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; 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
>    (`` `s2 ``) 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 / foreign-class method params, AND every
>    type-introducing decl — `StructDecl` / `EnumDecl` / `UnionDecl` /
>    `ErrorSetDecl` / `ProtocolDecl` / `ForeignClassDecl` / `UfcsAlias` /
>    `NamespaceDecl` / `ImportDecl` / `CImportDecl` / `LibraryDecl`.
>
>    - **Value position.** The parser skips `Type.fromName` for a raw identifier
>      in expression position ([src/parser.zig] `parsePrimary`), so `` `s2 `` is a
>      value identifier; a later bare reference resolves to the binding.
>    - **Type position.** `parseTypeExpr` emits a raw `type_expr` (no qualified /
>      `Closure` / parameterized continuation). 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 `` `s2 ``-declared type (struct / enum / union / alias), else a NORMAL
>      "unknown type 's2'" error (`UnknownTypeChecker.reportIfUnknownType` skips the
>      builtin-name exemption when raw). A bare `s2` in type position is still the
>      builtin int.
>    - **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.
> 2. **`#import c` foreign-name exemption.** `c_import.zig` synthesizes foreign
>    `#foreign` decls with `Param.is_raw = true` (and the synthesized `FnDecl`
>    `is_raw = true`), so generated C names that collide with reserved type names
>    (`s1`, `s2`) import unedited and a reserved-name foreign fn is bare-callable.
>
> **Bare-callable foreign / 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` foreign fn (the decl check guarantees
> no bare reserved-name fn exists). `s2(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 `s2` still the int),
> `examples/0155-types-backtick-typed-const-union-tag.sx` (typed const + union tag),
> `examples/1054-errors-backtick-reserved-binding.sx` (`catch`/`onfail` tag
> bindings), `examples/1220-ffi-c-import-reserved-name-params.{sx,h,c}` (foreign
> param + fn-name exemption, bare-callable foreign 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). Backtick lexer + `resolveNamed(skip_builtin)` unit
> tests in `src/lexer.zig` / `src/ir/type_resolver.test.zig`.
>
> The original report is preserved below.

---

## 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:

   ```sx
   `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):

```sx
#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.