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sx/examples/0778-modules-bare-generic-instance-by-value-receiver/b.sx
agra 6406d0fb1f fix(stdlib/E4): collapse generic-struct author matrix into four choke-points
The generic-struct author-selection matrix {bare,qualified} × {site} × {layout,
body} drifted per-site across 12 attempts because method bodies were resolved by
bare template name in `fn_ast_map["Box.method"]`, independent of which author
produced the instance's layout. Collapse it into four choke-points so
layout-author ≡ body-author by construction:

  CP-1 `selectGenericStructHead` — the single layout-head selector every generic
       struct head site funnels through (alias-RHS .call/.parameterized, array-
       literal, static head, resolveTypeCall/ParameterizedWithBindings). Emits the
       visibility / missing-member diagnostics inline; returns a control-flow-only
       union. No head site reads `struct_template_map` for selection directly.
  CP-2 author stamp — non-optional `decl: *StructDecl` on `StructTemplate` (set at
       the sole producer `buildGenericStructTemplate`) + `struct_instance_author`
       written at `instantiateGenericStruct` from the SAME `tmpl` that builds the
       layout; re-stamped on the dedup fast-path so an instance is never returned
       without an author.
  CP-3 alias metadata copy — mirror template/bindings/author from the mangled
       instance onto the alias display name, so an `ABox`-typed receiver is a
       first-class dispatch instance (Counter-2).
  CP-4 `genericInstanceMethod` / `ensureGenericInstanceMethodLowered` — the single
       body reader: inline methods select via the stamped author (`structMethodFn`,
       source-pin follows for free); impl-block methods fall back to the template-
       keyed `fn_ast_map` entry. Routes the four bespoke body sites (static head,
       instance dispatch, param typing, protocol thunk) + the new qualified static
       head (`a.Box(s64).make(7)`, finding #2).

A debug assert locks `struct_instance_author` / `struct_instance_template` keyset
coincidence so a future third writer that forgets the author trips a test.

Goldens 0777/0778/0780 (bare instance method — ptr/by-value/param-typed, finding
#1), 0779/0785 (qualified static head + missing member, finding #2), 0783 (alias
instance dispatch, Counter-2), 0782 (ambiguity containment). 0414/0415/0543 and
the FFI suites stay green.
2026-06-08 20:34:53 +03:00

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// The bare-VISIBLE author: a one-field generic `Box` (size 8) with a BY-VALUE
// receiver method `dbl` (`self: Box`). `b.sx` flat-imports `c.sx`, so a file
// importing only b.sx reaches `c.Box` at two hops and must NOT dispatch to it.
Box :: struct($T: Type) {
x: T;
make :: (value: T) -> Box(T) {
.{ x = value }
}
dbl :: (self: Box) -> T {
self.x * 2
}
}
#import "c.sx";