b9cfe2554f
Rewrote 20 issue writeups to the extern/runtime-class vocabulary (#foreign→extern, foreign_class_map→runtime_class_map, parseForeignClassDecl→parseRuntimeClassDecl, findForeignMethodInChain→findRuntimeMethodInChain, dedupeForeignSymbol→ dedupeExternSymbol, is_foreign_c_api→is_extern_c_api, stale filename refs to the renamed examples, foreign-class→runtime-class, bare foreign→extern). Renamed issues/0043-…-foreign-class-…→…-runtime-class-…. PHASE 9 COMPLETE — 9.4 GATE PASSES: zero 'foreign' across src/library/examples/ issues/docs/editors/specs/readme/CLAUDE, excluding only the SQLite API constant SQLITE_CONSTRAINT_FOREIGNKEY + vendored sqlite3.c/.h (upstream third-party). Suite green (644 corpus / 443 unit, 0 failed).
105 lines
4.9 KiB
Markdown
105 lines
4.9 KiB
Markdown
# 0123 — wrong arg counts to fixed-arity fns reach LLVM emission
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> **RESOLVED** (2026-06-12). Root cause: no dispatch path in `lowerCall`
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> ever compared the supplied arg count against the callee's declared
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> params (`coerceCallArgs` iterates `@min(args.len, params.len)`, so a
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> mismatch sailed through to the LLVM verifier). Fix: a shared
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> `checkCallArity` (src/ir/lower/call.zig) computes min (params without
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> trailing defaults) / max (`params.len`, unbounded past a variadic)
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> from the AST decl and rejects with a source-located diagnostic at the
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> five plain dispatch sites — bare selected-author + lazy, namespace
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> alias-gate + qualified, struct-method, ufcs. Pack / comptime / generic
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> / `#compiler` / `#builtin` callees are exempt (own dispatch). The
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> method/ufcs sites also gained the `appendDefaultArgs` fill the
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> generic-instance leg already had — trailing defaults on dot-calls
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> previously emitted under-arity calls (same verifier failure). Flushed
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> out en route: `lowerStmt`'s `.fn_decl => |fd| ... (&fd)` registered a
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> STACK address in `fn_ast_map`, so every local fn's map entry aliased
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> the most recently lowered one — pointer capture (`|*fd|`) fixes it.
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> Regressions: `examples/1167-diagnostics-call-arity-mismatch.sx`
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> (too many / too few, bare + stdlib + method + ufcs) and
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> `examples/0054-basic-dot-call-default-args.sx` (dot-call defaults,
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> variadic, `#caller_location`). Gates: zig build test 426/426, suite
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> 590/590 (fix in isolation), distribution repo 14/14.
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## Symptom
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Calling a fixed-arity function with the wrong number of arguments is
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not rejected by the frontend — the mismatched argument list flows all
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the way to LLVM emission, which fails verification instead of a
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source-located diagnostic.
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- **Observed**: `LLVM verification failed: Incorrect number of
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arguments passed to called function!` plus the raw IR call line —
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no file/line/snippet, no callee name in user terms.
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- **Expected**: a compile error at the call site naming the callee
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and its declared arity (matching the style of existing
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diagnostics, e.g. the "unresolved ..." errors with source
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snippets).
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Both directions are broken, on every plain dispatch path probed:
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- too MANY args, bare call: `concat("a", "b", "c")` (std's `concat`
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takes 2 strings) → LLVM verifier failure.
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- too FEW args, bare call: `add2(1)` with `add2 :: (a: i64, b: i64)`
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→ same.
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- methods / ufcs dot-calls: same shape, receiver included. Worse:
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a trailing-default param on a plain struct method or a ufcs fn is
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never filled on the dot-call path (`p.scaled()` with
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`scaled :: (self: Point, k: i64 = 2)` emits a 1-arg call to a
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2-param fn — bare calls fill defaults via `expandCallDefaults`,
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the method/ufcs sites never run `appendDefaultArgs`).
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Legitimate flexible shapes must keep working: slice variadics
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(`..xs: []T` — no upper bound), comptime/protocol packs (`..$args` /
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`..xs: P` — own dispatch), default-valued params (incl.
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`loc: Source_Location = #caller_location`), generic `$T` fns
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(explicit vs inferred type args make the count flexible), `extern`
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C variadics, `#compiler` / `#builtin` bodies.
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## Reproduction
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```sx
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#import "modules/std.sx";
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main :: () -> i32 {
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s := concat("a", "b", "c"); // concat takes (a: string, b: string)
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out(s);
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return 0;
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}
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```
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Observed at master b3b78e2: compiles past resolution, dies at LLVM
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verification with the verifier message above.
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## Investigation prompt
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Call argument binding never compares the supplied arg count against
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the callee's declared parameter list. Suspected area: the plain
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direct-dispatch sites in `src/ir/lower/call.zig` (`lowerCall`) — the
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bare-identifier selected-author and lazy-lower legs, the
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namespace-qualified legs, the qualified struct-method leg, and the
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ufcs leg. All of them run `packVariadicCallArgs` /
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`coerceCallArgs` and emit `builder.call` without an arity check;
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`coerceCallArgs` iterates `@min(args.len, params.len)` so a mismatch
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sails through to the emitter.
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The fix likely needs a shared `checkCallArity(fd, name, supplied,
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has_receiver, span)` helper consulted at each plain dispatch site,
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computing min (params without trailing defaults) / max
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(`fd.params.len`, unbounded when a variadic param exists) from the
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AST decl and emitting via `self.diagnostics.addFmt(.err, span, ...)`
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on violation. Pack (`isPackFn`), comptime (`hasComptimeParams`),
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generic (`type_params.len > 0`), `#compiler`, and `#builtin` callees
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bind args through their own dispatch and must be exempt. The
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method/ufcs sites also need `appendDefaultArgs` (the generic
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instance-method leg already runs it) so trailing defaults fill
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before the count is meaningful.
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Verification: the repro errors with a source-located diagnostic
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naming `concat` and its 2-arg signature; too-few errors likewise;
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variadic / pack / default / ufcs / generic calls keep compiling
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(`print`, `format`, `List.append`, `#caller_location` defaults).
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`zig build && zig build test`, `bash tests/run_examples.sh` all
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green; pin the repro as a diagnostics example per CLAUDE.md.
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