Use heuristics to recover parsing of missing `;` #65640

estebank · 2019-10-20T21:48:14Z

Detect , and : typos where ; was intended.
When the next token could have been the start of a new statement,
detect a missing semicolon.

Fix #48160, fix #44767 (after adding note about statements).

rust-highfive · 2019-10-20T21:48:18Z

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

estebank · 2019-10-20T21:49:32Z

Still needs a bit of a clean up, but the idea is to detect some common typos that can occur during development and the lack of a semicolon, which is also quite common when writing code.

src/libsyntax/parse/parser/diagnostics.rs

src/libsyntax/parse/token.rs

src/libsyntax/parse/parser/diagnostics.rs

src/libsyntax/parse/parser/item.rs

RalfJung · 2019-10-22T19:19:43Z

Could not resolve host: rust-lang-ci-mirrors.s3-us-west-1.amazonaws.com

@bors retry

estebank · 2019-10-24T00:26:21Z

r? @Centril

src/libsyntax/parse/parser/diagnostics.rs

Centril · 2019-10-24T00:45:37Z

src/libsyntax/parse/parser/diagnostics.rs

-                // When the spans are in the same line, it means that the only content
-                // between them is whitespace, point only at the found token.
-                err.span_label(sp, label_exp);
+        if !sm.is_multiline(prev_sp.until(sp)) {


The logic here seems very similar to the case in my comment above -- a refactoring opportunity?

src/libsyntax/parse/parser/diagnostics.rs

estebank · 2019-10-25T23:55:48Z

src/test/ui/parser/recover-missing-semi.stderr

 LL |     let _ = 3;
-   |     ^^^
+   |     --- unexpected token


I like the look of this error, but it is slightly misleading because it could have been any of the other expected tokens, but given it was followed by a "token capable of starting statement", I feel comfortable to ignore the other possibilities. What do you think?

Seems reasonable as a heuristic. You could optionally add a note below for the additional expected tokens. I'll leave that up to you.

JeanMertz · 2019-10-26T06:12:30Z

src/test/ui/macros/issue-54441.stderr

  --> $DIR/issue-54441.rs:3:9
   |
 LL |         let
-   |         ^^^ unexpected token
+   |         ^^^ expected one of `crate`, `fn`, `pub`, `static`, or `type` here


In the change above this one the word here is removed in this PR (“ ^^ expected fn here”), while it is still present in this change.

Is that as intended?

Updated these as well, but they affect a huge amount of tests, I'll leave it as a separate PR.

Centril · 2019-10-26T06:36:54Z

r=me with or without the additional note and "here".

- Detect `,` and `:` typos where `;` was intended. - When the next token could have been the start of a new statement, detect a missing semicolon.

estebank · 2019-10-28T18:11:17Z

@bors r=Centril

bors · 2019-10-28T18:11:18Z

📌 Commit e8016c2 has been approved by Centril

…ntril Use heuristics to recover parsing of missing `;` - Detect `,` and `:` typos where `;` was intended. - When the next token could have been the start of a new statement, detect a missing semicolon. Fix rust-lang#48160, fix rust-lang#44767 (after adding note about statements).

@ghost

Rollup of 9 pull requests Successful merges: - #65563 (Add long error explanation for E0587) - #65640 (Use heuristics to recover parsing of missing `;`) - #65643 (Correct handling of type flags with `ConstValue::Placeholder`) - #65825 (rustc: use IndexVec<DefIndex, T> instead of Vec<T>.) - #65858 (suggest `const_in_array_repeat_expression` flag) - #65877 (doc: introduce `once` in `iter::chain` document) - #65887 (doc: mention `get(_mut)` in Vec) - #65891 (self-profiling: Record something more useful for crate metadata generation event.) - #65893 (Output previous stable error messaging when using stable build.) Failed merges: r? @ghost

bors · 2019-10-29T00:37:18Z

☔ The latest upstream changes (presumably #65907) made this pull request unmergeable. Please resolve the merge conflicts.

rust-highfive assigned petrochenkov Oct 20, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 20, 2019