feat(t27b): lower switch expressions and negative const literals - #6353
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switch on an enum or integer operand lowers to a lazy select chain, so only the taken prong runs (#6328); the operand is evaluated once. Shapes the reference cannot compile are refused by name (not exhaustive, unreachable else, duplicate prong, prong, char prong #6329). `const X: i32 = -1;` lowers as the comptime int t27c prints. `f(x);` with a non-void f is refused where zig test analyzes the body (ExprCall(value ignored) statement), matching specs/fpga/bpsk.t27; bench blocks are no longer analysis roots, since t27c emits them as uncalled fns. Corpus vs t27c reference at f25dbee: counted 623 -> 629 / 720, checked pass 346 -> 352, mismatch 0 -> 0, no regressions. Closes #6352 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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This was referenced Oct 5, 2026
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Closes #6352
Refs #6063
What
switchexpressions incli/t27b, on an enum or an integer operand.Selects, so only the taken prong runs (feat(t27b): lower if-expressions natively; refuse what t27c misprints #6328).else, or the last prong when every value is listed.ifthrough a newselect_vals.const X: i32 = -1;lowers as the comptime int that t27c's Zig backend prints. It was refused asExprLiteral(negative literal).t27c test-report:ExprSwitch(not exhaustive)ExprSwitch(unreachable else)ExprSwitch(duplicate prong)ExprSwitch(prong): unknown variant, int prong on an enum, out-of-range value, or ident prong on an intExprSwitch(char prong):'a'prints as.'a'(t27c gen-zig drops needed parentheses: (if ..) + 1 and -(x - y) #6329)ExprCall(value ignored) statement: a new refusal forf(x);with a non-voidfin a bodyzig testanalyzes.specs/fpga/bpsk.t27is BLOCKED in the reference. Without the refusal, t27b would have passed that file once its negative literals lowered.fn bench_<name>() void, so Zig never analyzes it. Without that change, the refusal blocked 9 reference-passing testbench files.Corpus (
t27b corpus specs --blockers --reference t27c, master f25dbee, same t27c binary and reference cache both runs)Newly passing, each agreeing test for test with the reference:
specs/fpga/testbench/axi4_tb.t27(reference BLOCKED) changed from timeout to rejected. No file regressed.Tests
switch_runs_only_the_taken_prong: verdicts equalt27c test-report.taken_prong_trapsfails on thex - 10overflow.discarded_call_result_is_refused_where_reached: a droppedu32in an uncalled fn, a bench, or a fn only a bench names passes. In a test it is BLOCKED, as in the reference.enum_rejections_are_precise, the old "switch is unsupported" case now checksExprSwitch(unreachable else).Reference quirks seen (not fixed here)
const w: u16 = 1000;as the literal1000, so Zig peer-types aniforswitchwith au8arm tou8and refuses the value. The reference is BLOCKED where t27b passes. This is pre-existing forifand not counted.switch(for examplespecs/.../json.t27, reference BLOCKED) is not lowered.🤖 Generated with Claude Code