cmGlobalGenerator: give context about module queries

Some queries are merely investigating support in order to change
behavior. Let the method know so that any internal errors can be skipped
over.

Source/cmGeneratorTarget.cxx

@@ -9190,7 +9190,8 @@ void cmGeneratorTarget::CheckCxxModuleStatus(std::string const& config) const
 
   // If the generator doesn't support modules at all, error that we have
   // sources that require the support.
-  if (!this->GetGlobalGenerator()->CheckCxxModuleSupport()) {
+  if (!this->GetGlobalGenerator()->CheckCxxModuleSupport(
+        cmGlobalGenerator::CxxModuleSupportQuery::Expected)) {
     this->Makefile->IssueMessage(
       MessageType::FATAL_ERROR,
       cmStrCat(
@@ -9248,7 +9249,8 @@ bool cmGeneratorTarget::NeedCxxModuleSupport(std::string const& lang,
     return false;
   }
   return this->HaveCxxModuleSupport(config) == Cxx20SupportLevel::Supported &&
-    this->GetGlobalGenerator()->CheckCxxModuleSupport();
+    this->GetGlobalGenerator()->CheckCxxModuleSupport(
+      cmGlobalGenerator::CxxModuleSupportQuery::Inspect);
 }
 
 bool cmGeneratorTarget::NeedDyndep(std::string const& lang,
@@ -9304,7 +9306,8 @@ bool cmGeneratorTarget::NeedDyndepForSource(std::string const& lang,
       break;
   }
   bool haveGeneratorSupport =
-    this->GetGlobalGenerator()->CheckCxxModuleSupport();
+    this->GetGlobalGenerator()->CheckCxxModuleSupport(
+      cmGlobalGenerator::CxxModuleSupportQuery::Inspect);
   auto const sfProp = sf->GetProperty("CXX_SCAN_FOR_MODULES");
   if (sfProp.IsSet()) {
     return sfProp.IsOn();

Source/cmGlobalGenerator.h

@@ -156,7 +156,17 @@ public:
 
   virtual bool InspectConfigTypeVariables() { return true; }
 
-  virtual bool CheckCxxModuleSupport() { return false; }
+  enum class CxxModuleSupportQuery
+  {
+    // Support is expected at the call site.
+    Expected,
+    // The call site is querying for support and handles problems by itself.
+    Inspect,
+  };
+  virtual bool CheckCxxModuleSupport(CxxModuleSupportQuery /*query*/)
+  {
+    return false;
+  }
 
   virtual bool IsGNUMakeJobServerAware() const { return false; }
 

Source/cmGlobalNinjaGenerator.cxx

@@ -882,13 +882,14 @@ bool cmGlobalNinjaGenerator::CheckLanguages(
   return true;
 }
 
-bool cmGlobalNinjaGenerator::CheckCxxModuleSupport()
+bool cmGlobalNinjaGenerator::CheckCxxModuleSupport(CxxModuleSupportQuery query)
 {
   if (this->NinjaSupportsDyndepsCxx) {
     return true;
   }
   bool const diagnose = !this->DiagnosedCxxModuleNinjaSupport &&
-    !this->CMakeInstance->GetIsInTryCompile();
+    !this->CMakeInstance->GetIsInTryCompile() &&
+    query == CxxModuleSupportQuery::Expected;
   if (diagnose) {
     std::ostringstream e;
     /* clang-format off */

Source/cmGlobalNinjaGenerator.h

@@ -475,7 +475,7 @@ public:
 
   bool IsSingleConfigUtility(cmGeneratorTarget const* target) const;
 
-  bool CheckCxxModuleSupport() override;
+  bool CheckCxxModuleSupport(CxxModuleSupportQuery query) override;
 
 protected:
   void Generate() override;

Source/cmGlobalVisualStudioVersionedGenerator.h

@@ -48,7 +48,7 @@ public:
 
   const char* GetAndroidApplicationTypeRevision() const override;
 
-  bool CheckCxxModuleSupport() override
+  bool CheckCxxModuleSupport(CxxModuleSupportQuery /*query*/) override
   {
     return this->SupportsCxxModuleDyndep();
   }