Fix auto-application of associated generic functions with placeholders

[clubby789]

Fixes #101920

[rust-highfive]

r? @compiler-errors

(rust-highfive has picked a reviewer for you, use r? to override)

[clubby789]

I notice that even when the type is known and this isn't an issue (e.g)

fn main() {
        let b = Box::new("abc");
        let ptr = b.into_raw();
}

Applying the fix results in incorrect code: Box::<&str>::into_raw()
Should the fix instead transform this to Box::<&str>::into_raw(b)?

[compiler-errors]

Should the fix instead transform this to Box::<&str>::into_raw(b)?

I think so, yes.

[clubby789]

Currently working on automatically adjusting the arguments, but not sure how to handle the case of

struct GenericAssocMethod<T>(T);
impl<T> GenericAssocMethod<T> {
  fn default_hello() {}
}
let x = GenericAssocMethod(33);
x.default_hello();

Where the generic arguments can't be inferred in the GenericAssocMethod::<_>::default_hello form. Applying this or leaving it results in invalid code which causes cargo to print a bug message.

[clubby789]

I've temporarily commented out the problematic test case since this seems like incorrect behaviour from Cargo

[compiler-errors]

Can you be explicit about needing more information? If this isn't a MachineApplicable diagnostic, then it shouldn't be marked MachineApplicable I think.

[clubby789]

The case of x.default_hello() (or any case where the type can't be inferred) emits a HasPlaceholders diagnostic and suggests GenericAssocMethod::<_>::default_hello()

[compiler-errors]

Where the generic arguments can't be inferred in the GenericAssocMethod::<_>::default_hello form. Applying this or leaving it results in invalid code which causes cargo to print a bug message.

Then this suggestion should probably not be MachineApplicable, and we shouldn't have a test case that has // run-rustfix for it, but just a regular error test case for it.

[compiler-errors]

Marking this as S-waiting-on-author so it can be adjusted to make it not MachineApplicable if it doesn't actually fit the criteria for MachineApplicable, namely that it should produce code that compiles when applied.

[bors]

☔ The latest upstream changes (presumably #102306) made this pull request unmergeable. Please resolve the merge conflicts.

[clubby789]

@rustbot label -S-waiting-on-author +S-waiting-on-review

[bors]

☔ The latest upstream changes (presumably #102875) made this pull request unmergeable. Please resolve the merge conflicts.

[rustbot]

Some changes occurred in src/tools/cargo

cc @ehuss

[clubby789]

🤔 Sorry about the ping, I think I might have made a mistake while rebasing

[bors]

☔ The latest upstream changes (presumably #103310) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #103978) made this pull request unmergeable. Please resolve the merge conflicts.

[compiler-errors]

@bors r+

[compiler-errors]

Why didn't bors respond, lol

@bors r+

[bors]

📌 Commit 7df4b0b has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7df4b0b with merge 5eef9b2...

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing 5eef9b2 to master...

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing 5eef9b2 to master...

[rust-timer]

Finished benchmarking commit (5eef9b2): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.2%	[1.2%, 1.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-3.5%, -1.3%]	3
All ❌✅ (primary)	-	-	0

Cycles

This benchmark run did not return any relevant results for this metric.