From: =?utf-8?q?Timo_R=C3=B6hling?= <roehling@debian.org>
Date: Fri, 22 Oct 2021 15:32:20 +0200
Subject: Fix check_symbol_exists() with -pedantic-errors

Forwarded: https://gitlab.kitware.com/cmake/cmake/-/merge_requests/6656
---
 Modules/CheckSymbolExists.cmake                  | 15 +++++++++++++++
 Tests/CMakeOnly/CheckSymbolExists/CMakeLists.txt | 11 +++++++++++
 2 files changed, 26 insertions(+)

diff --git a/Modules/CheckSymbolExists.cmake b/Modules/CheckSymbolExists.cmake
index f8ca584..a87fdbd 100644
--- a/Modules/CheckSymbolExists.cmake
+++ b/Modules/CheckSymbolExists.cmake
@@ -67,14 +67,29 @@ cmake_policy(SET CMP0054 NEW) # if() quoted variables not dereferenced
 
 macro(CHECK_SYMBOL_EXISTS SYMBOL FILES VARIABLE)
   if(CMAKE_C_COMPILER_LOADED)
+    __CHECK_SYMBOL_EXISTS_FILTER_FLAGS(C)
     __CHECK_SYMBOL_EXISTS_IMPL("${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/CheckSymbolExists.c" "${SYMBOL}" "${FILES}" "${VARIABLE}" )
+    __CHECK_SYMBOL_EXISTS_RESTORE_FLAGS(C)
   elseif(CMAKE_CXX_COMPILER_LOADED)
+    __CHECK_SYMBOL_EXISTS_FILTER_FLAGS(CXX)
     __CHECK_SYMBOL_EXISTS_IMPL("${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/CheckSymbolExists.cxx" "${SYMBOL}" "${FILES}" "${VARIABLE}" )
+    __CHECK_SYMBOL_EXISTS_RESTORE_FLAGS(CXX)
   else()
     message(FATAL_ERROR "CHECK_SYMBOL_EXISTS needs either C or CXX language enabled")
   endif()
 endmacro()
 
+macro(__CHECK_SYMBOL_EXISTS_FILTER_FLAGS LANG)
+    set(__CMAKE_${LANG}_FLAGS_SAVED "${CMAKE_${LANG}_FLAGS}")
+    string(REGEX REPLACE "(^| )-Werror([= ][^ ]*)?( |$)" " " CMAKE_${LANG}_FLAGS "${CMAKE_${LANG}_FLAGS}")
+    string(REGEX REPLACE "(^| )-pedantic-errors( |$)" " " CMAKE_${LANG}_FLAGS "${CMAKE_${LANG}_FLAGS}")
+endmacro()
+
+macro(__CHECK_SYMBOL_EXISTS_RESTORE_FLAGS LANG)
+    set(CMAKE_${LANG}_FLAGS "${__CMAKE_${LANG}_FLAGS_SAVED}")
+    unset(__CMAKE_${LANG}_FLAGS_SAVED)
+endmacro()
+
 macro(__CHECK_SYMBOL_EXISTS_IMPL SOURCEFILE SYMBOL FILES VARIABLE)
   if(NOT DEFINED "${VARIABLE}" OR "x${${VARIABLE}}" STREQUAL "x${VARIABLE}")
     set(CMAKE_CONFIGURABLE_FILE_CONTENT "/* */\n")
diff --git a/Tests/CMakeOnly/CheckSymbolExists/CMakeLists.txt b/Tests/CMakeOnly/CheckSymbolExists/CMakeLists.txt
index 9a9bb2a..0ced696 100644
--- a/Tests/CMakeOnly/CheckSymbolExists/CMakeLists.txt
+++ b/Tests/CMakeOnly/CheckSymbolExists/CMakeLists.txt
@@ -48,4 +48,15 @@ if (CMAKE_COMPILER_IS_GNUCC)
   if (CSE_RESULT_O3)
     message(SEND_ERROR "CheckSymbolExists reported a nonexistent symbol as existing with optimization -O3")
   endif ()
+
+  string(APPEND CMAKE_C_FLAGS " -pedantic-errors")
+  unset(CS_RESULT_PEDANTIC_ERRORS CACHE)
+  message(STATUS "Testing with -pedantic-errors")
+
+  check_symbol_exists(fopen "stdio.h" CSE_RESULT_PEDANTIC_ERRORS)
+
+  if(NOT CSE_RESULT_PEDANTIC_ERRORS)
+    message(SEND_ERROR "ChecKSymbolExists reported an existing symbol as nonexisting with -pedantic-errors")
+  endif()
+
 endif ()