perry compile drops the source span on lowering errors — bare message, no file:line:col (perry check shows it)

[proggeramlug]

Summary

Lowering errors carry a source span (LowerError { message, span: Option<Span> }), and perry check renders it as a proper error[CODE] --> file:line:col diagnostic. But perry compile prints only the bare message with no location. On large/minified/generated inputs this makes any lowering wall effectively undiagnosable — you get a one-line error with no way to find the offending construct.

Repro

Same input, two front-ends:

// t.ts
for (var { a, b } = { a: 1, b: 2 }, i = 0; i < 1; i++) console.log(a, b, i);

$ perry check t.ts
error[U006]: Unsupported binding pattern
  --> t.ts:1:11
1 | for (var { a, b } = { a: 1, b: 2 }, i = 0; i < 1; i++) console.log(a, b, i);
  |          ^

$ perry compile t.ts -o /tmp/out
Error: Unsupported binding pattern        # <- no code, no file, no line:col

On a 13 MB single-file bundle the difference is stark: check pinpoints …:551:5336; compile gives you Error: Unsupported binding pattern and nothing else to go on.

Root cause

lower_bail! (crates/perry-hir/src/error.rs:46) correctly constructs a span-tagged LowerError:

macro_rules! lower_bail {
    ($span:expr, $($arg:tt)*) => {
        return Err(anyhow::Error::new(LowerError::new(format!($($arg)*), $span)))
    };
}

…but LowerError's Display (error.rs:34) emits only the message:

impl std::fmt::Display for LowerError {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.message)   // span is dropped
    }
}

perry check downcasts to LowerError and resolves span against the source map to print file:line:col + a code. The compile error path just prints the anyhow Display chain, so the captured span is silently discarded. (The module doc-comment even notes the span exists "so downstream tooling (notably perry check) can downcast and produce a diagnostic with a proper span instead of a locationless message" — compile just doesn't do that downcast.)

Suggested fix

Have the compile error path downcast to LowerError (as check already does) and render the span — error[CODE] --> file:line:col — falling back to the bare message only when span is None. Ideally share the diagnostic renderer between check and compile so both stay consistent.

Why it matters

A locationless lowering error is fine on a 5-line test but useless on generated/minified/bundled code, which is exactly where un-handled syntactic corners surface. The span is already captured; it's purely a rendering gap on the compile side.

Environment

• perry 0.5.1175, built from main @ a5d7b3e64