D362 - concat! defeats an implicit format capture

decided · 2026-08-29

The prose gate's advice is "use concat! of one-line literals instead", and applying it mechanically to the five files still carrying line-continued literals broke the build in three places:

error: there is no argument named `says`
error: there is no argument named `hole`
error: there is no argument named `serves`

An implicit capture needs a literal, and concat! is a macro call. format!("{says}") finds says in scope; format!(concat!("{says}")) does not, because by the time format! sees anything the argument list is already fixed and the braces are just text.

It fails loudly, which is the saving grace - but only at the site being converted. A conversion done in bulk without building would have been three quiet breakages in files nobody was reading.

The fix is a named argument: format!(concat!("...{says}..."), says = says). That keeps both the capture and the one-line-literal rule, and it says out loud what was implicit.

Worth writing down because the advice is given by a gate that cannot know about it: the gate sees a backslash and says what to do, and what to do is right in every case except this one.

Why the tree had five such files at once

They were written by a session working in parallel and were never its own to finish. With the tree quiet, they were fixed here rather than left - a gate that has been red for a day stops being read, which costs more than the files did.