c41f51aed3
The issue-0176 conformance gate was name-only, so an impl P for T with a mismatched return/param type (or arity) built a wrong-ABI thunk that silently miscompiled (exit 0, wrong value). firstUnimplementedMethod now validates arity (after self), each param type, and the return type against the protocol declaration, substituting protocol Self->concrete via resolveProtoTypeSubSelf (recurses through pointer/many-pointer/ optional/slice/array so []Self<->[]T match; conservative .unresolved for Self-in-generic-arg). Comparison is by structural formatTypeName (alias/module/spelling independent); typesClearlyDiffer skips when either side has an unresolved leaf at any depth, biasing against false-positives. Regressions: diagnostics/1201 (negative), protocols/0420 (positive, []Self param). Verified by 3+3 adversarial reviews (a mid-fix []Self false-positive was found and closed); suite 792/0.
65 lines
3.4 KiB
Markdown
65 lines
3.4 KiB
Markdown
# 0178 — protocol impl method with a mismatched return/param TYPE silently miscompiles
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> **RESOLVED.** The issue-0176 conformance gate was name-only, so an `impl P for
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> T` with a mismatched return/param type (or arity) built a wrong-ABI thunk that
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> silently miscompiled (exit 0, wrong value). Fix (`src/ir/lower/protocol.zig`):
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> `firstUnimplementedMethod` now validates each impl method's signature against
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> the protocol declaration — arity (after `self`), every param type, and the
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> return type — substituting protocol `Self`→concrete via `resolveProtoTypeSubSelf`
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> (recurses through pointer/many-pointer/optional/slice/array so `[]Self`↔`[]T`
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> etc. match; conservative `.unresolved` for `Self`-in-generic-arg). Comparison
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> is by structural `formatTypeName` (alias/module/spelling independent), and
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> `typesClearlyDiffer` skips when either side has an unresolved leaf at any depth
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> — biased against false-positives. Mismatch → located diagnostic. Verified by
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> 3+3 adversarial reviews (a mid-fix `[]Self` false-positive was found and
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> closed); suite 792/0. Regressions:
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> `examples/diagnostics/1201-diagnostics-protocol-impl-signature-mismatch.sx`
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> (negative), `examples/protocols/0420-protocol-self-in-slice-param.sx`
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> (positive). Known gaps (pre-existing, loud not silent — out of scope): a
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> `Self`-through-generic-arg mismatch (`Box(Self)`) and by-value array protocol
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> params (`[2]Self`) fail at LLVM verification, not silently.
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## Symptom
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An `impl P for T` whose method has the right NAME but a mismatched return type or
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parameter type is accepted (it satisfies the issue-0176 conformance gate, which
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is name-based), and dispatch through the erased protocol silently produces the
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WRONG result (exit 0). No diagnostic. (Arity mismatch and `#builtin`-body
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mismatch fail loudly — exit 1 — and are not this bug; the TYPE-mismatch cases are
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silent.)
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## Reproduction
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```sx
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#import "modules/std.sx";
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P :: protocol { val :: (self: *Self) -> i64; }
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T :: struct { n: i64 = 7; }
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impl P for T { val :: (self: *T) -> bool { return true; } } // return type bool ≠ i64
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main :: () {
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t := T.{ n = 7 };
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p : P = t;
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print("{}\n", p.val()); // prints "1" (the bool), silently wrong — no diagnostic
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}
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```
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A parameter-type mismatch (`x: bool` where the protocol declares `x: i64`)
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similarly dispatches silently wrong.
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## Investigation prompt
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The issue-0176 conformance gate (`firstUnimplementedMethod` in
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`src/ir/lower/protocol.zig`) checks method PRESENCE (and rejects `type_params >
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0`), but does NOT check that the impl method's SIGNATURE (parameter types,
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arity, return type) matches the protocol method's declared signature. A
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mismatched-type impl builds a thunk that calls the impl with the wrong ABI,
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silently miscompiling. Add signature validation when registering / gating an
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impl method against its protocol method: compare the impl method's params
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(after the erased `self`) and return type against the protocol declaration, and
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emit a located diagnostic on mismatch (arity, param type, or return type). The
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protocol method declaration is in `protocol_decl_map`; the impl FnDecl is in
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`fn_ast_map`. Decide whether this lives in the conformance gate or in
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`ProtocolResolver.registerImplBlock` (`src/ir/protocols.zig`). Follow the
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no-silent-fallback rule. Verify: the repro is now a clean diagnostic (exit 1);
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a correctly-typed impl still works; add an `examples/diagnostics/11xx-...`
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negative regression. (Found during adversarial review of issue 0176.)
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