obj) { py::print(obj->toString()); })
+        .def("print_object_1",
+             [](const TypeForHolderWithAddressOf *obj) { py::print(obj->toString()); })
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
         .def("print_object_2", [](HolderWithAddressOf obj) { py::print(obj.get()->toString()); })
-        .def("print_object_3", [](const HolderWithAddressOf &obj) { py::print(obj.get()->toString()); })
+        .def("print_object_3",
-        .def("print_object_4", [](const HolderWithAddressOf *obj) { py::print((*obj).get()->toString()); });
+             [](const HolderWithAddressOf &obj) { py::print(obj.get()->toString()); })
+        .def("print_object_4",
+             [](const HolderWithAddressOf *obj) { py::print((*obj).get()->toString()); });
 
     // test_move_only_holder_with_addressof_operator
     using MoveOnlyHolderWithAddressOf = unique_ptr_with_addressof_operator<TypeForMoveOnlyHolderWithAddressOf>;
@@ -411,6 +428,7 @@ TEST_SUBMODULE(smart_ptr, m) {
     // test_smart_ptr_from_default
     py::class_<HeldByDefaultHolder, std::unique_ptr<HeldByDefaultHolder>>(m, "HeldByDefaultHolder")
         .def(py::init<>())
+        // NOLINTNEXTLINE(performance-unnecessary-value-param)
         .def_static("load_shared_ptr", [](std::shared_ptr<HeldByDefaultHolder>) {});
 
     // test_shared_ptr_gc

tests/test_stl.cpp

@@ -202,6 +202,7 @@ TEST_SUBMODULE(stl, m) {
     }, py::arg_v("x", std::nullopt, "None"));
 
     m.def("nodefer_none_optional", [](std::optional<int>) { return true; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("nodefer_none_optional", [](py::none) { return false; });
 
     using opt_holder = OptionalHolder<std::optional, MoveOutDetector>;
@@ -245,13 +246,13 @@ TEST_SUBMODULE(stl, m) {
         using result_type = const char *;
 
         result_type operator()(int) { return "int"; }
-        result_type operator()(std::string) { return "std::string"; }
+        result_type operator()(const std::string &) { return "std::string"; }
         result_type operator()(double) { return "double"; }
         result_type operator()(std::nullptr_t) { return "std::nullptr_t"; }
     };
 
     // test_variant
-    m.def("load_variant", [](variant<int, std::string, double, std::nullptr_t> v) {
+    m.def("load_variant", [](const variant<int, std::string, double, std::nullptr_t> &v) {
         return py::detail::visit_helper<variant>::call(visitor(), v);
     });
     m.def("load_variant_2pass", [](variant<double, int> v) {
@@ -287,8 +288,11 @@ TEST_SUBMODULE(stl, m) {
     m.def("stl_pass_by_pointer", [](std::vector<int>* v) { return *v; }, "v"_a=nullptr);
 
     // #1258: pybind11/stl.h converts string to vector<string>
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("func_with_string_or_vector_string_arg_overload", [](std::vector<std::string>) { return 1; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("func_with_string_or_vector_string_arg_overload", [](std::list<std::string>) { return 2; });
+    // NOLINTNEXTLINE(performance-unnecessary-value-param)
     m.def("func_with_string_or_vector_string_arg_overload", [](std::string) { return 3; });
 
     class Placeholder {

tests/test_virtual_functions.cpp

@@ -17,7 +17,10 @@ class ExampleVirt  {
 public:
     ExampleVirt(int state) : state(state) { print_created(this, state); }
     ExampleVirt(const ExampleVirt &e) : state(e.state) { print_copy_created(this); }
-    ExampleVirt(ExampleVirt &&e) : state(e.state) { print_move_created(this); e.state = 0; }
+    ExampleVirt(ExampleVirt &&e) noexcept : state(e.state) {
+        print_move_created(this);
+        e.state = 0;
+    }
     virtual ~ExampleVirt() { print_destroyed(this); }
 
     virtual int run(int value) {
@@ -100,7 +103,10 @@ public:
 class NonCopyable {
 public:
     NonCopyable(int a, int b) : value{new int(a*b)} { print_created(this, a, b); }
-    NonCopyable(NonCopyable &&o) { value = std::move(o.value); print_move_created(this); }
+    NonCopyable(NonCopyable &&o) noexcept {
+        value = std::move(o.value);
+        print_move_created(this);
+    }
     NonCopyable(const NonCopyable &) = delete;
     NonCopyable() = delete;
     void operator=(const NonCopyable &) = delete;
@@ -120,7 +126,10 @@ class Movable {
 public:
     Movable(int a, int b) : value{a+b} { print_created(this, a, b); }
     Movable(const Movable &m) { value = m.value; print_copy_created(this); }
-    Movable(Movable &&m) { value = std::move(m.value); print_move_created(this); }
+    Movable(Movable &&m) noexcept {
+        value = m.value;
+        print_move_created(this);
+    }
     std::string get_value() const { return std::to_string(value); }
     ~Movable() { print_destroyed(this); }
 private: