Features: Fix C90 feature detection.

This bug caused c_function_prototypes to not be recorded at configure
time when compiling with -std=gnu99 or similar. In the case of feature
recording, that was not a problem, because the logic in
CMakeDetermineCompileFeatures.cmake currently assumes that a feature
present for an earlier standard is present for a later standard.

However, the detection strings are also used in WriteCompilerDetectionHeader,
so the feature macro has been defined to '0' when using a later language
dialect.

Fix that by not checking the existence of the __STDC_VERSION__ macro at
all when detecting C90 features.

1 files changed, 32 insertions, 0 deletions

diff --git a/Tests/CompileFeatures/CMakeLists.txt b/Tests/CompileFeatures/CMakeLists.txt
index 38c44c8..3ba1e0a 100644
--- a/Tests/CompileFeatures/CMakeLists.txt
+++ b/Tests/CompileFeatures/CMakeLists.txt
@@ -164,6 +164,38 @@ if (CMAKE_C_COMPILE_FEATURES)
       )
     endif()
   endif()
+
+  add_executable(CompileFeaturesGenex_C genex_test.c)
+  set_property(TARGET CompileFeaturesGenex_C PROPERTY C_STANDARD 11)
+
+  if (CMAKE_C_COMPILER_ID STREQUAL "GNU")
+    if (NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 4.6)
+      list(APPEND expected_defs
+        EXPECT_C_STATIC_ASSERT=1
+      )
+    else()
+      list(APPEND expected_defs
+        EXPECT_C_STATIC_ASSERT=0
+      )
+    endif()
+  elseif(CMAKE_C_COMPILER_ID STREQUAL "Clang"
+      OR CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
+    list(APPEND expected_defs
+      EXPECT_C_STATIC_ASSERT=1
+    )
+  endif()
+
+  list(APPEND expected_defs
+    EXPECT_C_FUNCTION_PROTOTYPES=1
+    EXPECT_C_RESTRICT=1
+  )
+
+  target_compile_definitions(CompileFeaturesGenex_C PRIVATE
+    HAVE_C_FUNCTION_PROTOTYPES=$<COMPILE_FEATURES:c_function_prototypes>
+    HAVE_C_RESTRICT=$<COMPILE_FEATURES:c_restrict>
+    HAVE_C_STATIC_ASSERT=$<COMPILE_FEATURES:c_static_assert>
+    ${expected_defs}
+  )
 endif()
 
 if (CMAKE_CXX_COMPILE_FEATURES)