Rollup merge of #69456 - contrun:fix-misleading-compiler-error, r=estebank

fix misleading type annotation diagonstics

This solves the method call part of issue https://github.com/rust-lang/rust/issues/69455
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Dylan DPC 2020-04-25 01:35:53 +02:00 committed by GitHub
commit 2e2080dee6
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3 changed files with 99 additions and 6 deletions

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// Regression test for #69455: projection predicate was not satisfied.
// Compiler should indicate the correct location of the
// unsatisfied projection predicate
pub trait Test<Rhs = Self> {
type Output;
fn test(self, rhs: Rhs) -> Self::Output;
}
impl Test<u32> for u64 {
type Output = u64;
fn test(self, other: u32) -> u64 {
self + (other as u64)
}
}
impl Test<u64> for u64 {
type Output = u64;
fn test(self, other: u64) -> u64 {
(self + other) as u64
}
}
fn main() {
let xs: Vec<u64> = vec![1, 2, 3];
println!("{}", 23u64.test(xs.iter().sum())); //~ ERROR: type annotations needed [E0284]
}

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error[E0284]: type annotations needed
--> $DIR/issue-69455.rs:29:26
|
LL | type Output;
| ------------ `<Self as Test<Rhs>>::Output` defined here
...
LL | println!("{}", 23u64.test(xs.iter().sum()));
| ------^^^^-----------------
| | |
| | cannot infer type for type `u64`
| this method call resolves to `<Self as Test<Rhs>>::Output`
|
= note: cannot satisfy `<u64 as Test<_>>::Output == _`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0284`.