[clang] Remove intrusive reference count from `DiagnosticOptions` (#139584)

The `DiagnosticOptions` class is currently intrusively
reference-counted, which makes reasoning about its lifetime very
difficult in some cases. For example, `CompilerInvocation` owns the
`DiagnosticOptions` instance (wrapped in `llvm::IntrusiveRefCntPtr`) and
only exposes an accessor returning `DiagnosticOptions &`. One would
think this gives `CompilerInvocation` exclusive ownership of the object,
but that's not the case:

```c++
void shareOwnership(CompilerInvocation &CI) {
  llvm::IntrusiveRefCntPtr<DiagnosticOptions> CoOwner = &CI.getDiagnosticOptions();
  // ...
}
```

This is a perfectly valid pattern that is being actually used in the
codebase.

I would like to ensure the ownership of `DiagnosticOptions` by
`CompilerInvocation` is guaranteed to be exclusive. This can be
leveraged for a copy-on-write optimization later on. This PR changes
usages of `DiagnosticOptions` across `clang`, `clang-tools-extra` and
`lldb` to not be intrusively reference-counted.

1 files changed, 4 insertions, 4 deletions

diff --git a/clang/lib/Tooling/CompilationDatabase.cpp b/clang/lib/Tooling/CompilationDatabase.cpp
index af18194..09596b9 100644
--- a/clang/lib/Tooling/CompilationDatabase.cpp
+++ b/clang/lib/Tooling/CompilationDatabase.cpp
@@ -243,13 +243,13 @@ std::string GetClangToolCommand() {
 static bool stripPositionalArgs(std::vector<const char *> Args,
                                 std::vector<std::string> &Result,
                                 std::string &ErrorMsg) {
-  IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts = new DiagnosticOptions();
+  DiagnosticOptions DiagOpts;
   llvm::raw_string_ostream Output(ErrorMsg);
-  TextDiagnosticPrinter DiagnosticPrinter(Output, &*DiagOpts);
+  TextDiagnosticPrinter DiagnosticPrinter(Output, DiagOpts);
   UnusedInputDiagConsumer DiagClient(DiagnosticPrinter);
   DiagnosticsEngine Diagnostics(
-      IntrusiveRefCntPtr<DiagnosticIDs>(new DiagnosticIDs()),
-      &*DiagOpts, &DiagClient, false);
+      IntrusiveRefCntPtr<DiagnosticIDs>(new DiagnosticIDs()), DiagOpts,
+      &DiagClient, false);
 
   // The clang executable path isn't required since the jobs the driver builds
   // will not be executed.