On structured suggestion for `let` -> `const` and `const` -> `let`, use
a proper `Span` and update tests to check the correct application.
Follow up to #80012.
If a symbol name can only be imported from one place for a type, and
as long as it was not glob-imported anywhere in the current crate, we
can trim its printed path and print only the name.
This has wide implications on error messages with types, for example,
shortening `std::vec::Vec` to just `Vec`, as long as there is no other
`Vec` importable anywhere.
This adds a new '-Z trim-diagnostic-paths=false' option to control this
feature.
On the good path, with no diagnosis printed, we should try to avoid
issuing this query, so we need to prevent trimmed_def_paths query on
several cases.
This change also relies on a previous commit that differentiates
between `Debug` and `Display` on various rustc types, where the latter
is trimmed and presented to the user and the former is not.
re https://github.com/rust-lang/rust/pull/72380#discussion_r438289385
Given the toy code
```rust
fn is_positive(n: usize) {
n > -1_isize;
}
```
We currently get a type mismatch error like the following:
```
error[E0308]: mismatched types
--> src/main.rs:2:9
|
2 | n > -1_isize;
| ^^^^^^^^ expected `usize`, found `isize`
|
help: you can convert an `isize` to `usize` and panic if the converted value wouldn't fit
|
2 | n > (-1_isize).try_into().unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
But clearly, `-1` can never fit into a `usize`, so the suggestion will
always panic. A more useful message would tell the user that the value
can never fit in the expected type:
```
error[E0308]: mismatched types
--> test.rs:2:9
|
2 | n > -1_isize;
| ^^^^^^^^ expected `usize`, found `isize`
|
note: `-1_isize` can never fit into `usize`
--> test.rs:2:9
|
2 | n > -1_isize;
| ^^^^^^^^
```
Which is what this commit implements.
I only added this check for negative literals because
- Currently we can only perform such a check for literals (constant
value propagation is outside the scope of the typechecker at this
point)
- A lint error for out-of-range numeric literals is already emitted
IMO it makes more sense to put this check in librustc_lint, but as far
as I can tell the typecheck pass happens before the lint pass, so I've
added it here.
r? @estebank
