Deprecate gtest_force_shared_crt

CMake 3.15 added MSVC_RUNTIME_LIBRARY, an official mechanism to
configure the runtime library used by targets. Setting the property
will properly set the MSVC runtime library. With MSVC_RUNTIME_LIBRARY
available, gtest_force_shared_crt is no longer necessary and is
deprecated, with a notice given.

Author: charles-lunarg

googletest/CMakeLists.txt

@@ -8,12 +8,10 @@
 # ctest. You can select which tests to run using 'ctest -R regex'.
 # For more options, run 'ctest --help'.
 
-# When other libraries are using a shared version of runtime libraries,
-# Google Test also has to use one.
-option(
-  gtest_force_shared_crt
-  "Use shared (DLL) run-time lib even when Google Test is built as static lib."
-  OFF)
+if (DEFINED gtest_force_shared_crt)
+  message(DEPRECATION
+    "gtest_force_shared_crt is deprecated and ignored. Use `CMAKE_MSVC_RUNTIME_LIBRARY` to configure the MSVC runtime library")
+endif()
 
 option(gtest_build_tests "Build all of gtest's own tests." OFF)
 

googletest/README.md

@@ -117,10 +117,16 @@ something like the following: gtest.lib(gtest-all.obj) : error LNK2038: mismatch
 detected for 'RuntimeLibrary': value 'MTd_StaticDebug' doesn't match value
 'MDd_DynamicDebug' in main.obj
 
-GoogleTest already has a CMake option for this: `gtest_force_shared_crt`
+This is resolved by forcing googletest to dynamically link to the C runtimes.
+CMake 3.15 added the variable `CMAKE_MSVC_RUNTIME_LIBRARY` as the way to
+select the C runtime used by projects.
+
+To do this, either add
+`set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>DLL")`
+to the project's CMakeLists.txt before including googletest, or set it
+on the command line with
+`-DCMAKE_MSVC_RUNTIME_LIBRARY="MultiThreaded$<$<CONFIG:Debug>:Debug>DLL"`.
 
-Enabling this option will make gtest link the runtimes dynamically too, and
-match the project in which it is included.
 
 #### C++ Standard Version
 

googletest/cmake/internal_utils.cmake

@@ -28,15 +28,6 @@ macro(fix_default_compiler_settings_)
              CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE
              CMAKE_CXX_FLAGS_MINSIZEREL CMAKE_CXX_FLAGS_RELWITHDEBINFO)
       if (NOT BUILD_SHARED_LIBS AND NOT gtest_force_shared_crt)
-        # When Google Test is built as a shared library, it should also use
-        # shared runtime libraries. Otherwise, it may end up with multiple
-        # copies of runtime library data in different modules, resulting in
-        # hard-to-find crashes. When it is built as a static library, it is
-        # preferable to use CRT as static libraries, as we don't have to rely
-        # on CRT DLLs being available. CMake always defaults to using shared
-        # CRT libraries, so we override that default here.
-        string(REPLACE "/MD" "-MT" ${flag_var} "${${flag_var}}")
-
         # When using Ninja with Clang, static builds pass -D_DLL on Windows.
         # This is incorrect and should not happen, so we fix that here.
         string(REPLACE "-D_DLL" "" ${flag_var} "${${flag_var}}")
@@ -70,6 +61,19 @@ macro(config_compiler_and_linker)
   endif()
 
   fix_default_compiler_settings_()
+
+  # When Google Test is built as a shared library, it should also use
+  # shared runtime libraries. Otherwise, it may end up with multiple
+  # copies of runtime library data in different modules, resulting in
+  # hard-to-find crashes. When it is built as a static library, it is
+  # preferable to use CRT as static libraries, as we don't have to rely
+  # on CRT DLLs being available. CMake defaults to using shared
+  # CRT libraries, so we change that here.
+  if (NOT BUILD_SHARED_LIBS AND NOT DEFINED CMAKE_MSVC_RUNTIME_LIBRARY)
+    set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
+  endif()
+
+
   if (MSVC)
     # Newlines inside flags variables break CMake's NMake generator.
     # TODO([email protected]): Add -RTCs and -RTCu to debug builds.