fix(clang-tidy): Add cppcoreguidelines-init-vars,slicing, and throw-by-value-catch-by-reference checks (#3094)

* clang-tidy: guard against more UB behavior

* Remove slicing check for now

.clang-tidy

@@ -1,10 +1,12 @@
 FormatStyle: file
 
 Checks: '
+cppcoreguidelines-init-variables,
 clang-analyzer-optin.cplusplus.VirtualCall,
 llvm-namespace-comment,
 misc-misplaced-const,
 misc-static-assert,
+misc-throw-by-value-catch-by-reference,
 misc-uniqueptr-reset-release,
 modernize-avoid-bind,
 modernize-redundant-void-arg,
@@ -33,6 +35,8 @@ readability-uniqueptr-delete-release,
 '
 
 CheckOptions:
+- key:             performance-for-range-copy.WarnOnAllAutoCopies
+  value:           true
 - key:             performance-unnecessary-value-param.AllowedTypes
   value:           'exception_ptr$;'
 

include/pybind11/eval.h

@@ -55,7 +55,7 @@ object eval(const str &expr, object global = globals(), object local = object())
        this seems to be the only alternative */
     std::string buffer = "# -*- coding: utf-8 -*-\n" + (std::string) expr;
 
-    int start;
+    int start = 0;
     switch (mode) {
         case eval_expr:             start = Py_eval_input;   break;
         case eval_single_statement: start = Py_single_input; break;
@@ -107,7 +107,7 @@ object eval_file(str fname, object global = globals(), object local = object())
 
     detail::ensure_builtins_in_globals(global);
 
-    int start;
+    int start = 0;
     switch (mode) {
         case eval_expr:             start = Py_eval_input;   break;
         case eval_single_statement: start = Py_single_input; break;

include/pybind11/pytypes.h

@@ -490,7 +490,7 @@ inline handle get_function(handle value) {
 inline PyObject * dict_getitemstring(PyObject *v, const char *key)
 {
 #if PY_MAJOR_VERSION >= 3
-    PyObject *kv, *rv;
+    PyObject *kv = nullptr, *rv = nullptr;
     kv = PyUnicode_FromString(key);
     if (kv == NULL) {
         throw error_already_set();
@@ -1016,8 +1016,8 @@ public:
             if (!temp)
                 pybind11_fail("Unable to extract string contents! (encoding issue)");
         }
-        char *buffer;
+        char *buffer = nullptr;
-        ssize_t length;
+        ssize_t length = 0;
         if (PYBIND11_BYTES_AS_STRING_AND_SIZE(temp.ptr(), &buffer, &length))
             pybind11_fail("Unable to extract string contents! (invalid type)");
         return std::string(buffer, (size_t) length);
@@ -1072,8 +1072,8 @@ public:
     explicit bytes(const pybind11::str &s);
 
     operator std::string() const {
-        char *buffer;
+        char *buffer = nullptr;
-        ssize_t length;
+        ssize_t length = 0;
         if (PYBIND11_BYTES_AS_STRING_AND_SIZE(m_ptr, &buffer, &length))
             pybind11_fail("Unable to extract bytes contents!");
         return std::string(buffer, (size_t) length);
@@ -1090,8 +1090,8 @@ inline bytes::bytes(const pybind11::str &s) {
         if (!temp)
             pybind11_fail("Unable to extract string contents! (encoding issue)");
     }
-    char *buffer;
+    char *buffer = nullptr;
-    ssize_t length;
+    ssize_t length = 0;
     if (PYBIND11_BYTES_AS_STRING_AND_SIZE(temp.ptr(), &buffer, &length))
         pybind11_fail("Unable to extract string contents! (invalid type)");
     auto obj = reinterpret_steal<object>(PYBIND11_BYTES_FROM_STRING_AND_SIZE(buffer, length));
@@ -1101,8 +1101,8 @@ inline bytes::bytes(const pybind11::str &s) {
 }
 
 inline str::str(const bytes& b) {
-    char *buffer;
+    char *buffer = nullptr;
-    ssize_t length;
+    ssize_t length = 0;
     if (PYBIND11_BYTES_AS_STRING_AND_SIZE(b.ptr(), &buffer, &length))
         pybind11_fail("Unable to extract bytes contents!");
     auto obj = reinterpret_steal<object>(PyUnicode_FromStringAndSize(buffer, (ssize_t) length));

include/pybind11/stl_bind.h

@@ -217,9 +217,10 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
     );
 
     /// Slicing protocol
-    cl.def("__getitem__",
+    cl.def(
+        "__getitem__",
         [](const Vector &v, slice slice) -> Vector * {
-            size_t start, stop, step, slicelength;
+            size_t start = 0, stop = 0, step = 0, slicelength = 0;
 
             if (!slice.compute(v.size(), &start, &stop, &step, &slicelength))
                 throw error_already_set();
@@ -234,12 +235,12 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
             return seq;
         },
         arg("s"),
-        "Retrieve list elements using a slice object"
+        "Retrieve list elements using a slice object");
-    );
 
-    cl.def("__setitem__",
+    cl.def(
+        "__setitem__",
         [](Vector &v, slice slice, const Vector &value) {
-            size_t start, stop, step, slicelength;
+            size_t start = 0, stop = 0, step = 0, slicelength = 0;
             if (!slice.compute(v.size(), &start, &stop, &step, &slicelength))
                 throw error_already_set();
 
@@ -251,8 +252,7 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
                 start += step;
             }
         },
-        "Assign list elements using a slice object"
+        "Assign list elements using a slice object");
-    );
 
     cl.def("__delitem__",
         [wrap_i](Vector &v, DiffType i) {
@@ -262,9 +262,10 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
         "Delete the list elements at index ``i``"
     );
 
-    cl.def("__delitem__",
+    cl.def(
+        "__delitem__",
         [](Vector &v, slice slice) {
-            size_t start, stop, step, slicelength;
+            size_t start = 0, stop = 0, step = 0, slicelength = 0;
 
             if (!slice.compute(v.size(), &start, &stop, &step, &slicelength))
                 throw error_already_set();
@@ -278,9 +279,7 @@ void vector_modifiers(enable_if_t<is_copy_constructible<typename Vector::value_t
                 }
             }
         },
-        "Delete list elements using a slice object"
+        "Delete list elements using a slice object");
-    );
-
 }
 
 // If the type has an operator[] that doesn't return a reference (most notably std::vector<bool>),

tests/test_eval.cpp

@@ -66,7 +66,7 @@ TEST_SUBMODULE(eval_, m) {
         auto local = py::dict();
         local["y"] = py::int_(43);
 
-        int val_out;
+        int val_out = 0;
         local["call_test2"] = py::cpp_function([&](int value) { val_out = value; });
 
         auto result = py::eval_file(std::move(filename), global, local);

tests/test_numpy_vectorize.cpp

@@ -92,7 +92,7 @@ TEST_SUBMODULE(numpy_vectorize, m) {
           [](const py::array_t<int, py::array::forcecast> &arg1,
              const py::array_t<float, py::array::forcecast> &arg2,
              const py::array_t<double, py::array::forcecast> &arg3) {
-              py::ssize_t ndim;
+              py::ssize_t ndim = 0;
               std::vector<py::ssize_t> shape;
               std::array<py::buffer_info, 3> buffers{
                   {arg1.request(), arg2.request(), arg3.request()}};

tests/test_sequences_and_iterators.cpp

@@ -84,7 +84,7 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
     py::class_<Sliceable>(m, "Sliceable")
         .def(py::init<int>())
         .def("__getitem__", [](const Sliceable &s, const py::slice &slice) {
-            py::ssize_t start, stop, step, slicelength;
+            py::ssize_t start = 0, stop = 0, step = 0, slicelength = 0;
             if (!slice.compute(s.size, &start, &stop, &step, &slicelength))
                 throw py::error_already_set();
             int istart = static_cast<int>(start);
@@ -204,7 +204,7 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
         /// Slicing protocol (optional)
         .def("__getitem__",
              [](const Sequence &s, const py::slice &slice) -> Sequence * {
-                 size_t start, stop, step, slicelength;
+                 size_t start = 0, stop = 0, step = 0, slicelength = 0;
                  if (!slice.compute(s.size(), &start, &stop, &step, &slicelength))
                      throw py::error_already_set();
                  auto *seq = new Sequence(slicelength);
@@ -216,7 +216,7 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
              })
         .def("__setitem__",
              [](Sequence &s, const py::slice &slice, const Sequence &value) {
-                 size_t start, stop, step, slicelength;
+                 size_t start = 0, stop = 0, step = 0, slicelength = 0;
                  if (!slice.compute(s.size(), &start, &stop, &step, &slicelength))
                      throw py::error_already_set();
                  if (slicelength != value.size())