fix(ffi): resolve protocol-only method metadata for block parameters - #71
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DjDeveloperr merged 1 commit intoAug 26, 2026
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This was referenced Aug 20, 2026
findClassForRuntimeClass only ever consulted the concrete class hierarchy (class_getSuperclass), so a selector declared solely on a conformed Objective-C protocol had no path to its metadata whenever the class that actually implements it doesn't carry that conformance in a header the metadata generator parsed -- a category/class-extension conformance, or (as with UIViewControllerTransitionCoordinator) a fully private concrete class. createEngineCallback then threw "Native callback metadata is unavailable." for any block parameter on such a method, forcing callers to hand-supply the ObjC encoding via interop.Block(fn, "..."). Adds a runtime protocol-conformance fallback (class_copyProtocolList + protocol_copyProtocolList, walked alongside the existing class walk), consulted only once the ordinary class/protocol-declared-on-header lookup misses, and cached per runtime Class so well-declared classes pay nothing extra. Deterministic tie-break for a class conforming to several protocols declaring the same selector: most-derived class first, then ancestors; within one class's own adopted-protocol list, class_copyProtocolList's order; each protocol's inherited protocols expanded depth-first ahead of its next sibling. First match wins. Covered by two new fixtures/tests mirroring the real-world shape (hidden vs. declared protocol conformance) plus the existing 717-test macOS suite (unchanged 8 pre-existing DBL_MAX failures, no new ones). Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01BQPGUU8YECUhbBvwkW4Kek
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What was broken
If a method your app calls is declared only on an Objective-C protocol
(not on any real class in the object's chain), and takes a block
parameter, calling it from JS with a plain closure threw:
Error: Native callback metadata is unavailable.
This happens whenever the class that actually implements the method
doesn't declare that conformance in a header the metadata generator
parsed -- e.g. conformance added via a category/class-extension, or a
fully private concrete class (UIViewControllerTransitionCoordinator
is the classic real-world case: every method lives on the protocol,
the concrete class is private). The only workaround was hand-supplying
the ObjC encoding: interop.Block(fn, "v@?@").
Root cause: findClassForRuntimeClass (ObjCBridge.mm) only walked the
concrete class hierarchy via class_getSuperclass, never consulting
protocol conformance, so method lookup for such selectors came up
empty and the block parameter's metadata was never resolved.
The fix
Adds a protocol-conformance fallback (class_copyProtocolList +
protocol_copyProtocolList, walked alongside the existing class walk),
consulted only once the ordinary class-hierarchy lookup misses, cached
per runtime Class so classes with complete metadata pay nothing
extra.
Duplicate-selector rule: most-derived class first, then ancestors;
within one class's own adopted-protocol list, class_copyProtocolList's
order (stable, reflects declaration order); each protocol's inherited
protocols expand depth-first before its next sibling. First match wins.
Verification
Two new fixtures (hidden vs. declared protocol conformance, same
selectors) prove the fix and that the already-working class path is
unaffected. Confirmed genuine repro: same tests fail with exactly this
error on the pre-fix code. Full macOS suite: 717 tests, 8 pre-existing
DBL_MAX-formatting failures (unchanged), 0 new failures.
Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com
https://claude.ai/code/session_01BQPGUU8YECUhbBvwkW4Kek