2018 edition `?` Kleene operator #51587

mark-i-m · 2018-06-16T02:52:25Z

This is my first attempt at implementing the migration lint + 2018 behavior as discussed in #48075

r? @nikomatsakis

mark-i-m · 2018-06-16T02:52:39Z

@nikomatsakis Is this close to what you had in mind?

mark-i-m · 2018-06-16T02:55:02Z

Also, I think I should add some more tests for 2015 vs 2018 behavior.

alexreg · 2018-06-16T19:34:49Z

Nice work, @mark-i-m! Hoping we can get this merged in soon.

mark-i-m · 2018-06-16T21:34:21Z

I'm not quite sure I got the lint right... it's currently a straight up warning...

alexreg · 2018-06-16T22:47:50Z

@mark-i-m Yes, there look to be 1001 different ways of linting in the compiler code. This is the sort of thing that could really do with a chapter in the rustc book!

mark-i-m · 2018-06-16T23:23:38Z

@alexreg https://rust-lang-nursery.github.io/rustc-guide/diag.html

alexreg · 2018-06-16T23:59:14Z

@mark-i-m Oh gosh, I really should have checked before making that comment! The rustc book has come a long way since I last read it. The one thing still really deficient is the macros chapter, sadly... Also, it reminds me I should submit a PR about incremental compilation tests.

nikomatsakis · 2018-06-18T17:16:08Z

src/libsyntax/ext/tt/quoted.rs

                        }
                        return (Some(token::Question), op);
                    }
-                    Ok(Ok(op)) => return (Some(token::Question), op),
+                    Ok(Ok(op)) => {
+                        if !features.macro_at_most_once_rep


I think the feature gate is not quite acting like I expect. My expectation is:

In Edition 2015:

If you do $()?[*+], then you get "? as separator".

Else, if you do $(foo)?[^*+], treat as "optional":

But if feature gate is not enabled, error

In Edition 2018:

If you do $(foo)?, then treat as "optional":

But if feature gate is not enabled, error.

My goal is that, when it comes time to stabilize, we can just "constant propagate" as if the feature gate was always enabled and get the final behavior we want:

in Rust 2015 we fallback to old behavior

in Rust 2018 we use new behavior all the time

(Is this the plan? Do we have an official, FCP'd proposal somewhere, anyway?)

(Is this the plan? Do we have an official, FCP'd proposal somewhere, anyway?)

No, we don't TMK

in Rust 2015 we fallback to old behavior

Given that this is behavior that will only last for another couple of months, my preference is to

just keep this unstable on 2015 and only enable in 2018

make the feature flag always turn on 2018 behavior

So to clarify:

In edition 2015:

Without feature flag: ? is a separator. ? is not a Kleene op.

With feature flag: same as 2018

In edition 2018

? is not a separator. ? is a Kleene op that does not accept a separator.

I would prefer this:

In edition 2015:

With or without feature flag: ? is a separator and there is no ?

However, using ? as a separator issues a rust_2018_migration warning

In edition 2018:

? is always a separator

and feature-gate is required until we stabilize

Point is, as before, that the feature-gate should just be a "error or no error" filter -- the behavior should model what we eventually want when all is said and done otherwise. And we never want Rust 2015 to support ?.

In edition 2018:
? is always a separator

You mean "in 2018, ? is always a kleene op", right?

(I'd sure hope so heh!)

mark-i-m · 2018-06-23T02:41:51Z

@nikomatsakis I think I have implemented what you specified with one major exception: currently, the warning for using ? as a separator in 2015 edition always fires (i.e. it's not informed by #[warn()]).

Do you know how I can hook up the warning to fire when the lint group is set? Also, should it be a rust_2018_compatibility warning or a rust_2018_idioms warning, as mentioned in #50620? My inclination is towards the former.

mark-i-m · 2018-06-24T00:33:46Z

This still needs some work. I am currently fixing/writing some tests.

mark-i-m · 2018-06-24T01:38:35Z

@nikomatsakis I pushed a few tests. Do these tests represent the behavior you were expecting?

mark-i-m · 2018-06-24T23:57:16Z

Ok, I think I've implemented and added tests for everything except that the migration warning is currently an unconditional warning.

All feedback is welcome!

mark-i-m · 2018-06-25T00:37:13Z

Doh. I forgot that I started using this in places in the compiler 😛

mark-i-m · 2018-06-25T00:40:53Z

Hmm... some of these are going to be hard to fix...

nikomatsakis

Looks good to me!

nikomatsakis · 2018-06-25T20:45:59Z

src/test/ui/macros/macro-at-most-once-rep-2018-feature-gate.rs

+// Feature gate test for macro_at_most_once_rep under 2018 edition.
+
+// gate-test-macro_at_most_once_rep
+// compile-flags: --edition=2018


unrelated, but we should really add a // edition: 2018 option, shouldn't we?

Created #51800

nikomatsakis · 2018-06-25T20:49:53Z

src/test/ui/macros/macro-at-most-once-rep-2018-feature-gate.stderr

@@ -0,0 +1,71 @@
+error[E0658]: Using the `?` macro Kleene operator for "at most one" repetition is unstable (see issue #48075)


Nit: start compiler messages w/ lower-case letters

nikomatsakis · 2018-06-25T20:51:49Z

@mark-i-m travis is unhappy, but this code looks good to me overall

mark-i-m · 2018-06-26T02:40:55Z

@nikomatsakis Is it ok that the warning is unconditional?

alexcrichton · 2018-07-23T14:23:10Z

Great! @mark-i-m want to rebase and I'll do a final once-over and r+?

mark-i-m · 2018-07-24T02:58:43Z

🎉 Rebased :)

alexcrichton · 2018-07-24T14:09:15Z

@bors: r+

bors · 2018-07-24T14:09:16Z

📌 Commit 10ee0f6 has been approved by alexcrichton

bors · 2018-07-24T15:12:03Z

⌛ Testing commit 10ee0f6 with merge f498e4e...

@nikomatsakis

2018 edition `?` Kleene operator This is my first attempt at implementing the migration lint + 2018 behavior as discussed in #48075 r? @nikomatsakis

bors · 2018-07-24T17:22:37Z

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing f498e4e to master...

rust-highfive · 2018-07-24T17:24:01Z

📣 Toolstate changed by #51587!

Tested on commit f498e4e.
Direct link to PR: #51587

💔 rls on windows: test-pass → build-fail (cc @nrc, @rust-lang/infra).
💔 rls on linux: test-pass → build-fail (cc @nrc, @rust-lang/infra).
💔 rustfmt on windows: test-pass → build-fail (cc @nrc, @rust-lang/infra).
💔 rustfmt on linux: test-pass → build-fail (cc @nrc, @rust-lang/infra).

@nrc

Tested on commit rust-lang/rust@f498e4e. Direct link to PR: <rust-lang/rust#51587> 💔 rls on windows: test-pass → build-fail (cc @nrc, @rust-lang/infra). 💔 rls on linux: test-pass → build-fail (cc @nrc, @rust-lang/infra). 💔 rustfmt on windows: test-pass → build-fail (cc @nrc, @rust-lang/infra). 💔 rustfmt on linux: test-pass → build-fail (cc @nrc, @rust-lang/infra).

kennytm · 2018-07-24T18:21:24Z

[01:09:02]   --> /cargo/registry/src/github.com-1ecc6299db9ec823/rustc-ap-syntax-182.0.0/ext/expand.rs:47:60
[01:09:02]    |
[01:09:02] 47 |             $(one fn $fold_ast:ident; fn $visit_ast:ident;)?
[01:09:02]    |                                                            ^
[01:09:02]    |
[01:09:02]    = note: `?` is not a macro repetition operator

We need to update rustc-ap-syntax?

Edit: We'll need to wait for rustc-ap-syntax v209 to include this PR that fixes the use of ? inside libsyntax.

This should fix the breakage caused by rust-lang/rust#51587.

rust-highfive assigned nikomatsakis Jun 16, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 16, 2018

mark-i-m mentioned this pull request Jun 16, 2018

tracking issue for ? macro repetition #48075

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mark-i-m changed the title ~~2018 edition ? Kleene operator~~ [WIP] 2018 edition ? Kleene operator Jun 16, 2018

nikomatsakis requested changes Jun 18, 2018

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mark-i-m force-pushed the at_most_once_rep_2018 branch from 21562f6 to e5ba108 Compare June 24, 2018 23:55

mark-i-m changed the title ~~[WIP] 2018 edition ? Kleene operator~~ [Almost not WIP] 2018 edition ? Kleene operator Jun 25, 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 Jun 25, 2018

mark-i-m added 7 commits July 23, 2018 21:54

Extend ParseSess to support buffering lints

2a7ae04

Implement 2015 vs 2018 ? kleene op + test

8eb4941

update nightly book

63c2d06

Fix test and errors

5d87272

make it a migration lint

b206aed

dump lints _after_ parsing macros

6cb09cc

Allow by default, fix tests

10ee0f6

mark-i-m force-pushed the at_most_once_rep_2018 branch from 42d4142 to 10ee0f6 Compare July 24, 2018 02:56

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-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. labels Jul 24, 2018

bors added a commit that referenced this pull request Jul 24, 2018

Auto merge of #51587 - mark-i-m:at_most_once_rep_2018, r=alexcrichton

f498e4e

2018 edition `?` Kleene operator This is my first attempt at implementing the migration lint + 2018 behavior as discussed in #48075 r? @nikomatsakis

bors mentioned this pull request Jul 24, 2018

clarify pointer offset function safety concerns #52668

Merged

bors merged commit 10ee0f6 into rust-lang:master Jul 24, 2018

kennytm added a commit to rust-lang/rustfmt that referenced this pull request Jul 26, 2018

Update rustc-ap-syntax to 209.0.0.

1e55de1

This should fix the breakage caused by rust-lang/rust#51587.

This was referenced Jul 26, 2018

Update rustc-ap-syntax to 209.0.0. rust-lang/rustfmt#2865

Merged

Update rustc-ap-syntax to 209.0.0. racer-rust/racer#911

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memoryruins mentioned this pull request Aug 16, 2018

subgoal_abstraction test fails on windows rust-lang/chalk#169

Closed

pnkfelix mentioned this pull request Oct 9, 2018

error: internal compiler error: Accessing (*_310) with the kind Write(Move) shouldn't be possible #54597

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mark-i-m deleted the at_most_once_rep_2018 branch November 14, 2018 16:40

mark-i-m mentioned this pull request Nov 29, 2018

Use ? Kleene operator again #56357

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Centril mentioned this pull request Dec 10, 2018

Extending ? macro repetition to Rust 2015 #56668

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		@@ -0,0 +1,71 @@
		error[E0658]: Using the `?` macro Kleene operator for "at most one" repetition is unstable (see issue #48075)

2018 edition ? Kleene operator #51587

2018 edition ? Kleene operator #51587

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mark-i-m commented Jun 16, 2018

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nikomatsakis commented Jun 25, 2018

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alexcrichton commented Jul 23, 2018

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alexcrichton commented Jul 24, 2018

bors commented Jul 24, 2018

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rust-highfive commented Jul 24, 2018

kennytm commented Jul 24, 2018 • edited Loading

2018 edition `?` Kleene operator #51587

2018 edition `?` Kleene operator #51587

kennytm commented Jul 24, 2018 •

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