[clang] [clang][DependencyScanning] Implementation of `CompilerInstanceWithContext` to Improve By-Name Queries (PR #164345)

[Qiongsi Wu via cfe-commits]

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@@ -339,6 +341,10 @@ class ModuleDepCollector final : public DependencyCollector {
   std::optional<P1689ModuleInfo> ProvidedStdCXXModule;
   std::vector<P1689ModuleInfo> RequiredStdCXXModules;
 
+  /// A pointer to the preprocessor callback so we can invoke it directly
+  /// if needed.
+  ModuleDepCollectorPP *CollectorPPPtr = nullptr;
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qiongsiwu wrote:

The `Preprocessor` owns the `PPCallbacks`' instance. `ModuleDepCollector::attachToPreprocessor` creates the `PPCallbacks` and moves it into the preprocessor.  See https://github.com/llvm/llvm-project/pull/164345/files#diff-6c14c5831345bba33e5cf69af62b76e8fea9d2d70474f6d9ccb024f99212c506R970

It is also the preprocessor who destroy the callbacks through `removePPCallbacks`. See https://github.com/llvm/llvm-project/pull/164345/files#diff-d80edc2f8b14e8ad634b54bc14c780e34a3d7c716b8b9811d1f831135b470f5eR1330

https://github.com/llvm/llvm-project/pull/164345