Add ok-wrapping to catch blocks, per RFC by scottmcm · Pull Request #49371 · rust-lang/rust

scottmcm · 2018-03-26T03:03:12Z

Updates the catch{} lowering to wrap the result in Try::from_ok.

r? @nikomatsakis

Fixes #41414
Fixes #43818

nikomatsakis · 2018-04-02T21:06:09Z

src/librustc/hir/lowering.rs

this seems ok; this has to do with #[foo] attributes

nikomatsakis · 2018-04-02T21:07:52Z

src/librustc/hir/lowering.rs

I think you want to call this.next_id() here

nikomatsakis · 2018-04-02T21:08:23Z

src/librustc/hir/lowering.rs

this would be where we report errors regarding this () expression; the block seems ok, but we might want to .. just use the closing brace }?

we probably also want to give it the "desugaring" span

nikomatsakis · 2018-04-02T21:10:36Z

src/librustc_mir/borrow_check/nll/mod.rs

How about we make a macro for this instead?

#[cfg(stage0)] macro_rules do_catch { ($t:expr) = { (|| $t)() } } #[cfg(not(stage0))] macro_rules do_catch { ($t:expr) = { do catch { $t } } }

And this way it can have ok-wrapping! 👍

nikomatsakis · 2018-04-02T21:10:45Z

src/librustc_mir/util/pretty.rs

nikomatsakis · 2018-04-02T21:11:56Z

src/librustc_mir/util/pretty.rs

nikomatsakis · 2018-04-02T21:17:48Z

first round of comments =) sorry for the delay. Cursed All Hands!

scottmcm · 2018-04-03T07:13:07Z

Ok, it looks like this is working now. Thanks for the pointers!

I added a UI test so you can see how the spans come out in type errors; if you would like them to be different please let me know how to do that -- this is my first time in this end of the compiler 🙂

TimNN · 2018-04-03T08:18:36Z

Your PR failed on Travis. Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:00:50] configure: rust.quiet-tests     := True
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[00:48:50] .................................................................................test [run-pass] run-pass/mir_heavy_promoted.rs has been running for over 60 seconds
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[01:28:26] command did not execute successfully: "/checkout/obj/build/bootstrap/debug/rustdoc" "--test" "/checkout/src/doc/unstable-book/src/language-features/catch-expr.md" "--test-args" ""
---
[01:28:26] ---- /checkout/src/doc/unstable-book/src/language-features/catch-expr.md - catch_expr (line 12) stdout ----
[01:28:26]  error[E0271]: type mismatch resolving `<std::result::Result<i32, std::num::ParseIntError> as std::ops::Try>::Ok == std::result::Result<i32, _>`
[01:28:26]   --> /checkout/src/doc/unstable-book/src/language-features/catch-expr.md:18:5
[01:28:26]    |
[01:28:26] 8  | /     Ok("1".parse::<i32>()?
[01:28:26] 9  | |         + "2".parse::<i32>()?
[01:28:26] 10 | |         + "3".parse::<i32>()?)
[01:28:26]    | |______________________________^ expected i32, found enum `std::result::Result`
[01:28:26]    |
[01:28:26]    = note: expected type `i32`
[01:28:26]               found type `std::result::Result<i32, _>`
[01:28:26]
[01:28:26] error[E0271]: type mismatch resolving `<std::result::Result<i32, std::num::ParseIntError> as std::ops::Try>::Ok == std::result::Result<i32, _>`
[01:28:26]   --> /checkout/src/doc/unstable-book/src/language-features/catch-expr.md:25:5
[01:28:26]    |
[01:28:26] 15 | /     Ok("1".parse::<i32>()?
[01:28:26] 16 | |         + "foo".parse::<i32>()?
[01:28:26] 17 | |         + "3".parse::<i32>()?)
[01:28:26]    | |______________________________^ expected i32, found enum `std::result::Result`
[01:28:26]    |
[01:28:26]    = note: expected type `i32`
[01:28:26]               found type `std::result::Result<i32, _>`
[01:28:26]
[01:28:26] thread 'rustc' panicked at 'couldn't compile the test', librustdoc/test.rs:306:13
---
[01:28:26] make: *** [check] Error 1
[01:28:26] Makefile:58: recipe for target 'check' failed

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN.

nikomatsakis

Left some thoughts about span

nikomatsakis · 2018-04-04T20:38:46Z

src/doc/unstable-book/src/language-features/catch-expr.md

nikomatsakis · 2018-04-04T20:40:22Z

src/test/run-pass/catch-expr.rs

interesting.

Yeah, I filed #49356 about this. (Edit: Which I put in the comment; duh.) It feels to me like it ought to work, since the type needed here is completely determined by the context.

I can imagine why it fails, we might be able to improve it.

nikomatsakis · 2018-04-04T20:42:27Z

src/test/ui/catch-block-type-error.stderr

Hmm, this is ungreat. Not sure what span would be best, maybe @estebank has thoughts. I think maybe just pointing to the end-brace would be good?:

error[E0271]: type mismatch resolving `<std::option::Option<i32> as std::ops::Try>::Ok == ()` --> $DIR/catch-block-type-error.rs:22:35 | LL | }; | ^ expected i32, found () | = note: expected type `i32` found type `()`

Also, the "type mismatch" line is kind of a mess, but that's separate I guess and maybe hard to fix -- we might be able to use the "extra info" from the span to help.

@scottmcm If you like how this looks I can give you a tip for how to achieve it =)

In general I think multi-line spans are to be avoided at basically any cost.

That seems plausible, though note that the multi-line span happens today for blocks:

error[E0308]: mismatched types --> src/main.rs:2:19 | 2 | let x: i32 = { | ___________________^ 3 | | println!("asdf"); 4 | | 3; 5 | | println!("asdf"); 6 | | }; | |_____^ expected i32, found () | = note: expected type `i32` found type `()`

I haven't looked into span futzing yet, so I don't know my unknowns. A few quick pointers would be great, or if you wanted to use me as a tester for a rustc book page...

note that the multi-line span happens today for blocks

yes, but that doesn't make it good =)

I haven't looked into span futzing yet, so I don't know my unknowns

I believe that the end_point function is what you want

Thanks! That did the trick. And huzzah for hosted compiler docs 🎉

nikomatsakis

very nice

nikomatsakis · 2018-04-10T16:44:41Z

@bors r+

bors · 2018-04-10T16:44:42Z

📌 Commit 9911de8 has been approved by nikomatsakis

bors · 2018-04-10T21:57:45Z

☔ The latest upstream changes (presumably #48914) made this pull request unmergeable. Please resolve the merge conflicts.

…place

scottmcm · 2018-04-11T04:54:07Z

Rebased; please re-r+.

nikomatsakis · 2018-04-11T17:54:41Z

@bors r+

bors · 2018-04-11T17:54:42Z

📌 Commit 311ff5b has been approved by nikomatsakis

nikomatsakis · 2018-04-11T17:54:49Z

@bors delegate=scottmcm

(For future rebases)

bors · 2018-04-11T17:54:50Z

✌️ @scottmcm can now approve this pull request

bors · 2018-04-12T05:38:55Z

⌛ Testing commit 311ff5b with merge 252a459...

@nikomatsakis

Add ok-wrapping to catch blocks, per RFC Updates the `catch{}` lowering to wrap the result in `Try::from_ok`. r? @nikomatsakis Fixes #41414 Fixes #43818

bors · 2018-04-12T08:29:05Z

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 252a459 to master...

See rust-lang/rust#49371

scottmcm assigned nikomatsakis Mar 26, 2018

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nikomatsakis reviewed Apr 2, 2018

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scottmcm force-pushed the catch-wrapping branch from b9ea258 to a957c61 Compare April 3, 2018 06:47

scottmcm changed the title ~~[Assistance Requested] Add ok-wrapping to catch blocks, per RFC~~ Add ok-wrapping to catch blocks, per RFC Apr 3, 2018

scottmcm force-pushed the catch-wrapping branch from 7923aba to 316a16f Compare April 3, 2018 07:10

rust-lang deleted a comment from TimNN Apr 3, 2018

scottmcm mentioned this pull request Apr 4, 2018

Add size_hints for btree iterators #49550

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scottmcm force-pushed the catch-wrapping branch from 0757abb to 9911de8 Compare April 10, 2018 07:46

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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-review Status: Awaiting review from the assignee but also interested parties. labels Apr 10, 2018

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 Apr 10, 2018

scottmcm added 4 commits April 10, 2018 20:03

Add ok-wrapping to catch blocks, per RFC

c4b6521

Add a UI test that the span for the catch type error is in the right …

aeb2353

…place

Fix the unstable book to account for ok-wrapping

c88efe4

Tweak span for ok-wrapping in no-tail block

311ff5b

scottmcm force-pushed the catch-wrapping branch from 9911de8 to 311ff5b Compare April 11, 2018 03:27

scottmcm added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 11, 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-review Status: Awaiting review from the assignee but also interested parties. labels Apr 11, 2018

bors added a commit that referenced this pull request Apr 12, 2018

Auto merge of #49371 - scottmcm:catch-wrapping, r=nikomatsakis

252a459

Add ok-wrapping to catch blocks, per RFC Updates the `catch{}` lowering to wrap the result in `Try::from_ok`. r? @nikomatsakis Fixes #41414 Fixes #43818

bors merged commit 311ff5b into rust-lang:master Apr 12, 2018

scottmcm deleted the catch-wrapping branch April 12, 2018 08:29

jonhoo added a commit to mit-pdos/noria that referenced this pull request Apr 19, 2018

do catch now wraps in Ok automatically

7ca16ec

See rust-lang/rust#49371

joshtriplett mentioned this pull request Apr 20, 2018

RFC: Reserve try for try { .. } block expressions rust-lang/rfcs#2388

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