lab/sx

Files

agra ba37d0b393 issues: file 0128 — [:0]u8 FFI returns silently u8; ?[:0]u8 unresolved panic

[:0]u8 aliases string (fat) and params already ABI-thin to char*, but
a foreign -> [:0]u8 return silently resolves to plain u8, and ?[:0]u8
never resolves at all (LLVM emission panic) even though ?string works.
Design contract recorded: ?[:0]u8 lowers to a nullable char* at the
boundary, length synthesized on the sx side; until then such returns
must be diagnosed, not mis-typed.

2026-06-12 13:21:19 +03:00

3.3 KiB

Raw Blame History

0128: `[:0]u8` at FFI boundaries — silent `u8` returns, unresolvable optional

Design contract (Agra, 2026-06-12)

?[:0]u8 should lower to a char * at the FFI boundary — a single nullable thin pointer — NOT a fat pointer. This is the natural sx type for every libc/sqlite-style API that returns a nullable C string (getenv, sqlite3_errmsg, sqlite3_column_text, ...).

Current state (verified at master `1bc60d3`)

[:0]u8 is an ALIAS for string (src/types.zig:145 — the '[' arm returns .string_type), i.e. a fat ptr+len value at the sx level. At a #foreign PARAM position the C-ABI lowering already thins it: sx string/slices coerce to a single pointer and the length is dropped (src/backend/llvm/abi.zig, the is_foreign_c_api knob) — so popen :: (cmd: [:0]u8, ...) works and matches the design contract.

The other two boundary positions are broken:

Defect A — `-> [:0]u8` foreign RETURN silently resolves to `u8`

#import "modules/std.sx";

libc :: #library "c";
getenv_s :: (name: [:0]u8) -> [:0]u8 #foreign libc "getenv";

main :: () -> i32 {
    v := getenv_s("PATH");
    print("len={}\n", v.len);   // error: field 'len' not found on type 'u8'
    return 0;
}

The declared return type [:0]u8 resolves to plain u8 — not the string alias, not an error. Whatever the return-position type-name path is, it disagrees with the table in types.zig and fails SILENTLY into a wrong type (the silent-fallback-default class this repo's CLAUDE.md forbids).

Defect B — `?[:0]u8` does not resolve; panics LLVM emission

#import "modules/std.sx";

libc :: #library "c";
getenv_opt :: (name: [:0]u8) -> ?[:0]u8 #foreign libc "getenv";

main :: () -> i32 {
    p := getenv_opt("PATH");
    if p == null { return 1; }
    return 0;
}

Panics: "unresolved type reached LLVM emission" (src/backend/llvm/types.zig:175). Meanwhile plain ?string resolves and works at the sx level — the '?' arm (types.zig:141) stores child_name = "[:0]u8", and whatever resolves the child later doesn't go through the same table that maps the bracket spelling to string_type. Minimum bar even without the feature: a diagnostic, not a panic.

Fix shape

Make the bracket spelling resolve identically everywhere — return position and optional child position must hit the same alias table that param position does (Defect A and the resolution half of B).
Implement the boundary contract for returns: a foreign -> [:0]u8 / -> ?[:0]u8 receives ONE pointer from C; the sx-side string is built by synthesizing the length (strlen) at the boundary, and for the optional a NULL pointer maps to null. If (2) is deferred, foreign string/optional-string RETURNS must be rejected with a diagnostic naming the workaround (?*u8).

Workaround in use

/Users/agra/projects/distribution/src/db/sqlite.sx declares every nullable C-string return as ?*u8 (null-pointer niche verified working in both JIT and AOT) and copies via a manual strlen helper; its header comment cites this issue's gap. std's own getenv :: -> *u8 + cast-check is the same dodge. Both can migrate to ?[:0]u8 once the contract lands.

Verification

Both reproducers behave: A prints a real PATH length; B answers null / non-null correctly for missing / present variables. zig build test, tests/run_examples.sh green; pin both as examples.

3.3 KiB Raw Blame History

0128: [:0]u8 at FFI boundaries — silent u8 returns, unresolvable optional