[clang-tools-extra] [clangd] Track IWYU pragmas for non-preamble includes (PR #75612)

[Sam McCall via cfe-commits]

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@@ -113,7 +113,7 @@ class PragmaIncludes {
   llvm::DenseSet<llvm::sys::fs::UniqueID> ShouldKeep;
 
   /// Owns the strings.
-  llvm::BumpPtrAllocator Arena;
+  std::shared_ptr<llvm::BumpPtrAllocator> Arena;
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sam-mccall wrote:

This doesn't look threadsafe. Two PIs associated with parallel ParsedAST builds will write into the same arena.

You could do some trick with shared_ptr<void> to keep all needed arenas alive, and a raw pointer to the current, I guess?

https://github.com/llvm/llvm-project/pull/75612