C17 support

Implements #17755.

Help/prop_gbl/CMAKE_C_KNOWN_FEATURES.rst

@@ -24,6 +24,9 @@ The features known to this version of CMake are:
 ``c_std_11``
   Compiler mode is at least C 11.
 
+``c_std_17``
+  Compiler mode is at least C 17.
+
 ``c_function_prototypes``
   Function prototypes, as defined in ``ISO/IEC 9899:1990``.
 

Help/prop_tgt/C_STANDARD.rst

@@ -11,7 +11,7 @@ flag such as ``-std=gnu11`` to the compile line.  For compilers that
 have no notion of a C standard level, such as Microsoft Visual C++ before
 VS 16.7, this property has no effect.
 
-Supported values are ``90``, ``99`` and ``11``.
+Supported values are ``90``, ``99``, ``11``, ``17``.
 
 If the value requested does not result in a compile flag being added for
 the compiler in use, a previous standard flag will be added instead.  This

Help/release/dev/c-std.rst

@@ -0,0 +1,6 @@
+c-std
+-----
+
+* :prop_tgt:`C_STANDARD` and the
+  :manual:`Compile Features <cmake-compile-features(7)>` functionality gained
+  support for C17.

Modules/CMakeCCompiler.cmake.in

@@ -9,6 +9,7 @@ set(CMAKE_C_COMPILE_FEATURES "@CMAKE_C_COMPILE_FEATURES@")
 set(CMAKE_C90_COMPILE_FEATURES "@CMAKE_C90_COMPILE_FEATURES@")
 set(CMAKE_C99_COMPILE_FEATURES "@CMAKE_C99_COMPILE_FEATURES@")
 set(CMAKE_C11_COMPILE_FEATURES "@CMAKE_C11_COMPILE_FEATURES@")
+set(CMAKE_C17_COMPILE_FEATURES "@CMAKE_C17_COMPILE_FEATURES@")
 
 set(CMAKE_C_PLATFORM_ID "@CMAKE_C_PLATFORM_ID@")
 set(CMAKE_C_SIMULATE_ID "@CMAKE_C_SIMULATE_ID@")

Modules/CMakeCCompilerId.c.in

@@ -39,6 +39,8 @@ char const *info_cray = "INFO" ":" "compiler_wrapper[CrayPrgEnv]";
 # else
 #  define C_DIALECT
 # endif
+#elif __STDC_VERSION__ >= 201710L
+# define C_DIALECT "17"
 #elif __STDC_VERSION__ >= 201000L
 # define C_DIALECT "11"
 #elif __STDC_VERSION__ >= 199901L

Modules/CMakeDetermineCompileFeatures.cmake

@@ -10,6 +10,7 @@ function(cmake_determine_compile_features lang)
     set(CMAKE_C90_COMPILE_FEATURES)
     set(CMAKE_C99_COMPILE_FEATURES)
     set(CMAKE_C11_COMPILE_FEATURES)
+    set(CMAKE_C17_COMPILE_FEATURES)
 
     include("${CMAKE_ROOT}/Modules/Internal/FeatureTesting.cmake")
 
@@ -20,6 +21,9 @@ function(cmake_determine_compile_features lang)
       return()
     endif()
 
+    if (CMAKE_C11_COMPILE_FEATURES AND CMAKE_C17_COMPILE_FEATURES)
+      list(REMOVE_ITEM CMAKE_C17_COMPILE_FEATURES ${CMAKE_C11_COMPILE_FEATURES})
+    endif()
     if (CMAKE_C99_COMPILE_FEATURES AND CMAKE_C11_COMPILE_FEATURES)
       list(REMOVE_ITEM CMAKE_C11_COMPILE_FEATURES ${CMAKE_C99_COMPILE_FEATURES})
     endif()
@@ -32,6 +36,7 @@ function(cmake_determine_compile_features lang)
         ${CMAKE_C90_COMPILE_FEATURES}
         ${CMAKE_C99_COMPILE_FEATURES}
         ${CMAKE_C11_COMPILE_FEATURES}
+        ${CMAKE_C17_COMPILE_FEATURES}
       )
     endif()
 
@@ -39,6 +44,7 @@ function(cmake_determine_compile_features lang)
     set(CMAKE_C90_COMPILE_FEATURES ${CMAKE_C90_COMPILE_FEATURES} PARENT_SCOPE)
     set(CMAKE_C99_COMPILE_FEATURES ${CMAKE_C99_COMPILE_FEATURES} PARENT_SCOPE)
     set(CMAKE_C11_COMPILE_FEATURES ${CMAKE_C11_COMPILE_FEATURES} PARENT_SCOPE)
+    set(CMAKE_C17_COMPILE_FEATURES ${CMAKE_C17_COMPILE_FEATURES} PARENT_SCOPE)
 
     message(CHECK_PASS "done")
 

Modules/Compiler/CMakeCommonCompilerMacros.cmake

@@ -64,6 +64,9 @@ endmacro()
 # Define to allow compile features to be automatically determined
 macro(cmake_record_c_compile_features)
   set(_result 0)
+  if(_result EQUAL 0 AND DEFINED CMAKE_C17_STANDARD_COMPILE_OPTION)
+    _has_compiler_features_c(17)
+  endif()
   if(_result EQUAL 0 AND DEFINED CMAKE_C11_STANDARD_COMPILE_OPTION)
     if(CMAKE_C11_STANDARD__HAS_FULL_SUPPORT)
       _has_compiler_features_c(11)

Source/cmStandardLevelResolver.cxx

@@ -308,8 +308,9 @@ struct StanardLevelComputer
 std::unordered_map<std::string, StanardLevelComputer> StandardComputerMapping =
   {
     { "C",
-      StanardLevelComputer{ "C", std::vector<int>{ 90, 99, 11 },
-                            std::vector<std::string>{ "90", "99", "11" } } },
+      StanardLevelComputer{
+        "C", std::vector<int>{ 90, 99, 11, 17 },
+        std::vector<std::string>{ "90", "99", "11", "17" } } },
     { "CXX",
       StanardLevelComputer{
         "CXX", std::vector<int>{ 98, 11, 14, 17, 20, 23 },

Source/cmake.h

@@ -739,6 +739,7 @@ private:
   F(c_std_90)                                                                 \
   F(c_std_99)                                                                 \
   F(c_std_11)                                                                 \
+  F(c_std_17)                                                                 \
   FOR_EACH_C90_FEATURE(F)                                                     \
   FOR_EACH_C99_FEATURE(F)                                                     \
   FOR_EACH_C11_FEATURE(F)

Tests/CompileFeatures/CMakeLists.txt

@@ -237,6 +237,7 @@ if (C_expected_features)
     if (std_flag_idx EQUAL -1)
       add_executable(default_dialect_C default_dialect.c)
       target_compile_definitions(default_dialect_C PRIVATE
+        DEFAULT_C17=$<EQUAL:${CMAKE_C_STANDARD_DEFAULT},17>
         DEFAULT_C11=$<EQUAL:${CMAKE_C_STANDARD_DEFAULT},11>
         DEFAULT_C99=$<EQUAL:${CMAKE_C_STANDARD_DEFAULT},99>
         DEFAULT_C90=$<EQUAL:${CMAKE_C_STANDARD_DEFAULT},90>

Tests/CompileFeatures/default_dialect.c

@@ -1,5 +1,9 @@
 
-#if DEFAULT_C11
+#if DEFAULT_C17
+#  if __STDC_VERSION__ < 201710L
+#    error Unexpected value for __STDC_VERSION__.
+#  endif
+#elif DEFAULT_C11
 #  if __STDC_VERSION__ < 201112L
 #    error Unexpected value for __STDC_VERSION__.
 #  endif