[clang] [clang][Dependency Scanning] Refactor Scanning Compiler Instance Initialization (PR #161300)

[Jan Svoboda via cfe-commits]

================
@@ -72,9 +74,77 @@ class DependencyScanningAction {
   bool DiagConsumerFinished = false;
 };
 
-// Helper functions
-void sanitizeDiagOpts(DiagnosticOptions &DiagOpts);
+// Helper functions and data types.
+std::unique_ptr<DiagnosticOptions>
+createDiagOptions(const std::vector<std::string> &CommandLine);
 
+struct DignosticsEngineWithCCommandLineAndDiagOpts {
+  // We need to bound the lifetime of the CCommandLine and the DiagOpts
+  // used to create the DiganosticsEngine with the DiagnosticsEngine itself.
----------------
jansvoboda11 wrote:

Can you clarify why? The `DiagnosticOptions` class should have value semantics, so I'm surprised you'd need to keep the `CCommandLine` alive.

https://github.com/llvm/llvm-project/pull/161300