Avoid IR cycle for compiler-builtin ObjC typedefs shadowing themselves#3387
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glandium wants to merge 1 commit into
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Avoid IR cycle for compiler-builtin ObjC typedefs shadowing themselves#3387glandium wants to merge 1 commit into
glandium wants to merge 1 commit into
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Objective-C's id/SEL/Class are compiler builtins, but SDK headers also redeclare them via a same-named typedef. Under clang 22, asking such a typedef for its underlying type reports back the same declaration instead of desugaring to the written-out type. Treating that as an ordinary Alias creates a cycle once resolve_typerefs resolves the deferred reference, and nothing that computes canonical types checks for cycles, so it recurses forever - a stack overflow, or an infinite loop if the recursion gets tail-call-optimized. Detect the same-USR case in CXType_Typedef handling and resolve directly as the inner kind instead of aliasing to it, so the cycle is never constructed. Adds a self-contained regression test (the typedef lives in an auxiliary header included via -isystem, so it doesn't need a real macOS SDK) that segfaults on main and passes with this fix. Fixes rust-lang#3386
emilio
reviewed
Jul 3, 2026
| // resolve directly as the inner kind instead of | ||
| // aliasing to it, exactly as we would if `ty` itself had | ||
| // reported that kind. | ||
| let same_underlying_decl = matches!( |
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Do we need to check the USR tho? Can we check cursor == inner.declaration() or so?
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Unfortunately, cursor == inner.declaration() is false for id/Class even in the exact case we want to catch, and cursor.canonical() == inner.declaration().canonical() is also false. Only the USR matches. Looks like the "builtin definitions" cursor libclang hands back for the inner type isn't the same node as the source-level typedef decl, just the same USR.
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Objective-C's id/SEL/Class are compiler builtins, but SDK headers also redeclare them via a same-named typedef.
Under clang 22, asking such a typedef for its underlying type reports back the same declaration instead of desugaring to the written-out type. Treating that as an ordinary Alias creates a cycle once resolve_typerefs resolves the deferred reference, and nothing that computes canonical types checks for cycles, so it recurses forever - a stack overflow, or an infinite loop if the recursion gets tail-call-optimized.
Detect the same-USR case in CXType_Typedef handling and resolve directly as the inner kind instead of aliasing to it, so the cycle is never constructed.
Adds a self-contained regression test (the typedef lives in an auxiliary header included via -isystem, so it doesn't need a real macOS SDK) that segfaults on main and passes with this fix.
Fixes #3386