It's only has a single remaining purpose: to ensure that a diagnostic is
printed when `trimmed_def_paths` is used. It's an annoying mechanism:
weak, with odd semantics, badly named, and gets in the way of other
changes.
This commit replaces it with a simpler `must_produce_diag` mechanism,
getting rid of a diagnostic `Level` along the way.
`-Ztreat-err-as-bug` treats normal errors and delayed bugs equally,
which can lead to some really surprising results.
This commit changes `-Ztreat-err-as-bug` so it ignores delayed bugs,
unless they get promoted to proper bugs and are printed.
This feels to me much simpler and more logical. And it simplifies the
implementation:
- The `-Ztreat-err-as-bug` check is removed from in
`DiagCtxt::{delayed_bug,span_delayed_bug}`.
- `treat_err_as_bug` doesn't need to count delayed bugs.
- The `-Ztreat-err-as-bug` panic message is simpler, because it doesn't
have to mention delayed bugs.
Output of delayed bugs is now more consistent. They're always printed
the same way. Previously when they triggered `-Ztreat-err-as-bug` they
would be printed slightly differently, via `span_bug` in
`span_delayed_bug` or `delayed_bug`.
A minor behaviour change: the "no errors encountered even though
`span_delayed_bug` issued" printed before delayed bugs is now a note
rather than a bug. This is done so it doesn't get counted as an error
that might trigger `-Ztreat-err-as-bug`, which would be silly.
This means that if you use `-Ztreat-err-as-bug=1` and there are no
normal errors but there are delayed bugs, the first delayed bug will be
shown (and the panic will happen after it's printed).
Also, I have added a second note saying "those delayed bugs will now be
shown as internal compiler errors". I think this makes it clearer what
is happening, because the whole concept of delayed bugs is non-obvious.
There are some test changes.
- equality-in-canonical-query.rs: Minor output changes, and the error
count reduces by one because the "no errors encountered even though
`span_delayed_bug` issued" message is no longer counted as an error.
- rpit_tait_equality_in_canonical_query.rs: Ditto.
- storage-live.rs: The query stack disappears because these delayed bugs
are now printed at the end, rather than when they are created.
- storage-return.rs, span_delayed_bug.rs: now need
`-Zeagerly-emit-delayed-bugs` because they need the delayed bugs
emitted immediately to preserve behaviour.
Errors in `DiagCtxtInner::emit_diagnostic` are never set to
`Level::Bug`, because the condition never succeeds, because
`self.treat_err_as_bug()` is called *before* the error counts are
incremented.
This commit switches to `self.treat_next_err_as_bug()`, fixing the
problem. This changes the error message output to actually say "internal
compiler error".
