cmSourceFile::GetPropertyForUser: return cmProp

also fix GetSafeProperty() return type

Source/cmGetPropertyCommand.cxx

@@ -391,7 +391,7 @@ bool HandleSourceMode(cmExecutionStatus& status, const std::string& name,
   if (cmSourceFile* sf =
         directory_makefile.GetOrCreateSource(source_file_absolute_path)) {
     return StoreResult(infoType, status.GetMakefile(), variable,
-                       sf->GetPropertyForUser(propertyName));
+                       cmToCStr(sf->GetPropertyForUser(propertyName)));
   }
   status.SetError(
     cmStrCat("given SOURCE name that could not be found or created: ",

Source/cmGetSourceFilePropertyCommand.cxx

@@ -4,6 +4,7 @@
 
 #include "cmExecutionStatus.h"
 #include "cmMakefile.h"
+#include "cmProperty.h"
 #include "cmSetPropertyCommand.h"
 #include "cmSourceFile.h"
 
@@ -57,14 +58,14 @@ bool cmGetSourceFilePropertyCommand(std::vector<std::string> const& args,
   }
 
   if (sf) {
-    const char* prop = nullptr;
+    cmProp prop = nullptr;
     if (!args[property_arg_index].empty()) {
       prop = sf->GetPropertyForUser(args[property_arg_index]);
     }
     if (prop) {
       // Set the value on the original Makefile scope, not the scope of the
       // requested directory.
-      status.GetMakefile().AddDefinition(var, prop);
+      status.GetMakefile().AddDefinition(var, *prop);
       return true;
     }
   }

Source/cmQtAutoGenInitializer.cxx

@@ -807,7 +807,7 @@ bool cmQtAutoGenInitializer::InitScanFiles()
           qrc.Generated = sf->GetIsGenerated();
           // RCC options
           {
-            std::string const opts = sf->GetSafeProperty(kw.AUTORCC_OPTIONS);
+            std::string const& opts = sf->GetSafeProperty(kw.AUTORCC_OPTIONS);
             if (!opts.empty()) {
               cmExpandList(opts, qrc.Options);
             }

Source/cmSourceFile.cxx

@@ -310,7 +310,7 @@ void cmSourceFile::AppendProperty(const std::string& prop,
   }
 }
 
-const char* cmSourceFile::GetPropertyForUser(const std::string& prop)
+cmProp cmSourceFile::GetPropertyForUser(const std::string& prop)
 {
   // This method is a consequence of design history and backwards
   // compatibility.  GetProperty is (and should be) a const method.
@@ -334,13 +334,12 @@ const char* cmSourceFile::GetPropertyForUser(const std::string& prop)
   // Similarly, LANGUAGE can be determined by the file extension
   // if it is requested by the user.
   if (prop == propLANGUAGE) {
-    // The c_str pointer is valid until `this->Language` is modified.
-    return this->GetOrDetermineLanguage().c_str();
+    // The pointer is valid until `this->Language` is modified.
+    return &this->GetOrDetermineLanguage();
   }
 
   // Perform the normal property lookup.
-  cmProp p = this->GetProperty(prop);
-  return p ? p->c_str() : nullptr;
+  return this->GetProperty(prop);
 }
 
 cmProp cmSourceFile::GetProperty(const std::string& prop) const
@@ -398,13 +397,15 @@ cmProp cmSourceFile::GetProperty(const std::string& prop) const
   return retVal;
 }
 
-const char* cmSourceFile::GetSafeProperty(const std::string& prop) const
+const std::string& cmSourceFile::GetSafeProperty(const std::string& prop) const
 {
   cmProp ret = this->GetProperty(prop);
-  if (!ret) {
-    return "";
+  if (ret) {
+    return *ret;
   }
-  return ret->c_str();
+
+  static std::string const s_empty;
+  return s_empty;
 }
 
 bool cmSourceFile::GetPropertyAsBool(const std::string& prop) const

Source/cmSourceFile.h

@@ -47,12 +47,12 @@ public:
   //! Might return a nullptr if the property is not set or invalid
   cmProp GetProperty(const std::string& prop) const;
   //! Always returns a valid pointer
-  const char* GetSafeProperty(const std::string& prop) const;
+  const std::string& GetSafeProperty(const std::string& prop) const;
   bool GetPropertyAsBool(const std::string& prop) const;
 
   /** Implement getting a property when called from a CMake language
       command like get_property or get_source_file_property.  */
-  const char* GetPropertyForUser(const std::string& prop);
+  cmProp GetPropertyForUser(const std::string& prop);
 
   //! Checks is the GENERATED property is set and true
   /// @return Equivalent to GetPropertyAsBool("GENERATED")