Features: Add infrastructure for C++ 17 language standard

Issue: #16468

4 files changed, 30 insertions, 8 deletions

diff --git a/Source/cmLocalGenerator.cxx b/Source/cmLocalGenerator.cxx
index 46e49dc..ead1e72 100644
--- a/Source/cmLocalGenerator.cxx
+++ b/Source/cmLocalGenerator.cxx
@@ -1470,6 +1470,7 @@ 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("17");
     langStdMap["CXX"].push_back("14");
     langStdMap["CXX"].push_back("11");
     langStdMap["CXX"].push_back("98");
diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index fecc983..ed0f73b 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -4064,7 +4064,7 @@ static const char* const CXX_FEATURES[] = { CM_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" };
+static const char* const CXX_STANDARDS[] = { "98", "11", "14", "17" };
 
 bool cmMakefile::AddRequiredTargetFeature(cmTarget* target,
                                           const std::string& feature,
@@ -4297,7 +4297,9 @@ bool cmMakefile::HaveCxxStandardAvailable(cmTarget const* target,
   bool needCxx98 = false;
   bool needCxx11 = false;
   bool needCxx14 = false;
-  this->CheckNeededCxxLanguage(feature, needCxx98, needCxx11, needCxx14);
+  bool needCxx17 = false;
+  this->CheckNeededCxxLanguage(feature, needCxx98, needCxx11, needCxx14,
+                               needCxx17);
 
   const char* existingCxxStandard = target->GetProperty("CXX_STANDARD");
   if (!existingCxxStandard) {
@@ -4336,7 +4338,7 @@ bool cmMakefile::HaveCxxStandardAvailable(cmTarget const* target,
 
 void cmMakefile::CheckNeededCxxLanguage(const std::string& feature,
                                         bool& needCxx98, bool& needCxx11,
-                                        bool& needCxx14) const
+                                        bool& needCxx14, bool& needCxx17) const
 {
   if (const char* propCxx98 =
         this->GetDefinition("CMAKE_CXX98_COMPILE_FEATURES")) {
@@ -4356,6 +4358,12 @@ void cmMakefile::CheckNeededCxxLanguage(const std::string& feature,
     cmSystemTools::ExpandListArgument(propCxx14, props);
     needCxx14 = std::find(props.begin(), props.end(), feature) != props.end();
   }
+  if (const char* propCxx17 =
+        this->GetDefinition("CMAKE_CXX17_COMPILE_FEATURES")) {
+    std::vector<std::string> props;
+    cmSystemTools::ExpandListArgument(propCxx17, props);
+    needCxx17 = std::find(props.begin(), props.end(), feature) != props.end();
+  }
 }
 
 bool cmMakefile::AddRequiredTargetCxxFeature(cmTarget* target,
@@ -4365,8 +4373,10 @@ bool cmMakefile::AddRequiredTargetCxxFeature(cmTarget* target,
   bool needCxx98 = false;
   bool needCxx11 = false;
   bool needCxx14 = false;
+  bool needCxx17 = false;
 
-  this->CheckNeededCxxLanguage(feature, needCxx98, needCxx11, needCxx14);
+  this->CheckNeededCxxLanguage(feature, needCxx98, needCxx11, needCxx14,
+                               needCxx17);
 
   const char* existingCxxStandard = target->GetProperty("CXX_STANDARD");
   if (existingCxxStandard) {
@@ -4393,11 +4403,17 @@ bool cmMakefile::AddRequiredTargetCxxFeature(cmTarget* target,
   bool setCxx98 = needCxx98 && !existingCxxStandard;
   bool setCxx11 = needCxx11 && !existingCxxStandard;
   bool setCxx14 = needCxx14 && !existingCxxStandard;
+  bool setCxx17 = needCxx17 && !existingCxxStandard;
 
-  if (needCxx14 && existingCxxStandard &&
+  if (needCxx17 && existingCxxStandard &&
       existingCxxIt < std::find_if(cmArrayBegin(CXX_STANDARDS),
                                    cmArrayEnd(CXX_STANDARDS),
-                                   cmStrCmp("14"))) {
+                                   cmStrCmp("17"))) {
+    setCxx17 = true;
+  } else if (needCxx14 && existingCxxStandard &&
+             existingCxxIt < std::find_if(cmArrayBegin(CXX_STANDARDS),
+                                          cmArrayEnd(CXX_STANDARDS),
+                                          cmStrCmp("14"))) {
     setCxx14 = true;
   } else if (needCxx11 && existingCxxStandard &&
              existingCxxIt < std::find_if(cmArrayBegin(CXX_STANDARDS),
@@ -4411,7 +4427,10 @@ bool cmMakefile::AddRequiredTargetCxxFeature(cmTarget* target,
     setCxx98 = true;
   }
 
-  if (setCxx14) {
+  if (setCxx17) {
+    target->SetProperty("CXX_STANDARD", "17");
+    target->SetProperty("CUDA_STANDARD", "17");
+  } else if (setCxx14) {
     target->SetProperty("CXX_STANDARD", "14");
     target->SetProperty("CUDA_STANDARD", "14");
   } else if (setCxx11) {
diff --git a/Source/cmMakefile.h b/Source/cmMakefile.h
index 859b3c8..3484e5a 100644
--- a/Source/cmMakefile.h
+++ b/Source/cmMakefile.h
@@ -905,7 +905,8 @@ private:
   void CheckNeededCLanguage(const std::string& feature, bool& needC90,
                             bool& needC99, bool& needC11) const;
   void CheckNeededCxxLanguage(const std::string& feature, bool& needCxx98,
-                              bool& needCxx11, bool& needCxx14) const;
+                              bool& needCxx11, bool& needCxx14,
+                              bool& needCxx17) const;
 
   bool HaveCStandardAvailable(cmTarget const* target,
                               const std::string& feature) const;
diff --git a/Source/cmake.h b/Source/cmake.h
index 0f1891d..5347745 100644
--- a/Source/cmake.h
+++ b/Source/cmake.h
@@ -549,6 +549,7 @@ private:
   F(cxx_std_98)                                                               \
   F(cxx_std_11)                                                               \
   F(cxx_std_14)                                                               \
+  F(cxx_std_17)                                                               \
   F(cxx_aggregate_default_initializers)                                       \
   F(cxx_alias_templates)                                                      \
   F(cxx_alignas)                                                              \