Xcode: Use legacy build system

Closes: #18099

Source/cmGlobalXCodeGenerator.cxx

@@ -3338,15 +3338,10 @@ void cmGlobalXCodeGenerator::OutputXCodeProject(
   }
   this->WriteXCodePBXProj(fout, root, generators);
 
-  // Since the lowest available Xcode version for testing was 6.4,
-  // I'm setting this as a limit then
-  if (this->XcodeVersion >= 64) {
-    if (root->GetMakefile()->GetCMakeInstance()->GetIsInTryCompile() ||
-        root->GetMakefile()->IsOn("CMAKE_XCODE_GENERATE_SCHEME")) {
-      this->OutputXCodeSharedSchemes(xcodeDir);
-      this->OutputXCodeWorkspaceSettings(xcodeDir);
-    }
+  if (this->IsGeneratingScheme(root)) {
+    this->OutputXCodeSharedSchemes(xcodeDir);
   }
+  this->OutputXCodeWorkspaceSettings(xcodeDir, root);
 
   this->ClearXCodeObjects();
 
@@ -3356,6 +3351,15 @@ void cmGlobalXCodeGenerator::OutputXCodeProject(
     root->GetBinaryDirectory());
 }
 
+bool cmGlobalXCodeGenerator::IsGeneratingScheme(cmLocalGenerator* root) const
+{
+  // Since the lowest available Xcode version for testing was 6.4,
+  // I'm setting this as a limit then
+  return this->XcodeVersion >= 64 &&
+    (root->GetMakefile()->GetCMakeInstance()->GetIsInTryCompile() ||
+     root->GetMakefile()->IsOn("CMAKE_XCODE_GENERATE_SCHEME"));
+}
+
 void cmGlobalXCodeGenerator::OutputXCodeSharedSchemes(
   const std::string& xcProjDir)
 {
@@ -3395,7 +3399,7 @@ void cmGlobalXCodeGenerator::OutputXCodeSharedSchemes(
 }
 
 void cmGlobalXCodeGenerator::OutputXCodeWorkspaceSettings(
-  const std::string& xcProjDir)
+  const std::string& xcProjDir, cmLocalGenerator* root)
 {
   std::string xcodeSharedDataDir = xcProjDir;
   xcodeSharedDataDir += "/project.xcworkspace/xcshareddata";
@@ -3417,8 +3421,15 @@ void cmGlobalXCodeGenerator::OutputXCodeWorkspaceSettings(
   xout.StartElement("plist");
   xout.Attribute("version", "1.0");
   xout.StartElement("dict");
-  xout.Element("key", "IDEWorkspaceSharedSettings_AutocreateContextsIfNeeded");
-  xout.Element("false");
+  if (this->XcodeVersion >= 100) {
+    xout.Element("key", "BuildSystemType");
+    xout.Element("string", "Original");
+  }
+  if (this->IsGeneratingScheme(root)) {
+    xout.Element("key",
+                 "IDEWorkspaceSharedSettings_AutocreateContextsIfNeeded");
+    xout.Element("false");
+  }
   xout.EndElement(); // dict
   xout.EndElement(); // plist
   xout.EndDocument();

Source/cmGlobalXCodeGenerator.h

@@ -182,9 +182,11 @@ private:
                           std::vector<cmLocalGenerator*>& generators);
   void OutputXCodeProject(cmLocalGenerator* root,
                           std::vector<cmLocalGenerator*>& generators);
+  bool IsGeneratingScheme(cmLocalGenerator* root) const;
   // Write shared scheme files for all the native targets
   void OutputXCodeSharedSchemes(const std::string& xcProjDir);
-  void OutputXCodeWorkspaceSettings(const std::string& xcProjDir);
+  void OutputXCodeWorkspaceSettings(const std::string& xcProjDir,
+                                    cmLocalGenerator* root);
   void WriteXCodePBXProj(std::ostream& fout, cmLocalGenerator* root,
                          std::vector<cmLocalGenerator*>& generators);
   cmXCodeObject* CreateXCodeFileReferenceFromPath(const std::string& fullpath,