Attempts 1–4 fixed the array-dimension paths but the same length-0
fabrication class survived on every other site that resolves a
compile-time integer. Unify them all on the single shared
`program_index.evalConstIntExpr` so they cannot diverge:
- All three Vector lane resolvers (resolveTypeCallWithBindings,
resolveParameterizedWithBindings, resolveArrayLiteralType) and both
generic value-param binders (instantiateGenericStruct,
instantiateTypeFunction) hand-rolled an `else => 0` switch. A
module-const lane `Vector(N, f32)` fabricated a 0-lane `<0 x float>`
(LLVM "huge alignment" abort); a value-param `Vec(N, f32)` fabricated
a 0 binding / wrong mangled name. They now fold through the shared
evaluator and emit a clean diagnostic + `.unresolved` on a non-const
operand (resolveVectorLane / resolveValueParamArg) — never 0.
- evalComptimeInt (inline-for bounds) delegated to the shared evaluator,
so `inline for 0..M` / `0..(M+1)` fold like array dims. The `<pack>.len`
leaf moved into the shared folder via a new `ctx.lookupPackLen`.
- The unknown-type semantic checker no longer walks a value-param
position (`Vector(N, …)` / `Vec(N, …)`) as a type name (was reporting
"unknown type 'N'").
- The parameterized-type-arg parser and the function-body lookahead
(hasFnBodyAfterArrow) accept a const-EXPRESSION in a value position, so
`Vector(M + 1, f32)` and `[M + 1]T` parse as a return type too (the
latter a pre-existing array-dim sibling that the same heuristic broke).
Regressions: examples/1501 (named-const + const-expr lane, direct +
alias, 3/4-lane reads), 1502 (runtime lane clean-halts, exit 1, no LLVM
crash), 0207 (Vec(N)/Vec(M+1) == Vec(3) instantiation), 0610 (inline-for
const bounds). Shared-evaluator unit test extended with the pack-len arm.
zig build && zig build test && bash tests/run_examples.sh: 395 passed,
0 failed.
