[clang] [clang] Introduce copy-on-write `CompilerInvocation` (PR #65412)

[Jan Svoboda via cfe-commits]

================
@@ -123,49 +123,101 @@ static Expected<std::optional<uint32_t>> parseToleranceOption(StringRef Arg) {
 }
 
 //===----------------------------------------------------------------------===//
-// Initialization.
+// Storage details.
 //===----------------------------------------------------------------------===//
 
-CompilerInvocationRefBase::CompilerInvocationRefBase()
-    : LangOpts(new LangOptions()), TargetOpts(new TargetOptions()),
-      DiagnosticOpts(new DiagnosticOptions()),
-      HeaderSearchOpts(new HeaderSearchOptions()),
-      PreprocessorOpts(new PreprocessorOptions()),
-      AnalyzerOpts(new AnalyzerOptions()) {}
-
-CompilerInvocationRefBase::CompilerInvocationRefBase(
-    const CompilerInvocationRefBase &X)
-    : LangOpts(new LangOptions(X.getLangOpts())),
-      TargetOpts(new TargetOptions(X.getTargetOpts())),
-      DiagnosticOpts(new DiagnosticOptions(X.getDiagnosticOpts())),
-      HeaderSearchOpts(new HeaderSearchOptions(X.getHeaderSearchOpts())),
-      PreprocessorOpts(new PreprocessorOptions(X.getPreprocessorOpts())),
-      AnalyzerOpts(new AnalyzerOptions(X.getAnalyzerOpts())) {}
-
-CompilerInvocationRefBase::CompilerInvocationRefBase(
-    CompilerInvocationRefBase &&X) = default;
-
-CompilerInvocationRefBase &
-CompilerInvocationRefBase::operator=(CompilerInvocationRefBase X) {
-  LangOpts.swap(X.LangOpts);
-  TargetOpts.swap(X.TargetOpts);
-  DiagnosticOpts.swap(X.DiagnosticOpts);
-  HeaderSearchOpts.swap(X.HeaderSearchOpts);
-  PreprocessorOpts.swap(X.PreprocessorOpts);
-  AnalyzerOpts.swap(X.AnalyzerOpts);
+namespace clang::CompilerInvocationDetail {
+namespace {
+template <class T> std::shared_ptr<T> make_shared(const T &X) {
----------------
jansvoboda11 wrote:

Because `std::make_shared(const T&)` doesn't deduce the return type as `std::shared_ptr<T>`, so you need to specify `T` explicitly. I find this super verbose, so this utility is here to support invoking the copy constructor of `T` without repeating the type.

https://github.com/llvm/llvm-project/pull/65412