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

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

✅ RESOLVED (foundation step F0.6). Two mechanisms, per Agra's design ruling; the final shape is the universal raw identifier (attempt 4): `name is THE LITERAL identifier name, usable in EVERY position — value, declaration, AND type — meaning only "treat this token as a plain identifier, never the reserved keyword/type." The backtick is never part of the name's text.

1. Backtick raw identifier. The lexer recognises a leading backtick (`i2) and emits an .identifier token whose span excludes the backtick, carrying a Token.is_raw flag ([src/lexer.zig], [src/token.zig]). The flag threads through ast.Identifier, ast.TypeExpr, and EVERY binding / capture / declaration node ([src/ast.zig]): VarDecl / ConstDecl / Param / FnDecl plus IfExpr / WhileExpr optional bindings, ForExpr capture + index, MatchArm capture, CatchExpr / OnFailStmt tag bindings, DestructureDecl per-name, protocol-default / runtime-class method params, AND every type-introducing decl — StructDecl / EnumDecl / UnionDecl / ErrorSetDecl / ProtocolDecl / RuntimeClassDecl / UfcsAlias / NamespaceDecl / ImportDecl / CImportDecl / LibraryDecl.

   • Value position. The parser skips Type.fromName for a raw identifier in expression position ([src/parser.zig] parsePrimary), so `i2 is a value identifier; a later bare reference resolves to the binding.
   • Type position. parseTypeExpr sets the raw flag on the type ATOM and lets it flow through the SAME continuations as a bare name (attempt 5), so a raw reference parameterizes a reserved-spelled template (`i2(i64)) and composes under the pointer / optional / slice wrappers; ParameterizedTypeExpr carries is_raw and resolveParameterizedWithBindings skips the Vector intrinsic when raw. Resolution skips the builtin classifier (TypeResolver.resolveNamed's skip_builtin, threaded from te.is_raw in [src/ir/lower.zig] and [src/ir/type_bridge.zig]) and looks up a `i2-declared type (struct / enum / union / alias), else a NORMAL "unknown type 'i2'" error (UnknownTypeChecker.reportIfUnknownType skips the builtin-name exemption when raw). A bare i2 in type position is still the builtin int. The SECOND (editor/LSP) classifier in [src/sema.zig] (Type.fromTypeExpr / resolveTypeNode / resolveTypeNameStr) honors is_raw too, so a backtick reserved-name annotation resolves to the user type in hover/completion, not the builtin (no two-resolver divergence). The raw bit is carried STRUCTURALLY through every COMPOUND shape's inner-name metadata — PointerTypeInfo / OptionalTypeInfo / SliceTypeInfo / ManyPointerTypeInfo / ArrayTypeInfo each store a REQUIRED is_raw ([src/types.zig], no default, so a future construction site cannot drop it) that every resolveTypeNameStr call passes as its skip_builtin — so *`i2, ?`i2, [N]`i2, []`i2, [*]`i2 field-access / unwrap / index / deref in the editor index all reach the user type instead of reclassifying the inner i2 to the builtin (the divergence the DIRECT-only attempt left for compound forms).
   • Declaration position. A bare reserved-name declaration of EVERY kind still errors (issue 0076 preserved); the backtick form is exempt. The check and the exemption are made structurally symmetric: checkBindingName / checkDeclName ([src/ir/semantic_diagnostics.zig]) take is_raw as a REQUIRED argument and skip inside the check — no call site can validate a name without also honoring the exemption, which is what kept the two from desyncing across the earlier attempts. On the PARSER side the symmetry is enforced structurally for the bug-prone node: ConstDecl's name_span + is_raw carry NO default (attempt 5), so the compiler rejects any construction site — including the two struct-body const forms (untyped `i2 :: 5 and typed `i2 : T : v) that previously dropped both — that omits them. FnDecl is built at every parser site through parseFnDecl, whose name_is_raw is a REQUIRED parameter (the equivalent guarantee); the type decls likewise route through parse-functions taking name_is_raw.
   • Member-name positions are exempt (Agra ruling, attempt 7). A struct field name, a union tag name, and a protocol method-signature name accept a bare reserved spelling: these sit in a member slot and are reached via obj.name / dispatched by string, so they are never type-classified and never mis-lower — the binding-name walk's struct_decl / union_decl / enum_decl / protocol_decl arms ([src/ir/semantic_diagnostics.zig]) check only the type name (and method params), not field / tag / variant / method-signature names. The backtick is optional there (obj.i2 and obj.`i2 resolve to the same member). This bare member-name exemption covers only the identifier-classified reserved spellings — i1..i64, u1..u64, bool, string, void, usize, isize, Any — which all lex as ordinary identifiers. The two keyword-classified spellings, f32 and f64, are lexer keywords ([src/token.zig]), and a member-name slot requires an identifier token ([src/parser.zig]); a bare f32 / f64 is therefore rejected at parse (expected field name in struct) even in a member position, and still needs the backtick there too — struct { `f32: i64; } / union { `f64: … } / protocol { `f32 :: () -> i64; } work as field / tag / method names. The exemption stops at member definitions: an impl method is a real function reached through the impl_block → fn_decl arm, so a reserved-spelled impl method needs the backtick (`i2 :: (self)), no more exempt than a free function (cf. examples/1122). Pinned by examples/0158-types-reserved-name-member-exempt.sx.

2. #import c extern-name exemption. c_import.zig synthesizes extern extern decls with Param.is_raw = true (and the synthesized FnDecl is_raw = true), so generated C names that collide with reserved type names (i1, i2) import unedited and a reserved-name extern fn is bare-callable.

Bare-callable extern / backtick fn. lowerCall rewrites a .type_expr callee to an identifier when a function of RAW provenance of that name is in scope ([src/ir/lower.zig]) — scoped to the callee FnDecl's is_raw flag, so it only ever fires for a backtick / #import c extern fn (the decl check guarantees no bare reserved-name fn exists). i2(4) resolves to the function (TypeName(val) is not a cast).

Regression tests. examples/0151-types-backtick-raw-identifier.sx (every VALUE position), examples/0152-types-backtick-control-flow.sx (every control-flow / capture form), examples/0153-types-backtick-const-fn-decl.sx (backtick :: const + fn decl, bare + backtick call), examples/0154-types-backtick-raw-type-reference.sx (raw in TYPE position — struct / enum / union / alias decl + reference; bare i2 still the int), examples/0155-types-backtick-typed-const-union-tag.sx (typed const + union tag), examples/0156-types-backtick-struct-const.sx (struct-body const, untyped + typed), examples/0157-types-backtick-parameterized-raw-type.sx (raw parameterized type + pointer/field wrappers), examples/0158-types-reserved-name-member-exempt.sx (bare reserved-name struct fields / union tag / protocol method signature — read & written bare and via backtick; impl method definition takes the backtick), examples/1054-errors-backtick-reserved-binding.sx (catch/onfail tag bindings), examples/1220-ffi-c-import-reserved-name-params.{sx,h,c} (extern param + fn-name exemption, bare-callable extern fn); negatives examples/1119/1121/1123 (bare reserved binding across forms), examples/1140-diagnostics-reserved-name-const-fn-decl.sx (bare const + fn decl), examples/1141-diagnostics-reserved-name-type-decl.sx (bare struct / enum / union / error / typed-const decl), examples/1142-diagnostics-reserved-name-struct-const.sx (bare struct-body const, caret on the name). Backtick lexer + resolveNamed(skip_builtin) unit tests in src/lexer.zig / src/ir/type_resolver.test.zig; the editor/LSP raw-type resolution (the second classifier) is pinned in src/sema.test.zig — the direct case plus raw provenance through every compound shape (*`i2 field access, ?`i2 unwrap, [N]`i2 index, parameterized `i2(i64)), each with a bare-spelling control that stays the builtin (fail-before verified).

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 i1, i2 (which collide with sx's signed-int type keywords i1..sN) produce:

error: 'i1' is a reserved type name and cannot be used as an identifier
error: 'i2' 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 (i2, 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 i1/i2.

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 extern) declarations are treated as RAW identifiers: extern 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:

   `i2 := 2.5;   // OK — identifier "i2", distinct from the i2 signed-int type
   i2 := 2.5;    // ERROR — bare i2 is still the reserved type name
   

   Prefix form (single leading backtick on the identifier). The raw identifier's TEXT is i2 (the backtick is not part of the name). A bare i2 used as a TYPE remains the signed-int type.

Reproduction

sx-side (minimal):

#import "modules/std.sx";
main :: () {
    `i2 := 2.5;            // must compile: identifier i2 = 2.5
    print("{}\n", `i2);    // 2.5
}

Import-side: a #import c block over a header declaring int i1, i2; (or stb_truetype.sx) must NOT emit the reserved-type-name error.