Provide suggestions through rustc_confusables annotations

[estebank]

Help with common API confusion, like asking for push when the data structure really has append.

error[E0599]: no method named `size` found for struct `Vec<{integer}>` in the current scope
  --> $DIR/rustc_confusables_std_cases.rs:17:7
   |
LL |     x.size();
   |       ^^^^
   |
help: you might have meant to use `len`
   |
LL |     x.len();
   |       ~~~
help: there is a method with a similar name
   |
LL |     x.resize();
   |       ~~~~~~

Fix #59450 (we can open subsequent tickets for specific cases).

Fix #108437:

error[E0599]: `Option<{integer}>` is not an iterator
   --> f101.rs:3:9
    |
3   |     opt.flat_map(|val| Some(val));
    |         ^^^^^^^^ `Option<{integer}>` is not an iterator
    |
   ::: /home/gh-estebank/rust/library/core/src/option.rs:571:1
    |
571 | pub enum Option<T> {
    | ------------------ doesn't satisfy `Option<{integer}>: Iterator`
    |
    = note: the following trait bounds were not satisfied:
            `Option<{integer}>: Iterator`
            which is required by `&mut Option<{integer}>: Iterator`
help: you might have meant to use `and_then`
    |
3   |     opt.and_then(|val| Some(val));
    |         ~~~~~~~~

On type error of method call arguments, look at confusables for suggestion. Fix #87212:

error[E0308]: mismatched types
    --> f101.rs:8:18
     |
8    |     stuff.append(Thing);
     |           ------ ^^^^^ expected `&mut Vec<Thing>`, found `Thing`
     |           |
     |           arguments to this method are incorrect
     |
     = note: expected mutable reference `&mut Vec<Thing>`
                           found struct `Thing`
note: method defined here
    --> /home/gh-estebank/rust/library/alloc/src/vec/mod.rs:2025:12
     |
2025 |     pub fn append(&mut self, other: &mut Self) {
     |            ^^^^^^
help: you might have meant to use `push`
     |
8    |     stuff.push(Thing);
     |           ~~~~

[rustbot]

r? @cjgillot

(rustbot has picked a reviewer for you, use r? to override)

[estebank]

r? @oli-obk

[chenyukang]

Fixes #87212

[chenyukang]

can you also add a annotation for #108437

[estebank]

@chenyukang added :)

[oli-obk]

whoops started reviewing this and got distracted. Will do another round tomorrow

[oli-obk]

@bors r+

[bors]

📌 Commit 9a950a5 has been approved by oli-obk

It is now in the queue for this repository.

[estebank]

@bors r=oli-obk

[bors]

📌 Commit 91d0b37 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 91d0b37 with merge a28d221...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing a28d221 to master...

[rust-timer]

Finished benchmarking commit (a28d221): 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)	2.9%	[0.2%, 5.6%]	2
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)	4.4%	[4.4%, 4.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

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)	2.0%	[1.6%, 2.3%]	5
Regressions ❌ (secondary)	2.5%	[1.8%, 4.2%]	14
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	2.0%	[1.6%, 2.3%]	5

Binary size

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

Bootstrap: 649.393s -> 651.286s (0.29%)
Artifact size: 310.95 MiB -> 310.96 MiB (0.00%)

[nnethercote]

For posterity: this caused a large performance regression in certain cases where errors were being emitted. I had an example involving a refactoring of rustc itself where I had hundreds of errors and each error was taking ~5 seconds to emit! Happily, #125100 fixes the problem.