[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, 6 insertions, 5 deletions

diff --git a/clang/unittests/Frontend/CompilerInstanceTest.cpp b/clang/unittests/Frontend/CompilerInstanceTest.cpp
index 6e9a6f5..a7b258d 100644
--- a/clang/unittests/Frontend/CompilerInstanceTest.cpp
+++ b/clang/unittests/Frontend/CompilerInstanceTest.cpp
@@ -53,9 +53,10 @@ TEST(CompilerInstance, DefaultVFSOverlayFromInvocation) {
   const std::string VFSArg = "-ivfsoverlay" + FileNameStr;
   const char *Args[] = {"clang", VFSArg.c_str(), "-xc++", "-"};
 
+  DiagnosticOptions DiagOpts;
   IntrusiveRefCntPtr<DiagnosticsEngine> Diags =
       CompilerInstance::createDiagnostics(*llvm::vfs::getRealFileSystem(),
-                                          new DiagnosticOptions());
+                                          DiagOpts);
 
   CreateInvocationOptions CIOpts;
   CIOpts.Diags = Diags;
@@ -76,17 +77,17 @@ TEST(CompilerInstance, DefaultVFSOverlayFromInvocation) {
 }
 
 TEST(CompilerInstance, AllowDiagnosticLogWithUnownedDiagnosticConsumer) {
-  auto DiagOpts = new DiagnosticOptions();
+  DiagnosticOptions DiagOpts;
   // Tell the diagnostics engine to emit the diagnostic log to STDERR. This
   // ensures that a chained diagnostic consumer is created so that the test can
   // exercise the unowned diagnostic consumer in a chained consumer.
-  DiagOpts->DiagnosticLogFile = "-";
+  DiagOpts.DiagnosticLogFile = "-";
 
   // Create the diagnostic engine with unowned consumer.
   std::string DiagnosticOutput;
   llvm::raw_string_ostream DiagnosticsOS(DiagnosticOutput);
-  auto DiagPrinter = std::make_unique<TextDiagnosticPrinter>(
-      DiagnosticsOS, new DiagnosticOptions());
+  auto DiagPrinter =
+      std::make_unique<TextDiagnosticPrinter>(DiagnosticsOS, DiagOpts);
   CompilerInstance Instance;
   IntrusiveRefCntPtr<DiagnosticsEngine> Diags =
       Instance.createDiagnostics(*llvm::vfs::getRealFileSystem(), DiagOpts,