Adds the one deferred A4.1 coverage item: a focused unit test for
GenericResolver.buildTypeBindings inferring a type param from value args
(strategy 2) with widest-match — add(1,2) => T=s64, and add(1.0,2) / add(1,2.0)
=> T=f64 regardless of argument order.
Previously this inference path was guarded only by the 0200 .ir snapshot; the
unit test pins it directly against the new generics.zig API. Test-only.
zig build test and tests/run_examples.sh (357/0) green.
Generic substitution and monomorphization-key construction now live in one
module, src/ir/generics.zig, behind a *Lowering facade (GenericResolver),
mirroring CallResolver / ExprTyper. Moved verbatim:
- mangleTypeName + mangleParamList (the mono-key fragment builder),
- mangleGenericName (generic mono key), appendComptimeValueMangle (comptime-value
fragment),
- buildTypeBindings (call-site type-param inference), inferGenericReturnType
(generic return resolution).
inferGenericReturnType now uses a scoped TypeBindingScope (enter/exit with defer)
instead of a manual type_bindings save/restore — the PLAN-ARCH A4.1 "scoped
substitution env" shape; a generics.test.zig assertion confirms the prior
bindings are restored (the issue-0048/0050 leak class, for this field).
Lowering keeps a thin pub mangleTypeName wrapper delegating to
genericResolver().mangleTypeName, because ~30 cross-cutting callers (impl-map
keys, conversion keys, shape keys) reach it well beyond generics. mangleParamList
(sole caller was mangleTypeName) moved fully. The other 4 originals are deleted
(no fallback); their 6 call sites now go through self.genericResolver()
(calls.zig via self.l.genericResolver()).
matchTypeParam / extractTypeParam / isTypeParamDecl widened to pub (the moved
substitution logic calls them); genericResolver() accessor added. The 2
mangleTypeName / inferGenericReturnType unit tests moved from lower.test.zig to
generics.test.zig (driving GenericResolver directly) and wired into the barrel.
monomorphizeFunction / monomorphizePackFn intentionally stay in lower.zig (they
save/restore three fields across nested mono and call emission helpers) — a
heavier scoped-env adoption deferred to an optional sub-step 3.
zig build, zig build test, and tests/run_examples.sh (357/0) all green — no .ir
snapshot churn, confirming the move preserved mono-key/substitution output.
