Lyric

What changed in v4.2.2 — 2026-08-27

Round 2 of the sweep. One diagnostic fixed, one limit documented, and two language questions recorded rather than answered — deciding them is not a sweep's job.

Fixed

• A diagnostic no longer tells you to wait for a newer compiler when your program is simply wrong. x == null, x ?? y and x ??= y on a value that is not optional reported LYR-IR0001 with the note "this compiler version cannot lower it yet". No version will lower it — there is nothing to lower — so the note sent a reader looking for a release that will never help. It now reads "a value of this type is never null".

  The check itself stays in the lowering, and that is correct: a generic body may write x == null or x ?? y over a T that IS instantiated with an optional, and only monomorphization knows. The code stays LYR-IR0001 — codes are stable identifiers, and LYR-IR0002..0010 stay free by decision. Only the aside changed, and only at the six sites where the default category was false.

Documentation

• An f-string interpolation holds a scalar, and the guide now says so. f"{p}" on a struct is refused even when the type conforms to Display, while println(p) works through the constraint. v4.1.0 made that gap felt rather than created it, by giving Instant and Duration a Display; guide 2 and guide 13 now state the limit and show .show() as the way through.

Probed and clean

Round 1's own fix re-checked: the guard's panic is NOT catchable as an IoError, and a computed max walking down to exactly one still reads. Beyond that: a LineReader walked inside a coroutine that is itself pulled from a task — a chain in a chain, with the file read at the bottom yielding past the inner chain to the scheduler; the same walk through map and filter; one handle used across two separate run() calls; fifty queued writes all landing; and the time types carried through a coroutine by value.

The full changelog →