CheckSourceCompiles: Avoid linker warning with -fembed-bitcode

When the Apple linker sees -headerpad_max_install_names and
bitcode is enabled with a flag like -fembed-bitcode, it issues a warning
and ignores the -headerpad_max_install_names flag. This causes
unrelated compiler and linker flag checks to fail for valid flags.
In f745e0497e (CheckCompilerFlags: Catch linker warning about ignored
flags, 2022-01-03), we started detecting linker warnings, which caused
a regression for projects that were setting -fembed-bitcode in their
CMAKE_CXX_FLAGS or similar. Prevent that regression by removing
the -headerpad_max_install_names linker flag when we know it will
warn and be ignored anyway.

Fixes: #23390
Issue: #23408

1 files changed, 69 insertions, 0 deletions

diff --git a/Modules/Internal/HeaderpadWorkaround.cmake b/Modules/Internal/HeaderpadWorkaround.cmake
new file mode 100644
index 0000000000..9a7f9f57e4
--- /dev/null
+++ b/Modules/Internal/HeaderpadWorkaround.cmake
@@ -0,0 +1,69 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file Copyright.txt or https://cmake.org/licensing for details.
+
+
+# Do NOT include this module directly into any of your code. It is used by
+# the try_compile() implementation to work around a specific issue with
+# conflicting flags when building for Apple platforms.
+if(NOT APPLE)
+  return()
+endif()
+
+cmake_policy(PUSH)
+cmake_policy(SET CMP0054 NEW) # if() quoted variables not dereferenced
+
+function(__cmake_internal_workaround_headerpad_flag_conflict _LANG)
+
+  # Until we can avoid hard-coding -Wl,-headerpad_max_install_names in the
+  # linker flags, we need to remove it here for cases where we know it will
+  # conflict with other flags, generate a warning and be ignored.
+  set(regex "(^| )(-fembed-bitcode(-marker|=(all|bitcode|marker))?|-bundle_bitcode)($| )")
+  set(remove_headerpad NO)
+
+  # Check arbitrary flags that the user or project has set. These compiler
+  # flags get added to the linker command line.
+  if("${CMAKE_${_LANG}_FLAGS}" MATCHES "${regex}")
+    set(remove_headerpad YES)
+  endif()
+  if(NOT remove_headerpad)
+    get_property(is_multi_config GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
+    if(is_multi_config)
+      # Only one of these config-specific variables will be set by try_compile()
+      # and the rest will be unset, but we can't easily tell which one is set.
+      # No harm to just add them all here, empty ones won't add flags to check.
+      foreach(config IN LISTS CMAKE_CONFIGURATION_TYPES)
+        if("${CMAKE_${_LANG}_FLAGS_${config}}" MATCHES "${regex}")
+          set(remove_headerpad YES)
+          break()
+        endif()
+      endforeach()
+    else()
+      if("${CMAKE_${_LANG}_FLAGS_${CMAKE_BUILD_TYPE}}" MATCHES "${regex}")
+        set(remove_headerpad YES)
+      endif()
+    endif()
+  endif()
+
+  # The try_compile() command passes compiler flags to check in a way that
+  # results in them being added to add_definitions(). Those don't end up on
+  # the linker command line, so we don't need to check them here.
+
+  if(remove_headerpad)
+    foreach(flag IN ITEMS
+      CMAKE_${_LANG}_LINK_FLAGS
+      CMAKE_SHARED_LIBRARY_CREATE_${_LANG}_FLAGS
+      CMAKE_SHARED_MODULE_CREATE_${_LANG}_FLAGS)
+      string(REPLACE "-Wl,-headerpad_max_install_names" "" ${flag} "${${flag}}")
+      set(${flag} "${${flag}}" PARENT_SCOPE)
+    endforeach()
+  endif()
+endfunction()
+
+get_property(__enabled_languages GLOBAL PROPERTY ENABLED_LANGUAGES)
+foreach(__lang IN LISTS __enabled_languages)
+  __cmake_internal_workaround_headerpad_flag_conflict(${__lang})
+endforeach()
+unset(__lang)
+unset(__enabled_languages)
+
+cmake_policy(POP)