MSVC: Refactor C compile features table for C90, C99, and C11

The custom "no modes" `cmake_record_c_compile_features` implementation
should only be used in `cl` versions prior to 19.27 because they had no
`-std:c*` flags for C standards.  For 19.27 we need a different custom
implementation to account for partial C11 support.  For 19.28 and above
we can use the default implementation through the `*__HAS_FULL_SUPPORT`
settings.

We already use this pattern in the MSVC C++ compile feature table.

1 files changed, 35 insertions, 29 deletions

diff --git a/Modules/Compiler/MSVC-C.cmake b/Modules/Compiler/MSVC-C.cmake
index 4ba1eea..aca7995 100644
--- a/Modules/Compiler/MSVC-C.cmake
+++ b/Modules/Compiler/MSVC-C.cmake
@@ -11,6 +11,20 @@ if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 19.27)
   set(CMAKE_C11_STANDARD_COMPILE_OPTION "-std:c11")
   set(CMAKE_C11_EXTENSION_COMPILE_OPTION "-std:c11")
 
+  if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 19.28)
+    set(CMAKE_C90_STANDARD__HAS_FULL_SUPPORT ON)
+    set(CMAKE_C99_STANDARD__HAS_FULL_SUPPORT ON)
+    set(CMAKE_C11_STANDARD__HAS_FULL_SUPPORT ON)
+  else()
+    # Special case for 19.27 (VS 16.7): C11 has partial support.
+    macro(cmake_record_c_compile_features)
+      _has_compiler_features_c(90)
+      _has_compiler_features_c(99)
+      list(APPEND CMAKE_C11_COMPILE_FEATURES c_std_11)
+      set(_result 0) # expected by cmake_determine_compile_features
+    endmacro()
+  endif()
+
   __compiler_check_default_language_standard(C 19.27 99)
 else()
   # MSVC has no specific options to set C language standards, but set them as
@@ -25,41 +39,33 @@ else()
 
   # There is no meaningful default for this
   set(CMAKE_C_STANDARD_DEFAULT "")
+
+  # There are no C compiler modes so we hard-code the known compiler supported
+  # features. Override the default macro for this special case.  Pretend that
+  # all language standards are available so that at least compilation
+  # can be attempted.
+  macro(cmake_record_c_compile_features)
+    list(APPEND CMAKE_C_COMPILE_FEATURES
+      c_std_90
+      c_std_99
+      c_std_11
+      c_function_prototypes
+      )
+    list(APPEND CMAKE_C90_COMPILE_FEATURES c_std_90 c_function_prototypes)
+    list(APPEND CMAKE_C99_COMPILE_FEATURES c_std_99)
+    list(APPEND CMAKE_C11_COMPILE_FEATURES c_std_11)
+    if (CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 14.0)
+      list(APPEND CMAKE_C_COMPILE_FEATURES c_variadic_macros)
+      list(APPEND CMAKE_C99_COMPILE_FEATURES c_variadic_macros)
+    endif()
+    set(_result 0) # expected by cmake_determine_compile_features
+  endmacro()
 endif()
 
 set(CMAKE_C_COMPILE_OPTIONS_EXPLICIT_LANGUAGE -TC)
 set(CMAKE_C_CLANG_TIDY_DRIVER_MODE "cl")
 set(CMAKE_C_INCLUDE_WHAT_YOU_USE_DRIVER_MODE "cl")
 
-# There are no C compiler modes so we hard-code the known compiler supported
-# features. Override the default macro for this special case.  Pretend that
-# all language standards are available so that at least compilation
-# can be attempted.
-macro(cmake_record_c_compile_features)
-  list(APPEND CMAKE_C_COMPILE_FEATURES
-    c_std_90
-    c_std_99
-    c_std_11
-    c_function_prototypes
-    )
-  list(APPEND CMAKE_C90_COMPILE_FEATURES c_std_90 c_function_prototypes)
-  list(APPEND CMAKE_C99_COMPILE_FEATURES c_std_99)
-  list(APPEND CMAKE_C11_COMPILE_FEATURES c_std_11)
-  if (CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 14.0)
-    list(APPEND CMAKE_C_COMPILE_FEATURES c_variadic_macros)
-    list(APPEND CMAKE_C99_COMPILE_FEATURES c_variadic_macros)
-  endif()
-  if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 19.27)
-    list(APPEND CMAKE_C_COMPILE_FEATURES c_restrict)
-    list(APPEND CMAKE_C99_COMPILE_FEATURES c_restrict)
-  endif()
-  if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 19.28)
-    list(APPEND CMAKE_C_COMPILE_FEATURES c_static_assert)
-    list(APPEND CMAKE_C11_COMPILE_FEATURES c_static_assert)
-  endif()
-  set(_result 0) # expected by cmake_determine_compile_features
-endmacro()
-
 # /JMC "Just My Code" is only supported by MSVC 19.05 onward.
 if (CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 19.05)
   set(CMAKE_C_COMPILE_OPTIONS_JMC "-JMC")