Genex $<COMPILE_LANGUAGE>: Extend contexts supported

When genex $<TARGET_PROPERTY:...> for properties like INCLUDE_DIRECTORIES
is evaluated as part of add_custom_command or add_custom_target,
genex $<COMPILE_LANGUAGE> and $<COMPLIE_LANG_AND_ID> should be supported.

Fixes: #20926

3 files changed, 15 insertions, 3 deletions

diff --git a/Source/cmGeneratorExpressionDAGChecker.cxx b/Source/cmGeneratorExpressionDAGChecker.cxx
index 4f379cd..e223f15 100644
--- a/Source/cmGeneratorExpressionDAGChecker.cxx
+++ b/Source/cmGeneratorExpressionDAGChecker.cxx
@@ -154,6 +154,14 @@ bool cmGeneratorExpressionDAGChecker::EvaluatingPICExpression() const
   return this->Top()->Property == "INTERFACE_POSITION_INDEPENDENT_CODE";
 }
 
+bool cmGeneratorExpressionDAGChecker::EvaluatingCompileExpression() const
+{
+  cm::string_view property(this->Top()->Property);
+
+  return property == "INCLUDE_DIRECTORIES"_s ||
+    property == "COMPILE_DEFINITIONS"_s || property == "COMPILE_OPTIONS"_s;
+}
+
 bool cmGeneratorExpressionDAGChecker::EvaluatingLinkExpression() const
 {
   cm::string_view property(this->Top()->Property);
diff --git a/Source/cmGeneratorExpressionDAGChecker.h b/Source/cmGeneratorExpressionDAGChecker.h
index c2c5b6b..ac2314c 100644
--- a/Source/cmGeneratorExpressionDAGChecker.h
+++ b/Source/cmGeneratorExpressionDAGChecker.h
@@ -68,6 +68,7 @@ struct cmGeneratorExpressionDAGChecker
 
   bool EvaluatingGenexExpression() const;
   bool EvaluatingPICExpression() const;
+  bool EvaluatingCompileExpression() const;
   bool EvaluatingLinkExpression() const;
   bool EvaluatingLinkOptionsExpression() const;
 
diff --git a/Source/cmGeneratorExpressionNode.cxx b/Source/cmGeneratorExpressionNode.cxx
index 4adc6a2..a1a0ae8 100644
--- a/Source/cmGeneratorExpressionNode.cxx
+++ b/Source/cmGeneratorExpressionNode.cxx
@@ -967,9 +967,10 @@ static const struct CompileLanguageNode : public cmGeneratorExpressionNode
     const std::vector<std::string>& parameters,
     cmGeneratorExpressionContext* context,
     const GeneratorExpressionContent* content,
-    cmGeneratorExpressionDAGChecker* /*dagChecker*/) const override
+    cmGeneratorExpressionDAGChecker* dagChecker) const override
   {
-    if (context->Language.empty()) {
+    if (context->Language.empty() &&
+        (!dagChecker || !dagChecker->EvaluatingCompileExpression())) {
       reportError(
         context, content->GetOriginalExpression(),
         "$<COMPILE_LANGUAGE:...> may only be used to specify include "
@@ -1014,7 +1015,9 @@ static const struct CompileLanguageAndIdNode : public cmGeneratorExpressionNode
     const GeneratorExpressionContent* content,
     cmGeneratorExpressionDAGChecker* dagChecker) const override
   {
-    if (!context->HeadTarget || context->Language.empty()) {
+    if (!context->HeadTarget ||
+        (context->Language.empty() &&
+         (!dagChecker || !dagChecker->EvaluatingCompileExpression()))) {
       // reportError(context, content->GetOriginalExpression(), "");
       reportError(
         context, content->GetOriginalExpression(),