Repository navigation
t27b: lower the parameter discard _ = p; (StmtAssign(undeclared)) #7057
Description
Refs #6063 (coverage lane 1).
Problem
A port that keeps a parameter for its interface writes _ = p;. t27c prints that as written in Zig and the reference passes it, but t27b treats _ as an assignment target and refuses the file with StmtAssign(undeclared): "assignment to undeclared _".
Sole blocker on main lab 38a6e30:
specs/port/browseros/trios/agent-server/apps/server/src/api/routes/queen-rehearsal.t27(_ = frame;)
First blocker, with a later one behind it:
specs/ml/rl/dqn.t27specs/port/trinity/src/tri/gen_gradient.t27specs/port/trios/crates/trios-cli/src/cmd/leaderboard.t27specs/tri/crypto/hex.t27
Plan
- Dogfood spec first:
specs/tri/t27b/conformance/param_discard.t27. It must passt27c test-report, and t27b must pass it non-vacuously. - In t27b, lower
_ = p;as a no-op whenpis a parameter of the current fn that the body names nowhere else and that no module declaration shares. - Refuse the shapes the reference cannot compile:
- Zig's AstGen refuses a pointless discard of a parameter the body also reads, and it does so in every fn, called or not.
- gen-zig renames a parameter that a module declaration shadows.
- Mutants, negative controls, cargo test and a corpus comparison against master, all run on the Railway lab.
Activity
t27b: a top-level `_ = p;` is deleted as the reference deletes it (Cl…
t27b: a nested `_ = p;` is refused only next to a use of `p` (Closes #…
Merge origin/master into claude/t27b-lane1-param-discard (Closes #7057)
queen-rehearsal: the caller owns the content buffer, no dangling slice (
t27b ledger and NOW entry for parameter discards (Closes #7057)
Merge origin/master into claude/t27b-lane1-param-discard (Closes #7057)
gHashTag commentedon Oct 6, 2026
Final rule in #7111, measured on the Railway lab: a top-level
_ = p;is always accepted, because t27c's dead-store pass deletes it. A nested_ = p;is refused only when the body also usesp, which is the case Zig rejects as a pointless discard. Discards alone compile, whether repeated, in both arms of anif, or for a parameter that shares a module declaration's name, and the reference passes them.Merge origin/master into claude/t27b-lane1-param-discard (Refs #7057)
t27b: `_ = p;` for a parameter lowers to nothing where the reference …