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
Filter away test annotations from UI test output
If you worked with UI tests for some time you could notice one issue affecting their readability and also readability of diffs when the tests change.
Look at the output of this test.
```rust
fn main() {
let 1 = 2; //~ ERROR refutable pattern in local binding
}
```
```
error[E0005]: refutable pattern in local binding: `-2147483648i32..=0i32` not covered
--> src/main.rs:2:9
|
2 | let 1 = 2; //~ ERROR refutable pattern in local binding
| ^ pattern `-2147483648i32..=0i32` not covered
error: aborting due to previous error
For more information about this error, try `rustc --explain E0005`.
```
You can see that the "refutable pattern in local binding" is duplicated.
One instance is the actual error, and the second instance is the expected error annotation.
This annotation is useful in the test input, but in the output it clutters the text and makes it harder to see what text refers to actual errors and what is just comments, especially if there are many errors in a single test file.
@estebank [reported](https://github.com/rust-lang/rust/pull/57379#discussion_r245523361) using the next trick to avoid the clutter
```rust
fn main() {
let 1 = 2;
//~^ ERROR refutable pattern in local binding
}
```
```
error[E0005]: refutable pattern in local binding: `-2147483648i32..=0i32` not covered
--> src/main.rs:2:9
|
2 | let 1 = 2;
| ^ pattern `-2147483648i32..=0i32` not covered
error: aborting due to previous error
For more information about this error, try `rustc --explain E0005`.
```
, i.e. using `//~^` and placing the annotation one line below will remove the annotation from the output.
However, this doesn't always works (consider errors with multi-line spans), and shouldn't be necessary in general!
`compiletest` could automatically filter away its own annotations from the output instead.
This is exactly what this PR does.
r? @davidtwco
