Fix incorrect #any capability for type parameters with union constraints#5337
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Fix incorrect #any capability for type parameters with union constraints#5337SeanTAllen wants to merge 1 commit into
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cap_union_constraint was missing many entries; pairs whose atomic members all live in #alias fell through to #any instead of returning #alias. The TK_VAL switch arm was also missing its trailing break; though the fall-through into TK_BOX happened to be harmless pre-fix. Closes #2674
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The
cap_union_constraintfunction insrc/libponyc/type/typeparam.cwas missing many entries. Pairs of caps whose atomic members all lived in#aliasfell through to#anyinstead of returning#alias. The most visible symptom was the original bug from #2674: a type parameter constrained by(_OutAsync tag | _OutSync ref)got cap#anyand produced "argument type is O #any !" when the value was passed to a helper that needed re-aliasing.The fix completes the cap-set table so the function uniformly returns the smallest cap-set containing both inputs. The
TK_VALswitch arm was also missing its trailingbreak;— harmless pre-fix because everybvalue reachable through the fall-through was also handled in theTK_VALarm, but the fix needs the break becauseTK_VALnow has aTK_CAP_ALIAScase that fall-through would otherwise clobber.The accompanying full-program regression test declares 26 generic primitives, each exercising one switch-arm + subcase pair, so a future regression of any one pair fails to type-check. Counterfactually verified: reverting the table additions produces 21 compile errors against the test.
The two adjacent concerns from the issue (forbidding reification with the literal union type; iftype completeness checks) are language-design RFC material, not bug fixes, and are out of scope here.
Closes #2674