A bracket literal can now be passed directly where a `set of <enum>`
parameter is expected, e.g. Configure([optA, optC]) or Report([]) — no
named intermediate variable needed.
Previously such a call failed overload resolution: a bare [a, b] is
analysed (lacking set context) as an open-array of the enum, which does
not match the set parameter. Now:
- ArgMatchScore matches a TArrayLiteralExpr argument against a set
parameter — non-empty when the members share the param's base enum,
and the empty [] against any set — checked before the nil-arg bail so
[] (which has no resolved type) is handled.
- AnalyseArrayLiteralExpr defers an empty [] to a nil type instead of
erroring outright; it is only meaningful with a set target.
- After overload resolution, RetypeSetLiteralArgs re-points each matched
set-literal argument's ResolvedType at the parameter's set type, so
codegen emits the bitmask (EmitArrayLiteralExpr dispatches on tySet).
- CheckTypesMatch gained a nil-actual guard (a clean "no value type"
error instead of a segfault on a stray []), and the assignment path
rejects an empty [] assigned to a non-set LHS.
Fixes a second, latent bug exposed by passing sets by value: a `set of`
value parameter of <=32 members (QBE type w) was spilled in the prologue
with storel, which QBE rejects. Added a tySet case to both param-spill
sites (storew for w sets, storel for l sets).
Tests: 6 IR/semantic cases in cp.test.sets (arg OK / empty / wrong-enum
/ empty-non-set-assign fail, bitmask fold, w-width param spill) and an
e2e in cp.test.e2e.misc. language-rationale updated. Full suite 2335
tests pass; fixpoint clean.
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