improve normalization of `Pointee::Metadata`
This PR makes it so that `<Wrapper<Tail> as Pointee>::Metadata` is normalized to `<Tail as Pointee>::Metadata` if we don't know `Wrapper<Tail>: Sized`. With that, the trait solver can prove projection predicates like `<Wrapper<Tail> as Pointee>::Metadata == <Tail as Pointee>::Metadata`, which makes it possible to use the metadata APIs to cast between the tail and the wrapper:
```rust
#![feature(ptr_metadata)]
use std::ptr::{self, Pointee};
fn cast_same_meta<T: ?Sized, U: ?Sized>(ptr: *const T) -> *const U
where
T: Pointee<Metadata = <U as Pointee>::Metadata>,
{
let (thin, meta) = ptr.to_raw_parts();
ptr::from_raw_parts(thin, meta)
}
struct Wrapper<T: ?Sized>(T);
fn cast_to_wrapper<T: ?Sized>(ptr: *const T) -> *const Wrapper<T> {
cast_same_meta(ptr)
}
```
Previously, this failed to compile:
```
error[E0271]: type mismatch resolving `<Wrapper<T> as Pointee>::Metadata == <T as Pointee>::Metadata`
--> src/lib.rs:16:5
|
15 | fn cast_to_wrapper<T: ?Sized>(ptr: *const T) -> *const Wrapper<T> {
| - found this type parameter
16 | cast_same_meta(ptr)
| ^^^^^^^^^^^^^^ expected `Wrapper<T>`, found type parameter `T`
|
= note: expected associated type `<Wrapper<T> as Pointee>::Metadata`
found associated type `<T as Pointee>::Metadata`
= note: an associated type was expected, but a different one was found
```
(Yes, you can already do this with `as` casts. But using functions is so much ✨ *safer* ✨, because you can't change the metadata on accident.)
---
This PR essentially changes the built-in impls of `Pointee` from this:
```rust
// before
impl Pointee for u8 {
type Metadata = ();
}
impl Pointee for [u8] {
type Metadata = usize;
}
// ...
impl Pointee for Wrapper<u8> {
type Metadata = ();
}
impl Pointee for Wrapper<[u8]> {
type Metadata = usize;
}
// ...
// This impl is only selected if `T` is a type parameter or unnormalizable projection or opaque type.
fallback impl<T: ?Sized> Pointee for Wrapper<T>
where
Wrapper<T>: Sized
{
type Metadata = ();
}
// This impl is only selected if `T` is a type parameter or unnormalizable projection or opaque type.
fallback impl<T /*: Sized */> Pointee for T {
type Metadata = ();
}
```
to this:
```rust
// after
impl Pointee for u8 {
type Metadata = ();
}
impl Pointee for [u8] {
type Metadata = usize;
}
// ...
impl<T: ?Sized> Pointee for Wrapper<T> {
// in the old solver this will instead project to the "deep" tail directly,
// e.g. `Wrapper<Wrapper<T>>::Metadata = T::Metadata`
type Metadata = <T as Pointee>::Metadata;
}
// ...
// This impl is only selected if `T` is a type parameter or unnormalizable projection or opaque type.
fallback impl<T /*: Sized */> Pointee for T {
type Metadata = ();
}
```
Rollup of 9 pull requests
Successful merges:
- #119592 (resolve: Unload speculatively resolved crates before freezing cstore)
- #120103 (Make it so that async-fn-in-trait is compatible with a concrete future in implementation)
- #120206 (hir: Make sure all `HirId`s have corresponding HIR `Node`s)
- #120214 (match lowering: consistently lower bindings deepest-first)
- #120688 (GVN: also turn moves into copies with projections)
- #120702 (docs: also check the inline stmt during redundant link check)
- #120727 (exhaustiveness: Prefer "`0..MAX` not covered" to "`_` not covered")
- #120734 (Add `SubdiagnosticMessageOp` as a trait alias.)
- #120739 (improve pretty printing for associated items in trait objects)
r? `@ghost`
`@rustbot` modify labels: rollup
improve pretty printing for associated items in trait objects
* Don't print a binder in front of associated items, because it's not valid syntax.
* e.g. print `dyn for<'a> Trait<'a, Assoc = &'a u8>` instead of `dyn for<'a> Trait<'a, for<'a> Assoc = &'a u8>`.
* Don't print associated items that are implied by a supertrait bound.
* e.g. if we have `trait Sub: Super<Assoc = u8> {}`, then just print `dyn Sub` instead of `dyn Sub<Assoc = u8>`.
I've added the test in the first commit, so you can see the diff of the compiler output in the second commit.
Stop bailing out from compilation just because there were incoherent traits
fixes#120343
but also has a lot of "type annotations needed" fallout. Some are fixed in the second commit.
Normalize type outlives obligations in NLL for new solver
Normalize the type outlives assumptions and obligations in MIR borrowck. This should fix any of the lazy-norm-related MIR borrowck problems.
Also some cleanups from last PR:
1. Normalize obligations in a loop in lexical region resolution
2. Use `deeply_normalize_with_skipped_universes` in lexical resolution since we may have, e.g. `for<'a> Alias<'a>: 'b`.
r? lcnr
Account for non-overlapping unmet trait bounds in suggestion
When a method not found on a type parameter could have been provided by any
of multiple traits, suggest each trait individually, instead of a single
suggestion to restrict the type parameter with *all* of them.
Before:
```
error[E0599]: the method `cmp` exists for reference `&T`, but its trait bounds were not satisfied
--> $DIR/method-on-unbounded-type-param.rs:5:10
|
LL | (&a).cmp(&b)
| ^^^ method cannot be called on `&T` due to unsatisfied trait bounds
|
= note: the following trait bounds were not satisfied:
`T: Ord`
which is required by `&T: Ord`
`&T: Iterator`
which is required by `&mut &T: Iterator`
`T: Iterator`
which is required by `&mut T: Iterator`
help: consider restricting the type parameters to satisfy the trait bounds
|
LL | fn g<T>(a: T, b: T) -> std::cmp::Ordering where T: Iterator, T: Ord {
| +++++++++++++++++++++++++
```
After:
```
error[E0599]: the method `cmp` exists for reference `&T`, but its trait bounds were not satisfied
--> $DIR/method-on-unbounded-type-param.rs:5:10
|
LL | (&a).cmp(&b)
| ^^^ method cannot be called on `&T` due to unsatisfied trait bounds
|
= note: the following trait bounds were not satisfied:
`T: Ord`
which is required by `&T: Ord`
`&T: Iterator`
which is required by `&mut &T: Iterator`
`T: Iterator`
which is required by `&mut T: Iterator`
= help: items from traits can only be used if the type parameter is bounded by the trait
help: the following traits define an item `cmp`, perhaps you need to restrict type parameter `T` with one of them:
|
LL | fn g<T: Ord>(a: T, b: T) -> std::cmp::Ordering {
| +++++
LL | fn g<T: Iterator>(a: T, b: T) -> std::cmp::Ordering {
| ++++++++++
```
Fix#108428.
Follow up to #120396, only last commit is relevant.
Account for unbounded type param receiver in suggestions
When encountering
```rust
fn f<T>(a: T, b: T) -> std::cmp::Ordering {
a.cmp(&b) //~ ERROR E0599
}
```
output
```
error[E0599]: no method named `cmp` found for type parameter `T` in the current scope
--> $DIR/method-on-unbounded-type-param.rs:2:7
|
LL | fn f<T>(a: T, b: T) -> std::cmp::Ordering {
| - method `cmp` not found for this type parameter
LL | a.cmp(&b)
| ^^^ method cannot be called on `T` due to unsatisfied trait bounds
|
= help: items from traits can only be used if the type parameter is bounded by the trait
help: the following traits define an item `cmp`, perhaps you need to restrict type parameter `T` with one of them:
|
LL | fn f<T: Ord>(a: T, b: T) -> std::cmp::Ordering {
| +++++
LL | fn f<T: Iterator>(a: T, b: T) -> std::cmp::Ordering {
| ++++++++++
```
Fix#120186.
Rollup of 8 pull requests
Successful merges:
- #119759 (Add FileCheck annotations to dataflow-const-prop tests)
- #120323 (On E0277 be clearer about implicit `Sized` bounds on type params and assoc types)
- #120473 (Only suggest removal of `as_*` and `to_` conversion methods on E0308)
- #120540 (add test for try-block-in-match-arm)
- #120547 (`#![feature(inline_const_pat)]` is no longer incomplete)
- #120552 (Correctly check `never_type` feature gating)
- #120555 (put pnkfelix (me) back on the review queue.)
- #120556 (Improve the diagnostics for unused generic parameters)
r? `@ghost`
`@rustbot` modify labels: rollup
```
error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
--> f100.rs:2:33
|
2 | let _ = std::mem::size_of::<[i32]>();
| ^^^^^ doesn't have a size known at compile-time
|
= help: the trait `Sized` is not implemented for `[i32]`
note: required by an implicit `Sized` bound in `std::mem::size_of`
--> /home/gh-estebank/rust/library/core/src/mem/mod.rs:312:22
|
312 | pub const fn size_of<T>() -> usize {
| ^ required by the implicit `Sized` requirement on this bound in `size_of`
```
Fix#120178.
Provide more context on derived obligation error primary label
Expand the primary span of E0277 when the immediate unmet bound is not what the user wrote:
```
error[E0277]: the trait bound `i32: Bar` is not satisfied
--> f100.rs:6:6
|
6 | <i32 as Foo>::foo();
| ^^^ the trait `Bar` is not implemented for `i32`, which is required by `i32: Foo`
|
help: this trait has no implementations, consider adding one
--> f100.rs:2:1
|
2 | trait Bar {}
| ^^^^^^^^^
note: required for `i32` to implement `Foo`
--> f100.rs:3:14
|
3 | impl<T: Bar> Foo for T {}
| --- ^^^ ^
| |
| unsatisfied trait bound introduced here
```
Fix#40120.
Expand the primary span of E0277 when the immediate unmet bound is not what the user wrote:
```
error[E0277]: the trait bound `i32: Bar` is not satisfied
--> f100.rs:6:6
|
6 | <i32 as Foo>::foo();
| ^^^ the trait `Bar` is not implemented for `i32`, which is required by `i32: Foo`
|
help: this trait has no implementations, consider adding one
--> f100.rs:2:1
|
2 | trait Bar {}
| ^^^^^^^^^
note: required for `i32` to implement `Foo`
--> f100.rs:3:14
|
3 | impl<T: Bar> Foo for T {}
| --- ^^^ ^
| |
| unsatisfied trait bound introduced here
```
Fix#40120.
When a method not found on a type parameter could have been provided by any
of multiple traits, suggest each trait individually, instead of a single
suggestion to restrict the type parameter with *all* of them.
Before:
```
error[E0599]: the method `cmp` exists for reference `&T`, but its trait bounds were not satisfied
--> $DIR/method-on-unbounded-type-param.rs:5:10
|
LL | (&a).cmp(&b)
| ^^^ method cannot be called on `&T` due to unsatisfied trait bounds
|
= note: the following trait bounds were not satisfied:
`T: Ord`
which is required by `&T: Ord`
`&T: Iterator`
which is required by `&mut &T: Iterator`
`T: Iterator`
which is required by `&mut T: Iterator`
help: consider restricting the type parameters to satisfy the trait bounds
|
LL | fn g<T>(a: T, b: T) -> std::cmp::Ordering where T: Iterator, T: Ord {
| +++++++++++++++++++++++++
```
After:
```
error[E0599]: the method `cmp` exists for reference `&T`, but its trait bounds were not satisfied
--> $DIR/method-on-unbounded-type-param.rs:5:10
|
LL | (&a).cmp(&b)
| ^^^ method cannot be called on `&T` due to unsatisfied trait bounds
|
= note: the following trait bounds were not satisfied:
`T: Ord`
which is required by `&T: Ord`
`&T: Iterator`
which is required by `&mut &T: Iterator`
`T: Iterator`
which is required by `&mut T: Iterator`
= help: items from traits can only be used if the type parameter is bounded by the trait
help: the following traits define an item `cmp`, perhaps you need to restrict type parameter `T` with one of them:
|
LL | fn g<T: Ord>(a: T, b: T) -> std::cmp::Ordering {
| +++++
LL | fn g<T: Iterator>(a: T, b: T) -> std::cmp::Ordering {
| ++++++++++
```
Fix#108428.
Normalize region obligation in lexical region resolution with next-gen solver
This normalizes region obligations when we `resolve_regions`, since they may be unnormalized with deferred projection equality.
It's pretty hard to add tests that exercise this without also triggering MIR borrowck errors (because we don't normalize there yet). I've added one test with two revisions that should test that we both 1. normalize region obligations in the param env, and 2. normalize registered region obligations during lexical region resolution.
When encountering
```rust
fn f<T>(a: T, b: T) -> std::cmp::Ordering {
a.cmp(&b) //~ ERROR E0599
}
```
output
```
error[E0599]: no method named `cmp` found for type parameter `T` in the current scope
--> $DIR/method-on-unbounded-type-param.rs:2:7
|
LL | fn f<T>(a: T, b: T) -> std::cmp::Ordering {
| - method `cmp` not found for this type parameter
LL | a.cmp(&b)
| ^^^ method cannot be called on `T` due to unsatisfied trait bounds
|
= help: items from traits can only be used if the type parameter is bounded by the trait
help: the following traits define an item `cmp`, perhaps you need to restrict type parameter `T` with one of them:
|
LL | fn f<T: Ord>(a: T, b: T) -> std::cmp::Ordering {
| +++++
LL | fn f<T: Iterator>(a: T, b: T) -> std::cmp::Ordering {
| ++++++++++
```
Fix#120186.
Remove some unnecessary check logic for lang items in HIR typeck
Obvious bugs with `#[no_core]` do not deserve customized recovery logic, since they are bugs we do not expect users to ever encounter, and if users are experimenting with `#[no_core]`, they should really be familiar with the compiler implementation.
These error recoveries are implemented now only where issues have been reported in the past, rather than systematically validating lang items.
See https://github.com/rust-lang/compiler-team/issues/620
> In particular, one-off fixes for particular assumptions about lang items or intrinsics that introduce additional complexity into the compiler are not accepted.
r? Nilstrieb
Deduplicate more sized errors on call exprs
Change the implicit `Sized` `Obligation` `Span` for call expressions to include the whole expression. This aids the existing deduplication machinery to reduce the number of errors caused by a single unsized expression.
only assemble alias bound candidates for rigid aliases
fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/77
This also causes `<Wrapper<?0> as Trait>::Unwrap: Trait` to always be ambig, as we now normalize the self type before checking whether it is an inference variable.
I cannot think of an approach to the underlying issues here which does not require the "may-define means must-define" restriction for opaque types. Going to go ahead with this and added this restriction to the tracking issue for the new solver to make sure we don't stabilize it without getting types + lang signoff here.
r? `@compiler-errors`
The test was using an internal feature which doesn't really matter, but
more importantly, we're now fatally exiting after the duplicate lang
item, so this tests nothing.
Do not attempt to provide an accurate suggestion for `impl Trait`
in bare trait types when linting. Instead, only do the object
safety check when an E0782 is already going to be emitted in the
2021 edition.
Fix#120241.
