Fix Clang builds on Windows (#1021)

Fixes #974. The `cxx_feature_check` now has an additional optional argument which can be used to supply extra cmake flags to pass to the `try_compile` command. The `CMAKE_CXX_STANDARD=14` flag was determined to be the minimum flag necessary to correctly compile and run the regex feature checks when compiling with Clang under Windows (n.b. this does *not* refer to clang-cl, the frontend to the MSVC compiler). The additional flag is not enabled for any other compiler/platform tuple.

Fix Clang builds on Windows (#1021)
01c0ab7c · Jeremy Ong · GitHub · 48579623 · 01c0ab7c · 01c0ab7c
Unverified Commit 01c0ab7c authored Aug 27, 2020 by Jeremy Ong Committed by GitHub Aug 27, 2020
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Showing with 15 additions and 3 deletions

CMakeLists.txt CMakeLists.txt +10 -3

CXXFeatureCheck.cmake cmake/CXXFeatureCheck.cmake +5 -0

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--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -245,11 +245,17 @@ if (BENCHMARK_USE_LIBCXX)
  endif()
 endif(BENCHMARK_USE_LIBCXX)

+set(EXTRA_CXX_FLAGS "")
+if (WIN32 AND "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
+  # Clang on Windows fails to compile the regex feature check under C++11
+  set(EXTRA_CXX_FLAGS "-DCMAKE_CXX_STANDARD=14")
+endif()
+
 # C++ feature checks
 # Determine the correct regular expression engine to use
-cxx_feature_check(STD_REGEX)
-cxx_feature_check(GNU_POSIX_REGEX)
-cxx_feature_check(POSIX_REGEX)
+cxx_feature_check(STD_REGEX ${EXTRA_CXX_FLAGS})
+cxx_feature_check(GNU_POSIX_REGEX ${EXTRA_CXX_FLAGS})
+cxx_feature_check(POSIX_REGEX ${EXTRA_CXX_FLAGS})
 if(NOT HAVE_STD_REGEX AND NOT HAVE_GNU_POSIX_REGEX AND NOT HAVE_POSIX_REGEX)
  message(FATAL_ERROR "Failed to determine the source files for the regular expression backend")
 endif()
@@ -257,6 +263,7 @@ if (NOT BENCHMARK_ENABLE_EXCEPTIONS AND HAVE_STD_REGEX
        AND NOT HAVE_GNU_POSIX_REGEX AND NOT HAVE_POSIX_REGEX)
  message(WARNING "Using std::regex with exceptions disabled is not fully supported")
 endif()
+
 cxx_feature_check(STEADY_CLOCK)
 # Ensure we have pthreads
 set(THREADS_PREFER_PTHREAD_FLAG ON)

--- a/cmake/CXXFeatureCheck.cmake
+++ b/cmake/CXXFeatureCheck.cmake
@@ -27,6 +27,11 @@ function(cxx_feature_check FILE)
    return()
  endif()

+  if (ARGC GREATER 1)
+    message(STATUS "Enabling additional flags: ${ARGV1}")
+    list(APPEND BENCHMARK_CXX_LINKER_FLAGS ${ARGV1})
+  endif()
+
  if (NOT DEFINED COMPILE_${FEATURE})
    message(STATUS "Performing Test ${FEATURE}")
    if(CMAKE_CROSSCOMPILING)