Add suggestion to `.to_owned()` used on `Cow` when borrowing
fixesrust-lang/rust#144792
supersedes rust-lang/rust#144925 with the review comments addressed
the tests suggested from @Kivooeo from https://github.com/rust-lang/rust/pull/144925#discussion_r2252703007 didn't work entirely, because these tests failed due to error `[E0308]` mismatched types, which actually already provides a suggestion, that actually makes the code compile:
```
$ cargo check
error[E0308]: mismatched types
--> src/main.rs:3:5
|
1 | fn test_cow_suggestion() -> String {
| ------ expected `std::string::String` because of return type
2 | let os_string = std::ffi::OsString::from("test");
3 | os_string.to_string_lossy().to_owned()
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `String`, found `Cow<'_, str>`
|
= note: expected struct `std::string::String`
found enum `std::borrow::Cow<'_, str>`
help: try using a conversion method
|
3 | os_string.to_string_lossy().to_owned().to_string()
| ++++++++++++
```
now this suggestion is of course not good or efficient code, but via clippy with `-Wclippy::nursery` lint group you can actually get to the correct code, so i don't think this is too much of an issue:
<details>
<summary>the clippy suggestions</summary>
```
$ cargo clippy -- -Wclippy::nursery
warning: this `to_owned` call clones the `Cow<'_, str>` itself and does not cause its contents to become owned
--> src/main.rs:3:5
|
3 | os_string.to_string_lossy().to_owned().to_string()
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/beta/index.html#suspicious_to_owned
= note: `#[warn(clippy::suspicious_to_owned)]` on by default
help: depending on intent, either make the `Cow` an `Owned` variant
|
3 | os_string.to_string_lossy().into_owned().to_string()
| ++
help: or clone the `Cow` itself
|
3 - os_string.to_string_lossy().to_owned().to_string()
3 + os_string.to_string_lossy().clone().to_string()
|
$ # apply first suggestion
$ cargo c -- -Wclippy::nursery
warning: redundant clone
--> src/main.rs:3:45
|
3 | os_string.to_string_lossy().into_owned().to_string()
| ^^^^^^^^^^^^ help: remove this
|
note: this value is dropped without further use
--> src/main.rs:3:5
|
3 | os_string.to_string_lossy().into_owned().to_string()
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= help: for further information visit https://rust-lang.github.io/rust-clippy/beta/index.html#redundant_clone
= note: `-W clippy::redundant-clone` implied by `-W clippy::nursery`
= help: to override `-W clippy::nursery` add `#[allow(clippy::redundant_clone)]`
```
</details>
the actual error that we are looking for is error `[E0515]`, cannot return value referencing local variable, which was only present in the original issue due to automatic type inference assuming you want to return a cloned `Cow<'_, str>`, which is of course not possible. this is why i took the original test functions and turned them into closures, where it's less obvious that it's trying to return the wrong type.
r? davidtwco
(because you reviewed the last attempt)
(also, let me know if i should squash this down to one commit and add myself as the co-contributor)
`ty::Alias` refactor
This PR changes the following alias-related types from this:
```rust
pub enum AliasTyKind {
Projection,
Inherent,
Opaque,
Free,
}
pub struct AliasTy<I: Interner> {
pub args: I::GenericArgs,
pub def_id: I::DefId,
}
pub enum TyKind<I: Interner> {
...
Alias(AliasTyKind, AliasTy<I>),
}
```
Into this:
```rust
pub enum AliasTyKind<I: Interner> {
Projection { def_id: I::DefId },
Inherent { def_id: I::DefId },
Opaque { def_id: I::DefId },
Free { def_id: I::DefId },
}
pub struct AliasTy<I: Interner> {
pub args: I::GenericArgs,
pub kind: AliasTyKind<I>,
}
pub enum TyKind<I: Interner> {
...
Alias(AliasTy<I>),
}
```
... and then does a thousand other changes to accommodate for this change everywhere.
This brings us closer to being able to have `AliasTyKind`s which don't require a `DefId` (and thus can be more easily created, etc). Although notably we depend on both `AliasTyKind -> DefId` and `DefId -> AliasTyKind` conversions in a bunch of places still.
r? lcnr
----
A lot of these changes were done either by search & replace (via `ast-grep`) or on auto pilot, so I'm not quite sure I didn't mess up somewhere, but at least tests pass...
Rollup of 3 pull requests
Successful merges:
- rust-lang/rust#154554 (emit error on `#[track_caller]` with `extern fn`)
- rust-lang/rust#154858 (Change api of formatting diagnostic attribute strings.)
- rust-lang/rust#154876 (attr parsing: make sure we pass the right target when errors could be emitted)
borrowck: Don't mention unused vars in closure outlive errors
When there is a closure arg lifetime error, the code does its best to find variables that correspond to the lifetimes involved. This commit stops mentioning arguments that are unused in closures, since they are not relevant. This removes the "red herring" of rust-lang/rust#113121.
The `user_arg_index` nomenclature can be applied more broadly, but then the diff becomes annoyingly big, so I chose not to do that.
Review each commit individually for a nicer experience.
When there is a lifetime error, the code does its best to find variables
that correspond to the lifetimes involved. This commit stops mentioning
arguments that are unused in closures, since they are not relevant.
See the diff of the blessed test to get a good clue of what that means.
Introduce #[diagnostic::on_move(message)]
cc rust-lang/rust#149862
This is a first proposal. I have deliberately kept it simpler than `diagnostic::on_unimplemented`.
Few questions/remarks:
- Do I need to move the OnMoveDirective logic into a dedicated module perhaps ? let's say into compiler/rustc_borrowck/src/diagnostics/on_move.rs
- No problems to depend on crates like `rustc_ast` from the borrowck ?
- Notes are not supported yet. While message and label are very static , in the sense that they are emitted in the same way from the same place in the borrowck, it is not the case for the notes. It would make the code more complex. But, I can add support for notes if it does make sense.
Suggestions are welcomed !
Show named lifetime in closure upvar diagnostics
Fixesrust-lang/rust#153545.
When a closure captures a variable whose type involves a named lifetime from the parent function (e.g., `'a`), the borrow checker's region renumbering creates a separate `RegionVid` for each occurrence of the erased lifetime in the closure's upvar type. These new `RegionVid`s have no `external_name`, so diagnostics fall back to synthetic names like `'1`.
This PR recovers the original lifetime name by matching the closure's upvar type against the parent function's parameter type (obtained via `liberate_late_bound_regions`). Both types have the same structure but different region representations, the parent has `ReLateParam`/`ReEarlyParam` with real names, the closure has `ReVar` from renumbering. Walking them in parallel with `for_each_free_region` lets us find which named lifetime corresponds to the anonymous `RegionVid`.
Before:
```rust
error[E0716]: temporary value dropped while borrowed
--> test.rs:11:21
|
6 | fn apply<'a>(
| -- lifetime `'1` defined here
```
After:
```rust
error[E0716]: temporary value dropped while borrowed
--> test.rs:11:21
|
6 | fn apply<'a>(
| -- lifetime `'a` defined here
```
The fix gracefully falls back to the existing `'1` naming when it can't match, nested closures, local variables (not parameters), destructuring patterns, or partial captures where the type structures diverge.
```
error[E0382]: use of moved value: `foo`
--> $DIR/as-ref-2.rs:10:14
|
LL | let foo = Some(Struct);
| --- move occurs because `foo` has type `Option<Struct>`, which does not implement the `Copy` trait
LL | let _x: Option<Struct> = foo.map(|s| bar(&s));
| ---------------- `foo` moved due to this method call
LL | let _y = foo;
| ^^^ value used here after move
|
note: `Option::<T>::map` takes ownership of the receiver `self`, which moves `foo`
--> $SRC_DIR/core/src/option.rs:LL:COL
help: consider calling `.as_ref()` to borrow the value's contents
|
LL | let _x: Option<Struct> = foo.as_ref().map(|s| bar(&s));
| +++++++++
help: consider calling `.as_mut()` to mutably borrow the value's contents
|
LL | let _x: Option<Struct> = foo.as_mut().map(|s| bar(&s));
| +++++++++
```
Unify same-span labels in move error diagnostics
Fixesrust-lang/rust#153506.
When there's a single binding in a move error, we emit "data moved here" and "move occurs because ... does not implement the Copy trait" as two separate labels on the same span. This combines them into one label via a new `TypeNoCopy::LabelMovedHere` variant.
The multi-binding case still uses separate labels + a note since they point at different spans.
cc @estebank
This might be helpful for smart pointers to explains why they aren't Copy
and what to do instead or just to let the user know that .clone() is very
cheap and can be called without a performance penalty.
It's defined in `rustc_span::source_map` which doesn't make any sense
because it has nothing to do with source maps. This commit moves it to
the crate root, a more sensible spot for something this basic.
Overhaul `ensure_ok`
The interaction of `ensure_ok` and the `return_result_from_ensure_ok` query modifier is weird and hacky. This PR cleans it up. Details in the individual commits.
r? @Zalathar
`ensure_ok` provides a special, more efficient way of calling a query
when its return value isn't needed. But there is a complication: if the
query is marked with the `return_result_from_ensure_ok` modifier, then
it will return `Result<(), ErrorGuaranteed`. This is clunky and feels
tacked on. It's annoying to have to add a modifier to a query to declare
information present in its return type, and it's confusing that queries
called via `ensure_ok` have different return types depending on the
modifier.
This commit:
- Eliminates the `return_result_from_ensure_ok` modifier. The proc macro
now looks at the return type and detects if it matches `Result<_,
ErrorGuarantee>`. If so, it adds the modifier
`returns_error_guaranteed`. (Aside: We need better terminology to
distinguish modifiers written by the user in a `query` declaration
(e.g. `cycle_delayed_bug`) from modifiers added by the proc macro
(e.g. `cycle_error_handling`.))
- Introduces `ensure_result`, which replaces the use of `ensure_ok` for
queries that return `Result<_, ErrorGuarantee>`. As a result,
`ensure_ok` can now only be used for the "ignore the return value"
case.
Two places where `ensure_ok` can be used but currently isn't. (These
queries are marked with `return_result_from_ensure_ok`, which means that
`ensure_ok` returns `Result<(), ErrorGuaranteed>`.) This is potentially
a perf win, because `ensure_ok` query calls can be faster.
Clean up the eager formatting API
For https://github.com/rust-lang/rust/issues/151366#event-22181360642
Previously eager formatting worked by throwing the arguments into a diag, formatting, then removing the args again. This is ugly so instead we now just do the formatting completely separately.
This PR has nice commits, so I recommend reviewing commit by commit.
r? @GuillaumeGomez
Suppress invalid suggestions in destructuring assignment
Fixesrust-lang/rust#152694
When destructuring assignment hits a type with `Drop`, the compiler was emitting two broken suggestions: `ref *&mut String::new()` (invalid syntax) and `.clone()` on a temporary (useless).
Root cause: the suggestion logic didn't know these bindings were synthetic from assign desugaring. The fix reuses the existing `AssignDesugar` detection in `BindingFinder` to collect those spans and skip both suggestions.
refactor(mgca): Change `DefKind::Const` and `DefKind::AssocConst` to have a `is_type_const` flag
Addresses rust-lang/rust#152940
- Changed `DefKind::Const` and `DefKind::AssocConst` to have a `is_type_const` flag.
- changed `is_type_const` query to check for this flag
- removed `is_rhs_type_const` query
r? @BoxyUwU
* refactor: add `is_type_const` flag to `DefKind::Const` and `AssocConst`
* refactor(cleanup) remove the `rhs_is_type_const` query
* style: fix formatting
* refactor: refactor stuff in librustdoc for new Const and AssocConst
* refactor: refactor clippy for the changes
* chore: formatting
* fix: fix test
* fix: fix suggestions
* Update context.rs
Co-authored-by: Boxy <rust@boxyuwu.dev>
* changed AssocKind::Const to store data about being a type const
`IntoQueryParam` is a trait that lets query callers be a bit sloppy with
the passed-in key.
- Types similar to `DefId` will be auto-converted to `DefId`. Likewise
for `LocalDefId`.
- Reference types will be auto-derefed.
The auto-conversion is genuinely useful; the auto-derefing much less so.
In practice it's only used for passing `&DefId` to queries that accept
`DefId`, which is an anti-pattern because `DefId` is marked with
`#[rustc_pass_by_value]`.
This commit removes the auto-deref impl and makes the necessary sigil
adjustments. (I generally avoid using `*` to deref manually at call
sites, preferring to deref via `&` in patterns or via `*` in match
expressions. Mostly because that way a single deref often covers
multiple call sites.)
Mark Rousskov