Remove manual WF hack

[compiler-errors]

We do not need this hack anymore since we fixed the candidate selection problems with Sized bounds. We prefer built-in sized bounds now since #138176, which fixes the only regression this hack was intended to fix.

While this theoretically is broken for some code, for example, when there a param-env bound that shadows an impl or built-in trait, we don't see it in practice and IMO it's not worth the burden of having to maintain this wart in compare_method_predicate_entailment.

The code that regresses is, for example:

trait Bar<'a> {}

trait Foo<'a, T> {
    fn method(&self)
    where
        Self: Bar<'a>;
}

struct W<'a, T>(&'a T)
where
    Self: Bar<'a>;

impl<'a, 'b, T> Bar<'a> for W<'b, T> {}

impl<'a, 'b, T> Foo<'a, T> for W<'b, T> {
    fn method(&self) {}
}

Specifically, I don't believe this is really going to be encountered in practice. For this to fail, there must be a where clause in the trait method that would shadow an impl or built-in (non-Sized) candidate in the trait, and this shadowing would need to be encountered when solving a nested WF goal from the impl self type.

See #108544 for the original regression. Crater run is clean!

r? lcnr

[compiler-errors]

@bors try

[bors]

⌛ Trying commit 1b99dca with merge fc545c6...

[bors]

☀️ Try build successful - checks-actions
Build commit: fc545c6 (fc545c6b951a304df08b327c158f92678582f435)

[lcnr]

@craterbot check

[craterbot]

👌 Experiment pr-140557 created and queued.
🤖 Automatically detected try build fc545c6
🔍 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-140557 is now running

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

[craterbot]

🚨 Report generation of pr-140557 failed: timed out waiting for connection
🛠️ If the error is fixed use the retry-report command.

🆘 Can someone from the infra team check in on this? @rust-lang/infra
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[lcnr]

@craterbot retry-report

[craterbot]

🛠️ Generation of the report for pr-140557 queued again.

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

[craterbot]

🚨 Report generation of pr-140557 failed: timed out waiting for connection
🛠️ If the error is fixed use the retry-report command.

🆘 Can someone from the infra team check in on this? @rust-lang/infra
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[compiler-errors]

@craterbot retry-report

[craterbot]

🛠️ Generation of the report for pr-140557 queued again.

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

[craterbot]

🚨 Report generation of pr-140557 failed: timed out waiting for connection
🛠️ If the error is fixed use the retry-report command.

🆘 Can someone from the infra team check in on this? @rust-lang/infra
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[compiler-errors]

@craterbot retry-report

[craterbot]

🛠️ Generation of the report for pr-140557 queued again.

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

[craterbot]

🎉 Experiment pr-140557 is completed!
📊 4 regressed and 5 fixed (624228 total)
📰 Open the full report.

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

[compiler-errors]

@craterbot check crates=https://gist.githubusercontent.com/compiler-errors/33c51a36d7aaf1d5b389ba0fd34fe3f6/raw/d01a01565c5a82de036882968100d90b0c77dd38/regressed-plus-unknowns.txt

[craterbot]

👌 Experiment pr-140557-1 created and queued.
🤖 Automatically detected try build fc545c6
🔍 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-140557-1 is now running

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

[craterbot]

🎉 Experiment pr-140557-1 is completed!
📊 0 regressed and 0 fixed (2599 total)
📰 Open the full report.

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

[compiler-errors]

@rfcbot fcp merge

[rfcbot]

Team member @compiler-errors has proposed to merge this. The next step is review by the rest of the tagged team members:

• @BoxyUwU
• @compiler-errors
• @jackh726
• @lcnr
• @nikomatsakis
• @oli-obk
• @spastorino

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[lcnr]

I am in favor of reverting this hack and we can easily revert it if we encounter a new regression. I think maintaining such warts long time is bound to cause issues at some point.

@rfcbot reviewed

[oli-obk]

yay hack gone