resolve: Simplify import resolution for mixed 2015/2018 edition mode
Non-controversial part of https://github.com/rust-lang/rust/pull/57745.
Before:
| Local edition (per-span) | Global edition (--edition) | Imports (`use foo;`) | Absolute paths (`::foo`) |
| ------------- |----------------|-----------------------------------------|------------------------------------------------|
| 2018 | Any | Uniform | Extern prelude |
| 2015 | 2015 | Crate-relative | Crate-relative |
| 2015 | 2018 | Crate-relative with fallback to Uniform (future-proofed to error if the result is not Crate-relative or from Extern prelude) | Crate-relative with fallback to Extern prelude |
After:
| Local edition (per-span) | Global edition (--edition) | Imports (`use foo;`) | Absolute paths (`::foo`) |
| ------------- |----------------|-----------------------------------------|------------------------------------------------|
| 2018 | Any | Uniform | Extern prelude |
| 2015 | 2015 | Crate-relative | Crate-relative |
| 2015 | 2018 | Crate-relative with fallback to Extern prelude | Crate-relative with fallback to Extern prelude |
I.e. only the behavior of the mixed local-2015-global-2018 mode is changed.
This mixed mode has two goals:
- Address regressions from https://github.com/rust-lang/rust/pull/56053#issuecomment-440826397.
Both "before" and "after" variants address those regressions.
- Be retrofit-able to "full 2015" edition (https://github.com/rust-lang/rust/pull/57745).
Any more complex fallback scheme (with more candidates) than "Crate-relative with fallback to Extern prelude" will give more regressions than https://github.com/rust-lang/rust/pull/57745#issuecomment-455855089 and is therefore less retrofit-able while also being, well, more complex.
So, we can settle on "Crate-relative with fallback to Extern prelude".
(I'll hopefully proceed with https://github.com/rust-lang/rust/pull/57745 after mid-February.)
r? @Centril
ignore higher-ranked object bound conditions created by WF
In the `issue-53548` test added in this PR, the `Box<dyn Trait>` type is expanded to `Box<dyn Trait + 'static>`, but the generator "witness" that results is `for<'r> { Box<dyn Trait + 'r> }`. The WF code was encountering an ICE (when debug-assertions were enabled) and an unexpected compilation error (without debug-asserions) when trying to process this `'r` region bound. In particular, to be WF, the region bound must meet the requirements of the trait, and hence we got `for<'r> { 'r: 'static }`. This would ICE because the `Binder` constructor we were using was assering that no higher-ranked regions were involved (because the WF code is supposed to skip those). The error (if debug-asserions were disabled) came because we obviously cannot prove that `'r: 'static` for any region `'r`. Pursuant with
our "lazy WF" strategy for higher-ranked regions, the fix is not to require that `for<'r> { 'r: 'static }` holds (this is also analogous to what we would do for higher-ranked regions appearing within the trait in other positions).
Fixes#53548
r? @pnkfelix
Fix#54822 and associated faulty tests
Type checking associated constants can require trait bounds, but an empty
parameter environment was provided to the trait solver. Providing an
appropriate parameter environment seems to fix#54822 and also make one of the
cases in src/test/ui/nll/trait-associated-constant.rs that should compile
successfully do so. It also (slightly) improves the error message in
src/test/ui/associated-const/associated-const-generic-obligations.rs
In the `issue-53548` test added in this commit, the `Box<dyn Trait>`
type is expanded to `Box<dyn Trait + 'static>`, but the generator
"witness" that results is `for<'r> { Box<dyn Trait + 'r> }`. The WF
code was encountering an ICE (when debug-assertions were enabled) and
an unexpected compilation error (without debug-asserions) when trying
to process this `'r` region bound. In particular, to be WF, the region
bound must meet the requirements of the trait, and hence we got
`for<'r> { 'r: 'static }`. This would ICE because the `Binder`
constructor we were using was assering that no higher-ranked regions
were involved (because the WF code is supposed to skip those). The
error (if debug-asserions were disabled) came because we obviously
cannot prove that `'r: 'static` for any region `'r`. Pursuant with
our "lazy WF" strategy for higher-ranked regions, the fix is not to
require that `for<'r> { 'r: 'static }` holds (this is also analogous
to what we would do for higher-ranked regions appearing within the
trait in other positions).
Warning period for detecting nested impl trait
Here is some proposed code for making a warning period for the new checking of nested impl trait.
It undoes some of the corrective effects of PR #57730, by using boolean flags to track parts of the analysis that were previously skipped prior to PRs #57730 and #57981 landing.
Cc #57979
Make migrate mode work at item level granularity
Migrate mode now works entirely at the item level rather than the body level,
ensuring that we don't lose any errors in contained closures.
Closes#58776
r? @pnkfelix
Type checking associated constants can require trait bounds, but an empty
parameter environment was provided to the trait solver. Providing an
appropriate parameter environment seems to fix#54822 and also make one of the
cases in src/test/ui/nll/trait-associated-constant.rs that should compile
successfully do so. It also (slightly) improves the error message in
src/test/ui/associated-const/associated-const-generic-obligations.rs
Refactor passes and pass execution to be more parallel
For `syntex_syntax` (with 16 threads and 8 cores):
- Cuts `misc checking 1` from `0.096s` to `0.08325s`.
- Cuts `misc checking 2` from `0.3575s` to `0.2545s`.
- Cuts `misc checking 3` from `0.34625s` to `0.21375s`.
- Cuts `wf checking` from `0.3085s` to `0.05025s`.
Reduces overall execution time for `syntex_syntax` (with 8 threads and cores) from `4.92s` to `4.34s`.
Subsumes https://github.com/rust-lang/rust/pull/58494
Blocked on https://github.com/rust-lang/rust/pull/58250
r? @michaelwoerister
overhaul unused doc comments lint
This PR contains a number of improvements to the `unused_doc_comments` lint.
- Extends the span to cover the entire comment when using sugared doc comments.
- Triggers the lint for all unused doc comments on a node, instead of just the first one.
- Triggers the lint on macro expansions, and provides a help note explaining that doc comments must be expanded by the macro.
- Adds a label pointing at the node that cannot be documented.
Furthermore, this PR fixes any instances in rustc where a macro expansion was erroneously documented.
