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cstage+selfhost+test: refuse let/param shadow of imported module (#19)

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When `use fmt;` is in scope and a local/param named `fmt` shadows it,
`fmt.X` in the body silently resolved to the str-typed value sym and
emitted `CALL AX` through str.ptr → runtime crash. Surfaced during
#15 (lib/log's printfln family); worked around by renaming the param
`fmt`→`format`.

Per rob + user, option (C): "value names and module names are
disjoint." Refuse the shadow at the decl site. Single rule, no
non-local reasoning, no silent footgun if a future lib/X exports a
new leaf.

cstage: src_imports walks file->list for N_USE entries (skipping
self-imports where u->module == u->str — same-module fixtures like
lib/fmt/fmttest.ww carry these); check_module_shadow runs before
each SK_PARAM / SK_VAR scope_define (param, clet, mlet, forrange
single + tuple, mcase). Wwstage mirror in check.ww; wwdump-only
diagnostic today, full enforcement waits on #11 checkfile pass.

Bootstrap byte-id holds — no codegen change. One source patch in
selfhost/cmd/w6a/main.ww renames an outer `let asm: asm_;` to `s` to
sidestep task #27 (cstage localoff scope-blind dedup); unrelated to
#19 but the new rule's first run flagged it as a self-shadow.

Test 708 (param_shadow_mod): 4 rows — neg_param (param shadow errs
at fn decl line), neg_let (let shadow errs at let decl), pos_rename
(rename compiles + runs), pos_selfimp (in-module use is skipped).
4 wired sites without dedicated rows deferred to task #28.

Follow-up: lib/log can revert format→fmt now that the silent
crash is impossible.
This commit is contained in:
Hojun-Cho
2026-05-16 08:39:35 +09:00
parent 1aece29d53
commit c9bbfcb6a6
15 changed files with 584 additions and 14 deletions
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10
selfhost/cmd/w6a/main.combined.ww
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@@ -2965,13 +2965,13 @@ export fn main(argc: i32, argv: **u8) i32 = {
};
let ar: *arena = newarena();
let asm: asm_;
let s: asm_;
let nlen: u64 = cstrlen(src);
let fname: str = astrndup(ar, src, nlen);
init(&asm, ar, fname, buf, blen);
init(&s, ar, fname, buf, blen);
if (parse(&asm) != 0) { return 1; };
if (encode(&asm) != 0) { return 1; };
if (parse(&s) != 0) { return 1; };
if (encode(&s) != 0) { return 1; };
// Open output for write.
let fd: i32 = os.open(out, os.flag.WRONLY | os.flag.CREATE | os.flag.TRUNC, 420i32); // 0o644
@@ -2979,7 +2979,7 @@ export fn main(argc: i32, argv: **u8) i32 = {
os.write(2, "w6a: cannot open output\n".ptr, 23u64);
return 1;
};
let rc: i32 = emitelf(&asm, fd);
let rc: i32 = emitelf(&s, fd);
os.close(fd);
return rc;
};