Genex: Enable COMPILE_LANGUAGE for file(GENERATE) with Visual Studio

Issue: #17435

Source/cmGeneratorExpressionNode.cxx

@@ -828,12 +828,16 @@ static const struct CompileLanguageNode : public cmGeneratorExpressionNode
     }
     std::string genName = gg->GetName();
     if (genName.find("Visual Studio") != std::string::npos) {
-      reportError(context, content->GetOriginalExpression(),
-                  "$<COMPILE_LANGUAGE:...> may not be used with Visual Studio "
-                  "generators.");
-      return std::string();
-    }
-    if (genName.find("Xcode") != std::string::npos) {
+      if (dagChecker && (dagChecker->EvaluatingCompileDefinitions() ||
+                         dagChecker->EvaluatingCompileOptions() ||
+                         dagChecker->EvaluatingIncludeDirectories())) {
+        reportError(
+          context, content->GetOriginalExpression(),
+          "$<COMPILE_LANGUAGE:...> may only be used for file(GENERATE) "
+          "with the Visual Studio generator.");
+        return std::string();
+      }
+    } else if (genName.find("Xcode") != std::string::npos) {
       if (dagChecker && (dagChecker->EvaluatingCompileDefinitions() ||
                          dagChecker->EvaluatingIncludeDirectories())) {
         reportError(

Tests/RunCMake/COMPILE_LANGUAGE-genex/CompileDefinitions-stderr-VS.txt

@@ -3,6 +3,7 @@ CMake Error at CompileDefinitions.cmake:5 \(target_compile_definitions\):
 
     \$<COMPILE_LANGUAGE:CXX>
 
-  \$<COMPILE_LANGUAGE:...> may not be used with Visual Studio generators.
+  \$<COMPILE_LANGUAGE:...> may only be used for file\(GENERATE\) with the Visual
+  Studio generator.
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)

Tests/RunCMake/COMPILE_LANGUAGE-genex/CompileOptions-stderr-VS.txt

@@ -3,6 +3,7 @@ CMake Error at CompileOptions.cmake:5 \(target_compile_options\):
 
     \$<COMPILE_LANGUAGE:CXX>
 
-  \$<COMPILE_LANGUAGE:...> may not be used with Visual Studio generators.
+  \$<COMPILE_LANGUAGE:...> may only be used for file\(GENERATE\) with the Visual
+  Studio generator.
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)

Tests/RunCMake/COMPILE_LANGUAGE-genex/IncludeDirectories-stderr-VS.txt

@@ -3,6 +3,7 @@ CMake Error at IncludeDirectories.cmake:5 \(target_include_directories\):
 
     \$<COMPILE_LANGUAGE:CXX>
 
-  \$<COMPILE_LANGUAGE:...> may not be used with Visual Studio generators.
+  \$<COMPILE_LANGUAGE:...> may only be used for file\(GENERATE\) with the Visual
+  Studio generator.
 Call Stack \(most recent call first\):
   CMakeLists.txt:3 \(include\)

Tests/RunCMake/File_Generate/RunCMakeTest.cmake

@@ -21,15 +21,13 @@ if (NOT file_contents MATCHES "generated.cpp.rule")
   message(SEND_ERROR "Rule file not in target sources! ${file_contents}")
 endif()
 
-if (NOT RunCMake_GENERATOR MATCHES "Visual Studio")
-  run_cmake(COMPILE_LANGUAGE-genex)
-  foreach(l CXX C)
-    file(READ "${RunCMake_BINARY_DIR}/COMPILE_LANGUAGE-genex-build/opts-${l}.txt" l_defs)
-    if (NOT l_defs STREQUAL "LANG_IS_${l}\n")
-      message(FATAL_ERROR "File content does not match: ${l_defs}")
-    endif()
-  endforeach()
-endif()
+run_cmake(COMPILE_LANGUAGE-genex)
+foreach(l CXX C)
+  file(READ "${RunCMake_BINARY_DIR}/COMPILE_LANGUAGE-genex-build/opts-${l}.txt" l_defs)
+  if (NOT l_defs STREQUAL "LANG_IS_${l}\n")
+    message(FATAL_ERROR "File content does not match: ${l_defs}")
+  endif()
+endforeach()
 
 set(timeformat "%Y%j%H%M%S")