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Better Diagnostics When Using Wrong Brackets to Create an Array #87672

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Hpmason opened this issue Jul 31, 2021 · 1 comment · Fixed by #87830
Closed

Better Diagnostics When Using Wrong Brackets to Create an Array #87672

Hpmason opened this issue Jul 31, 2021 · 1 comment · Fixed by #87830
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@hkmatsumoto
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A-diagnostics Area: Messages for errors, warnings, and lints C-enhancement Category: An issue proposing an enhancement or a PR with one. D-newcomer-roadblock Diagnostics: Confusing error or lint; hard to understand for new users. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@Hpmason
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Hpmason commented Jul 31, 2021 •
edited by rustbot
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I ended up spending way too much time debugging the following error, since I was trying to port some C code to rust.

const ARR: [u8; 3] = {
    1, 2, 3
}

Give the error:

error: expected one of `.`, `;`, `?`, `}`, or an operator, found `,`
 --> src/lib.rs:2:6
  |
2 |     1, 2, 3,
  |      ^ expected one of `.`, `;`, `?`, `}`, or an operator

error: aborting due to previous error

error: could not compile `playground`

The error message is very vague and hard to determine the actual error here.
Seeing as though some programming languages like Java and C use {} for arrays, I think it'd make sense for the compiler to suggest using [] if the user is trying to create an array.
@inquisitivecrystal inquisitivecrystal added A-diagnostics Area: Messages for errors, warnings, and lints D-newcomer-roadblock Diagnostics: Confusing error or lint; hard to understand for new users. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. C-enhancement Category: An issue proposing an enhancement or a PR with one. labels Jul 31, 2021
@hkmatsumoto
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I suppose adding manual diagnostic somewhere around rustc_parse::parse::parse_block_expr will get the job done.
@rustbot claim

@hkmatsumoto hkmatsumoto mentioned this issue Aug 6, 2021
Merged
bors added a commit to rust-lang-ci/rust that referenced this issue Sep 21, 2021
@bors
Auto merge of rust-lang#87830 - hkmatsumoto:suggest-brackets-for-arra…
e7958d3 
…y-esque-block-expr, r=estebank

Suggest replacing braces for brackets on array-esque invalid block expr

Newcomers may write `{1, 2, 3}` for making arrays, and the current error message is not informative enough to quickly convince them what is needed to fix the error.

This PR implements a diagnostic for this case, and its output looks like this:
```text
error: this code is interpreted as a block expression, not an array
 --> src/lib.rs:1:22
  |
1 |   const FOO: [u8; 3] = {
  |  ______________________^
2 | |     1, 2, 3
3 | | };
  | |_^
  |
  = note: to define an array, one would use square brackets instead of curly braces
help: try using [] instead of {}
  |
1 | const FOO: [u8; 3] = [
2 |     1, 2, 3
3 | ];
  |
```

Fix rust-lang#87672
@bors bors closed this as completed in 21eff8f Sep 21, 2021
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A-diagnostics Area: Messages for errors, warnings, and lints C-enhancement Category: An issue proposing an enhancement or a PR with one. D-newcomer-roadblock Diagnostics: Confusing error or lint; hard to understand for new users. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Suggest replacing braces for brackets on array-esque invalid block expr hkmatsumoto/rust
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@Hpmason @inquisitivecrystal @hkmatsumoto