WCDH: optionally omit error code for unknown compilers or compiler versions

This allows one to generate a header that will basically always work. In case
an unknown compiler or compiler version is encountered it simply falls back to
the unsupported case.

1 files changed, 29 insertions, 1 deletions

diff --git a/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt b/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt
index 8b251d73fe..9f229f9994 100644
--- a/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt
+++ b/Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt
@@ -4,6 +4,7 @@ project(WriteCompilerDetectionHeader)
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
 
 include(WriteCompilerDetectionHeader)
+include(CheckCXXSourceCompiles)
 
 get_property(cxx_known_features GLOBAL PROPERTY CMAKE_CXX_KNOWN_FEATURES)
 get_property(c_known_features GLOBAL PROPERTY CMAKE_C_KNOWN_FEATURES)
@@ -26,7 +27,6 @@ if (NOT CMAKE_CXX_COMPILE_FEATURES AND NOT CMAKE_C_COMPILE_FEATURES)
   add_executable(WriteCompilerDetectionHeader "${CMAKE_CURRENT_BINARY_DIR}/dummy.cpp")
 
   if(UNIX OR NOT CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-    include(CheckCXXSourceCompiles)
     check_cxx_source_compiles("#include \"${CMAKE_CURRENT_BINARY_DIR}/test_compiler_detection.h\"\nint main() { return 0; }\n"
       file_include_works
     )
@@ -156,3 +156,31 @@ if (CMAKE_C_COMPILER_ID STREQUAL "GNU"
   set_defines(WriteCompilerDetectionHeader_C11_multi "EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES;EXPECTED_COMPILER_C_RESTRICT" "")
   target_include_directories(WriteCompilerDetectionHeader_C11_multi PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/compiler_multi_files)
 endif()
+
+# test for ALLOW_UNKNOWN_COMPILERS
+
+# use a compiler does not match the current one,
+# so one always hits the fallback code
+if (CMAKE_CXX_COMPILER_ID STREQUAL "SunPro")
+  set(OTHER_CXX "Intel")
+else()
+  set(OTHER_CXX "SunPro")
+endif()
+
+write_compiler_detection_header(
+  FILE "${CMAKE_CURRENT_BINARY_DIR}/test_compiler_detection_allow_unknown.h"
+  PREFIX TEST
+  COMPILERS ${OTHER_CXX}
+  FEATURES cxx_nullptr
+  ALLOW_UNKNOWN_COMPILERS
+)
+
+# intentionally abuse the TEST_NULLPR variable: this will only work
+# with the fallback code.
+check_cxx_source_compiles("#include \"${CMAKE_CURRENT_BINARY_DIR}/test_compiler_detection_allow_unknown.h\"
+int main() {\n int i = TEST_NULLPTR;\n return 0; }\n"
+  file_include_works_allow_unknown
+)
+if (NOT file_include_works_allow_unknown)
+  message(SEND_ERROR "Inclusion of ${CMAKE_CURRENT_BINARY_DIR}/test_compiler_detection_allow_unknown.h was expected to work, but did not.")
+endif()