From fad5d3386ce76807a6195d069bed8b0fee5ddcab Mon Sep 17 00:00:00 2001
From: Jason Rhinelander <jason@imaginary.ca>
Date: Wed, 12 Jul 2017 14:59:16 -0400
Subject: [PATCH] Detect c++ standard unconditionally

Currently select_cxx_standard(), which sets PYBIND11_CPP_STANDARD when
not externally set, is only called from pybind11_add_module(), but the
embed target setup (which runs unconditionally) makes use of
${PYBIND11_CPP_STANDARD}, which isn't set yet.  This commit removes the
`select_cxx_standard` function completely and just always runs the
standard detection code.

This also tweaks the detection code to not bothering checking for the
`-std=c++11` flag when the `-std=c++14` detection succeeded.
---
 tools/pybind11Config.cmake.in |  1 -
 tools/pybind11Tools.cmake     | 29 ++++++++++++++---------------
 2 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/tools/pybind11Config.cmake.in b/tools/pybind11Config.cmake.in
index 6f0a406fb..3dd1b2c1a 100644
--- a/tools/pybind11Config.cmake.in
+++ b/tools/pybind11Config.cmake.in
@@ -90,7 +90,6 @@ if(NOT TARGET ${PN}::pybind11)
       set_property(TARGET ${PN}::module APPEND PROPERTY INTERFACE_LINK_LIBRARIES ${PYTHON_LIBRARIES})
     endif()
 
-    select_cxx_standard()
     set_property(TARGET ${PN}::pybind11 APPEND PROPERTY INTERFACE_COMPILE_OPTIONS "${PYBIND11_CPP_STANDARD}")
 
     get_property(_iid TARGET ${PN}::pybind11 PROPERTY INTERFACE_INCLUDE_DIRECTORIES)
diff --git a/tools/pybind11Tools.cmake b/tools/pybind11Tools.cmake
index 62de9c9fd..86ccd58d3 100644
--- a/tools/pybind11Tools.cmake
+++ b/tools/pybind11Tools.cmake
@@ -18,27 +18,27 @@ find_package(PythonLibsNew ${PYBIND11_PYTHON_VERSION} REQUIRED)
 include(CheckCXXCompilerFlag)
 include(CMakeParseArguments)
 
-function(select_cxx_standard)
-  if(NOT PYBIND11_CPP_STANDARD)
-    if(NOT MSVC)
-      check_cxx_compiler_flag("-std=c++14" HAS_CPP14_FLAG)
-      check_cxx_compiler_flag("-std=c++11" HAS_CPP11_FLAG)
+if(NOT PYBIND11_CPP_STANDARD)
+  if(NOT MSVC)
+    check_cxx_compiler_flag("-std=c++14" HAS_CPP14_FLAG)
 
-      if (HAS_CPP14_FLAG)
-        set(PYBIND11_CPP_STANDARD -std=c++14)
-      elseif (HAS_CPP11_FLAG)
+    if (HAS_CPP14_FLAG)
+      set(PYBIND11_CPP_STANDARD -std=c++14)
+    else()
+      check_cxx_compiler_flag("-std=c++11" HAS_CPP11_FLAG)
+      if (HAS_CPP11_FLAG)
         set(PYBIND11_CPP_STANDARD -std=c++11)
       else()
         message(FATAL_ERROR "Unsupported compiler -- pybind11 requires C++11 support!")
       endif()
-    elseif(MSVC)
-      set(PYBIND11_CPP_STANDARD /std:c++14)
     endif()
-
-    set(PYBIND11_CPP_STANDARD ${PYBIND11_CPP_STANDARD} CACHE STRING
-        "C++ standard flag, e.g. -std=c++11, -std=c++14, /std:c++14.  Defaults to C++14 mode." FORCE)
+  elseif(MSVC)
+    set(PYBIND11_CPP_STANDARD /std:c++14)
   endif()
-endfunction()
+
+  set(PYBIND11_CPP_STANDARD ${PYBIND11_CPP_STANDARD} CACHE STRING
+      "C++ standard flag, e.g. -std=c++11, -std=c++14, /std:c++14.  Defaults to C++14 mode." FORCE)
+endif()
 
 # Checks whether the given CXX/linker flags can compile and link a cxx file.  cxxflags and
 # linkerflags are lists of flags to use.  The result variable is a unique variable name for each set
@@ -165,7 +165,6 @@ function(pybind11_add_module target_name)
     endif()
   endif()
 
-  select_cxx_standard()
   # Make sure C++11/14 are enabled
   target_compile_options(${target_name} PUBLIC ${PYBIND11_CPP_STANDARD})