Genex: Enable COMPILE_LANGUAGE for COMPILE_DEFINITIONS with VS and Xcode

The set of compile flags used for a target's C and C++ sources is based
on the linker language.  By default this is always the C++ flags if any
C++ sources appear in the target, and otherwise the C flags.  Therefore
we can define the `COMPILE_LANGUAGE` generator expression in
`COMPILE_DEFINITIONS` to match the selected language.

This is not exactly the same as for other generators, but is the best VS
and Xcode can do.  It is also sufficient for many use cases since the
set of definitions for C and C++ is frequently similar but may be
distinct from those for other languages like CUDA.

Issue: #17435

5 files changed, 23 insertions, 12 deletions

diff --git a/Source/cmGeneratorExpressionNode.cxx b/Source/cmGeneratorExpressionNode.cxx
index 3d311d6..597112a 100644
--- a/Source/cmGeneratorExpressionNode.cxx
+++ b/Source/cmGeneratorExpressionNode.cxx
@@ -828,20 +828,20 @@ static const struct CompileLanguageNode : public cmGeneratorExpressionNode
     }
     std::string genName = gg->GetName();
     if (genName.find("Visual Studio") != std::string::npos) {
-      if (dagChecker && (dagChecker->EvaluatingCompileDefinitions() ||
-                         dagChecker->EvaluatingIncludeDirectories())) {
+      if (dagChecker && dagChecker->EvaluatingIncludeDirectories()) {
         reportError(
           context, content->GetOriginalExpression(),
-          "$<COMPILE_LANGUAGE:...> may only be used for COMPILE_OPTIONS "
+          "$<COMPILE_LANGUAGE:...> may only be used for COMPILE_OPTIONS, "
+          "COMPILE_DEFINITIONS, "
           "and file(GENERATE) with the Visual Studio generator.");
         return std::string();
       }
     } else if (genName.find("Xcode") != std::string::npos) {
-      if (dagChecker && (dagChecker->EvaluatingCompileDefinitions() ||
-                         dagChecker->EvaluatingIncludeDirectories())) {
+      if (dagChecker && dagChecker->EvaluatingIncludeDirectories()) {
         reportError(
           context, content->GetOriginalExpression(),
-          "$<COMPILE_LANGUAGE:...> may only be used for COMPILE_OPTIONS "
+          "$<COMPILE_LANGUAGE:...> may only be used for COMPILE_OPTIONS, "
+          "COMPILE_DEFINITIONS, "
           "and file(GENERATE) with the Xcode generator.");
         return std::string();
       }
diff --git a/Source/cmGlobalXCodeGenerator.cxx b/Source/cmGlobalXCodeGenerator.cxx
index 338c2b4..d22356e 100644
--- a/Source/cmGlobalXCodeGenerator.cxx
+++ b/Source/cmGlobalXCodeGenerator.cxx
@@ -1703,6 +1703,7 @@ void cmGlobalXCodeGenerator::CreateBuildSettings(cmGeneratorTarget* gtgt,
       gtgt->GetName().c_str());
     return;
   }
+  std::string const& langForPreprocessor = llang;
 
   if (gtgt->IsIPOEnabled(llang, configName)) {
     const char* ltoValue =
@@ -1723,7 +1724,10 @@ void cmGlobalXCodeGenerator::CreateBuildSettings(cmGeneratorTarget* gtgt,
     this->AppendDefines(ppDefs, exportMacro);
   }
   std::vector<std::string> targetDefines;
-  gtgt->GetCompileDefinitions(targetDefines, configName, "C");
+  if (!langForPreprocessor.empty()) {
+    gtgt->GetCompileDefinitions(targetDefines, configName,
+                                langForPreprocessor);
+  }
   this->AppendDefines(ppDefs, targetDefines);
   buildSettings->AddAttribute("GCC_PREPROCESSOR_DEFINITIONS",
                               ppDefs.CreateList());
diff --git a/Source/cmLocalVisualStudio7Generator.cxx b/Source/cmLocalVisualStudio7Generator.cxx
index 4cc6e3c..003163e 100644
--- a/Source/cmLocalVisualStudio7Generator.cxx
+++ b/Source/cmLocalVisualStudio7Generator.cxx
@@ -705,7 +705,9 @@ void cmLocalVisualStudio7Generator::WriteConfiguration(
   targetOptions.Parse(defineFlags.c_str());
   targetOptions.ParseFinish();
   std::vector<std::string> targetDefines;
-  target->GetCompileDefinitions(targetDefines, configName, "CXX");
+  if (!langForClCompile.empty()) {
+    target->GetCompileDefinitions(targetDefines, configName, langForClCompile);
+  }
   targetOptions.AddDefines(targetDefines);
   targetOptions.SetVerboseMakefile(
     this->Makefile->IsOn("CMAKE_VERBOSE_MAKEFILE"));
@@ -812,7 +814,8 @@ void cmLocalVisualStudio7Generator::WriteConfiguration(
   }
   fout << "\"\n";
   targetOptions.OutputFlagMap(fout, "\t\t\t\t");
-  targetOptions.OutputPreprocessorDefinitions(fout, "\t\t\t\t", "\n", "CXX");
+  targetOptions.OutputPreprocessorDefinitions(fout, "\t\t\t\t", "\n",
+                                              langForClCompile);
   fout << "\t\t\t\tObjectFile=\"$(IntDir)\\\"\n";
   if (target->GetType() <= cmStateEnums::OBJECT_LIBRARY) {
     // Specify the compiler program database file if configured.
diff --git a/Source/cmVisualStudio10TargetGenerator.cxx b/Source/cmVisualStudio10TargetGenerator.cxx
index 7074624..5533652 100644
--- a/Source/cmVisualStudio10TargetGenerator.cxx
+++ b/Source/cmVisualStudio10TargetGenerator.cxx
@@ -2391,6 +2391,7 @@ bool cmVisualStudio10TargetGenerator::ComputeClOptions(
       }
     }
   }
+  this->LangForClCompile = langForClCompile;
   if (!langForClCompile.empty()) {
     std::string baseFlagVar = "CMAKE_";
     baseFlagVar += langForClCompile;
@@ -2434,8 +2435,10 @@ bool cmVisualStudio10TargetGenerator::ComputeClOptions(
   std::vector<std::string> targetDefines;
   switch (this->ProjectType) {
     case vcxproj:
-      this->GeneratorTarget->GetCompileDefinitions(targetDefines, configName,
-                                                   "CXX");
+      if (!langForClCompile.empty()) {
+        this->GeneratorTarget->GetCompileDefinitions(targetDefines, configName,
+                                                     langForClCompile);
+      }
       break;
     case csproj:
       this->GeneratorTarget->GetCompileDefinitions(targetDefines, configName,
@@ -2512,7 +2515,7 @@ void cmVisualStudio10TargetGenerator::WriteClOptions(
                        "%(AdditionalIncludeDirectories)");
   clOptions.OutputFlagMap(*this->BuildFileStream, "      ");
   clOptions.OutputPreprocessorDefinitions(*this->BuildFileStream, "      ",
-                                          "\n", "CXX");
+                                          "\n", this->LangForClCompile);
 
   if (this->NsightTegra) {
     if (const char* processMax =
diff --git a/Source/cmVisualStudio10TargetGenerator.h b/Source/cmVisualStudio10TargetGenerator.h
index 3f56959..b1a09eb 100644
--- a/Source/cmVisualStudio10TargetGenerator.h
+++ b/Source/cmVisualStudio10TargetGenerator.h
@@ -183,6 +183,7 @@ private:
   OptionsMap MasmOptions;
   OptionsMap NasmOptions;
   OptionsMap LinkOptions;
+  std::string LangForClCompile;
   std::string PathToProjectFile;
   std::string ProjectFileExtension;
   enum VsProjectType