sx/issues/0089-backtick-raw-identifier.md

0089 — backtick raw-identifier escape + #import c foreign-name exemption from the reserved-type-name rule

✅ RESOLVED (foundation step F0.6). Two mechanisms, per Agra's design ruling:

1. Backtick raw identifier. The lexer recognises a leading backtick (`s2) and emits an .identifier token whose span excludes the backtick, carrying a new Token.is_raw flag ([src/lexer.zig], [src/token.zig]). A raw identifier is NEVER type-classified — the parser skips Type.fromName for it in expression position ([src/parser.zig] parsePrimary), so it is always a value identifier. The flag threads to VarDecl.is_raw / Param.is_raw ([src/ast.zig]) at the binding sites, and UnknownTypeChecker skips the reserved-name check for raw bindings ([src/ir/semantic_diagnostics.zig]). Because the token tag stays .identifier, the escape works in every position (local, global, param, field, function name, struct member, later reference) with no per-site parser change.
2. #import c foreign-name exemption. c_import.zig synthesizes foreign #foreign decls with Param.is_raw = true, so generated C param names that collide with reserved type names (s1, s2) import unedited.

A bare reserved-name binding in sx still errors (issue 0076 preserved): the is_raw-gated skip only fires for backtick / foreign names. Regression tests: examples/0151-types-backtick-raw-identifier.sx (backtick, every position), examples/1220-ffi-c-import-reserved-name-params.{sx,h,c} (foreign exemption), examples/1119-diagnostics-reserved-type-name-as-identifier.sx (negative — bare binding still rejected). Backtick lexer unit tests in src/lexer.zig.

The original report is preserved below.

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Symptom

Importing non-sx source whose names collide with sx reserved type names is rejected. library/modules/stb_truetype.sx is a #import c { ... } block over a vendored C header (vendors/stb_truetype/stb_truetype.h); C identifiers s1, s2 (which collide with sx's signed-int type keywords s1..sN) produce:

error: 's1' is a reserved type name and cannot be used as an identifier
error: 's2' is a reserved type name and cannot be used as an identifier

The user cannot hand-edit these — they are generated from the vendored C header. Separately, sx-authored code has NO way to deliberately use a reserved-name-spelled identifier even when it wants to.

Root cause

The parser classifies any reserved-type-name spelling (s2, u8, f64, …) as a .type_expr via name_class.Type.fromName, never as an .identifier. The F0.1 / issue-0076 fix added UnknownTypeChecker.checkBindingName (src/ir/semantic_diagnostics.zig) to reject a value binding / param spelled as a reserved type name (the .type_expr-vs-.identifier mismatch otherwise breaks address-of / autoref lowering). F0.1 deliberately extended this check to imported declarations — which is what now fires on the C-imported s1/s2.

Desired behaviour (Agra ruling)

External / imported source does NOT need to conform to sx naming standards. Two mechanisms:

1. Auto-exempt imports. #import c (and other foreign) declarations are treated as RAW identifiers: foreign names are never type-classified and never reserved-checked, so generated bindings "just work" with zero user edits.

2. Backtick raw-identifier for sx code. A leading backtick makes the following identifier raw — an identifier that is NEVER type-classified, so it bypasses the reserved-name rule:

   `s2 := 2.5;   // OK — identifier "s2", distinct from the s2 signed-int type
   s2 := 2.5;    // ERROR — bare s2 is still the reserved type name
   

   Prefix form (single leading backtick on the identifier). The raw identifier's TEXT is s2 (the backtick is not part of the name). A bare s2 used as a TYPE remains the signed-int type.

Reproduction

sx-side (minimal):

#import "modules/std.sx";
main :: () {
    `s2 := 2.5;            // must compile: identifier s2 = 2.5
    print("{}\n", `s2);    // 2.5
}

Import-side: a #import c block over a header declaring int s1, s2; (or stb_truetype.sx) must NOT emit the reserved-type-name error.