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r? compiler-errors @bors r+ rollup

📌 Commit 9ff1376 has been approved by compiler-errors

It is now in the queue for this repository.

CI is red (not just spellcheck) @bors r-

oops :D

|

• help: consider restricting type parameter U with trait Fn
• |
• LL | fn foo<U: Fn() -> _>(t: U) {

The suggestion here is valid, but since the return type is unknown (-> _), the suggestion ofc won't compile. And since we use MachineApplicable for this, maybe we should skip the return value if it is an unknown type? I tried to do that (not sure if ty.has_infer() is the right way to detect _ though).

@rustbot ready

@rustbot ready

Hey errs 👋 Just wanted to ask if I should reroll? I know you have a lot of PRs assigned.

Yeah, actually now that I think of it, I don't think this is the right way of doing it. I don't think we should be creating a new trait ref just to call into the existing code for suggestions -- this probably should be integrated in a more first class way.

I'm on vacation anyways so I will reroll.

@rustbot author
r? compiler

@bors r+

📌 Commit 6f1c20d has been approved by SparrowLii

It is now in the queue for this repository.

Yeah, actually now that I think of it, I don't think this is the right way of doing it. I don't think we should be creating a new trait ref just to call into the existing code for suggestions -- this probably should be integrated in a more first class way.

I'm on vacation anyways so I will reroll.

@rustbot author r? compiler

Ah sry that didn't get this in time

@bors r-

I think that the diagnostics for that are already pretty good:

 Compiling playground v0.0.1 (/playground)
error[E0057]: this function takes 2 arguments but 1 argument was supplied
 --> src/main.rs:2:5
 |
2 | f(1)
 | ^--- argument #2 of type `u32` is missing
 |
note: callable defined here
 --> src/main.rs:1:11
 |
1 | fn foo<F: Fn(u32, u32) -> u32>(f: F) -> u32 {
 | ^^^^^^^^^^^^^^^^^^^
help: provide the argument
 |
2 | f(1, /* u32 */)
 | +++++++++++

I was specifically aiming at the use-case where the bound doesn't contain Fn already.

I think that the diagnostics for that are already pretty good:

 Compiling playground v0.0.1 (/playground)
error[E0057]: this function takes 2 arguments but 1 argument was supplied
 --> src/main.rs:2:5
 |
2 | f(1)
 | ^--- argument #2 of type `u32` is missing
 |
note: callable defined here
 --> src/main.rs:1:11
 |
1 | fn foo<F: Fn(u32, u32) -> u32>(f: F) -> u32 {
 | ^^^^^^^^^^^^^^^^^^^
help: provide the argument
 |
2 | f(1, /* u32 */)
 | +++++++++++

I was specifically aiming at the use-case where the bound doesn't contain Fn already.

We can think of suggesting F: Fn(u32) -> u32 instead of providing the argument here. However, this suggestion probably be inappropriate, as it is very likely to be a typeck error in statements where foo are called.

So maybe we can lift the suggestion of this PR to statements which calling foo and use type of the argument be provided. In this way we may avoid to make a new trait_ref

So maybe we can lift the suggestion of this PR to statements which calling foo and use type of the argument be provided. In this way we may avoid to make a new trait_ref

Sorry, I didn't understand that suggestions. Nor do I fully grok what Michael originally meant 😆 I probably don't have enough experience with this subsystem to suggest a more "first-class" solution.