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Before #78430, string literals worked because `specialize_constructor`
didn't actually care too much which constructor was passed to it unless
needed. Since then, string literals are special cased and a bit hacky. I
did not anticipate patterns for the `&str` type other than string
literals, hence this bug. This makes string literals less hacky.
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Cleanup constant matching in exhaustiveness checking
This supercedes https://github.com/rust-lang/rust/pull/77390. I made the `Opaque` constructor work.
I have opened two issues https://github.com/rust-lang/rust/issues/78071 and https://github.com/rust-lang/rust/issues/78057 from the discussion we had on the previous PR. They are not regressions nor directly related to the current PR so I thought we'd deal with them separately.
I left a FIXME somewhere because I didn't know how to compare string constants for equality. There might even be some unicode things that need to happen there. In the meantime I preserved previous behavior.
EDIT: I accidentally fixed #78071
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opaque
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For example, if you had this code:
fn foo(x: i32, y: f32) -> f32 {
x * y
}
You would get this error:
error[E0277]: cannot multiply `f32` to `i32`
--> src/lib.rs:2:7
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2 | x * y
| ^ no implementation for `i32 * f32`
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= help: the trait `Mul<f32>` is not implemented for `i32`
However, that's not usually how people describe multiplication. People
usually describe multiplication like how the division error words it:
error[E0277]: cannot divide `i32` by `f32`
--> src/lib.rs:2:7
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2 | x / y
| ^ no implementation for `i32 / f32`
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= help: the trait `Div<f32>` is not implemented for `i32`
So that's what this change does. It changes this:
error[E0277]: cannot multiply `f32` to `i32`
--> src/lib.rs:2:7
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2 | x * y
| ^ no implementation for `i32 * f32`
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= help: the trait `Mul<f32>` is not implemented for `i32`
To this:
error[E0277]: cannot multiply `i32` by `f32`
--> src/lib.rs:2:7
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2 | x * y
| ^ no implementation for `i32 * f32`
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= help: the trait `Mul<f32>` is not implemented for `i32`
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Stabilize move_ref_pattern
# Implementation
- Initially the rule was added in the run-up to 1.0. The AST-based borrow checker was having difficulty correctly enforcing match expressions that combined ref and move bindings, and so it was decided to simplify forbid the combination out right.
- The move to MIR-based borrow checking made it possible to enforce the rules in a finer-grained level, but we kept the rule in place in an effort to be conservative in our changes.
- In #68376, @Centril lifted the restriction but required a feature-gate.
- This PR removes the feature-gate.
Tracking issue: #68354.
# Description
This PR is to stabilize the feature `move_ref_pattern`, which allows patterns
containing both `by-ref` and `by-move` bindings at the same time.
For example: `Foo(ref x, y)`, where `x` is `by-ref`,
and `y` is `by-move`.
The rules of moving a variable also apply here when moving *part* of a variable,
such as it can't be referenced or moved before.
If this pattern is used, it would result in *partial move*, which means that
part of the variable is moved. The variable that was partially moved from
cannot be used as a whole in this case, only the parts that are still
not moved can be used.
## Documentation
- The reference (rust-lang/reference#881)
- Rust by example (rust-lang/rust-by-example#1377)
## Tests
There are many tests, but I think one of the comperhensive ones:
- [borrowck-move-ref-pattern-pass.rs](https://github.com/Centril/rust/blob/85fbf49ce0e2274d0acf798f6e703747674feec3/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern-pass.rs)
- [borrowck-move-ref-pattern.rs](https://github.com/Centril/rust/blob/85fbf49ce0e2274d0acf798f6e703747674feec3/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern.rs)
# Examples
```rust
#[derive(PartialEq, Eq)]
struct Finished {}
#[derive(PartialEq, Eq)]
struct Processing {
status: ProcessStatus,
}
#[derive(PartialEq, Eq)]
enum ProcessStatus {
One,
Two,
Three,
}
#[derive(PartialEq, Eq)]
enum Status {
Finished(Finished),
Processing(Processing),
}
fn check_result(_url: &str) -> Status {
// fetch status from some server
Status::Processing(Processing {
status: ProcessStatus::One,
})
}
fn wait_for_result(url: &str) -> Finished {
let mut previous_status = None;
loop {
match check_result(url) {
Status::Finished(f) => return f,
Status::Processing(p) => {
match (&mut previous_status, p.status) {
(None, status) => previous_status = Some(status), // first status
(Some(previous), status) if *previous == status => {} // no change, ignore
(Some(previous), status) => { // Now it can be used
// new status
*previous = status;
}
}
}
}
}
}
```
Before, we would have used:
```rust
match (&previous_status, p.status) {
(Some(previous), status) if *previous == status => {} // no change, ignore
(_, status) => {
// new status
previous_status = Some(status);
}
}
```
Demonstrating *partial move*
```rust
fn main() {
#[derive(Debug)]
struct Person {
name: String,
age: u8,
}
let person = Person {
name: String::from("Alice"),
age: 20,
};
// `name` is moved out of person, but `age` is referenced
let Person { name, ref age } = person;
println!("The person's age is {}", age);
println!("The person's name is {}", name);
// Error! borrow of partially moved value: `person` partial move occurs
//println!("The person struct is {:?}", person);
// `person` cannot be used but `person.age` can be used as it is not moved
println!("The person's age from person struct is {}", person.age);
}
```
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the main constant
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Improve unresolved use error message
"use of undeclared type or module `foo`" doesn't mention that it could be a crate.
This error can happen when users forget to add a dependency to `Cargo.toml`, so I think it's important to mention that it could be a missing crate.
I've used a heuristic based on Rust's naming conventions. It complains about an unknown type if the ident starts with an upper-case letter, and crate or module otherwise. It seems to work very well. The expanded error help covers both an unknown type and a missing crate case.
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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.
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Fix ICEs with `@ ..` binding
This reverts #74557 and introduces an alternative fix while ensuring that #74954 is not broken.
The diagnostics are verbose though, it fixes three related issues.
cc #74954, #74539, and #74702
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propagation
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When encountering an used moved value where the previous move happened
in a `match` or `if let` pattern, suggest using `ref`. Fix #63988.
When encountering a `&mut` value that is used in multiple iterations of
a loop, suggest reborrowing it with `&mut *`. Fix #62112.
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Add some regression tests
Closes #68532
Closes #70121
Closes #71042
CC #56445
r? @matthewjasper since they (except for #71042) are related to #72362.
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This however unearthed a bug, hence the FIXME and the workaround.
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Previously, we threw away the `Span` associated with a definition's
identifier when we encoded crate metadata, causing us to lose location
and hygiene information.
We now store the identifier's `Span` in the crate metadata.
When we decode items from the metadata, we combine
the name and span back into an `Ident`.
This improves the output of several tests, which previously had messages
suppressed due to dummy spans.
This is a prerequisite for #68686, since throwing away a `Span` means
that we lose hygiene information.
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Some of the nested OR paths were being missed
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Reference issue #67311
Tests combinations of the following pattern features:
- bindings_after_at
- or_patterns
- slice_patterns
- box_patterns
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Bless tests
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Update tests
Extend to other operations
Refractor check in a separate function
Fix more tests
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Make issue references consistent
Fixes https://github.com/rust-lang/rust/issues/62976
cc https://github.com/rust-lang/rust/pull/63008
r? @varkor because you reviewed the original pr
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