Fixes https://github.com/rust-lang/rust/issues/93959
This change was accepted in https://rust-lang.github.io/rfcs/2580-ptr-meta.html
Note that this changes the signature of **stable** functions.
The change should be backward-compatible, but it is **insta-stable**
since it cannot (easily, at all?) be made available only
through a `#![feature(…)]` opt-in.
The RFC also proposed the same change for `NonNull::dangling`,
which makes sense it terms of its signature but not in terms of its implementation.
`dangling` uses `align_of()` as an address. But what `align_of()` should be for
extern types or whether it should be allowed at all remains an open question.
This commit depends on https://github.com/rust-lang/rust/pull/93977, which is not yet
part of the bootstrap compiler. So `#[cfg]` is used to only apply the change in
stage 1+. As far a I know bounds cannot be made conditional with `#[cfg]`, so the
entire functions are duplicated. This is unfortunate but temporary.
Since this duplication makes it less obvious in the diff,
the new definitions differ in:
* More permissive bounds (`Thin` instead of implied `Sized`)
* Different implementation
* Having `rustc_allow_const_fn_unstable(ptr_metadata)`
This attempts to bring better error messages to invalid method calls, by applying some heuristics to identify common mistakes.
The algorithm is inspired by Levenshtein distance and longest common sub-sequence. In essence, we treat the types of the function, and the types of the arguments you provided as two "words" and compute the edits to get from one to the other.
We then modify that algorithm to detect 4 cases:
- A function input is missing
- An extra argument was provided
- The type of an argument is straight up invalid
- Two arguments have been swapped
- A subset of the arguments have been shuffled
(We detect the last two as separate cases so that we can detect two swaps, instead of 4 parameters permuted.)
It helps to understand this argument by paying special attention to terminology: "inputs" refers to the inputs being *expected* by the function, and "arguments" refers to what has been provided at the call site.
The basic sketch of the algorithm is as follows:
- Construct a boolean grid, with a row for each argument, and a column for each input. The cell [i, j] is true if the i'th argument could satisfy the j'th input.
- If we find an argument that could satisfy no inputs, provided for an input that can't be satisfied by any other argument, we consider this an "invalid type".
- Extra arguments are those that can't satisfy any input, provided for an input that *could* be satisfied by another argument.
- Missing inputs are inputs that can't be satisfied by any argument, where the provided argument could satisfy another input
- Swapped / Permuted arguments are identified with a cycle detection algorithm.
As each issue is found, we remove the relevant inputs / arguments and check for more issues. If we find no issues, we match up any "valid" arguments, and start again.
Note that there's a lot of extra complexity:
- We try to stay efficient on the happy path, only computing the diagonal until we find a problem, and then filling in the rest of the matrix.
- Closure arguments are wrapped in a tuple and need to be unwrapped
- We need to resolve closure types after the rest, to allow the most specific type constraints
- We need to handle imported C functions that might be variadic in their inputs.
I tried to document a lot of this in comments in the code and keep the naming clear.
by using an opaque type obligation to bubble up comparisons between opaque types and other types
Also uses proper obligation causes so that the body id works, because out of some reason nll uses body ids for logic instead of just diagnostics.
suggest casting between i/u32 and char
As discussed in https://github.com/rust-lang/rust/issues/91063 , this adds a suggestion for converting between i32/u32 <-> char with `as`, and a short explanation for why this is safe
... if they use arbitrary enum discriminant. Code like
```rust
enum Enum {
Foo = 1,
Bar(),
Baz{}
}
```
seems to be unintentionally allowed so we couldn't disallow them now,
but we could disallow them if arbitrary enum discriminant is used before
1.56 hits stable.
* On suggestions that include deletions, use a diff inspired output format
* When suggesting addition, use `+` as underline
* Color highlight modified span
Use more precise span for E0282 in cast expressions
This pull request fixes#85586. The example code given there:
```rust
fn main() {
let a = [1, 2, 3].iter().sum();
let b = (a + 1) as usize;
}
```
currently produces
```
error[E0282]: type annotations needed
--> issue-85586.rs:3:13
|
3 | let b = (a + 1) as usize;
| ^^^^^^^^^^^^^^^^ cannot infer type
|
= note: type must be known at this point
error: aborting due to previous error
```
even though the type of the entire cast expression quite clearly should be `usize`. The error is in the cast's left-hand side, which is made explicit by the changes in this PR:
```
error[E0282]: type annotations needed
--> issue-85586.rs:3:13
|
3 | let b = (a + 1) as usize;
| ^^^^^^^ cannot infer type
|
= note: type must be known at this point
error: aborting due to previous error
```
Fix incorrect suggestions for E0605
Fixes#84598. Here is a simplified version of the problem presented in issue #84598:
```Rust
#![allow(unused_variables)]
#![allow(dead_code)]
trait T { fn t(&self) -> i32; }
unsafe fn foo(t: *mut dyn T) {
(t as &dyn T).t();
}
fn main() {}
```
The current output is:
```
error[E0605]: non-primitive cast: `*mut (dyn T + 'static)` as `&dyn T`
--> src/main.rs:7:5
|
7 | (t as &dyn T).t();
| ^^^^^^^^^^^^^ invalid cast
|
help: borrow the value for the cast to be valid
|
7 | (&t as &dyn T).t();
| ^
```
This is incorrect, though: The cast will _not_ be valid when writing `&t` instead of `t`:
```
error[E0277]: the trait bound `*mut (dyn T + 'static): T` is not satisfied
--> t4.rs:7:6
|
7 | (&t as &dyn T).t();
| ^^ the trait `T` is not implemented for `*mut (dyn T + 'static)`
|
= note: required for the cast to the object type `dyn T`
```
The correct suggestion is `&*t`, which I have implemented in this pull request. Of course, this suggestion will always require an unsafe block, but arguably, that's what the user really wants if they're trying to cast a pointer to a reference.
In any case, claiming that the cast will be valid after implementing the suggestion is overly optimistic, as the coercion logic doesn't seem to resolve all nested obligations, i.e. the cast may still be invalid after implementing the suggestion. I have therefore rephrased the suggestion slightly ("consider borrowing the value" instead of "borrow the value for the cast to be valid").
Additionally, I have fixed another incorrect suggestion not mentioned in #84598, which relates to casting immutable references to mutable ones:
```rust
fn main() {
let mut x = 0;
let m = &x as &mut i32;
}
```
currently leads to
```
error[E0605]: non-primitive cast: `&i32` as `&mut i32`
--> t5.rs:3:13
|
3 | let m = &x as &mut i32;
| ^^^^^^^^^^^^^^ invalid cast
|
help: borrow the value for the cast to be valid
|
3 | let m = &mut &x as &mut i32;
| ^^^^
```
which is obviously incorrect:
```
error[E0596]: cannot borrow data in a `&` reference as mutable
--> t5.rs:3:13
|
3 | let m = &mut &x as &mut i32;
| ^^^^^^^ cannot borrow as mutable
```
I've changed the suggestion to a note explaining the problem:
```
error[E0605]: non-primitive cast: `&i32` as `&mut i32`
--> t5.rs:3:13
|
3 | let m = &x as &mut i32;
| ^^^^^^^^^^^^^^ invalid cast
|
note: this reference is immutable
--> t5.rs:3:13
|
3 | let m = &x as &mut i32;
| ^^
note: trying to cast to a mutable reference type
--> t5.rs:3:19
|
3 | let m = &x as &mut i32;
| ^^^^^^^^
```
In this example, it would have been even nicer to suggest replacing `&x` with `&mut x`, but this would be much more complex because we would have to take apart the expression to be cast (currently, we only look at its type), and `&x` could be stored in a variable, where such a suggestion would not even be directly applicable:
```rust
fn main() {
let mut x = 0;
let r = &x;
let m = r as &mut i32;
}
```
My solution covers this case, too.
Deprecate the core::raw / std::raw module
It only contains the `TraitObject` struct which exposes components of wide pointer. Pointer metadata APIs are designed to replace this: https://github.com/rust-lang/rust/issues/81513
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.
- Suggest borrowing expression if it would allow cast to work.
- Suggest using `<Type>::from(<expr>)` when appropriate.
- Minor tweak to `;` typo suggestion.
Partily address #47136.
`hir::BorrowKind::Raw` borrows and casting a reference to a raw
pointer no longer do a reborrow followed by a cast. Instead we
dereference and take the address.
