Issue #50974 : Suboptimal error in case of duplicate `,` in struct constructor #51184

lambtowolf · 2018-05-29T19:52:48Z

rust-highfive · 2018-05-29T19:52:58Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nikomatsakis (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

estebank · 2018-05-29T21:36:34Z

src/libsyntax/parse/parser.rs

@@ -767,6 +767,9 @@ impl<'a> Parser<'a> {
            err.span_label(self.span, format!("expected identifier, found {}", token_descr));
        } else {
            err.span_label(self.span, "expected identifier");
+            if self.token == token::Comma {
+                err.span_suggestion(self.span, "remove this comma", ",".into());


The third argument here should be an empty string. This will change the output to help: remove this comma.

estebank · 2018-05-29T21:46:22Z

src/libsyntax/parse/parser.rs

@@ -767,6 +767,9 @@ impl<'a> Parser<'a> {
            err.span_label(self.span, format!("expected identifier, found {}", token_descr));
        } else {
            err.span_label(self.span, "expected identifier");
+            if self.token == token::Comma {


I'm not sure this is the best thing to do, as is. I would only add this suggestion if the next token is indeed an ident:

if self.token == token::Comma && self.look_ahead(1, |t| *t.is_ident()) {

I think it will still be useful even if the next token is not an identifier. We should not ever have 2 commas in a row in a struct constructor.

struct Bar { a: u8, b: u8 } let foo = Bar { a: 42, b: 42,, };

In this example, the user still has to remove the duplicate comma to get his code to compile.

nikomatsakis · 2018-05-29T21:49:53Z

src/libsyntax/parse/parser.rs

-                    self.recover_stmt();
-                    break;
+
+                    if self.token != token::Comma {


This confuses me a bit — when does this , token get dropped, if not by recover_stmt?

It gets dropped afterwards at line 2541 :

self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)])

Should I add a comment to clarify this?

Ah, I see now. Yes, put a comment if you don't mind.

nikomatsakis · 2018-05-31T16:21:46Z

@lambtowolf think you can add that explanatory comment? =)

nikomatsakis · 2018-06-05T17:05:58Z

@bors r+

bors · 2018-06-05T17:05:59Z

📌 Commit 01559fb has been approved by nikomatsakis

Issue rust-lang#50974 : Suboptimal error in case of duplicate `,` in struct constructor Fixes rust-lang#50974

bors · 2018-06-06T05:30:12Z

🔒 Merge conflict

nikomatsakis · 2018-06-06T20:43:59Z

@lambtowolf Needs rebase 😿

pietroalbini · 2018-06-08T16:11:08Z

@lambtowolf you should rebase on master, even if you don't see any conflict at first glance.

pietroalbini · 2018-06-18T08:54:12Z

Ping from triage @lambtowolf! It's been a while since we heard from you, will you have time to work on this again?

bors · 2018-06-21T06:12:09Z

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

git checkout master (switch to your branch)
git fetch upstream master (retrieve the latest master)
git rebase upstream/master -p (rebase on top of it)
Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
git push self master --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

Auto-merging src/libsyntax/parse/parser.rs
CONFLICT (file/directory): There is a directory with name src/libbacktrace in heads/homu-tmp. Adding src/libbacktrace as src/libbacktrace~HEAD
Automatic merge failed; fix conflicts and then commit the result.

bors · 2018-06-22T01:17:44Z

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

git checkout master (switch to your branch)
git fetch upstream master (retrieve the latest master)
git rebase upstream/master -p (rebase on top of it)
Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
git push self master --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

Auto-merging src/libsyntax/parse/parser.rs
CONFLICT (file/directory): There is a directory with name src/libbacktrace in heads/homu-tmp. Adding src/libbacktrace as src/libbacktrace~HEAD
Automatic merge failed; fix conflicts and then commit the result.

…truct constructor

Only display the "remove this comma" suggestion when followed by an identifier

pietroalbini · 2018-06-22T09:40:33Z

Rebased this on top of the latest master.

@bors r=nikomatsakis

bors · 2018-06-22T09:40:33Z

📌 Commit a99767f has been approved by nikomatsakis

bors · 2018-06-22T11:10:29Z

⌛ Testing commit a99767f with merge 01dbfda...

Issue #50974 : Suboptimal error in case of duplicate `,` in struct constructor Fixes #50974

bors · 2018-06-22T13:18:37Z

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 01dbfda to master...

rust-highfive assigned nikomatsakis May 29, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 29, 2018

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nikomatsakis approved these changes May 30, 2018

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nikomatsakis 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 May 30, 2018

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 5, 2018

Mark-Simulacrum added a commit to Mark-Simulacrum/rust that referenced this pull request Jun 5, 2018

Rollup merge of rust-lang#51184 - lambtowolf:master, r=nikomatsakis

8e9a5e9

Issue rust-lang#50974 : Suboptimal error in case of duplicate `,` in struct constructor Fixes rust-lang#50974

Mark-Simulacrum mentioned this pull request Jun 5, 2018

Rollup of 5 pull requests #51379

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bors 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-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jun 6, 2018

lambtowolf added 4 commits June 22, 2018 11:38

Issue rust-lang#50974: Suboptimal error in case of duplicate , in s…

7969b78

…truct constructor

Issue rust-lang#50974: Change text of suggestion to be more direct

783815d

Issue rust-lang#50974: Adding tests

5c022af

Issue rust-lang#50974: Adding issue number in the test

6c962e3

lambtowolf and others added 3 commits June 22, 2018 11:38

Fix when the help message is displayed

fadb86f

Only display the "remove this comma" suggestion when followed by an identifier

Issue rust-lang#50974: Fix compilation error and test

815765d

add an explanatory comment for recovery behavior

a99767f

pietroalbini force-pushed the master branch from 01559fb to a99767f Compare June 22, 2018 09:39

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 22, 2018

bors added a commit that referenced this pull request Jun 22, 2018

Auto merge of #51184 - lambtowolf:master, r=nikomatsakis

01dbfda

Issue #50974 : Suboptimal error in case of duplicate `,` in struct constructor Fixes #50974

bors merged commit a99767f into rust-lang:master Jun 22, 2018

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Issue #50974 : Suboptimal error in case of duplicate `,` in struct constructor #51184

Issue #50974 : Suboptimal error in case of duplicate `,` in struct constructor #51184

lambtowolf commented May 29, 2018

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Issue #50974 : Suboptimal error in case of duplicate , in struct constructor #51184

Issue #50974 : Suboptimal error in case of duplicate , in struct constructor #51184

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Issue #50974 : Suboptimal error in case of duplicate `,` in struct constructor #51184

Issue #50974 : Suboptimal error in case of duplicate `,` in struct constructor #51184

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