Files
sx/examples/224-inferred-widening-reject.sx
agra d2cba4e460 ERR/E1.4b: whole-program inferred error sets + empty-inferred warning
The type-convergence side of E1.4 (the SCC slice). A bare `-> !` function's
error set is now converged whole-program from its literal raises plus the
sets of the pure-failable functions it `try`s.

- convergeInferredErrorSets: a pre-lowering fix-point pass (lowerRoot Pass
  1d, after scanDecls / before body lowering) that walks each top-level
  bare-`!` function's body AST (collectErrorSites, stopping at nested-fn
  boundaries) for literal `raise error.X` tags + pure `try g()` edges, then
  unions each set with its edges' sets until stable. Stored in a side map
  `inferred_error_sets` (fn name -> sorted []u32) — sidesteps the name-only
  error-set interning collision (the shared `!` placeholder stays empty).
- lowerTry widening: a named caller `try`-ing a bare-`!` callee now checks
  the callee's converged set (previously a false-negative — the empty
  placeholder was trivially a subset). Factored diagTagsNotInSet out of
  checkErrorSetSubset.
- empty-inferred warning: a top-level non-main bare-`!` function with an
  empty converged set warns. Not user-visible yet (the compile driver
  renders diagnostics only on failure — a LANG follow-up), so unit-tested
  on the DiagnosticList.
- corrected two now-stale bail messages (failable-`or` -> E2.4;
  value-carrying `try` -> E2).

Deferred to E2.4: failable-`or` chains / value-terminators (and `try`
fallback routing) — gated on the value-carrying tuple ABI.

Tests: examples/223-inferred-error-sets.sx (transitive convergence +
widening passes, exit 7), examples/224-inferred-widening-reject.sx
(transitive widening rejection, exit 1), unit test in lower.test.zig.
Gates: zig build, zig build test, 262/262 examples.
2026-05-31 20:21:44 +03:00

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// Inferred-set widening rejection (ERR step E1.4b). When a named caller
// (`-> !A`) `try`s a bare-`!` callee, the callee's WHOLE-PROGRAM-CONVERGED
// inferred set must be a subset of A. Before the SCC pass this was a
// false-negative (the bare-`!` placeholder was empty, so the check trivially
// passed); now the converged tags are checked. `deep`'s converged set is
// {Foo} (raised transitively through `via`), which is not in A = {Bar}.
// The positive case lives in `examples/223-inferred-error-sets.sx`.
#import "modules/std.sx";
A :: error { Bar }
deep :: () -> ! {
raise error.Foo; // deep's inferred set = {Foo}
}
via :: () -> ! {
try deep(); // via absorbs {Foo}
return;
}
caller :: () -> !A {
try via(); // error: Foo (via's converged set) not in A
return;
}
main :: () -> s32 {
e := caller();
return 0;
}