feat: add block scoping for if/elif/else and match arms#254
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Scope is-bindings and pattern bindings to their own block frame, reusing the while-block scope machinery: each if/elif/else branch and each match arm pushes a frame on entry and pops it at the next branch boundary or `fi`/`end`. A binding is visible only inside its branch/arm, never in a sibling branch, the else, or after the block. Implicit bindings that would shadow an accessible block-local or function-level variable are rejected (DuplicateName); globals remain a separate, exempt namespace and explicit `= x` may still mutate an outer variable. Refactor every compiler, stdlib, and lsp site that relied on a binding leaking past its block (the early-return guard idiom) to the positive form `if X Variant(b) is then <body> fi` or an `.unwrap` hoist, so the compiler bootstraps under the stricter rules. Closes #248 Closes #249
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Summary
Implements strict block scoping for
if/elif/else/fi(#248) andmatcharms (#249), reusing the while-block scope machinery from #251.if/elif/elsebranch and eachmatcharm gets its own scope frame: push on entry, pop at the next branch boundary orfi/end.is-binding or pattern binding is visible only inside its own branch/arm — not in a sibling branch, not in theelse, not after the block.DuplicateName. Globals are a separate, exempt namespace; explicit= xmay still mutate an outer variable, and a new= xwith no outer binding is block-local.To bootstrap under the stricter rules, every compiler / stdlib / lsp site that relied on a binding leaking past its block (the early-return guard idiom) was refactored to the positive form
if X Variant(b) is then <body> fior an.unwraphoist — no behavioral change, just no leak.Test plan
test_scope: 13 new cases — is-binding then-only / not-in-else / not-after-fi, elif independence, outer mutation, block-local new var, shadow error; match per-arm visibility, cross-arm invisibility, shadow error, outer mutation, block-local new varif_is_binding_out_of_scope,match_arm_binding_out_of_scope(UNDEFINED_NAME);if_binding_shadow,match_binding_shadow(DUPLICATE_NAME)lsp.casaandformatter/format.casabuild; all changed filescasafmt-cleanCloses #248
Closes #249