28b18f812a
A match (`if subject == { case ... }`) whose arms all diverge (each
`return`s / `raise`s) failed LLVM verification with a `void` phi plus
"Terminator found in the middle of a basic block". Two causes in lowerMatch:
- The value-arm path did `lowerBlockValue(arm.body) orelse constInt(0, …)`,
emitting the fallback `const` into a block the body had ALREADY terminated
(a diverging arm), so `currentBlockHasTerminator()` then saw the const (not
the `ret`) and emitted a `br merge` after the terminator. Fix: materialize
the fallback value + branch only when the block hasn't terminated.
- A fully-diverging match infers `result_type == .noreturn` yet still built a
value-merge phi. Fix: `has_value_merge` excludes `.noreturn`, so such a
match builds no phi; its arms terminate and the merge block is unreachable.
Also: inferMatchResultType now skips `.noreturn` arms (a diverging arm doesn't
decide the result type) and reports `.noreturn` only when EVERY arm diverges —
so a mixed match (some arms yield values, some diverge) infers the value type.
This unblocks ERR E1.5's `catch` match-body form (`x catch e == { case .A:
return …; else: raise e; }`), which desugars to an all-diverging match.
Regression: examples/225-match-diverging-arms.sx (all-diverging + mixed,
exit 134). Gates: zig build, zig build test, 263/263 examples.
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134
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