From 93b7d3d29221f98388c7fa20568cd0b769a26774 Mon Sep 17 00:00:00 2001
From: Raul Tambre <raul@tambre.ee>
Date: Sat, 6 Feb 2021 18:54:13 +0200
Subject: C17 support

Implements #17755.
---
 Help/prop_gbl/CMAKE_C_KNOWN_FEATURES.rst         | 3 +++
 Help/prop_tgt/C_STANDARD.rst                     | 2 +-
 Help/release/dev/c-std.rst                       | 6 ++++++
 Modules/CMakeCCompiler.cmake.in                  | 1 +
 Modules/CMakeCCompilerId.c.in                    | 2 ++
 Modules/CMakeDetermineCompileFeatures.cmake      | 6 ++++++
 Modules/Compiler/CMakeCommonCompilerMacros.cmake | 3 +++
 Source/cmStandardLevelResolver.cxx               | 5 +++--
 Source/cmake.h                                   | 1 +
 Tests/CompileFeatures/CMakeLists.txt             | 1 +
 Tests/CompileFeatures/default_dialect.c          | 6 +++++-
 11 files changed, 32 insertions(+), 4 deletions(-)
 create mode 100644 Help/release/dev/c-std.rst

diff --git a/Help/prop_gbl/CMAKE_C_KNOWN_FEATURES.rst b/Help/prop_gbl/CMAKE_C_KNOWN_FEATURES.rst
index 7166381..9ea63fa 100644
--- a/Help/prop_gbl/CMAKE_C_KNOWN_FEATURES.rst
+++ b/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``.
 
diff --git a/Help/prop_tgt/C_STANDARD.rst b/Help/prop_tgt/C_STANDARD.rst
index 3f0d242..4fbde35 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``.
 
 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..475a4e4
--- /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.
diff --git a/Modules/CMakeCCompiler.cmake.in b/Modules/CMakeCCompiler.cmake.in
index 7f73891..74487d1 100644
--- a/Modules/CMakeCCompiler.cmake.in
+++ b/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@")
diff --git a/Modules/CMakeCCompilerId.c.in b/Modules/CMakeCCompilerId.c.in
index e6662b8..f1175f4 100644
--- a/Modules/CMakeCCompilerId.c.in
+++ b/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
diff --git a/Modules/CMakeDetermineCompileFeatures.cmake b/Modules/CMakeDetermineCompileFeatures.cmake
index c03a85f..49b8169 100644
--- a/Modules/CMakeDetermineCompileFeatures.cmake
+++ b/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")
 
diff --git a/Modules/Compiler/CMakeCommonCompilerMacros.cmake b/Modules/Compiler/CMakeCommonCompilerMacros.cmake
index cd897c5..ac20d5f 100644
--- a/Modules/Compiler/CMakeCommonCompilerMacros.cmake
+++ b/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)
diff --git a/Source/cmStandardLevelResolver.cxx b/Source/cmStandardLevelResolver.cxx
index bf6925e..e290663 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 },
+        std::vector<std::string>{ "90", "99", "11", "17" } } },
     { "CXX",
       StanardLevelComputer{
         "CXX", std::vector<int>{ 98, 11, 14, 17, 20, 23 },
diff --git a/Source/cmake.h b/Source/cmake.h
index 82e028c..95eb113 100644
--- a/Source/cmake.h
+++ b/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)
diff --git a/Tests/CompileFeatures/CMakeLists.txt b/Tests/CompileFeatures/CMakeLists.txt
index cff98e3..046b858 100644
--- a/Tests/CompileFeatures/CMakeLists.txt
+++ b/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>
diff --git a/Tests/CompileFeatures/default_dialect.c b/Tests/CompileFeatures/default_dialect.c
index 6160c2f..e090067 100644
--- a/Tests/CompileFeatures/default_dialect.c
+++ b/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
-- 
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