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.

8 files changed, 153 insertions, 3 deletions

diff --git a/Modules/Compiler/AppleClang-C-FeatureTests.cmake b/Modules/Compiler/AppleClang-C-FeatureTests.cmake
index 6f3d6a7..e80b526 100644
--- a/Modules/Compiler/AppleClang-C-FeatureTests.cmake
+++ b/Modules/Compiler/AppleClang-C-FeatureTests.cmake
@@ -7,5 +7,5 @@ set(AppleClang_C99 "${_cmake_oldestSupported} && defined(__STDC_VERSION__) && __
 set(_cmake_feature_test_c_restrict "${AppleClang_C99}")
 set(_cmake_feature_test_c_variadic_macros "${AppleClang_C99}")
 
-set(AppleClang_C90 "${_cmake_oldestSupported} && !defined(__STDC_VERSION__)")
+set(AppleClang_C90 "${_cmake_oldestSupported}")
 set(_cmake_feature_test_c_function_prototypes "${AppleClang_C90}")
diff --git a/Modules/Compiler/Clang-C-FeatureTests.cmake b/Modules/Compiler/Clang-C-FeatureTests.cmake
index 2d8673d..99c2252 100644
--- a/Modules/Compiler/Clang-C-FeatureTests.cmake
+++ b/Modules/Compiler/Clang-C-FeatureTests.cmake
@@ -7,5 +7,5 @@ set(Clang_C99 "${_cmake_oldestSupported} && defined(__STDC_VERSION__) && __STDC_
 set(_cmake_feature_test_c_restrict "${Clang_C99}")
 set(_cmake_feature_test_c_variadic_macros "${Clang_C99}")
 
-set(Clang_C90 "${_cmake_oldestSupported} && !defined(__STDC_VERSION__)")
+set(Clang_C90 "${_cmake_oldestSupported}")
 set(_cmake_feature_test_c_function_prototypes "${Clang_C90}")
diff --git a/Modules/Compiler/GNU-C-FeatureTests.cmake b/Modules/Compiler/GNU-C-FeatureTests.cmake
index d8e456c..b3fe33f 100644
--- a/Modules/Compiler/GNU-C-FeatureTests.cmake
+++ b/Modules/Compiler/GNU-C-FeatureTests.cmake
@@ -13,5 +13,5 @@ set(GNU44_C99 "(__GNUC__ * 100 + __GNUC_MINOR__) >= 404 && defined(__STDC_VERSIO
 set(_cmake_feature_test_c_restrict "${GNU44_C99}")
 set(_cmake_feature_test_c_variadic_macros "${GNU44_C99}")
 
-set(GNU_C90 "${_cmake_oldestSupported} && !defined(__STDC_VERSION__)")
+set(GNU_C90 "${_cmake_oldestSupported}")
 set(_cmake_feature_test_c_function_prototypes "${GNU_C90}")
diff --git a/Tests/CompileFeatures/CMakeLists.txt b/Tests/CompileFeatures/CMakeLists.txt
index 38c44c8..3ba1e0a 100644
--- a/Tests/CompileFeatures/CMakeLists.txt
+++ b/Tests/CompileFeatures/CMakeLists.txt
@@ -164,6 +164,38 @@ if (CMAKE_C_COMPILE_FEATURES)
       )
     endif()
   endif()
+
+  add_executable(CompileFeaturesGenex_C genex_test.c)
+  set_property(TARGET CompileFeaturesGenex_C PROPERTY C_STANDARD 11)
+
+  if (CMAKE_C_COMPILER_ID STREQUAL "GNU")
+    if (NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 4.6)
+      list(APPEND expected_defs
+        EXPECT_C_STATIC_ASSERT=1
+      )
+    else()
+      list(APPEND expected_defs
+        EXPECT_C_STATIC_ASSERT=0
+      )
+    endif()
+  elseif(CMAKE_C_COMPILER_ID STREQUAL "Clang"
+      OR CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
+    list(APPEND expected_defs
+      EXPECT_C_STATIC_ASSERT=1
+    )
+  endif()
+
+  list(APPEND expected_defs
+    EXPECT_C_FUNCTION_PROTOTYPES=1
+    EXPECT_C_RESTRICT=1
+  )
+
+  target_compile_definitions(CompileFeaturesGenex_C PRIVATE
+    HAVE_C_FUNCTION_PROTOTYPES=$<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)
diff --git a/Tests/CompileFeatures/genex_test.c b/Tests/CompileFeatures/genex_test.c
new file mode 100644
index 0000000..b1215bd
--- /dev/null
+++ b/Tests/CompileFeatures/genex_test.c
@@ -0,0 +1,38 @@
+#ifndef EXPECT_C_STATIC_ASSERT
+# error EXPECT_C_STATIC_ASSERT not defined
+#endif
+#ifndef EXPECT_C_FUNCTION_PROTOTYPES
+# error EXPECT_C_FUNCTION_PROTOTYPES not defined
+#endif
+#ifndef EXPECT_C_RESTRICT
+# error EXPECT_C_RESTRICT not defined
+#endif
+
+#if !EXPECT_C_STATIC_ASSERT
+#if EXPECT_C_STATIC_ASSERT
+#error "Expect c_static_assert feature"
+#endif
+#else
+#if !EXPECT_C_STATIC_ASSERT
+#error "Expect no c_static_assert feature"
+#endif
+#endif
+
+#if !EXPECT_C_FUNCTION_PROTOTYPES
+#  error Expect c_function_prototypes support
+#endif
+
+#if !EXPECT_C_RESTRICT
+#  if EXPECT_C_RESTRICT
+#    error Expect c_restrict support
+#  endif
+#else
+#  if !EXPECT_C_RESTRICT
+#    error Expect no c_restrict support
+#  endif
+#endif
+
+int main()
+{
+
+}
diff --git a/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt b/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt
index e70a977..c538280 100644
--- a/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt
+++ b/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt
@@ -84,6 +84,15 @@ if (CMAKE_C_COMPILER_ID STREQUAL "GNU"
   add_executable(C_undefined c_undefined.c)
   set_property(TARGET C_undefined PROPERTY C_STANDARD 90)
   target_compile_options(C_undefined PRIVATE -Werror=undef)
+
+  add_executable(WriteCompilerDetectionHeader_C main.c)
+  set_property(TARGET WriteCompilerDetectionHeader_C PROPERTY C_STANDARD 90)
+  set_defines(WriteCompilerDetectionHeader_C "EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES" "EXPECTED_COMPILER_C_RESTRICT")
+
+  add_executable(WriteCompilerDetectionHeader_C_multi main_multi.c)
+  set_property(TARGET WriteCompilerDetectionHeader_C_multi PROPERTY C_STANDARD 90)
+  set_defines(WriteCompilerDetectionHeader_C_multi "EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES" "EXPECTED_COMPILER_C_RESTRICT")
+  target_include_directories(WriteCompilerDetectionHeader_C_multi PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/compiler_multi_files)
 endif()
 
 add_executable(WriteCompilerDetectionHeader main.cpp)
@@ -130,3 +139,16 @@ add_executable(multi_files_11 multi_files.cpp)
 set_property(TARGET multi_files_11 PROPERTY CXX_STANDARD 11)
 target_include_directories(multi_files_11 PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/compiler_multi_files)
 set_defines(multi_files_11 "${true_defs}" "${false_defs}")
+
+if (CMAKE_C_COMPILER_ID STREQUAL "GNU"
+    OR CMAKE_C_COMPILER_ID STREQUAL "Clang"
+    OR CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
+  add_executable(WriteCompilerDetectionHeader_C11 main.c)
+  set_property(TARGET WriteCompilerDetectionHeader_C11 PROPERTY C_STANDARD 11)
+  set_defines(WriteCompilerDetectionHeader_C11 "EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES;EXPECTED_COMPILER_C_RESTRICT" "")
+
+  add_executable(WriteCompilerDetectionHeader_C11_multi main_multi.c)
+  set_property(TARGET WriteCompilerDetectionHeader_C11_multi PROPERTY C_STANDARD 11)
+  set_defines(WriteCompilerDetectionHeader_C11_multi "EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES;EXPECTED_COMPILER_C_RESTRICT" "")
+  target_include_directories(WriteCompilerDetectionHeader_C11_multi PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/compiler_multi_files)
+endif()
diff --git a/Tests/Module/WriteCompilerDetectionHeader/main.c b/Tests/Module/WriteCompilerDetectionHeader/main.c
new file mode 100644
index 0000000..9023b0f
--- /dev/null
+++ b/Tests/Module/WriteCompilerDetectionHeader/main.c
@@ -0,0 +1,29 @@
+
+#include "test_compiler_detection.h"
+
+#if !defined(TEST_COMPILER_C_FUNCTION_PROTOTYPES) || !TEST_COMPILER_C_FUNCTION_PROTOTYPES
+#  error Expected TEST_COMPILER_C_FUNCTION_PROTOTYPES
+#endif
+
+#if !EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES
+#  error Expected EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES
+#endif
+
+#if !defined(TEST_COMPILER_C_RESTRICT) || !TEST_COMPILER_C_RESTRICT
+#  if EXPECTED_COMPILER_C_RESTRICT
+#    error Expected TEST_COMPILER_C_RESTRICT
+#  endif
+#else
+#  if !EXPECTED_COMPILER_C_RESTRICT
+#    error Expect no TEST_COMPILER_C_RESTRICT
+#  endif
+#endif
+
+#ifdef TEST_COMPILER_CXX_STATIC_ASSERT
+#error Expect no CXX features defined
+#endif
+
+int main()
+{
+  return 0;
+}
diff --git a/Tests/Module/WriteCompilerDetectionHeader/main_multi.c b/Tests/Module/WriteCompilerDetectionHeader/main_multi.c
new file mode 100644
index 0000000..6f4573f
--- /dev/null
+++ b/Tests/Module/WriteCompilerDetectionHeader/main_multi.c
@@ -0,0 +1,29 @@
+
+#include "multi_file_compiler_detection.h"
+
+#if !defined(MULTI_COMPILER_C_FUNCTION_PROTOTYPES) || !MULTI_COMPILER_C_FUNCTION_PROTOTYPES
+#  error Expected MULTI_COMPILER_C_FUNCTION_PROTOTYPES
+#endif
+
+#if !EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES
+#  error Expected EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES
+#endif
+
+#if !defined(MULTI_COMPILER_C_RESTRICT) || !MULTI_COMPILER_C_RESTRICT
+#  if EXPECTED_COMPILER_C_RESTRICT
+#    error Expected MULTI_COMPILER_C_RESTRICT
+#  endif
+#else
+#  if !EXPECTED_COMPILER_C_RESTRICT
+#    error Expect no MULTI_COMPILER_C_RESTRICT
+#  endif
+#endif
+
+#ifdef MULTI_COMPILER_CXX_STATIC_ASSERT
+#error Expect no CXX features defined
+#endif
+
+int main()
+{
+  return 0;
+}