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Suggest syntax when finding method on array #44970

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estebank
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@estebank estebank commented Oct 2, 2017

On a file like the following:

fn main() {
    let a = [1, 2, 3];
    let _ = [i32; 3]::clone(&a);
}

it is a fair assumption that what was meant was to use an associated
type on an array, so we suggest the correct syntax:

error: expected one of `.`, `;`, `?`, or an operator, found `::`
 --> file.rs:3:21
  |
3 |     let _ = [i32; 3]::clone(&a);
  |             --------^^
  |             |       |
  |             |       expected one of `.`, `;`, `?`, or an operator here
  |             help: did you mean to use an associated type?: `<[i32; 3]>::`

Fix #42187.

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r? @pnkfelix

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

@estebank estebank added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 2, 2017
@petrochenkov petrochenkov assigned petrochenkov and unassigned pnkfelix Oct 2, 2017
bors added a commit that referenced this pull request Oct 2, 2017
@bors
Auto merge of #44970 - estebank:associated-item, r=<try>
6a98224 
Suggest syntax when finding method on array

On a file like the following:

```rust
fn main() {
    let a = [1, 2, 3];
    let _ = [i32; 3]::clone(&a);
}
```

it is a fair assumption that what was meant was to use an associated
type on an array, so we suggest the correct syntax:

```
error: expected one of `.`, `;`, `?`, or an operator, found `::`
 --> file.rs:3:21
  |
3 |     let _ = [i32; 3]::clone(&a);
  |             --------^^
  |             |       |
  |             |       expected one of `.`, `;`, `?`, or an operator here
  |             help: did you mean to use an associated type?: `<[i32; 3]>::`
```

Fix #42187.
@rust-lang rust-lang deleted a comment from bors Oct 2, 2017
@estebank
Suggest syntax when finding method on array
ae6d470 
On a file like the following:

```rust
fn main() {
    let a = [1, 2, 3];
    let _ = [i32; 3]::clone(&a);
}
```

it is a fair assumption that what was meant was to use an associated
type on an array, so we suggest the correct syntax:

```
error: expected one of `.`, `;`, `?`, or an operator, found `::`
 --> file.rs:3:21
  |
3 |     let _ = [i32; 3]::clone(&a);
  |             --------^^
  |             |       |
  |             |       expected one of `.`, `;`, `?`, or an operator here
  |             help: did you mean to use an associated type?: `<[i32; 3]>::`
```
@estebank
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estebank commented Oct 2, 2017

r? @petrochenkov

Current error is unrelated to this PR:

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
0.04s$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Mon Oct  2 20:13:25 UTC 2017
Mon, 02 Oct 2017 20:13:25 GMT

@petrochenkov
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There's much more potential for diagnostics/recovery here than just let ... = [...]::.

I'd actually test for :: after each successfully parsed type (parse_ty_common), expression (parse_expr), and pattern (parse_pat) and then parse/recover as a qualified type/expression/pattern path respectively.
:: can never occur in those positions legally.
(There can be some false positives for expressions/patterns, but they should be rare in practice and can be fixed later.)

You can omit recovery for a start and just report extra help in those cases.
TYPE :: -> <TYPE>::, EXPR :: -> <EXPR>::, PAT :: -> <PAT>::

petrochenkov
petrochenkov reviewed Oct 3, 2017
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src/test/ui/suggestions/associated-item-from-array.stderr
| --------^^
| | |
| | expected one of `.`, `;`, `?`, or an operator here
| help: did you mean to use an associated type?: `<[i32; 3]>::`
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clone is not an associated type.
"associated item" maybe?

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bors commented Oct 8, 2017

☔ The latest upstream changes (presumably #45100) made this pull request unmergeable. Please resolve the merge conflicts.

@aidanhs aidanhs added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 12, 2017
@aidanhs
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aidanhs commented Oct 12, 2017

Hi @estebank, I can see there are some merge conflicts that need to be resolved!

@alexcrichton
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Triage again! I'm going to close this for now to help clear out the queue, but of course feel free to resubmit with a rebase!

@petrochenkov petrochenkov mentioned this pull request Dec 17, 2017
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bors added a commit that referenced this pull request Dec 17, 2017
@bors
Auto merge of #46788 - petrochenkov:assocrecov, r=estebank
dc39c31 
syntax: recovery for incorrect associated item paths like `[T; N]::clone`

cc #44970
Fixes #42187
r? @estebank
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