Improve renaming suggestion for names with leading underscores
Fixes#125650
Before:
```
error[E0425]: cannot find value `p` in this scope
--> test.rs:2:13
|
2 | let _ = p;
| ^
|
help: a local variable with a similar name exists, consider renaming `_p` into `p`
|
1 | fn a(p: i32) {
| ~
```
After:
```
error[E0425]: cannot find value `p` in this scope
--> test.rs:2:13
|
1 | fn a(_p: i32) {
| -- `_p` defined here
2 | let _ = p;
| ^
|
help: the leading underscore in `_p` marks it as unused, consider renaming it to `p`
|
1 | fn a(p: i32) {
| ~
```
This change doesn't exactly conform to what was proposed in the issue:
1. I've kept the suggested code instead of solely replacing it with the label
2. I've removed the "...similar name exists..." message instead of relocating to the usage span
3. You could argue that it still isn't completely clear that the change is referring to the definition (not the usage), but I'm not sure how to do this without playing down the fact that the error was caused by the usage of an undefined name.
Make TLS accessors closures that return pointers
The current TLS macros generate a function that returns an `Option<&'static T>`. This is both risky as we lie about lifetimes, and necessitates that those functions are `unsafe`. By returning a `*const T` instead, the accessor function do not have safety requirements any longer and can be made closures without hassle. This PR does exactly that!
For native TLS, the closure approach makes it trivial to select the right accessor function at compile-time, which could result in a slight speed-up (I have the hope that the accessors are now simple enough for the MIR-inliner to kick in).
Do not suggest unresolvable builder methods
Fixes#125303
The issue was that when a builder method cannot be resolved we are suggesting alternatives that themselves cannot be resolved. This PR adds a check that filters them from the list of suggestions.
Remove braces when fixing a nested use tree into a single item
[Back in 2019](https://github.com/rust-lang/rust/pull/56645) I added rustfix support for the `unused_imports` lint, to automatically remove them when running `cargo fix`. For the most part this worked great, but when removing all but one childs of a nested use tree it turned `use foo::{Unused, Used}` into `use foo::{Used}`. This is slightly annoying, because it then requires you to run `rustfmt` to get `use foo::Used`.
This PR automatically removes braces and the surrouding whitespace when all but one child of a nested use tree are unused. To get it done I had to add the span of the nested use tree to the AST, and refactor a bit the code I wrote back then.
A thing I noticed is, there doesn't seem to be any `//@ run-rustfix` test for fixing the `unused_imports` lint. I created a test in `tests/suggestions` (is that the right directory?) that for now tests just what I added in the PR. I can followup in a separate PR to add more tests for fixing `unused_lints`.
This PR is best reviewed commit-by-commit.
```
error[E0499]: cannot borrow `foo` as mutable more than once at a time
--> $DIR/suggest-split-at-mut.rs:13:18
|
LL | let a = &mut foo[..2];
| --- first mutable borrow occurs here
LL | let b = &mut foo[2..];
| ^^^ second mutable borrow occurs here
LL | a[0] = 5;
| ---- first borrow later used here
|
= help: use `.split_at_mut(position)` or similar method to obtain two mutable non-overlapping sub-slices
```
Address most of #58792.
For follow up work, we should emit a structured suggestion for cases where we can identify the exact `let (a, b) = foo.split_at_mut(2);` call that is needed.
```
error[E0507]: cannot move out of `bar`, a captured variable in an `FnMut` closure
--> $DIR/borrowck-move-by-capture.rs:9:29
|
LL | let bar: Box<_> = Box::new(3);
| --- captured outer variable
LL | let _g = to_fn_mut(|| {
| -- captured by this `FnMut` closure
LL | let _h = to_fn_once(move || -> isize { *bar });
| ^^^^^^^^^^^^^^^^ ----
| | |
| | variable moved due to use in closure
| | move occurs because `bar` has type `Box<isize>`, which does not implement the `Copy` trait
| `bar` is moved here
|
help: clone the value before moving it into the closure
|
LL ~ let value = bar.clone();
LL ~ let _h = to_fn_once(move || -> isize { value });
|
```
```
error[E0382]: use of moved value: `t`
--> $DIR/use_of_moved_value_copy_suggestions.rs:7:9
|
LL | fn duplicate_t<T>(t: T) -> (T, T) {
| - move occurs because `t` has type `T`, which does not implement the `Copy` trait
...
LL | (t, t)
| - ^ value used here after move
| |
| value moved here
|
help: if `T` implemented `Clone`, you could clone the value
--> $DIR/use_of_moved_value_copy_suggestions.rs:4:16
|
LL | fn duplicate_t<T>(t: T) -> (T, T) {
| ^ consider constraining this type parameter with `Clone`
...
LL | (t, t)
| - you could clone this value
help: consider restricting type parameter `T`
|
LL | fn duplicate_t<T: Copy>(t: T) -> (T, T) {
| ++++++
```
The `help` is new. On ADTs, we also extend the output with span labels:
```
error[E0507]: cannot move out of static item `FOO`
--> $DIR/issue-17718-static-move.rs:6:14
|
LL | let _a = FOO;
| ^^^ move occurs because `FOO` has type `Foo`, which does not implement the `Copy` trait
|
note: if `Foo` implemented `Clone`, you could clone the value
--> $DIR/issue-17718-static-move.rs:1:1
|
LL | struct Foo;
| ^^^^^^^^^^ consider implementing `Clone` for this type
...
LL | let _a = FOO;
| --- you could clone this value
help: consider borrowing here
|
LL | let _a = &FOO;
| +
```
Rollup of 7 pull requests
Successful merges:
- #120929 (Wrap dyn type with parentheses in suggestion)
- #122591 (Suggest using type args directly instead of equality constraint)
- #122598 (deref patterns: lower deref patterns to MIR)
- #123048 (alloc::Layout: explicitly document size invariant on the type level)
- #123993 (Do `check_coroutine_obligations` once per typeck root)
- #124218 (Allow nesting subdiagnostics in #[derive(Subdiagnostic)])
- #124285 (Mark ``@RUSTC_BUILTIN`` search path usage as unstable)
r? `@ghost`
`@rustbot` modify labels: rollup
Suggest using type args directly instead of equality constraint
When type arguments are written erroneously using an equality constraint we suggest specifying them directly without the equality constraint.
Fixes#122162
Changes the diagnostic in the issue from:
```rust
error[E0229]: associated type bindings are not allowed here
9 | impl std::cmp::PartialEq<Rhs = T> for S {
| ^^^^^^^ associated type not allowed here
|
```
to
```rust
error[E0229]: associated type bindings are not allowed here
9 | impl std::cmp::PartialEq<Rhs = T> for S {
| ^^^^^^^ associated type not allowed here
|
help: to use `T` as a generic argument specify it directly
|
| impl std::cmp::PartialEq<T> for S {
| ~
```
Use fulfillment in method probe, not evaluation
This PR reworks method probing to use fulfillment instead of a `for`-loop of `evaluate_predicate` calls, and moves normalization from method candidate assembly into the `consider_probe`, where it's applied to *all* candidates. This last part coincidentally fixes https://github.com/rust-lang/rust/issues/121643#issuecomment-1975371248.
Regarding *why* this large rewrite is done: In general, it's an anti-pattern to do `for o in obligations { evaluate(o); }` because it's not compatible with the way that the new solver emits alias-relate obligations which constrain variables that may show up in other predicates.
r? lcnr
Detect borrow checker errors where `.clone()` would be an appropriate user action
When a value is moved twice, suggest cloning the earlier move:
```
error[E0509]: cannot move out of type `U2`, which implements the `Drop` trait
--> $DIR/union-move.rs:49:18
|
LL | move_out(x.f1_nocopy);
| ^^^^^^^^^^^
| |
| cannot move out of here
| move occurs because `x.f1_nocopy` has type `ManuallyDrop<RefCell<i32>>`, which does not implement the `Copy` trait
|
help: consider cloning the value if the performance cost is acceptable
|
LL | move_out(x.f1_nocopy.clone());
| ++++++++
```
When a value is borrowed by an `fn` call, consider if cloning the result of the call would be reasonable, and suggest cloning that, instead of the argument:
```
error[E0505]: cannot move out of `a` because it is borrowed
--> $DIR/variance-issue-20533.rs:53:14
|
LL | let a = AffineU32(1);
| - binding `a` declared here
LL | let x = bat(&a);
| -- borrow of `a` occurs here
LL | drop(a);
| ^ move out of `a` occurs here
LL | drop(x);
| - borrow later used here
|
help: consider cloning the value if the performance cost is acceptable
|
LL | let x = bat(&a).clone();
| ++++++++
```
otherwise, suggest cloning the argument:
```
error[E0505]: cannot move out of `a` because it is borrowed
--> $DIR/variance-issue-20533.rs:59:14
|
LL | let a = ClonableAffineU32(1);
| - binding `a` declared here
LL | let x = foo(&a);
| -- borrow of `a` occurs here
LL | drop(a);
| ^ move out of `a` occurs here
LL | drop(x);
| - borrow later used here
|
help: consider cloning the value if the performance cost is acceptable
|
LL - let x = foo(&a);
LL + let x = foo(a.clone());
|
```
This suggestion doesn't attempt to square out the types between what's cloned and what the `fn` expects, to allow the user to make a determination on whether to change the `fn` call or `fn` definition themselves.
Special case move errors caused by `FnOnce`:
```
error[E0382]: use of moved value: `blk`
--> $DIR/once-cant-call-twice-on-heap.rs:8:5
|
LL | fn foo<F:FnOnce()>(blk: F) {
| --- move occurs because `blk` has type `F`, which does not implement the `Copy` trait
LL | blk();
| ----- `blk` moved due to this call
LL | blk();
| ^^^ value used here after move
|
note: `FnOnce` closures can only be called once
--> $DIR/once-cant-call-twice-on-heap.rs:6:10
|
LL | fn foo<F:FnOnce()>(blk: F) {
| ^^^^^^^^ `F` is made to be an `FnOnce` closure here
LL | blk();
| ----- this value implements `FnOnce`, which causes it to be moved when called
```
Account for redundant `.clone()` calls in resulting suggestions:
```
error[E0507]: cannot move out of dereference of `S`
--> $DIR/needs-clone-through-deref.rs:15:18
|
LL | for _ in self.clone().into_iter() {}
| ^^^^^^^^^^^^ ----------- value moved due to this method call
| |
| move occurs because value has type `Vec<usize>`, which does not implement the `Copy` trait
|
note: `into_iter` takes ownership of the receiver `self`, which moves value
--> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
help: you can `clone` the value and consume it, but this might not be your desired behavior
|
LL | for _ in <Vec<usize> as Clone>::clone(&self).into_iter() {}
| ++++++++++++++++++++++++++++++ ~
```
We use the presence of `&mut` values in a move error as a proxy for the user caring about side effects, so we don't emit a clone suggestion in that case:
```
error[E0505]: cannot move out of `s` because it is borrowed
--> $DIR/borrowck-overloaded-index-move-index.rs:53:7
|
LL | let mut s = "hello".to_string();
| ----- binding `s` declared here
LL | let rs = &mut s;
| ------ borrow of `s` occurs here
...
LL | f[s] = 10;
| ^ move out of `s` occurs here
...
LL | use_mut(rs);
| -- borrow later used here
```
We properly account for `foo += foo;` errors where we *don't* suggest `foo.clone() += foo;`, instead suggesting `foo += foo.clone();`.
---
Each commit can be reviewed in isolation. There are some "cleanup" commits, but kept them separate in order to show *why* specific changes were being made, and their effect on tests' output.
Fix#49693, CC #64167.
Avoid more NonNull-raw-NonNull roundtrips in Vec
r? the8472
The standard library in general has a lot of these round-trips from niched types to their raw innards and back. Such round-trips have overhead in debug builds since https://github.com/rust-lang/rust/pull/120594. I removed some such round-trips in that initial PR and I've been meaning to come back and hunt down more such examples (this is the last item on https://github.com/rust-lang/rust/issues/120848).
Account for trait/impl difference when suggesting changing argument from ref to mut ref
Do not ICE when encountering a lifetime error involving an argument with an immutable reference of a method that differs from the trait definition.
Fix#123414.
```
error[E0507]: cannot move out of `*x` which is behind a shared reference
--> $DIR/borrowck-fn-in-const-a.rs:6:16
|
LL | return *x
| ^^ move occurs because `*x` has type `String`, which does not implement the `Copy` trait
|
help: consider cloning the value if the performance cost is acceptable
|
LL - return *x
LL + return x.clone()
|
```
Do not ICE when encountering a lifetime error involving an argument with
an immutable reference of a method that differs from the trait definition.
Fix#123414.
Note that the caller chooses a type for type param
```
error[E0308]: mismatched types
--> $DIR/return-impl-trait.rs:23:5
|
LL | fn other_bounds<T>() -> T
| - -
| | |
| | expected `T` because of return type
| | help: consider using an impl return type: `impl Trait`
| expected this type parameter
...
LL | ()
| ^^ expected type parameter `T`, found `()`
|
= note: expected type parameter `T`
found unit type `()`
= note: the caller chooses the type of T which can be different from ()
```
Tried to see if "expected this type parameter" can be replaced, but that goes all the way to `rustc_infer` so seems not worth the effort and can affect other diagnostics.
Revives #112088 and #104755.
Split an item bounds and an item's super predicates
This is the moral equivalent of #107614, but instead for predicates this applies to **item bounds**. This PR splits out the item bounds (i.e. *all* predicates that are assumed to hold for the alias) from the item *super predicates*, which are the subset of item bounds which share the same self type as the alias.
## Why?
Much like #107614, there are places in the compiler where we *only* care about super-predicates, and considering predicates that possibly don't have anything to do with the alias is problematic. This includes things like closure signature inference (which is at its core searching for `Self: Fn(..)` style bounds), but also lints like `#[must_use]`, error reporting for aliases, computing type outlives predicates.
Even in cases where considering all of the `item_bounds` doesn't lead to bugs, unnecessarily considering irrelevant bounds does lead to a regression (#121121) due to doing extra work in the solver.
## Example 1 - Trait Aliases
This is best explored via an example:
```
type TAIT<T> = impl TraitAlias<T>;
trait TraitAlias<T> = A + B where T: C;
```
The item bounds list for `Tait<T>` will include:
* `Tait<T>: A`
* `Tait<T>: B`
* `T: C`
While `item_super_predicates` query will include just the first two predicates.
Side-note: You may wonder why `T: C` is included in the item bounds for `TAIT`? This is because when we elaborate `TraitAlias<T>`, we will also elaborate all the predicates on the trait.
## Example 2 - Associated Type Bounds
```
type TAIT<T> = impl Iterator<Item: A>;
```
The `item_bounds` list for `TAIT<T>` will include:
* `Tait<T>: Iterator`
* `<Tait<T> as Iterator>::Item: A`
But the `item_super_predicates` will just include the first bound, since that's the only bound that is relevant to the *alias* itself.
## So what
This leads to some diagnostics duplication just like #107614, but none of it will be user-facing. We only see it in the UI test suite because we explicitly disable diagnostic deduplication.
Regarding naming, I went with `super_predicates` kind of arbitrarily; this can easily be changed, but I'd consider better names as long as we don't block this PR in perpetuity.
Fix bad span for explicit lifetime suggestions
Fixes#121267
Current explicit lifetime suggestions are not showing correct spans for some lifetimes - e.g. elided lifetime generic parameters;
This should be done correctly regarding elided lifetime kind like the following code
43fdd4916d/compiler/rustc_resolve/src/late/diagnostics.rs (L3015-L3044)
