[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, 2 deletions

diff --git a/clang/unittests/Serialization/ModuleCacheTest.cpp b/clang/unittests/Serialization/ModuleCacheTest.cpp
index 38003e9..de6e13a 100644
--- a/clang/unittests/Serialization/ModuleCacheTest.cpp
+++ b/clang/unittests/Serialization/ModuleCacheTest.cpp
@@ -108,8 +108,9 @@ TEST_F(ModuleCacheTest, CachedModuleNewPath) {
   MCPArg.append(ModuleCachePath);
   CreateInvocationOptions CIOpts;
   CIOpts.VFS = llvm::vfs::createPhysicalFileSystem();
+  DiagnosticOptions DiagOpts;
   IntrusiveRefCntPtr<DiagnosticsEngine> Diags =
-      CompilerInstance::createDiagnostics(*CIOpts.VFS, new DiagnosticOptions());
+      CompilerInstance::createDiagnostics(*CIOpts.VFS, DiagOpts);
   CIOpts.Diags = Diags;
 
   // First run should pass with no errors
@@ -157,8 +158,9 @@ TEST_F(ModuleCacheTest, CachedModuleNewPathAllowErrors) {
   MCPArg.append(ModuleCachePath);
   CreateInvocationOptions CIOpts;
   CIOpts.VFS = llvm::vfs::createPhysicalFileSystem();
+  DiagnosticOptions DiagOpts;
   IntrusiveRefCntPtr<DiagnosticsEngine> Diags =
-      CompilerInstance::createDiagnostics(*CIOpts.VFS, new DiagnosticOptions());
+      CompilerInstance::createDiagnostics(*CIOpts.VFS, DiagOpts);
   CIOpts.Diags = Diags;
 
   // First run should pass with no errors