Factor IDE folder name retrieval out into helper method

Add a `cmGeneratorTarget::GetEffectiveFolderName` helper to abstract
lookup of the `FOLDER` property in combination with checking for
generator support of folders.

Source/cmGeneratorTarget.cxx

@@ -1767,6 +1767,22 @@ std::string cmGeneratorTarget::GetMacContentDirectory(
   return fpath;
 }
 
+std::string cmGeneratorTarget::GetEffectiveFolderName() const
+{
+  std::string effectiveFolder;
+
+  if (!this->GlobalGenerator->UseFolderProperty()) {
+    return effectiveFolder;
+  }
+
+  const char* targetFolder = this->GetProperty("FOLDER");
+  if (targetFolder) {
+    effectiveFolder += targetFolder;
+  }
+
+  return effectiveFolder;
+}
+
 cmGeneratorTarget::CompileInfo const* cmGeneratorTarget::GetCompileInfo(
   const std::string& config) const
 {

Source/cmGeneratorTarget.h

@@ -220,6 +220,9 @@ public:
   std::string GetMacContentDirectory(const std::string& config = CM_NULLPTR,
                                      bool implib = false) const;
 
+  /** @return folder prefix for IDEs. */
+  std::string GetEffectiveFolderName() const;
+
   cmTarget* Target;
   cmMakefile* Makefile;
   cmLocalGenerator* LocalGenerator;

Source/cmGhsMultiTargetGenerator.cxx

@@ -44,9 +44,7 @@ cmGhsMultiTargetGenerator::~cmGhsMultiTargetGenerator()
 std::string cmGhsMultiTargetGenerator::GetRelBuildFilePath(
   const cmGeneratorTarget* target)
 {
-  std::string output;
-  char const* folderProp = target->GetProperty("FOLDER");
-  output = NULL == folderProp ? "" : folderProp;
+  std::string output = target->GetEffectiveFolderName();
   cmSystemTools::ConvertToUnixSlashes(output);
   if (!output.empty()) {
     output += "/";

Source/cmGlobalGenerator.cxx

@@ -2377,7 +2377,7 @@ const char* cmGlobalGenerator::GetPredefinedTargetsFolder()
   return "CMakePredefinedTargets";
 }
 
-bool cmGlobalGenerator::UseFolderProperty()
+bool cmGlobalGenerator::UseFolderProperty() const
 {
   const char* prop =
     this->GetCMakeInstance()->GetState()->GetGlobalProperty("USE_FOLDERS");

Source/cmGlobalGenerator.h

@@ -334,6 +334,8 @@ public:
       i.e. "Can I build Debug and Release in the same tree?" */
   virtual bool IsMultiConfig() const { return false; }
 
+  virtual bool UseFolderProperty() const;
+
   std::string GetSharedLibFlagsForLanguage(std::string const& lang) const;
 
   /** Generate an <output>.rule file path for a given command output.  */
@@ -463,7 +465,6 @@ protected:
     std::string const& name) const;
 
   const char* GetPredefinedTargetsFolder();
-  virtual bool UseFolderProperty();
 
 private:
 #if defined(CMAKE_BUILD_WITH_CMAKE)

Source/cmGlobalGhsMultiGenerator.cxx

@@ -439,11 +439,7 @@ void cmGlobalGhsMultiGenerator::UpdateBuildFiles(
        tgtsI != tgts.end(); ++tgtsI) {
     const cmGeneratorTarget* tgt = *tgtsI;
     if (IsTgtForBuild(tgt)) {
-      char const* rawFolderName = tgt->GetProperty("FOLDER");
-      if (NULL == rawFolderName) {
-        rawFolderName = "";
-      }
-      std::string folderName(rawFolderName);
+      std::string folderName = tgt->GetEffectiveFolderName();
       if (this->TargetFolderBuildStreams.end() ==
           this->TargetFolderBuildStreams.find(folderName)) {
         this->AddFilesUpToPath(

Source/cmGlobalVisualStudio7Generator.cxx

@@ -409,8 +409,8 @@ void cmGlobalVisualStudio7Generator::WriteTargetsToSolution(
     // Create "solution folder" information from FOLDER target property
     //
     if (written && this->UseFolderProperty()) {
-      const char* targetFolder = target->GetProperty("FOLDER");
-      if (targetFolder) {
+      const std::string targetFolder = target->GetEffectiveFolderName();
+      if (!targetFolder.empty()) {
         std::vector<cmsys::String> tokens =
           cmSystemTools::SplitString(targetFolder, '/', false);
 

Source/cmGlobalXCodeGenerator.cxx

@@ -2723,8 +2723,8 @@ cmXCodeObject* cmGlobalXCodeGenerator::CreateOrGetPBXGroup(
 {
   std::string s;
   std::string target;
-  const char* targetFolder = gtgt->GetProperty("FOLDER");
-  if (targetFolder) {
+  const std::string targetFolder = gtgt->GetEffectiveFolderName();
+  if (!targetFolder.empty()) {
     target = targetFolder;
     target += "/";
   }