https://github.com/rust-lang/rust http://git.dreamy.place/mirrors/rust/atom?h=auto 2023-01-11T09:32:08+00:00 2023-01-11T09:32:08+00:00 Albert Larsan 74931857+albertlarsan68@users.noreply.github.com 2023-01-05T08:13:28+00:00 urn:sha1:cf2dff2b1e3fa55fa5415d524200070d0d7aacfe 2022-11-05T01:12:58+00:00 clubby789 jamie@hill-daniel.co.uk 2022-11-05T01:11:50+00:00 urn:sha1:2f882c014f3bfabb811177d24bfb72e3f6b6d271 2022-10-01T10:03:06+00:00 Maybe Waffle waffle.lapkin@gmail.com 2022-09-18T15:55:36+00:00 urn:sha1:13b67fb9d2849b4e59d5651b0e4fc82ef8b088aa 2022-08-24T02:14:12+00:00 Joshua Nelson jnelson@cloudflare.com 2022-07-14T13:30:38+00:00 urn:sha1:31e39446ec2f251efbcaf9eb22c80e93021f9bbc # Stabilization proposal The feature was implemented in https://github.com/rust-lang/rust/pull/50045 by est31 and has been in nightly since 2018-05-16 (over 4 years now). There are [no open issues][issue-label] other than the tracking issue. There is a strong consensus that `break` is the right keyword and we should not use `return`. There have been several concerns raised about this feature on the tracking issue (other than the one about tests, which has been fixed, and an interaction with try blocks, which has been fixed). 1. nrc's original comment about cost-benefit analysis: https://github.com/rust-lang/rust/issues/48594#issuecomment-422235234 2. joshtriplett's comments about seeing use cases: https://github.com/rust-lang/rust/issues/48594#issuecomment-422281176 3. withoutboats's comments that Rust does not need more control flow constructs: https://github.com/rust-lang/rust/issues/48594#issuecomment-450050630 Many different examples of code that's simpler using this feature have been provided: - A lexer by rpjohnst which must repeat code without label-break-value: https://github.com/rust-lang/rust/issues/48594#issuecomment-422502014 - A snippet by SergioBenitez which avoids using a new function and adding several new return points to a function: https://github.com/rust-lang/rust/issues/48594#issuecomment-427628251. This particular case would also work if `try` blocks were stabilized (at the cost of making the code harder to optimize). - Several examples by JohnBSmith: https://github.com/rust-lang/rust/issues/48594#issuecomment-434651395 - Several examples by Centril: https://github.com/rust-lang/rust/issues/48594#issuecomment-440154733 - An example by petrochenkov where this is used in the compiler itself to avoid duplicating error checking code: https://github.com/rust-lang/rust/issues/48594#issuecomment-443557569 - Amanieu recently provided another example related to complex conditions, where try blocks would not have helped: https://github.com/rust-lang/rust/issues/48594#issuecomment-1184213006 Additionally, petrochenkov notes that this is strictly more powerful than labelled loops due to macros which accidentally exit a loop instead of being consumed by the macro matchers: https://github.com/rust-lang/rust/issues/48594#issuecomment-450246249 nrc later resolved their concern, mostly because of the aforementioned macro problems. joshtriplett suggested that macros could be able to generate IR directly (https://github.com/rust-lang/rust/issues/48594#issuecomment-451685983) but there are no open RFCs, and the design space seems rather speculative. joshtriplett later resolved his concerns, due to a symmetry between this feature and existing labelled break: https://github.com/rust-lang/rust/issues/48594#issuecomment-632960804 withoutboats has regrettably left the language team. joshtriplett later posted that the lang team would consider starting an FCP given a stabilization report: https://github.com/rust-lang/rust/issues/48594#issuecomment-1111269353 [issue-label]: https://github.com/rust-lang/rust/issues?q=is%3Aissue+is%3Aopen+label%3AF-label_break_value+ ## Report + Feature gate: - https://github.com/rust-lang/rust/blob/d695a497bbf4b20d2580b75075faa80230d41667/src/test/ui/feature-gates/feature-gate-label_break_value.rs + Diagnostics: - https://github.com/rust-lang/rust/blob/6b2d3d5f3cd1e553d87b5496632132565b6779d3/compiler/rustc_parse/src/parser/diagnostics.rs#L2629 - https://github.com/rust-lang/rust/blob/f65bf0b2bb1a99f73095c01a118f3c37d3ee614c/compiler/rustc_resolve/src/diagnostics.rs#L749 - https://github.com/rust-lang/rust/blob/f65bf0b2bb1a99f73095c01a118f3c37d3ee614c/compiler/rustc_resolve/src/diagnostics.rs#L1001 - https://github.com/rust-lang/rust/blob/111df9e6eda1d752233482c1309d00d20a4bbf98/compiler/rustc_passes/src/loops.rs#L254 - https://github.com/rust-lang/rust/blob/d695a497bbf4b20d2580b75075faa80230d41667/compiler/rustc_parse/src/parser/expr.rs#L2079 - https://github.com/rust-lang/rust/blob/d695a497bbf4b20d2580b75075faa80230d41667/compiler/rustc_parse/src/parser/expr.rs#L1569 + Tests: - https://github.com/rust-lang/rust/blob/master/src/test/ui/label/label_break_value_continue.rs - https://github.com/rust-lang/rust/blob/master/src/test/ui/label/label_break_value_unlabeled_break.rs - https://github.com/rust-lang/rust/blob/master/src/test/ui/label/label_break_value_illegal_uses.rs - https://github.com/rust-lang/rust/blob/master/src/test/ui/lint/unused_labels.rs - https://github.com/rust-lang/rust/blob/master/src/test/ui/run-pass/for-loop-while/label_break_value.rs ## Interactions with other features Labels follow the hygiene of local variables. label-break-value is permitted within `try` blocks: ```rust let _: Result<(), ()> = try { 'foo: { Err(())?; break 'foo; } }; ``` label-break-value is disallowed within closures, generators, and async blocks: ```rust 'a: { || break 'a //~^ ERROR use of unreachable label `'a` //~| ERROR `break` inside of a closure } ``` label-break-value is disallowed on [_BlockExpression_]; it can only occur as a [_LoopExpression_]: ```rust fn labeled_match() { match false 'b: { //~ ERROR block label not supported here _ => {} } } macro_rules! m { ($b:block) => { 'lab: $b; //~ ERROR cannot use a `block` macro fragment here unsafe $b; //~ ERROR cannot use a `block` macro fragment here |x: u8| -> () $b; //~ ERROR cannot use a `block` macro fragment here } } fn foo() { m!({}); } ``` [_BlockExpression_]: https://doc.rust-lang.org/nightly/reference/expressions/block-expr.html [_LoopExpression_]: https://doc.rust-lang.org/nightly/reference/expressions/loop-expr.html 2022-08-05T17:28:00+00:00 Yiming Lei yiming.lei@futurewei.com 2022-08-03T04:46:07+00:00 urn:sha1:9815667b8b59e5351c257f7a62f6c0874fabd7ca when loop as tail expression for miss match type E0308 error, recursively get the return statement and add diagnostic information on it use rustc_hir::intravisit to collect the return expression modified: compiler/rustc_typeck/src/check/coercion.rs new file: src/test/ui/typeck/issue-98982.rs new file: src/test/ui/typeck/issue-98982.stderr 2022-07-19T03:07:54+00:00 Michael Goulet michael@errs.io 2022-06-21T02:25:52+00:00 urn:sha1:01b2379e4902658de68fcdca2a15b48fe4d57875 2022-06-02T17:24:32+00:00 Camille GILLOT gillot.camille@gmail.com 2022-05-05T18:49:48+00:00 urn:sha1:a265c49b252a932b06a94d5715013c8311989139 2022-05-03T19:09:52+00:00 Joshua Nelson jnelson@cloudflare.com 2022-05-03T19:07:36+00:00 urn:sha1:cd63b22e80e61fc4deb3da85a733d6c9266783e1 2021-11-18T15:09:34+00:00 Caio c410.f3r@gmail.com 2021-11-18T15:09:34+00:00 urn:sha1:41d9abd76cd514aca23e3409fe6896a3a7d61d1a 2021-11-14T17:38:42+00:00 Caio c410.f3r@gmail.com 2021-11-14T17:38:42+00:00 urn:sha1:ab5434f9b8d3937fe33f813b3f8e1a43a4657781