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fix: diagnose unknown generic #builtin instead of silently returning 0 (issue 0144)

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A bodiless #builtin with a $T: Type param routes through monomorphization.
When resolveBuiltin returned null for an unrecognized name, the builtin-body
branch fell through to ensureTerminator's constInt(0) -- a silent-fallback
default the CLAUDE.md REJECTED PATTERNS forbid. Emit a loud
'error: unknown #builtin <name>' diagnostic instead.

Regression: examples/1189-diagnostics-unknown-builtin.sx
This commit is contained in:
agra
2026-06-21 09:10:38 +03:00
parent 6ed29621ad
commit ad45ae07ef
6 changed files with 41 additions and 0 deletions
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16
examples/1189-diagnostics-unknown-builtin.sx Normal file
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@@ -0,0 +1,16 @@
// A bodiless `#builtin` carrying a `$T: Type` parameter, whose name the
// compiler does not recognize, must fail LOUDLY with an "unknown #builtin"
// diagnostic — not silently evaluate to 0 (the CLAUDE.md silent-fallback
// pattern). The generic monomorphization path (monomorphizeFunction's
// builtin-body branch) now diagnoses an unresolved builtin name instead of
// falling through to `ensureTerminator`'s `constInt(0)`.
//
// Regression (issue 0144).
#import "modules/std.sx";
// `mystery` is not a recognized builtin.
mystery :: ($T: Type, x: T) -> T #builtin;
main :: () {
print("mystery(42) = {}\n", mystery(i64, 42));
}

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examples/expected/1189-diagnostics-unknown-builtin.exit Normal file
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@@ -0,0 +1 @@
1

5
examples/expected/1189-diagnostics-unknown-builtin.stderr Normal file
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@@ -0,0 +1,5 @@
error: unknown #builtin 'mystery'
--> examples/1189-diagnostics-unknown-builtin.sx:12:1
|
12 | mystery :: ($T: Type, x: T) -> T #builtin;
| ^^^^^^^

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examples/expected/1189-diagnostics-unknown-builtin.stdout Normal file
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8
issues/0144-unrecognized-type-param-builtin-silent-zero.md
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@@ -1,5 +1,13 @@
# 0144 — unrecognized `$T`-param `#builtin` silently returns 0
> **RESOLVED.** The generic monomorphization path (`monomorphizeFunction`'s
> `builtin_expr` body branch in `src/ir/lower/generic.zig`) no longer falls
> through to `ensureTerminator`'s silent `constInt(0)` when `resolveBuiltin`
> returns null for an unknown name. It now emits a loud
> `error: unknown #builtin '<name>'` diagnostic — removing exactly the
> silent-fallback-default the CLAUDE.md REJECTED PATTERNS forbid. Regression
> test: `examples/1189-diagnostics-unknown-builtin.sx`.
## Symptom
A **bodiless `#builtin`** whose signature takes a `$T: Type` parameter, when the

10
src/ir/lower/generic.zig
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@@ -152,6 +152,16 @@ pub fn monomorphizeFunction(self: *Lowering, fd: *const ast.FnDecl, mangled_name
const result = self.builder.callBuiltin(bid, &.{param0}, ret_ty);
self.builder.ret(result, ret_ty);
} else {
// Unknown bodiless #builtin: the name is not claimed by any
// recognizer (atomics/reflection are handled earlier in call.zig).
// Emitting `ensureTerminator(ret_ty)` here would synthesize a
// silent `constInt(0, ret_ty)` for a non-void return — a silent
// fallback default (issue 0144). Surface the failure loudly.
const span = if (fd.name_span.end != 0) fd.name_span else fd.body.span;
if (self.diagnostics) |d|
d.addFmt(.err, span, "unknown #builtin '{s}'", .{fd.name});
// Lowering has already failed; close the block with a terminator
// so the IR stays well-formed for the rest of the pass.
self.ensureTerminator(ret_ty);
}
self.builder.finalize();