Merge topic 'features-c++20'

8570dc7f64 Help: Update compiler versions in cmake-compile-features.7.rst
874d3d2948 Help: Add release note for C++ 20 support
7f295b1bd3 Features: Activate C++ 20 support for Clang 5.0+
71cb8ce3a1 Features: Activate C++ 20 support for GNU 8.0+
8f146c4508 Features: Activate C++ 20 support for MSVC 19.12.25835+
7fe580a362 Features: Add infrastructure for C++ 20 language standard
1b328e09a3 Features: Use -std=c++17 for C++ 17 on Clang 5.0+
0bc3e5788a Features: Use -std=c++17 for C++ 17 on GNU 8.0+

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !1892

4 files changed, 20 insertions, 7 deletions

diff --git a/Source/cmLocalGenerator.cxx b/Source/cmLocalGenerator.cxx
index e942ff4..629d54a 100644
--- a/Source/cmLocalGenerator.cxx
+++ b/Source/cmLocalGenerator.cxx
@@ -1561,6 +1561,7 @@ void cmLocalGenerator::AddCompilerRequirementFlag(
   static std::map<std::string, std::vector<std::string>> langStdMap;
   if (langStdMap.empty()) {
     // Maintain sorted order, most recent first.
+    langStdMap["CXX"].push_back("20");
     langStdMap["CXX"].push_back("17");
     langStdMap["CXX"].push_back("14");
     langStdMap["CXX"].push_back("11");
diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index c270629..3ecd7eb 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -4223,7 +4223,7 @@ static const char* const CXX_FEATURES[] = { nullptr FOR_EACH_CXX_FEATURE(
 #undef FEATURE_STRING
 
 static const char* const C_STANDARDS[] = { "90", "99", "11" };
-static const char* const CXX_STANDARDS[] = { "98", "11", "14", "17" };
+static const char* const CXX_STANDARDS[] = { "98", "11", "14", "17", "20" };
 
 bool cmMakefile::AddRequiredTargetFeature(cmTarget* target,
                                           const std::string& feature,
@@ -4473,8 +4473,9 @@ bool cmMakefile::HaveCxxStandardAvailable(cmTarget const* target,
   bool needCxx11 = false;
   bool needCxx14 = false;
   bool needCxx17 = false;
+  bool needCxx20 = false;
   this->CheckNeededCxxLanguage(feature, needCxx98, needCxx11, needCxx14,
-                               needCxx17);
+                               needCxx17, needCxx20);
 
   const char* existingCxxStandard = target->GetProperty("CXX_STANDARD");
   if (!existingCxxStandard) {
@@ -4494,7 +4495,8 @@ bool cmMakefile::HaveCxxStandardAvailable(cmTarget const* target,
 
   /* clang-format off */
   const char* const* needCxxLevel =
-    needCxx17 ? &CXX_STANDARDS[3]
+    needCxx20 ? &CXX_STANDARDS[4]
+    : needCxx17 ? &CXX_STANDARDS[3]
     : needCxx14 ? &CXX_STANDARDS[2]
     : needCxx11 ? &CXX_STANDARDS[1]
     : needCxx98 ? &CXX_STANDARDS[0]
@@ -4506,7 +4508,8 @@ bool cmMakefile::HaveCxxStandardAvailable(cmTarget const* target,
 
 void cmMakefile::CheckNeededCxxLanguage(const std::string& feature,
                                         bool& needCxx98, bool& needCxx11,
-                                        bool& needCxx14, bool& needCxx17) const
+                                        bool& needCxx14, bool& needCxx17,
+                                        bool& needCxx20) const
 {
   if (const char* propCxx98 =
         this->GetDefinition("CMAKE_CXX98_COMPILE_FEATURES")) {
@@ -4532,6 +4535,12 @@ void cmMakefile::CheckNeededCxxLanguage(const std::string& feature,
     cmSystemTools::ExpandListArgument(propCxx17, props);
     needCxx17 = std::find(props.begin(), props.end(), feature) != props.end();
   }
+  if (const char* propCxx20 =
+        this->GetDefinition("CMAKE_CXX20_COMPILE_FEATURES")) {
+    std::vector<std::string> props;
+    cmSystemTools::ExpandListArgument(propCxx20, props);
+    needCxx20 = std::find(props.begin(), props.end(), feature) != props.end();
+  }
 }
 
 bool cmMakefile::AddRequiredTargetCxxFeature(cmTarget* target,
@@ -4542,9 +4551,10 @@ bool cmMakefile::AddRequiredTargetCxxFeature(cmTarget* target,
   bool needCxx11 = false;
   bool needCxx14 = false;
   bool needCxx17 = false;
+  bool needCxx20 = false;
 
   this->CheckNeededCxxLanguage(feature, needCxx98, needCxx11, needCxx14,
-                               needCxx17);
+                               needCxx17, needCxx20);
 
   const char* existingCxxStandard = target->GetProperty("CXX_STANDARD");
   const char* const* existingCxxLevel = nullptr;
@@ -4589,7 +4599,8 @@ bool cmMakefile::AddRequiredTargetCxxFeature(cmTarget* target,
 
   /* clang-format off */
   const char* const* needCxxLevel =
-    needCxx17 ? &CXX_STANDARDS[3]
+    needCxx20 ? &CXX_STANDARDS[4]
+    : needCxx17 ? &CXX_STANDARDS[3]
     : needCxx14 ? &CXX_STANDARDS[2]
     : needCxx11 ? &CXX_STANDARDS[1]
     : needCxx98 ? &CXX_STANDARDS[0]
diff --git a/Source/cmMakefile.h b/Source/cmMakefile.h
index 419cb6e..d2626cd 100644
--- a/Source/cmMakefile.h
+++ b/Source/cmMakefile.h
@@ -991,7 +991,7 @@ private:
                             bool& needC99, bool& needC11) const;
   void CheckNeededCxxLanguage(const std::string& feature, bool& needCxx98,
                               bool& needCxx11, bool& needCxx14,
-                              bool& needCxx17) const;
+                              bool& needCxx17, bool& needCxx20) const;
 
   bool HaveCStandardAvailable(cmTarget const* target,
                               const std::string& feature) const;
diff --git a/Source/cmake.h b/Source/cmake.h
index 1ac549b..cc56a07 100644
--- a/Source/cmake.h
+++ b/Source/cmake.h
@@ -574,6 +574,7 @@ private:
   F(cxx_std_11)                                                               \
   F(cxx_std_14)                                                               \
   F(cxx_std_17)                                                               \
+  F(cxx_std_20)                                                               \
   F(cxx_aggregate_default_initializers)                                       \
   F(cxx_alias_templates)                                                      \
   F(cxx_alignas)                                                              \