unused_must_use: Don't warn on `Result<(), Uninhabited>` or `ControlFlow<Uninhabited, ()>`
This suppresses warnings on things like `Result<(), !>`, which helps simplify code using the common pattern of having an `Error` associated type: code will only have to check the error if there is a possibility of error.
This will, for instance, help with future refactorings of `write!` in the standard library.
As this is a user-visible change to lint behavior, it'll require a lang FCP.
---
My proposal, here, is that we handle this simple case to make common patterns more usable. This does not rule out the possibility of adding more cases in the future, including general trait-based cases. However, I don't think we should make this common case wait on the more general cases. In particular, this solution does not close any doors on replacing this special case with a general case.
This would unblock some planned work in the standard library to make `write!` more usable for infallible cases (e.g. writing into a `Vec` or `String`).
This suppresses warnings on things like `Result<(), !>`, which helps
simplify code using the common pattern of having an `Error` associated
type: code will only have to check the error if there is a possibility
of error.
test: Subtract code_offset from width for ui_testing
`annotate-snippets` does not have a "UI test" mode like `rustc`, [where the code offset is not subtracted from the column width](https://github.com/rust-lang/rust/blob/f34ba774c78ea32b7c40598b8ad23e75cdac42a6/compiler/rustc_errors/src/emitter.rs#L1985-L1987). This makes it so `annotate-snippets` will shift the output for some very long tests 5 - 7 columns to the left. As part of my work to have `rustc` use `annotate-snippets`, and to reduce the test differences between the two, I figured it would be best if `rustc` started subtracting the code offset from the width as well.
The first commit exists to keep the test output changes of adding a new line to a test separate from adding the `--diagnostic-width` flag in the second commit. This makes it easier to verify that adding the flag does not affect the test's output.
[Zulip discussion](https://rust-lang.zulipchat.com/#narrow/channel/147480-t-compiler.2Fdiagnostics/topic/annotate-snippets.20hurdles)
Keep space if arg does not follow punctuation when lint unused parens
Fixesrust-lang/rust#138234
If the arg follows punctuation, still pass `left_pos` with `None` and no space will be added, else then pass `left_pos` with `Some(arg.span.lo())`, so that we can add the space as expected.
And `emit_unused_delims` can make sure no more space will be added if the expr follows space.
---
Edited:
Directly use the `value_span` to check whether the expr removed parens will follow identifier or be followed by identifier.
Mainly, we realise that the non-null assumption on a Box<_> argument
does not depend on what side of the FFI boundary the function is on.
And anyway, this is not the way to deal with this assumption being maybe violated.
On unused binding or binding not present in all patterns, suggest potential typo of unit struct/variant or const
When encountering an or-pattern with a binding not available in all patterns, look for consts and unit struct/variants that have similar names as the binding to detect typos.
```
error[E0408]: variable `Ban` is not bound in all patterns
--> $DIR/binding-typo.rs:22:9
|
LL | (Foo, _) | (Ban, Foo) => {}
| ^^^^^^^^ --- variable not in all patterns
| |
| pattern doesn't bind `Ban`
|
help: you might have meant to use the similarly named unit variant `Bar`
|
LL - (Foo, _) | (Ban, Foo) => {}
LL + (Foo, _) | (Bar, Foo) => {}
|
```
For items that are not in the immedate scope, suggest the full path for them:
```
error[E0408]: variable `Non` is not bound in all patterns
--> $DIR/binding-typo-2.rs:51:16
|
LL | (Non | Some(_))=> {}
| --- ^^^^^^^ pattern doesn't bind `Non`
| |
| variable not in all patterns
|
help: you might have meant to use the similarly named unit variant `None`
|
LL - (Non | Some(_))=> {}
LL + (core::option::Option::None | Some(_))=> {}
|
```
When encountering a typo in a pattern that gets interpreted as an unused binding, look for unit struct/variant of the same type as the binding:
```
error: unused variable: `Non`
--> $DIR/binding-typo-2.rs:36:9
|
LL | Non => {}
| ^^^
|
help: if this is intentional, prefix it with an underscore
|
LL | _Non => {}
| +
help: you might have meant to pattern match on the similarly named variant `None`
|
LL - Non => {}
LL + std::prelude::v1::None => {}
|
```
Suggest constant on unused binding in a pattern
```
error: unused variable: `Batery`
--> $DIR/binding-typo-2.rs:110:9
|
LL | Batery => {}
| ^^^^^^
|
help: if this is intentional, prefix it with an underscore
|
LL | _Batery => {}
| +
help: you might have meant to pattern match on the similarly named constant `Battery`
|
LL | Battery => {}
| +
```
Fixrust-lang/rust#51976.
When encountering a typo in a pattern that gets interpreted as an unused binding, look for unit struct/variant of the same type as the binding:
```
error: unused variable: `Non`
--> $DIR/binding-typo-2.rs:36:9
|
LL | Non => {}
| ^^^
|
help: if this is intentional, prefix it with an underscore
|
LL | _Non => {}
| +
help: you might have meant to pattern match on the similarly named variant `None`
|
LL - Non => {}
LL + std::prelude::v1::None => {}
|
```
No source fixes
This PR started as a fix for a rendering bug that [got noticed in #143661](https://github.com/rust-lang/rust/pull/143661#discussion_r2199109530), but turned into a fix for any rendering bugs related to files with no source.
- Don't add an end column separator after a file with no source
- Add column separator before secondary messages with no source
- Render continuation between no source labels
Before
```
error[E0423]: expected function, tuple struct or tuple variant, found struct `std::collections::HashMap`
╭▸ $DIR/multi-suggestion.rs:17:13
│
LL │ let _ = std::collections::HashMap();
│ ━━━━━━━━━━━━━━━━━━━━━━━━━━━
╭▸ $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
│
╰ note: `std::collections::HashMap` defined here
╰╴
note: constructor is not visible here due to private fields
╭▸ $SRC_DIR/alloc/src/boxed.rs:LL:COL
│
╰ note: private field
│
╰ note: private field
```
After
```
error[E0423]: expected function, tuple struct or tuple variant, found struct `std::collections::HashMap`
╭▸ $DIR/multi-suggestion.rs:17:13
│
LL │ let _ = std::collections::HashMap();
│ ━━━━━━━━━━━━━━━━━━━━━━━━━━━
╰╴
╭▸ $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
│
╰ note: `std::collections::HashMap` defined here
note: constructor is not visible here due to private fields
╭▸ $SRC_DIR/alloc/src/boxed.rs:LL:COL
│
├ note: private field
│
╰ note: private field
```
Note: This PR also makes it so `rustc` and `annotate-snippets` match in these cases
mention lint group in default level lint note
### Summary
This PR updates lint diagnostics so that default-level notes now mention the lint group they belong to, if any.
Fixes: rust-lang/rust#65464.
### Example
```rust
fn main() {
let x = 5;
}
```
Before:
```
= note: `#[warn(unused_variables)]` on by default
```
After:
```
= note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default
```
### Unchanged Cases
Messages remain the same when the lint level is explicitly set, e.g.:
* Attribute on the lint `#[warn(unused_variables)]`:
```
note: the lint level is defined here
LL | #[warn(unused_variables)]
| ^^^^^^^^^^^^^^^^
```
* Attribute on the group `#[warn(unused)]:`:
```
= note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`
```
* CLI option `-W unused`:
```
= note: `-W unused-variables` implied by `-W unused`
= help: to override `-W unused` add `#[allow(unused_variables)]`
```
* CLI option `-W unused-variables`:
```
= note: requested on the command line with `-W unused-variables`
```
Stuart Cook