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Rollup merge of #120828 - nnethercote:fix-stash-steal, r=oli-obk

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Fix `ErrorGuaranteed` unsoundness with stash/steal.

When you stash an error, the error count is incremented. You can then use the non-zero error count to get an `ErrorGuaranteed`. You can then steal the error, which decrements the error count. You can then cancel the error.

Example code:
```
fn unsound(dcx: &DiagCtxt) -> ErrorGuaranteed {
    let sp = rustc_span::DUMMY_SP;
    let k = rustc_errors::StashKey::Cycle;
    dcx.struct_err("bogus").stash(sp, k);           // increment error count on stash
    let guar = dcx.has_errors().unwrap();           // ErrorGuaranteed from error count > 0
    let err = dcx.steal_diagnostic(sp, k).unwrap(); // decrement error count on steal
    err.cancel();                                   // cancel error
    guar                                            // ErrorGuaranteed with no error emitted!
}
```

This commit fixes the problem in the simplest way: by not counting stashed errors in `DiagCtxt::{err_count,has_errors}`.

However, just doing this without any other changes leads to over 40 ui test failures. Mostly because of uninteresting extra errors (many saying "type annotations needed" when type inference fails), and in a few cases, due to delayed bugs causing ICEs when no normal errors are printed.

To fix these, this commit adds `DiagCtxt::stashed_err_count`, and uses it in three places alongside `DiagCtxt::{has_errors,err_count}`. It's dodgy to rely on it, because unlike `DiagCtxt::err_count` it can go up and down. But it's needed to preserve existing behaviour, and at least the three places that need it are now obvious.

r? oli-obk
This commit is contained in:
Matthias Krüger 2024-02-09 14:41:52 +01:00 • committed by GitHub
commit 2f1ac412ec
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5 changed files with 65 additions and 42 deletions
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4
compiler/rustc_interface/src/passes.rs
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@ -778,6 +778,10 @@ fn analysis(tcx: TyCtxt<'_>, (): ()) -> Result<()> {
// kindck is gone now). -nmatsakis
if let Some(reported) = sess.dcx().has_errors() {
return Err(reported);
} else if sess.dcx().stashed_err_count() > 0 {
// Without this case we sometimes get delayed bug ICEs and I don't
// understand why. -nnethercote
return Err(sess.dcx().delayed_bug("some stashed error is waiting for use"));
}
sess.time("misc_checking_3", || {