Merge topic 'c_17_23'

8211b4706f IntelLLVM: C17 support
b9c3acac02 GNU: C23 support
c9f0613c2a GNU: C17 support
10a72c0f1c Clang: Default C standard doesn't depend on compatibility mode
6c2e309a66 Clang: Set standard flags according to frontend variant
9f81591dbf Clang: MSVC-style C flags
72f4984cdc Clang: C23 support
82239d43f8 Clang: C17 default version
...

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !5783

15 files changed, 123 insertions, 29 deletions

diff --git a/Help/prop_gbl/CMAKE_C_KNOWN_FEATURES.rst b/Help/prop_gbl/CMAKE_C_KNOWN_FEATURES.rst
index 7166381..2bd0feb 100644
--- a/Help/prop_gbl/CMAKE_C_KNOWN_FEATURES.rst
+++ b/Help/prop_gbl/CMAKE_C_KNOWN_FEATURES.rst
@@ -24,6 +24,12 @@ 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_std_23``
+  Compiler mode is at least C 23.
+
 ``c_function_prototypes``
   Function prototypes, as defined in ``ISO/IEC 9899:1990``.
 
diff --git a/Help/prop_tgt/C_STANDARD.rst b/Help/prop_tgt/C_STANDARD.rst
index 3f0d242..e22b775 100644
--- a/Help/prop_tgt/C_STANDARD.rst
+++ b/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``, ``23``.
 
 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
diff --git a/Help/release/dev/c-std.rst b/Help/release/dev/c-std.rst
new file mode 100644
index 0000000..44daa85
--- /dev/null
+++ b/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 and C23.
diff --git a/Modules/CMakeCCompiler.cmake.in b/Modules/CMakeCCompiler.cmake.in
index 7f73891..754f235 100644
--- a/Modules/CMakeCCompiler.cmake.in
+++ b/Modules/CMakeCCompiler.cmake.in
@@ -9,6 +9,8 @@ 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_C23_COMPILE_FEATURES "@CMAKE_C23_COMPILE_FEATURES@")
 
 set(CMAKE_C_PLATFORM_ID "@CMAKE_C_PLATFORM_ID@")
 set(CMAKE_C_SIMULATE_ID "@CMAKE_C_SIMULATE_ID@")
diff --git a/Modules/CMakeCCompilerId.c.in b/Modules/CMakeCCompilerId.c.in
index 8ba6abc..716b975 100644
--- a/Modules/CMakeCCompilerId.c.in
+++ b/Modules/CMakeCCompilerId.c.in
@@ -33,13 +33,16 @@ char const *info_cray = "INFO" ":" "compiler_wrapper[CrayPrgEnv]";
 @CMAKE_C_COMPILER_ID_PLATFORM_CONTENT@
 @CMAKE_C_COMPILER_ID_ERROR_FOR_TEST@
 
-#if !defined(__STDC__)
-# if (defined(_MSC_VER) && !defined(__clang__)) \
-  || (defined(__ibmxl__) || defined(__IBMC__))
+#if !defined(__STDC__) && !defined(__clang__)
+# if defined(_MSC_VER) || defined(__ibmxl__) || defined(__IBMC__)
 #  define C_DIALECT "90"
 # else
 #  define C_DIALECT
 # endif
+#elif __STDC_VERSION__ > 201710L
+# define C_DIALECT "23"
+#elif __STDC_VERSION__ >= 201710L
+# define C_DIALECT "17"
 #elif __STDC_VERSION__ >= 201000L
 # define C_DIALECT "11"
 #elif __STDC_VERSION__ >= 199901L
diff --git a/Modules/CMakeDetermineCompileFeatures.cmake b/Modules/CMakeDetermineCompileFeatures.cmake
index c03a85f..f767847 100644
--- a/Modules/CMakeDetermineCompileFeatures.cmake
+++ b/Modules/CMakeDetermineCompileFeatures.cmake
@@ -10,6 +10,8 @@ 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)
+    set(CMAKE_C23_COMPILE_FEATURES)
 
     include("${CMAKE_ROOT}/Modules/Internal/FeatureTesting.cmake")
 
@@ -20,6 +22,12 @@ function(cmake_determine_compile_features lang)
       return()
     endif()
 
+    if (CMAKE_C17_COMPILE_FEATURES AND CMAKE_C23_COMPILE_FEATURES)
+      list(REMOVE_ITEM CMAKE_C23_COMPILE_FEATURES ${CMAKE_C17_COMPILE_FEATURES})
+    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 +40,8 @@ function(cmake_determine_compile_features lang)
         ${CMAKE_C90_COMPILE_FEATURES}
         ${CMAKE_C99_COMPILE_FEATURES}
         ${CMAKE_C11_COMPILE_FEATURES}
+        ${CMAKE_C17_COMPILE_FEATURES}
+        ${CMAKE_C23_COMPILE_FEATURES}
       )
     endif()
 
@@ -39,6 +49,8 @@ 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)
+    set(CMAKE_C23_COMPILE_FEATURES ${CMAKE_C23_COMPILE_FEATURES} PARENT_SCOPE)
 
     message(CHECK_PASS "done")
 
diff --git a/Modules/Compiler/CMakeCommonCompilerMacros.cmake b/Modules/Compiler/CMakeCommonCompilerMacros.cmake
index cd897c5..29e6730 100644
--- a/Modules/Compiler/CMakeCommonCompilerMacros.cmake
+++ b/Modules/Compiler/CMakeCommonCompilerMacros.cmake
@@ -64,6 +64,12 @@ 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_C23_STANDARD_COMPILE_OPTION)
+    _has_compiler_features_c(23)
+  endif()
+  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)
diff --git a/Modules/Compiler/Clang-C.cmake b/Modules/Compiler/Clang-C.cmake
index 5609abf..cf493d7 100644
--- a/Modules/Compiler/Clang-C.cmake
+++ b/Modules/Compiler/Clang-C.cmake
@@ -25,37 +25,60 @@ elseif("x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xGNU")
   endif()
 endif()
 
-if(NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 3.4)
-  if(NOT "x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC")
+if("x${CMAKE_C_COMPILER_FRONTEND_VARIANT}" STREQUAL "xGNU")
+  if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 2.1)
     set(CMAKE_C90_STANDARD_COMPILE_OPTION "-std=c90")
     set(CMAKE_C90_EXTENSION_COMPILE_OPTION "-std=gnu90")
-    set(CMAKE_C90_STANDARD__HAS_FULL_SUPPORT ON)
 
     set(CMAKE_C99_STANDARD_COMPILE_OPTION "-std=c99")
     set(CMAKE_C99_EXTENSION_COMPILE_OPTION "-std=gnu99")
-    set(CMAKE_C99_STANDARD__HAS_FULL_SUPPORT ON)
+  endif()
 
+  if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 3.1)
     set(CMAKE_C11_STANDARD_COMPILE_OPTION "-std=c11")
     set(CMAKE_C11_EXTENSION_COMPILE_OPTION "-std=gnu11")
-    set(CMAKE_C11_STANDARD__HAS_FULL_SUPPORT ON)
-  else()
-    # clang-cl doesn't have any of these
-    set(CMAKE_C90_STANDARD_COMPILE_OPTION "")
-    set(CMAKE_C90_EXTENSION_COMPILE_OPTION "")
-    set(CMAKE_C90_STANDARD__HAS_FULL_SUPPORT ON)
+  elseif(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 3.0)
+    set(CMAKE_C11_STANDARD_COMPILE_OPTION "-std=c1x")
+    set(CMAKE_C11_EXTENSION_COMPILE_OPTION "-std=gnu1x")
+  endif()
+
+  if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 6.0)
+    set(CMAKE_C17_STANDARD_COMPILE_OPTION "-std=c17")
+    set(CMAKE_C17_EXTENSION_COMPILE_OPTION "-std=gnu17")
+  endif()
+
+  if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 9.0)
+    set(CMAKE_C23_STANDARD_COMPILE_OPTION "-std=c2x")
+    set(CMAKE_C23_EXTENSION_COMPILE_OPTION "-std=gnu2x")
+  endif()
+else()
+  set(CMAKE_C90_STANDARD_COMPILE_OPTION "")
+  set(CMAKE_C90_EXTENSION_COMPILE_OPTION "")
+  set(CMAKE_C99_STANDARD_COMPILE_OPTION "")
+  set(CMAKE_C99_EXTENSION_COMPILE_OPTION "")
 
-    set(CMAKE_C99_STANDARD_COMPILE_OPTION "")
-    set(CMAKE_C99_EXTENSION_COMPILE_OPTION "")
-    set(CMAKE_C99_STANDARD__HAS_FULL_SUPPORT ON)
+  if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 13.0)
+    set(CMAKE_C11_STANDARD_COMPILE_OPTION "/std:c11")
+    set(CMAKE_C11_EXTENSION_COMPILE_OPTION "/std:c11")
 
+    set(CMAKE_C17_STANDARD_COMPILE_OPTION "/std:c17")
+    set(CMAKE_C17_EXTENSION_COMPILE_OPTION "/std:c17")
+  else()
     set(CMAKE_C11_STANDARD_COMPILE_OPTION "")
     set(CMAKE_C11_EXTENSION_COMPILE_OPTION "")
-    set(CMAKE_C11_STANDARD__HAS_FULL_SUPPORT ON)
+
+    set(CMAKE_C17_STANDARD_COMPILE_OPTION "")
+    set(CMAKE_C17_EXTENSION_COMPILE_OPTION "")
   endif()
 endif()
 
-if(NOT "x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC")
-  __compiler_check_default_language_standard(C 3.4 99 3.6 11)
-else()
-  set(CMAKE_C_STANDARD_DEFAULT "")
+if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 2.1)
+  set(CMAKE_C90_STANDARD__HAS_FULL_SUPPORT ON)
+  set(CMAKE_C99_STANDARD__HAS_FULL_SUPPORT ON)
 endif()
+
+if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 3.0)
+  set(CMAKE_C11_STANDARD__HAS_FULL_SUPPORT ON)
+endif()
+
+__compiler_check_default_language_standard(C 2.1 99 3.5.2 11 11.0 17)
diff --git a/Modules/Compiler/GNU-C.cmake b/Modules/Compiler/GNU-C.cmake
index 86b4d83..39e9c72 100644
--- a/Modules/Compiler/GNU-C.cmake
+++ b/Modules/Compiler/GNU-C.cmake
@@ -36,4 +36,14 @@ elseif (NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 4.6)
   set(CMAKE_C11_EXTENSION_COMPILE_OPTION "-std=gnu1x")
 endif()
 
-__compiler_check_default_language_standard(C 3.4 90 5.0 11)
+if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 8.1)
+  set(CMAKE_C17_STANDARD_COMPILE_OPTION "-std=c17")
+  set(CMAKE_C17_EXTENSION_COMPILE_OPTION "-std=gnu17")
+endif()
+
+if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 9.1)
+  set(CMAKE_C23_STANDARD_COMPILE_OPTION "-std=c23")
+  set(CMAKE_C23_EXTENSION_COMPILE_OPTION "-std=gnu23")
+endif()
+
+__compiler_check_default_language_standard(C 3.4 90 5.0 11 8.1 17)
diff --git a/Modules/Compiler/IntelLLVM-C.cmake b/Modules/Compiler/IntelLLVM-C.cmake
index fce2971..beb7132 100644
--- a/Modules/Compiler/IntelLLVM-C.cmake
+++ b/Modules/Compiler/IntelLLVM-C.cmake
@@ -37,6 +37,9 @@ if(NOT "x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC")
 
   set(CMAKE_C11_STANDARD_COMPILE_OPTION "-std=c11")
   set(CMAKE_C11_EXTENSION_COMPILE_OPTION "-std=gnu11")
+
+  set(CMAKE_C17_STANDARD_COMPILE_OPTION "-std=c17")
+  set(CMAKE_C17_EXTENSION_COMPILE_OPTION "-std=gnu17")
 else()
   # clang-cl doesn't have any of these
   set(CMAKE_C90_STANDARD_COMPILE_OPTION "")
@@ -47,12 +50,13 @@ else()
 
   set(CMAKE_C11_STANDARD_COMPILE_OPTION "")
   set(CMAKE_C11_EXTENSION_COMPILE_OPTION "")
+
+  set(CMAKE_C17_STANDARD_COMPILE_OPTION "")
+  set(CMAKE_C17_EXTENSION_COMPILE_OPTION "")
 endif()
 
 if(NOT "x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC")
-  # FIXME: The compiler actually defaults to C17, but
-  # CMake does not yet model or detect that standard.
-  __compiler_check_default_language_standard(C 2020 11)
+  __compiler_check_default_language_standard(C 2020 17)
 else()
   set(CMAKE_C_STANDARD_DEFAULT "")
 endif()
diff --git a/Source/cmStandardLevelResolver.cxx b/Source/cmStandardLevelResolver.cxx
index bf6925e..280e508 100644
--- a/Source/cmStandardLevelResolver.cxx
+++ b/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, 23 },
+        std::vector<std::string>{ "90", "99", "11", "17", "23" } } },
     { "CXX",
       StanardLevelComputer{
         "CXX", std::vector<int>{ 98, 11, 14, 17, 20, 23 },
diff --git a/Source/cmake.h b/Source/cmake.h
index 82e028c..d6d129f 100644
--- a/Source/cmake.h
+++ b/Source/cmake.h
@@ -739,6 +739,8 @@ private:
   F(c_std_90)                                                                 \
   F(c_std_99)                                                                 \
   F(c_std_11)                                                                 \
+  F(c_std_17)                                                                 \
+  F(c_std_23)                                                                 \
   FOR_EACH_C90_FEATURE(F)                                                     \
   FOR_EACH_C99_FEATURE(F)                                                     \
   FOR_EACH_C11_FEATURE(F)
diff --git a/Tests/CompileFeatures/CMakeLists.txt b/Tests/CompileFeatures/CMakeLists.txt
index cff98e3..7771967 100644
--- a/Tests/CompileFeatures/CMakeLists.txt
+++ b/Tests/CompileFeatures/CMakeLists.txt
@@ -237,6 +237,8 @@ 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_C23=$<EQUAL:${CMAKE_C_STANDARD_DEFAULT},23>
+        DEFAULT_C17=$<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>
diff --git a/Tests/CompileFeatures/default_dialect.c b/Tests/CompileFeatures/default_dialect.c
index 6160c2f..b990e53 100644
--- a/Tests/CompileFeatures/default_dialect.c
+++ b/Tests/CompileFeatures/default_dialect.c
@@ -1,5 +1,13 @@
 
-#if DEFAULT_C11
+#if DEFAULT_C23
+#  if __STDC_VERSION__ <= 201710L
+#    error Unexpected value for __STDC_VERSION__.
+#  endif
+#elif 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
diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index fed0841..354a04e 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -417,6 +417,15 @@ function(add_RunCMake_test_try_compile)
       set(CMAKE_C_STANDARD_DEFAULT "")
     endif()
   endif()
+  if(CMAKE_VERSION VERSION_LESS 3.20.20210225 AND "x${CMAKE_C_COMPILER_ID}" STREQUAL "xClang")
+    # Older CMake versions do not know about Clang MSVC compatibility mode
+    # standards. Approximate the logic from Clang-C.cmake.
+    if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 11.0)
+      set(CMAKE_C_STANDARD_DEFAULT 17)
+    elseif(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 3.5.2)
+      set(CMAKE_C_STANDARD_DEFAULT 11)
+    endif()
+  endif()
   foreach(var
       CMAKE_SYSTEM_NAME
       CMAKE_C_COMPILER_ID