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lang 2.4: enforce interface-only access on pack elements

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A protocol-constrained pack element exposes only the constraint protocol's
interface (the locked decision): `xs[i].<member>` is rejected unless `<member>`
is one of the protocol's methods. `xs[i].v` (a concrete field of IntCell, not
declared on Box) now errors, like a constrained generic — even though the
substituted element is concretely an IntCell.

monomorphizePackFn records the pack param's constraint protocol in a new
`pack_constraint` map (pack-name → protocol); lowerFieldAccess checks it on an
`xs[i]` (index_expr) base BEFORE substitution erases the "constrained to P"
context. Protocol method calls (`xs[i].get()`) pass — the name is in the
protocol. Regression: examples/195-pack-interface-only.sx.
This commit is contained in:
agra
2026-05-29 19:34:03 +03:00
parent e604868ffb
commit 19bc644b11
4 changed files with 66 additions and 1 deletions
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tests/expected/195-pack-interface-only.exit Normal file
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error: 'v' is not part of protocol 'Box' — a pack element exposes only the protocol's interface
--> /Users/agra/projects/sx/examples/195-pack-interface-only.sx:16:12
|
16 | return xs[0].v; // `v` is not part of Box — error
| ^^^^^^^