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Author SHA1 Message Date
est31
7b55d17a2f Reduce span of let else irrefutable_let_patterns warning 
Huge spans aren't good for IDE users as they underline constructs that
are possibly multiline.
 2022-10-30 05:05:21 +01:00
Maybe Waffle
a17ccfa621 Accept TyCtxt instead of TyCtxtAt in Ty::is_* functions 
Functions in answer:

- `Ty::is_freeze`
- `Ty::is_sized`
- `Ty::is_unpin`
- `Ty::is_copy_modulo_regions`
 2022-10-27 15:06:08 +04:00
Michael Goulet
6e6fe30d0f Comment why normalization is needed for debug assertions 2022-10-23 17:23:35 +00:00
Cameron Steffen
2928e9ef2c Introduce InhabitedPredicate 2022-10-22 13:20:06 -05:00
bors
b15e2c129e Auto merge of #101832 - compiler-errors:dyn-star-plus, r=eholk 
Make `dyn*` casts into a coercion, allow `dyn*` upcasting

I know that `dyn*` is likely not going to be a feature exposed to surface Rust, but this makes it slightly more ergonomic to write tests for these types anyways. ... and this was just fun to implement anyways.

1. Make `dyn*` into a coercion instead of a cast
2. Enable `dyn*` upcasting since we basically get it for free
3. Simplify some of the cast checking code since we're using the coercion path now

r? `@eholk` but feel free to reassign
cc `@nikomatsakis` and `@tmandry` who might care about making `dyn*` casts into a coercion
 2022-10-15 07:36:38 +00:00
Dylan DPC
7cf09c57a2
Rollup merge of #103031 - est31:match_guard_irrefutable_let, r=oli-obk 
Suppress irrefutable let patterns lint for prefixes in match guards

In match guards, irrefutable prefixes might use the bindings created by the match pattern. Ideally, we check for this, but we can do the next best thing and just not lint for irrefutable prefixes in match guards.

Fixes #98361
 2022-10-14 16:19:16 +05:30
Dylan DPC
77064b7f0a
Rollup merge of #103018 - Rageking8:more-dupe-word-typos, r=TaKO8Ki 
More dupe word typos

I only picked those changes (from the regex search) that I am pretty certain doesn't change meaning and is just a typo fix. Do correct me if any fix is undesirable and I can revert those. Thanks.
 2022-10-14 16:19:15 +05:30
Rageking8
7122abaddf more dupe word typos 2022-10-14 12:57:56 +08:00
Michael Goulet
76386bd65e Make dyn* cast into a coercion 2022-10-14 04:27:01 +00:00
est31
eab41a136a Suppress irrefutable let patterns lint for prefixes in match guards 
In match guards, irrefutable prefixes might use the bindings created
by the match pattern. Ideally, we check for this, but we can do the
next best thing and just not lint for irrefutable prefixes in match
guards.
 2022-10-14 02:16:40 +02:00
Gary Guo
de0396c718 Ensure enum cast moves 2022-10-13 16:44:47 +01:00
Dylan DPC
5a09b72156
Rollup merge of #102853 - cjgillot:skip-opaque-cast, r=jackh726 
Skip chained OpaqueCast when building captures.

Fixes https://github.com/rust-lang/rust/issues/102089
 2022-10-10 13:43:42 +05:30
Camille GILLOT
e828ce53b9 Skip chained OpaqueCast when building captures. 2022-10-09 16:18:16 +00:00
Eric Huss
be1c7aad72 Show let-else suggestion on stable. 2022-10-08 14:39:25 -07:00
Matthias Krüger
c731646d6a
Rollup merge of #102675 - ouz-a:mir-technical-debt, r=oli-obk 
Remove `mir::CastKind::Misc`

As discussed in #97649 `mir::CastKind::Misc` is not clear, this PR addresses that by creating a new enum variant for every valid cast.

r? ````@oli-obk````
 2022-10-08 14:38:18 +02:00
Cameron Steffen
283abbf0e7 Change InferCtxtBuilder from enter to build 2022-10-07 07:10:40 -05:00
Cameron Steffen
349415d1c6 Remove TypeckResults from InferCtxt 2022-10-07 07:06:19 -05:00
ouz-a
d59c7ff000 Remove mir::CastKind::Misc 2022-10-06 15:32:41 +03:00
bors
0152393048 Auto merge of #99324 - reez12g:issue-99144, r=jyn514 
Enable doctests in compiler/ crates

Helps with https://github.com/rust-lang/rust/issues/99144
 2022-10-06 03:01:57 +00:00
bors
c97d02cdb5 Auto merge of #102394 - dingxiangfei2009:issue-102317, r=oli-obk 
Fix unwind drop glue for if-then scopes

cc `@est31`

Fix #102317
Fix #99852

This PR fixes the drop glue for unwinding from a panic originated in a drop while breaking out for the else block in an `if-then` scope.
MIR validation does not fail for the synchronous versions of the test program, because `StorageDead` statements are skipped over in the unwinding process. It is only becoming a problem when it is inside a generator where `StorageDead` must be kept around.
 2022-10-05 20:47:39 +00:00
Ding Xiang Fei
565c35aa5c
fix doc and dedup diverge_cleanup 2022-10-05 22:24:12 +08:00
bors
744e397d88 Auto merge of #101986 - WaffleLapkin:move_lint_note_to_the_bottom, r=estebank 
Move lint level source explanation to the bottom

So, uhhhhh

r? `@estebank`

## User-facing change

"note: `#[warn(...)]` on by default" and such are moved to the bottom of the diagnostic:
```diff
-   = note: `#[warn(unsupported_calling_conventions)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #87678 <https://github.com/rust-lang/rust/issues/87678>
+   = note: `#[warn(unsupported_calling_conventions)]` on by default
```

Why warning is enabled is the least important thing, so it shouldn't be the first note the user reads, IMO.

## Developer-facing change

`struct_span_lint` and similar methods have a different signature.

Before: `..., impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>)`
After: `..., impl Into<DiagnosticMessage>, impl for<'a, 'b> FnOnce(&'b mut DiagnosticBuilder<'a, ()>) -> &'b mut DiagnosticBuilder<'a, ()>`

The reason for this is that `struct_span_lint` needs to edit the diagnostic _after_ `decorate` closure is called. This also makes lint code a little bit nicer in my opinion.

Another option is to use `impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>) -> DiagnosticBuilder<'a, ()>` altough I don't _really_ see reasons to do `let lint = lint.build(message)` everywhere.

## Subtle problem

By moving the message outside of the closure (that may not be called if the lint is disabled) `format!(...)` is executed earlier, possibly formatting `Ty` which may call a query that trims paths that crashes the compiler if there were no warnings...

I don't think it's that big of a deal, considering that we move from `format!(...)` to `fluent` (which is lazy by-default) anyway, however this required adding a workaround which is unfortunate.

## P.S.

I'm sorry, I do not how to make this PR smaller/easier to review. Changes to the lint API affect SO MUCH 😢
 2022-10-01 10:44:25 +00:00
Maybe Waffle
a8f7e244b7 Refactor rustc lint API 2022-10-01 10:03:06 +00:00
X
fb52dc7c3b
apply suggestion 
Co-authored-by: SafariMonkey <charlton.rodda@gmail.com>
 2022-09-30 21:03:08 +08:00
bors
1bb8d276c9 Auto merge of #101887 - nnethercote:shrink-Res, r=spastorino 
Shrink `hir::def::Res`

r? `@spastorino`
 2022-09-29 22:45:24 +00:00
Oli Scherer
f22f149dbd Some path updates 2022-09-29 09:33:30 +00:00
reez12g
9a4c5abe45 Remove from compiler/ crates 2022-09-29 16:49:04 +09:00
Nicholas Nethercote
f07d4efc45 Shrink hir::def::Res. 
`Res::SelfTy` currently has two `Option`s. When the second one is `Some`
the first one is never consulted. So we can split it into two variants,
`Res::SelfTyParam` and `Res::SelfTyAlias`, reducing the size of `Res`
from 24 bytes to 12. This then shrinks `hir::Path` and
`hir::PathSegment`, which are the HIR types that take up the most space.
 2022-09-29 08:44:52 +10:00
Ding Xiang Fei
4a2c1a12b6
fix unwind drop glue for if-then scopes 2022-09-28 18:45:11 +08:00
lcnr
1fc86a63f4 rustc_typeck to rustc_hir_analysis 2022-09-27 10:37:23 +02:00
bors
1d1f142660 Auto merge of #102257 - cjgillot:let-else-lint, r=dingxiangfei2009 
Fix lint scoping for let-else.

The scoping for let-else is inconsistent with HIR nesting.  This creates cases, in `ui/let-else/let-else-allow-unused.rs` for instance, where an `allow` lint attribute does not apply to the bindings created by `let-else`.

This PR is an attempt to correct this.

As there is no lint that currently relies on this, the test for this behaviour is https://github.com/rust-lang/rust/pull/101500.

cc `@dingxiangfei2009` as you filed https://github.com/rust-lang/rust/pull/101894
 2022-09-26 17:17:07 +00:00
Pietro Albini
3975d55d98
remove cfg(bootstrap) 2022-09-26 10:14:45 +02:00
Camille GILLOT
73c52bc4dc Fix scoping for let-else. 2022-09-25 11:30:49 +02:00
b-naber
a705e65605 rename Unevaluated to UnevaluatedConst 2022-09-23 14:27:34 +02:00
b-naber
9f3784df89 introduce mir::Unevaluated 2022-09-22 12:35:28 +02:00
Michael Howell
b149c48186
Rollup merge of #102021 - lcnr:tyConst-fun, r=b-naber,BoxyUwU 
some post-valtree cleanup

r? project-const-generics cc ```@b-naber```
 2022-09-20 10:13:01 -07:00
bors
4136b59b7d Auto merge of #99806 - oli-obk:unconstrained_opaque_type, r=estebank 
Allow patterns to constrain the hidden type of opaque types

fixes #96572

reverts a revert as original PR was a perf regression that was fixed by reverting it: https://github.com/rust-lang/rust/pull/99368#issuecomment-1186587864)

TODO:

* check if https://github.com/rust-lang/rust/issues/99685 is avoided
 2022-09-20 12:09:52 +00:00
bors
2019147c56 Auto merge of #101894 - dingxiangfei2009:let-else-avoid-duplicate-storage-live, r=oli-obk 
Avoid duplicating StorageLive in let-else

cc `@est31`

Fix #101867
Fix #101932

#101410 introduced directives to activate storages of bindings in let-else earlier. However, since it is using the machinery of `match` and friends for pattern matching and binding, those storages are activated for the second time. This PR adjusts this behavior and avoid the duplicated activation for let-else statements.
 2022-09-19 17:27:30 +00:00
Oli Scherer
1905f8c441 Document projection condition 2022-09-19 15:33:36 +00:00
lcnr
526856768d ctfe, const_to_op only for mir constants 2022-09-19 16:17:33 +02:00
lcnr
647052fc04 remove the Subst trait, always use EarlyBinder 2022-09-19 11:37:27 +02:00
Ding Xiang Fei
48c1c1d190
avoid duplicating StorageLive in let-else 2022-09-18 12:10:53 +08:00
Dylan DPC
3ad81e0dd8
Rollup merge of #93628 - est31:stabilize_let_else, r=joshtriplett 
Stabilize `let else`

🎉  **Stabilizes the `let else` feature, added by [RFC 3137](https://github.com/rust-lang/rfcs/pull/3137).** 🎉

Reference PR: https://github.com/rust-lang/reference/pull/1156

closes #87335 (`let else` tracking issue)

FCP: https://github.com/rust-lang/rust/pull/93628#issuecomment-1029383585

----------

## Stabilization report

### Summary

The feature allows refutable patterns in `let` statements if the expression is
followed by a diverging `else`:

```Rust
fn get_count_item(s: &str) -> (u64, &str) {
    let mut it = s.split(' ');
    let (Some(count_str), Some(item)) = (it.next(), it.next()) else {
        panic!("Can't segment count item pair: '{s}'");
    };
    let Ok(count) = u64::from_str(count_str) else {
        panic!("Can't parse integer: '{count_str}'");
    };
    (count, item)
}
assert_eq!(get_count_item("3 chairs"), (3, "chairs"));
```

### Differences from the RFC / Desugaring

Outside of desugaring I'm not aware of any differences between the implementation and the RFC. The chosen desugaring has been changed from the RFC's [original](https://rust-lang.github.io/rfcs/3137-let-else.html#reference-level-explanations). You can read a detailed discussion of the implementation history of it in `@cormacrelf` 's [summary](https://github.com/rust-lang/rust/pull/93628#issuecomment-1041143670) in this thread, as well as the [followup](https://github.com/rust-lang/rust/pull/93628#issuecomment-1046598419). Since that followup, further changes have happened to the desugaring, in #98574, #99518, #99954. The later changes were mostly about the drop order: On match, temporaries drop in the same order as they would for a `let` declaration. On mismatch, temporaries drop before the `else` block.

### Test cases

In chronological order as they were merged.

Added by df9a2e0687 (#87688):

* [`ui/pattern/usefulness/top-level-alternation.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/pattern/usefulness/top-level-alternation.rs) to ensure the unreachable pattern lint visits patterns inside `let else`.

Added by 5b95df4bdc (#87688):

* [`ui/let-else/let-else-bool-binop-init.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/let-else-bool-binop-init.rs) to ensure that no lazy boolean expressions (using `&&` or `||`) are allowed in the expression, as the RFC mandates.
* [`ui/let-else/let-else-brace-before-else.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/let-else-brace-before-else.rs) to ensure that no `}` directly preceding the `else` is allowed in the expression, as the RFC mandates.
* [`ui/let-else/let-else-check.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/let-else-check.rs) to ensure that `#[allow(...)]` attributes added to the entire `let` statement apply for the `else` block.
* [`ui/let-else/let-else-irrefutable.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/let-else-irrefutable.rs) to ensure that the `irrefutable_let_patterns` lint fires.
* [`ui/let-else/let-else-missing-semicolon.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/let-else-missing-semicolon.rs) to ensure the presence of semicolons at the end of the `let` statement.
* [`ui/let-else/let-else-non-diverging.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/let-else-non-diverging.rs) to ensure the `else` block diverges.
* [`ui/let-else/let-else-run-pass.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/let-else-run-pass.rs) to ensure the feature works in some simple test case settings.
* [`ui/let-else/let-else-scope.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/let-else-scope.rs) to ensure the bindings created by the outer `let` expression are not available in the `else` block of it.

Added by bf7c32a447 (#89965):

* [`ui/let-else/issue-89960.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/issue-89960.rs) as a regression test for the ICE-on-error bug #89960 . Later in 102b9125e1 this got removed in favour of more comprehensive tests.

Added by 856541963c (#89974):

* [`ui/let-else/let-else-if.rs`](https://github.com/rust-lang/rust/blob/1.58.1/src/test/ui/let-else/let-else-if.rs) to test for the improved error message that points out that `let else if` is not possible.

Added by 9b45713b6c:

* [`ui/let-else/let-else-allow-unused.rs`](https://github.com/rust-lang/rust/blob/1.61.0/src/test/ui/let-else/let-else-allow-unused.rs) as a regression test for #89807, to ensure that `#[allow(...)]` attributes added to the entire `let` statement apply for bindings created by the `let else` pattern.

Added by 61bcd8d307 (#89841):

* [`ui/let-else/let-else-non-copy.rs`](https://github.com/rust-lang/rust/blob/1.61.0/src/test/ui/let-else/let-else-non-copy.rs) to ensure that a copy is performed out of non-copy wrapper types. This mirrors `if let` behaviour. The test case bases on rustc internal changes originally meant for #89933 but then removed from the PR due to the error prior to the improvements of #89841.
* [`ui/let-else/let-else-source-expr-nomove-pass.rs `](https://github.com/rust-lang/rust/blob/1.61.0/src/test/ui/let-else/let-else-source-expr-nomove-pass.rs) to ensure that while there is a move of the binding in the successful case, the `else` case can still access the non-matching value. This mirrors `if let` behaviour.

Added by 102b9125e1 (#89841):

* [`ui/let-else/let-else-ref-bindings.rs`](https://github.com/rust-lang/rust/blob/1.61.0/src/test/ui/let-else/let-else-ref-bindings.rs) and [`ui/let-else/let-else-ref-bindings-pass.rs `](https://github.com/rust-lang/rust/blob/1.61.0/src/test/ui/let-else/let-else-ref-bindings-pass.rs) to check `ref` and `ref mut` keywords in the pattern work correctly and error when needed.

Added by 2715c5f984 (#89841):

* Match ergonomic tests adapted from the `rfc2005` test suite.

Added by fec8a507a2 (#89841):

* [`ui/let-else/let-else-deref-coercion-annotated.rs`](https://github.com/rust-lang/rust/blob/1.61.0/src/test/ui/let-else/let-else-deref-coercion-annotated.rs) and [`ui/let-else/let-else-deref-coercion.rs`](https://github.com/rust-lang/rust/blob/1.61.0/src/test/ui/let-else/let-else-deref-coercion.rs) to check deref coercions.

#### Added since this stabilization report was originally written (2022-02-09)

Added by 76ea566677 (#94211):

* [`ui/let-else/let-else-destructuring.rs`](https://github.com/rust-lang/rust/blob/1.63.0/src/test/ui/let-else/let-else-destructuring.rs) to give a nice error message if an user tries to do an assignment with a (possibly refutable) pattern and an `else` block, like asked for in #93995.

Added by e7730dcb7e (#94208):

* [`ui/let-else/let-else-allow-in-expr.rs`](https://github.com/rust-lang/rust/blob/1.61.0/src/test/ui/let-else/let-else-allow-in-expr.rs) to test whether `#[allow(unused_variables)]` works in the expr, as well as its non presence, as well as putting it on the entire `let else` *affects* the expr, too. This was adding a missing test as pointed out by the stabilization report.
* Expansion of `ui/let-else/let-else-allow-unused.rs` and `ui/let-else/let-else-check.rs` to ensure that non-presence of `#[allow(unused)]` does issue the unused lint. This was adding a missing test case as pointed out by the stabilization report.

Added by 5bd71063b3 (#94208):

* [`ui/let-else/let-else-slicing-error.rs`](https://github.com/rust-lang/rust/blob/1.61.0/src/test/ui/let-else/let-else-slicing-error.rs), a regression test for #92069, which got fixed without addition of a regression test. This resolves a missing test as pointed out by the stabilization report.

Added by 5374688e1d (#98574):

* [`src/test/ui/async-await/async-await-let-else.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui/async-await/async-await-let-else.rs) to test the interaction of async/await with `let else`

Added by 6c529ded86 (#98574):

* [`src/test/ui/let-else/let-else-temporary-lifetime.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui/let-else/let-else-temporary-lifetime.rs) as a (partial) regression test for #98672

Added by 9b56640106 (#99518):

* [`src/test/ui/let-else/let-else-temp-borrowck.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui/let-else/let-else-temporary-lifetime.rs) as a regression test for #93951
* Extension of `src/test/ui/let-else/let-else-temporary-lifetime.rs` to include a partial regression test for #98672 (especially regarding `else` drop order)

Added by baf9a7cb57 (#99518):

* Extension of `src/test/ui/let-else/let-else-temporary-lifetime.rs` to include a partial regression test for #93951, similar to `let-else-temp-borrowck.rs`

Added by 60be2de8b7 (#99518):

* Extension of `src/test/ui/let-else/let-else-temporary-lifetime.rs` to include a program that can now be compiled thanks to borrow checker implications of #99518

Added by 47a7a91c96 (#100132):

* [`src/test/ui/let-else/issue-100103.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui/let-else/issue-100103.rs), as a regression test for #100103, to ensure that there is no ICE when doing `Err(...)?` inside else blocks.

Added by e3c5bd617d (#100443):

* [`src/test/ui/let-else/let-else-then-diverge.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui/let-else/let-else-then-diverge.rs), to verify that there is no unreachable code error with the current desugaring.

Added by 981852677c (#100443):

* [`src/test/ui/let-else/issue-94176.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui/let-else/issue-94176.rs), to make sure that a correct span is emitted for a missing trailing expression error. Regression test for #94176.

Added by e182d12a84 (#100434):

* [src/test/ui/unpretty/pretty-let-else.rs](https://github.com/rust-lang/rust/blob/master/src/test/ui/unpretty/pretty-let-else.rs), as a regression test to ensure pretty printing works for `let else` (this bug surfaced in many different ways)

Added by e26285603c (#99954):

* [`src/test/ui/let-else/let-else-temporary-lifetime.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui/let-else/let-else-temporary-lifetime.rs) extended to contain & borrows as well, as this was identified as an earlier issue with the desugaring: https://github.com/rust-lang/rust/issues/98672#issuecomment-1200196921

Added by 2d8460ef43 (#99291):

* [`src/test/ui/let-else/let-else-drop-order.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui/let-else/let-else-drop-order.rs) a matrix based test for various drop order behaviour of `let else`. Especially, it verifies equality of `let` and `let else` drop orders, [resolving](https://github.com/rust-lang/rust/pull/93628#issuecomment-1238498468) a [stabilization blocker](https://github.com/rust-lang/rust/pull/93628#issuecomment-1055738523).

Added by 1b87ce0d40 (#101410):

* Edit to `src/test/ui/let-else/let-else-temporary-lifetime.rs` to add the `-Zvalidate-mir` flag, as a regression test for #99228

Added by af591ebe4d (#101410):

* [`src/test/ui/let-else/issue-99975.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui/let-else/issue-99975.rs) as a regression test for the ICE #99975.

Added by this PR:

* `ui/let-else/let-else.rs`, a simple run-pass check, similar to `ui/let-else/let-else-run-pass.rs`.

### Things not currently tested

* ~~The `#[allow(...)]` tests check whether allow works, but they don't check whether the non-presence of allow causes a lint to fire.~~ → *test added by e7730dcb7eb29a10ee73f269f4dc6e9d606db0da*
* ~~There is no `#[allow(...)]` test for the expression, as there are tests for the pattern and the else block.~~ → *test added by e7730dcb7eb29a10ee73f269f4dc6e9d606db0da*
* ~~`let-else-brace-before-else.rs` forbids the `let ... = {} else {}` pattern and there is a rustfix to obtain `let ... = ({}) else {}`. I'm not sure whether the `.fixed` files are checked by the tooling that they compile. But if there is no such check, it would be neat to make sure that `let ... = ({}) else {}` compiles.~~ → *test added by e7730dcb7eb29a10ee73f269f4dc6e9d606db0da*
* ~~#92069 got closed as fixed, but no regression test was added. Not sure it's worth to add one.~~ → *test added by 5bd71063b3810d977aa376d1e6dd7cec359330cc*
* ~~consistency between `let else` and `if let` regarding lifetimes and drop order: https://github.com/rust-lang/rust/pull/93628#issuecomment-1055738523~~ → *test added by 2d8460ef43d902f34ba2133fe38f66ee8d2fdafc*

Edit: they are all tested now.

### Possible future work / Refutable destructuring assignments

[RFC 2909](https://rust-lang.github.io/rfcs/2909-destructuring-assignment.html) specifies destructuring assignment, allowing statements like `FooBar { a, b, c } = foo();`.
As it was stabilized, destructuring assignment only allows *irrefutable* patterns, which before the advent of `let else` were the only patterns that `let` supported.
So the combination of `let else` and destructuring assignments gives reason to think about extensions of the destructuring assignments feature that allow refutable patterns, discussed in #93995.

A naive mapping of `let else` to destructuring assignments in the form of `Some(v) = foo() else { ... };` might not be the ideal way. `let else` needs a diverging `else` clause as it introduces new bindings, while assignments have a default behaviour to fall back to if the pattern does not match, in the form of not performing the assignment. Thus, there is no good case to require divergence, or even an `else` clause at all, beyond the need for having *some* introducer syntax so that it is clear to readers that the assignment is not a given (enums and structs look similar). There are better candidates for introducer syntax however than an empty `else {}` clause, like `maybe` which could be added as a keyword on an edition boundary:

```Rust
let mut v = 0;
maybe Some(v) = foo(&v);
maybe Some(v) = foo(&v) else { bar() };
```

Further design discussion is left to an RFC, or the linked issue.
 2022-09-17 15:31:06 +05:30
bors
c524c7dd25 Auto merge of #98588 - b-naber:valtrees-cleanup, r=lcnr 
Use only ty::Unevaluated<'tcx, ()> in type system

r? `@lcnr`
 2022-09-17 03:04:22 +00:00
Oli Scherer
dab1074b91 Only generate OpaqueCast for opaque types 2022-09-16 11:37:50 +00:00
Oli Scherer
40e2de8c41 Revert "Revert "Rollup merge of #98582 - oli-obk:unconstrained_opaque_type, r=estebank"" 
This reverts commit 4a742a691e.
 2022-09-16 11:36:39 +00:00
Oli Scherer
5d664f7a8f Merge two arguments into one 2022-09-16 11:36:09 +00:00
est31
173eb6f407 Only enable the let_else feature on bootstrap 
On later stages, the feature is already stable.

Result of running:

rg -l "feature.let_else" compiler/ src/librustdoc/ library/ | xargs sed -s -i "s#\\[feature.let_else#\\[cfg_attr\\(bootstrap, feature\\(let_else\\)#"
 2022-09-15 21:06:45 +02:00
est31
5633e863bd Remove feature gate from let else suggestion 
The let else suggestion added by 0d92752b8a
does not need a feature gate any more.
 2022-09-15 21:06:45 +02:00
Ding Xiang Fei
4a5d2a561c
add diagram to explain the MIR structure 2022-09-15 10:08:14 +08:00