Autogen: Clear sources meta data cache

Adds cmGeneratorTarget::clearSourcesCache() which clears the cache
of precomputed sources lists and object names. The cache gets
recomputed on demand.

Clearing the cache is necessary in case an OBJECT library
gets a source added after a target (ORIGIN) that includes it
computed it's external sources cache.
This may happen in AUTOMOC when ORIGIN is processed before the
OBJECT library which gets a mocs_compilation.cpp file added.

Closes #17152
Closes #17139
Closes #17085
Closes #15967

Source/cmGeneratorTarget.cxx

@@ -326,6 +326,13 @@ std::string cmGeneratorTarget::GetOutputName(
   return i->second;
 }
 
+void cmGeneratorTarget::ClearSourcesCache()
+{
+  this->KindedSourcesMap.clear();
+  this->LinkImplementationLanguageIsContextDependent = true;
+  this->Objects.clear();
+}
+
 void cmGeneratorTarget::AddSourceCommon(const std::string& src)
 {
   cmListFileBacktrace lfbt = this->Makefile->GetBacktrace();
@@ -333,8 +340,7 @@ void cmGeneratorTarget::AddSourceCommon(const std::string& src)
   CM_AUTO_PTR<cmCompiledGeneratorExpression> cge = ge.Parse(src);
   cge->SetEvaluateForBuildsystem(true);
   this->SourceEntries.push_back(new TargetPropertyEntry(cge));
-  this->KindedSourcesMap.clear();
-  this->LinkImplementationLanguageIsContextDependent = true;
+  this->ClearSourcesCache();
 }
 
 void cmGeneratorTarget::AddSource(const std::string& src)

Source/cmGeneratorTarget.h

@@ -491,6 +491,11 @@ public:
   std::string GetOutputName(const std::string& config,
                             cmStateEnums::ArtifactType artifact) const;
 
+  /** Clears cached meta data for local and external source files.
+    * The meta data will be recomputed on demand.
+    */
+  void ClearSourcesCache();
+
   void AddSource(const std::string& src);
   void AddTracedSources(std::vector<std::string> const& srcs);
 

Source/cmQtAutoGeneratorInitializer.cxx

@@ -919,6 +919,12 @@ void cmQtAutoGeneratorInitializer::InitializeAutogenTarget(
     }
   }
 
+  // cmGeneratorTarget::GetConfigCommonSourceFiles computes the target's
+  // sources meta data cache. Clear it so that OBJECT library targets that
+  // are AUTOGEN initialized after this target get their added
+  // mocs_compilation.cpp source acknowledged by this target.
+  target->ClearSourcesCache();
+
   // Convert std::set to std::vector
   const std::vector<std::string> autogenDepends(autogenDependsSet.begin(),
                                                 autogenDependsSet.end());