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Stabilize `#![feature(label_break_value)]`
See the stabilization report in https://github.com/rust-lang/rust/issues/48594#issuecomment-1186213313.
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spastorino:coherence-negative-impls-implied-bounds, r=lcnr
Coherence negative impls implied bounds
Fixes #93875
This PR is rebased on top of #100789 and it would need to include that one which is already r+ed.
r? ``@nikomatsakis``
cc ``@lcnr`` (which I've talked about https://github.com/rust-lang/rust/commit/3222f420d9d2312efe0735eb48160c7b070adc54, I guess after you finish your reordering of modules and work with OutlivesEnvironmentEnv this commit can just be reverted).
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# 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
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InferCtxt tainted_by_errors_flag should be Option<ErrorGuaranteed>
Fixes #100321.
Use Cell<Option<ErrorGuaranteed>> to guarantee that we emit an error when that flag is set.
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Use separate infcx to solve obligations during negative coherence
I feel like I fixed this already but I may have fixed it then forgot to push the branch...
Also fixes up some redundant param-envs being passed around (since they're already passed around in the `Obligation`)
Fixes #99662
r? ``@spastorino``
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This was left as a TODO in #92268, and brings the trait more in
line with what was defined in MCP411.
`Assume::visibility` has been renamed to `Assume::safety`, as
library safety is what's actually being assumed; visibility is
just the mechanism by which it is currently checked (this may
change).
ref: https://github.com/rust-lang/compiler-team/issues/411
ref: https://github.com/rust-lang/rust/issues/99571
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Rollup of 5 pull requests
Successful merges:
- #93162 (Std module docs improvements)
- #99386 (Add tests that check `Vec::retain` predicate execution order.)
- #99915 (Recover keywords in trait bounds)
- #100694 (Migrate rustc_ast_passes diagnostics to `SessionDiagnostic` and translatable messages (first part))
- #100757 (Catch overflow early)
Failed merges:
- #99917 (Move Error trait into core)
r? `@ghost`
`@rustbot` modify labels: rollup
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Catch overflow early
Although this code should raise an overflow error, it didn't because [check_recursion_limit](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_trait_selection/traits/select/struct.SelectionContext.html#method.check_recursion_limit) it checks for `depth = 128` but not for `129` which should have triggered the overflow error. Anyways this catches that error early.
Fixes #95134
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implied bounds: explicitly state which types are assumed to be wf
Adds a new query which maps each definition to the types which that definition assumes to be well formed. The intent is to make it easier to reason about implied bounds.
This change should not influence the user-facing behavior of rustc. Notably, `borrowck` still only assumes that the function signature of associated functions is well formed while `wfcheck` assumes that the both the function signature and the impl trait ref is well formed. Not sure if that by itself can trigger UB or whether it's just annoying.
As a next step, we can add `WellFormed` predicates to `predicates_of` of these items and can stop adding the wf bounds at each place which uses them. I also intend to move the computation from `assumed_wf_types` to `implied_bounds` into the `param_env` computation. This requires me to take a deeper look at `compare_predicate_entailment` which is currently somewhat weird wrt implied bounds so I am not touching this here.
r? `@nikomatsakis`
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r=compiler-errors
Refactor: remove unnecessary string searchings
This patch removes unnecessary string searchings for checking if function arguments have `&` and `&mut`.
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TaKO8Ki:suggest-adding-reference-to-trait-assoc-item, r=cjgillot
Suggest adding a reference to a trait assoc item
fixes #100289
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remove unnecessary string searchings for checking if function arguments have `&` and `&mut`
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Revert "Rollup merge of #97346 - JohnTitor:remove-back-compat-hacks, …
…r=oli-obk"
This reverts commit c703d11dccb4a895c7aead3b2fcd8cea8c483184, reversing
changes made to 64eb9ab869bc3f9ef3645302fbf22e706eea16cf.
it didn't apply cleanly, so now it works the same for RPIT and for TAIT instead of just working for RPIT, but we should keep those in sync anyway. It also exposed a TAIT bug (see the feature gated test that now ICEs).
r? `@pnkfelix`
fixes #99536
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Delay span bug when failing to normalize negative coherence impl subject due to other malformed impls
Fixes #100191
r? ``@spastorino``
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orphan check: rationalize our handling of constants
cc `@rust-lang/types` `@rust-lang/project-const-generics` on whether you agree with this reasoning.
r? types
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to other malformed impls
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Keep going if normalized projection has unevaluated consts in `QueryNormalizer`
#100312 was the wrong approach, I think this is the right one.
When normalizing a type, if we see that it's a projection, we currently defer to `tcx.normalize_projection_ty`, which normalizes the projections away but doesn't touch the unevaluated constants. So now we just continue to fold the type if it has unevaluated constants so we make sure to evaluate those too, if we can.
Fixes #100217
Fixes #83972
Fixes #84669
Fixes #86710
Fixes #82268
Fixes #73298
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consider unnormalized types for implied bounds
extracted, and slightly modified, from #98900
The idea here is that generally, rustc is split into things which can assume its inputs are well formed[^1], and things which have verify that themselves.
Generally most predicates should only deal with well formed inputs, e.g. a `&'a &'b (): Trait` predicate should be able to assume that `'b: 'a` holds. Normalization can loosen wf requirements (see #91068) and must therefore not be used in places which still have to check well formedness. The only such place should hopefully be `WellFormed` predicates
fixes #87748 and #98543
r? `@jackh726` cc `@rust-lang/types`
[^1]: These places may still encounter non-wf inputs and have to deal with them without causing an ICE as we may check for well formedness out of order.
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r=lcnr,notriddle,camelid
Don't document impossible to call default trait items on impls
Closes #100176
This only skips documenting _default_ trait items on impls, not ones that are written inside the impl block. This is a conservative approach, since I think we should document all items written in an impl block (I guess unless hidden or whatever), but the existence of this new query I added makes this easy to extend to other rustdoc cases.
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this allows us to soundly use unnormalized projections for wf
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