bors d4de1f230c Auto merge of #93368 - eddyb:diagbld-guarantee, r=estebank ... rustc_errors: let `DiagnosticBuilder::emit` return a "guarantee of emission". That is, `DiagnosticBuilder` is now generic over the return type of `.emit()`, so we'll now have: * `DiagnosticBuilder<ErrorReported>` for error (incl. fatal/bug) diagnostics * can only be created via a `const L: Level`-generic constructor, that limits allowed variants via a `where` clause, so not even `rustc_errors` can accidentally bypass this limitation * asserts `diagnostic.is_error()` on emission, just in case the construction restriction was bypassed (e.g. by replacing the whole `Diagnostic` inside `DiagnosticBuilder`) * `.emit()` returns `ErrorReported`, as a "proof" token that `.emit()` was called (though note that this isn't a real guarantee until after completing the work on #69426) * `DiagnosticBuilder<()>` for everything else (warnings, notes, etc.) * can also be obtained from other `DiagnosticBuilder`s by calling `.forget_guarantee()` This PR is a companion to other ongoing work, namely: * #69426 and it's ongoing implementation: #93222 the API changes in this PR are needed to get statically-checked "only errors produce `ErrorReported` from `.emit()`", but doesn't itself provide any really strong guarantees without those other `ErrorReported` changes * #93244 would make the choices of API changes (esp. naming) in this PR fit better overall In order to be able to let `.emit()` return anything trustable, several changes had to be made: * `Diagnostic`'s `level` field is now private to `rustc_errors`, to disallow arbitrary "downgrade"s from "some kind of error" to "warning" (or anything else that doesn't cause compilation to fail) * it's still possible to replace the whole `Diagnostic` inside the `DiagnosticBuilder`, sadly, that's harder to fix, but it's unlikely enough that we can paper over it with asserts on `.emit()` * `.cancel()` now consumes `DiagnosticBuilder`, preventing `.emit()` calls on a cancelled diagnostic * it's also now done internally, through `DiagnosticBuilder`-private state, instead of having a `Level::Cancelled` variant that can be read (or worse, written) by the user * this removes a hazard of calling `.cancel()` on an error then continuing to attach details to it, and even expect to be able to `.emit()` it * warnings were switched to *only* `can_emit_warnings` on emission (instead of pre-cancelling early) * `struct_dummy` was removed (as it relied on a pre-`Cancelled` `Diagnostic`) * since `.emit()` doesn't consume the `DiagnosticBuilder` <sub>(I tried and gave up, it's much more work than this PR)</sub>, we have to make `.emit()` idempotent wrt the guarantees it returns * thankfully, `err.emit(); err.emit();` can return `ErrorReported` both times, as the second `.emit()` call has no side-effects *only* because the first one did do the appropriate emission * `&mut Diagnostic` is now used in a lot of function signatures, which used to take `&mut DiagnosticBuilder` (in the interest of not having to make those functions generic) * the APIs were already mostly identical, allowing for low-effort porting to this new setup * only some of the suggestion methods needed some rework, to have the extra `DiagnosticBuilder` functionality on the `Diagnostic` methods themselves (that change is also present in #93259) * `.emit()`/`.cancel()` aren't available, but IMO calling them from an "error decorator/annotator" function isn't a good practice, and can lead to strange behavior (from the caller's perspective) * `.downgrade_to_delayed_bug()` was added, letting you convert any `.is_error()` diagnostic into a `delay_span_bug` one (which works because in both cases the guarantees available are the same) This PR should ideally be reviewed commit-by-commit, since there is a lot of fallout in each. r? `@estebank` cc `@Manishearth` `@nikomatsakis` `@mark-i-m`		2022-02-25 00:46:04 +00:00
..
src	Auto merge of #93368 - eddyb:diagbld-guarantee, r=estebank	2022-02-25 00:46:04 +00:00
Cargo.toml	Migrate to 2021	2021-09-20 22:21:42 -04:00