Check normalized call signature for WF in mir typeck

[compiler-errors]

Unfortunately we don't check that the built-in implementations for Fn* traits are actually well-formed in the same way that we do for user-provided impls.

Essentially, when checking a call terminator, we end up with a signature that references an unnormalized <[closure] as FnOnce<...>>::Output in its output. That output type, due to the built-in impl, doesn't follow the expected rule that WF(ty) implies WF(normalized(ty)). We fix this by also checking the normalized signature here.

See boxy's detailed and useful explanation comment which explains this in more detail: #114936 (comment)

Fixes #114936
Fixes #118876

r? types
cc @BoxyUwU @lcnr

[lcnr]

nit: do we want to only emit those in case normalization actually changed the arg/ret ty

[lcnr]

r=me after crater and types FCP

@bors try

[bors]

⌛ Trying commit dd748cb with merge 8bdbfd4...

[bors]

☀️ Try build successful - checks-actions
Build commit: 8bdbfd4 (8bdbfd41bed26c4938a9f14bd20556eac1de8437)

[lcnr]

@craterbot check

[lcnr]

@craterbot ping

[compiler-errors]

@craterbot check

[craterbot]

🚨 Error: missing start toolchain

🆘 If you have any trouble with Crater please ping @rust-lang/infra!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[compiler-errors]

@craterbot check start=master#27d8a577138c0d319a572cd1a464c2b755e577de end=try#8bdbfd41bed26c4938a9f14bd20556eac1de8437

[craterbot]

👌 Experiment pr-118882 created and queued.
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🚧 Experiment pr-118882 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-118882 is completed!
📊 54 regressed and 3 fixed (399389 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[compiler-errors]

Regression:

use std::iter::FromIterator;

struct Foo;

impl<'a, U: Clone> FromIterator<&'a U> for Foo {
    fn from_iter<T: IntoIterator<Item = &'a U>>(iter: T) -> Self { 
        for x in iter {}

        Foo
     }
}

fn main() {}

error[E0309]: the parameter type `U` may not live long enough
 --> /home/gh-compiler-errors/test.rs:7:18
  |
5 | impl<'a, U: Clone> FromIterator<&'a U> for Foo {
  |      -- the parameter type `U` must be valid for the lifetime `'a` as defined here...
6 |     fn from_iter<T: IntoIterator<Item = &'a U>>(iter: T) -> Self { 
7 |         for x in iter {}
  |                  ^^^^ ...so that the type `U` will meet its required lifetime bounds
  |
help: consider adding an explicit lifetime bound
  |
5 | impl<'a, U: Clone + 'a> FromIterator<&'a U> for Foo {
  |                   ++++

[aliemjay]

Regression:

fixed by #104098?

[compiler-errors]

@aliemjay: Yes it looks clear that the PR would fix it!

[lcnr]

marking as blocked on #104098 then

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[lcnr]

r=me after fixing CI

[compiler-errors]

@bors r=lcnr

[bors]

📌 Commit 2b4a2b9 has been approved by lcnr

It is now in the queue for this repository.

[alexcrichton]

I've opened #124984 which cargo bisect-rustc points to this PR as the cause of the regression so wanted to flag it here as well.