Handle `impl Trait` where `Trait` has an assoc type with missing bounds
When encountering a type parameter that needs more bounds the trivial case is `T` `where T: Bound`, but it can also be an `impl Trait` param that needs to be decomposed to a type param for cleaner code. For example, given
```rust
fn foo(constraints: impl Iterator) {
for constraint in constraints {
println!("{:?}", constraint);
}
}
```
the previous output was
```
error[E0277]: `<impl Iterator as std::iter::Iterator>::Item` doesn't implement `std::fmt::Debug`
--> src/main.rs:3:26
|
1 | fn foo(constraints: impl Iterator) {
| - help: consider further restricting the associated type: `where <impl Iterator as std::iter::Iterator>::Item: std::fmt::Debug`
2 | for constraint in constraints {
3 | println!("{:?}", constraint);
| ^^^^^^^^^^ `<impl Iterator as std::iter::Iterator>::Item` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
|
= help: the trait `std::fmt::Debug` is not implemented for `<impl Iterator as std::iter::Iterator>::Item`
= note: required by `std::fmt::Debug::fmt`
```
which is incorrect as `where <impl Iterator as std::iter::Iterator>::Item: std::fmt::Debug` is not valid syntax nor would it restrict the positional `impl Iterator` parameter if it were.
The output being introduced is
```
error[E0277]: `<impl Iterator as std::iter::Iterator>::Item` doesn't implement `std::fmt::Debug`
--> src/main.rs:3:26
|
3 | println!("{:?}", constraint);
| ^^^^^^^^^^ `<impl Iterator as std::iter::Iterator>::Item` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
|
= help: the trait `std::fmt::Debug` is not implemented for `<impl Iterator as std::iter::Iterator>::Item`
= note: required by `std::fmt::Debug::fmt`
help: introduce a type parameter with a trait bound instead of using `impl Trait`
|
LL | fn foo<T: Iterator>(constraints: T) where <T as std::iter::Iterator>::Item: std::fmt::Debug {
| ^^^^^^^^^^^^^ ^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
This suggestion is correct and lead the user in the right direction: because you have an associated type restriction you can no longer use `impl Trait`, the only reasonable alternative is to introduce a named type parameter, bound by `Trait` and with a `where` binding on the associated type for the new type parameter `as Trait` for the missing bound.
*Ideally*, we would want to suggest something like the following, but that is not valid syntax today
```
error[E0277]: `<impl Iterator as std::iter::Iterator>::Item` doesn't implement `std::fmt::Debug`
--> src/main.rs:3:26
|
3 | println!("{:?}", constraint);
| ^^^^^^^^^^ `<impl Iterator as std::iter::Iterator>::Item` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
|
= help: the trait `std::fmt::Debug` is not implemented for `<impl Iterator as std::iter::Iterator>::Item`
= note: required by `std::fmt::Debug::fmt`
help: introduce a type parameter with a trait bound instead of using `impl Trait`
|
LL | fn foo(constraints: impl Iterator<Item: std::fmt::Debug>) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
Fix#69638.
The compiler normalizes source when reading files initially (removes BOMs, etc), but not when loading external sources.
Fixes#70874 by normalizing when loading external sources too. Adds a test to verify normalization.
rustc: Add a warning count upon completion
This adds a `build completed with one warning/x warnings` message, similar to the already present `aborted due to previous error` message.
x.py sets it unconditionally, so want it for plain "cargo build".
We need to load one of the panic runtimes that is in src (vs. pre-built in the
compiler's sysroot) to ensure that we don't load libpanic_unwind from the
sysroot. That would lead to a load of libcore, also from the sysroot, and create
lots of errors about duplicate lang items.
The code was broken because it printed "llvm-config" instead of the
absolute path to the llvm-config executable, causing Cargo to always
rebuild librustc_llvm if using system LLVM.
Also, it's not the build system's job to rebuild when a system library
changes, so we simply don't emit "rerun-if-changed" if a path to LLVM
was not explicitly provided.
Rollup of 5 pull requests
Successful merges:
- #70644 (Clean up `ModuleConfig` initialization)
- #70937 (Fix staticlib name for *-pc-windows-gnu targets)
- #70996 (Add or_insert_with_key to Entry of HashMap/BTreeMap)
- #71020 (Store UNICODE_VERSION as a tuple)
- #71021 (Use write!-style syntax for MIR assert terminator)
Failed merges:
r? @ghost
Store UNICODE_VERSION as a tuple
Remove the UnicodeVersion struct containing
major, minor and update fields and replace it with
a 3-tuple containing the version number.
As the value of each field is limited to 255
use u8 to store them.
Add or_insert_with_key to Entry of HashMap/BTreeMap
Going along with `or_insert_with`, `or_insert_with_key` provides the `Entry`'s key to the lambda, avoiding the need to either clone the key or the need to reimplement this body of this method from scratch each time.
This is useful when the initial value for a map entry is derived from the key. For example, the introductory Rust book has an example Cacher struct that takes an expensive-to-compute lambda and then can, given an argument to the lambda, produce either the cached result or execute the lambda.
---
I'm fairly new to Rust, so any optimizations, corrections to types, better names, better documentation, or whatever else would be appreciated. I'd like to thank Arnavion on freenode for helping me to implement a very similar method when I found that `or_insert_with_key` was unavailable.
As a somewhat-related note, this implements https://github.com/rust-lang/rfcs/issues/1202 from 2015, so if this pull request is accepted, that should be closed.
Rollup of 5 pull requests
Successful merges:
- #69573 (tests encoding current behavior for various cases of "binding" to _.)
- #70881 (bootstrap: work around "unused attribute" errors in incremental stdlib rebuilds.)
- #70957 (Normalize MIR locals' types for generator layout computation.)
- #70962 (added machine hooks to track deallocations)
- #70982 (Normalize function signature in function casting check procedure)
Failed merges:
r? @ghost
Remove the UnicodeVersion struct containing
major, minor and update fields and replace it with
a 3-tuple containing the version number.
As the value of each field is limited to 255
use u8 to store them.
tests encoding current behavior for various cases of "binding" to _.
The `_` binding form is special, in that it encodes a "no-op": nothing is actually bound, and thus nothing is moved or borrowed in this scenario. Usually we do the "right" thing in all such cases. The exceptions are explicitly pointed out in this test case, so that we keep track of whether they are eventually fixed.
Cc #53114.
(This does not close the aforementioned issue; it just adds the tests encoding the current behavior, which we hope to eventually fix.)
Normalize function signature in function casting check procedure
Fixes#54094
```rust
trait Zoo {
type X;
}
impl Zoo for u16 {
type X = usize;
}
fn foo(abc: <u16 as Zoo>::X) {}
fn main() {
let x: *const u8 = foo as _;
}
```
Currently a `FnDef` need to be checked if it's able to cast to `FnPtr` before it is actually casted. But the signature of `FnPtr` target's associated types are not normalized:
96d77f0e5f/src/librustc_typeck/check/cast.rs (L536-L553)
However, during the coercion check, the signature of `FnPtr` target's associated types are normalized (The `<u16 as Zoo>::X` turns into `usize`).
96d77f0e5f/src/librustc_typeck/check/coercion.rs (L687-L729)
This inconsistency leads to the error:`Err(Sorts(ExpectedFound { expected: <u16 as Zoo>::X, found: usize }))`.
