[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, 6 deletions

diff --git a/clang/unittests/AST/CommentParser.cpp b/clang/unittests/AST/CommentParser.cpp
index aa08b67..67fabe5 100644
--- a/clang/unittests/AST/CommentParser.cpp
+++ b/clang/unittests/AST/CommentParser.cpp
@@ -33,16 +33,14 @@ const bool MY_DEBUG = true;
 class CommentParserTest : public ::testing::Test {
 protected:
   CommentParserTest()
-    : FileMgr(FileMgrOpts),
-      DiagID(new DiagnosticIDs()),
-      Diags(DiagID, new DiagnosticOptions, new IgnoringDiagConsumer()),
-      SourceMgr(Diags, FileMgr),
-      Traits(Allocator, CommentOptions()) {
-  }
+      : FileMgr(FileMgrOpts), DiagID(new DiagnosticIDs()),
+        Diags(DiagID, DiagOpts, new IgnoringDiagConsumer()),
+        SourceMgr(Diags, FileMgr), Traits(Allocator, CommentOptions()) {}
 
   FileSystemOptions FileMgrOpts;
   FileManager FileMgr;
   IntrusiveRefCntPtr<DiagnosticIDs> DiagID;
+  DiagnosticOptions DiagOpts;
   DiagnosticsEngine Diags;
   SourceManager SourceMgr;
   llvm::BumpPtrAllocator Allocator;