WF checks on closure arguments.

[LorrensP-2158466]

Fixes #104478.

Enables WF checks on the arguments of a closure.

The now removed function ascribe_user_type_skip_wf mentioned that skipping WF was done due to backwards compatibility reasons. We should probably run a crater-check and other things, right?

r? @lcnr

[LorrensP-2158466]

I find that the error message is a bit worse now, compared to the old:

error[E0521]: borrowed data escapes outside of closure
  --> src/lib.rs:10:44
   |
10 |     let _: for<'x> fn(MyTy<&'x str>) = |x| wf(x); // FAIL
   |                                         -  ^^^^^
   |                                         |  |
   |                                         |  `x` escapes the closure body here
   |                                         |  argument requires that `'1` must outlive `'static`
   |                                         `x` is a reference that is only valid in the closure body
   |                                         has type `MyTy<&'1 str>`

[LorrensP-2158466]

This also looks wrong, is it due to the removed normalization?

[LorrensP-2158466]

I don't like the name right now, so TODO.

Also, this test, when run with current nightly, indeeds performs a use-after-free. But now we error on it, it can thus be removed to this:

use std::sync::OnceLock;

type Payload = Box<i32>;

static STORAGE: OnceLock<& ()> = OnceLock::new();

trait Store {}
impl Store for &'static Payload {}

struct MyTy<T: Store>(T);

trait IsFn {}
impl IsFn for for<'x> fn(&'x Payload) -> MyTy<&'x Payload> {}

fn bar<F: IsFn>(_: F) {}

fn main() {
    bar::<for<'a> fn(&'a Payload) -> MyTy<&'a Payload>>(|x| unsafe {
        std::mem::transmute::<&Payload, MyTy<&Payload>>(x)
    });
}

[LorrensP-2158466]

CI x86_64-gnu-tools failed with an error I don't understand:

..............................F................... (50/146)
.................................................. (100/146)
..............................................     (146/146)
======== tests/rustdoc-gui/globals.goml ========
[ERROR] line 14: The following errors happened: [Property named `"searchIndex"` doesn't exist]: for command `assert-window-property-false: {"searchIndex": null}`
    at <file:///checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc-gui/doc/test_docs/index.html?search=Foo>
======== tests/rustdoc-gui/search-result-display.goml ========
[WARNING] line 39: Delta is 0 for "x", maybe try to use `compare-elements-position` instead?

[lcnr]

@bors try

[rust-bors]

☀️ Try build successful (CI)
Build commit: 1baf923 (1baf923b9c3a455162afe43e18647f494c1a4b73, parent: 021fc25b7a48f6051bee1e1f06c7a277e4de1cc9)

[lcnr]

@craterbot check

[craterbot]

👌 Experiment pr-151510 created and queued.
🤖 Automatically detected try build 1baf923
🔍 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

[rust-bors]

☔ The latest upstream changes (presumably #151701) made this pull request unmergeable. Please resolve the merge conflicts.