Match ergonomics 2024: Implement eat-one-layer#123512
Conversation
rustbot
added
S-waiting-on-review
Jules-Bertholet
force-pushed
the
ref-pat-eat-one-layer-2024
branch
2 times, most recently
from
0c430f7 to
2f730c1
Compare
| if let Some(&mut Some(&x)) = &Some(&mut Some(0)) { | ||
| let _: u32 = x; | ||
| } | ||
| if let Some(&Some(&mut x)) = &mut Some(& Some(0)) { | ||
| let _: u32 = x; | ||
| } |
There was a problem hiding this comment.
These two are weird, shouldn't we be eating references in the same order as in the type?
There was a problem hiding this comment.
Does this typecheck?
if let Some(&Some(x)) = &mut Some(&Some(0)) {
let _: &mut u32 = x;
}There was a problem hiding this comment.
Does this typecheck?
Not any longer, pushed a fix so we now properly downgrade the mutability of the inherited reference.
Shouldn't we be eating references in the same order as in the type?
No, that would be unnecessarily restrictive, as demonstrated by this newly added test:
if let Some(Some(&mut x)) = &Some(Some(&mut 0)) {
let _: &u32 = x;
}(let &mut x = &&mut 0 does not work currently, but I think it should, will try to fix edit: also works now)
There was a problem hiding this comment.
Hm, I would not expect these tests to work personally.
I would expect we want a rule like: let &mut x = <expr>; x: T iff let x = <expr>; x: &mut T, no?
There was a problem hiding this comment.
I don't see any good reason we should restrict it to that, when the currently implemented rule (if the pattern can match against the inherited reference, do so; otherwise match against a reference in the scrutinee type) is strictly more useful. let Some(&mut x) = &Some(&mut 0) is more convenient than let &Some(&mut (ref x)) = &Some(&mut 0), why should we force people to use the latter?
There was a problem hiding this comment.
Wouldn't let Some(&x) = &Some(&mut 0) work just as well?
There was a problem hiding this comment.
No, that would make x an &mut {integer} instead of an &{integer}, and then the compiler yells at you that you can't move out of a shared reference
There was a problem hiding this comment.
Oh I see. Well, I'm happy to merge your design, this is an implementation review not a design review. I'll just need some time to wrap my head around the new commits
Jules-Bertholet
force-pushed
the
ref-pat-eat-one-layer-2024
branch
from
cf7cdfc to
e5b63c2
Compare
|
Some changes occurred in match checking cc @Nadrieril |
Nadrieril
left a comment
Nadrieril
left a comment
There was a problem hiding this comment.
Alright, that looks quite good. I'm ok with most of the implementation, I'd just like to try and simplify calc_default_binding_mode further because it's becoming thorny.
compiler/rustc_hir_typeck/src/pat.rs
Outdated
| AdjustMode::ResetAndConsumeRef(ref_pat_mutbl) => { | ||
| let mutbls_match = def_bm.0 == ByRef::Yes(ref_pat_mutbl); | ||
| if pat.span.at_least_rust_2024() && self.tcx.features().ref_pat_eat_one_layer_2024 { | ||
| let max_ref_mutbl = cmp::min(max_ref_mutbl, ref_pat_mutbl); |
There was a problem hiding this comment.
Intuitively I'd expect we can just cap def_bm by max_ref_mutbl just before returning from the function, and cap it by ref_pat_mutbl at the end of this if. Does that work? The peel_off_references change I just suggested could help.
There was a problem hiding this comment.
I made a slight tweak to this function, but didn't go as far as that. The capping by max_ref_mutbl has to be gated by edition/feature gate, so needs to stay inside the if.
|
@rustbot author |
rustbot
added
S-waiting-on-author
rustbot
added
S-waiting-on-review
|
☔ The latest upstream changes (presumably #123991) made this pull request unmergeable. Please resolve the merge conflicts. |
Jules-Bertholet
force-pushed
the
ref-pat-eat-one-layer-2024
branch
from
a4640f4 to
3efbe3e
Compare
|
Looks good, ty! @bors r+ |
bors
added
S-waiting-on-bors
…llaumeGomez Rollup of 7 pull requests Successful merges: - rust-lang#122811 (Move `SourceMap` initialization) - rust-lang#123512 (Match ergonomics 2024: Implement eat-one-layer) - rust-lang#123811 (Use queue-based `RwLock` on more platforms) - rust-lang#123859 (Remove uneeded clones now that TrustedStep implies Copy) - rust-lang#123979 (Subtype predicates only exist on inference types, so we can allow them to register opaque types within them.) - rust-lang#124016 (Outline default query and hook provider function implementations) - rust-lang#124023 (Allow workproducts without object files.) r? `@ghost` `@rustbot` modify labels: rollup
Rollup merge of rust-lang#123512 - Jules-Bertholet:ref-pat-eat-one-layer-2024, r=Nadrieril Match ergonomics 2024: Implement eat-one-layer r? `@Nadrieril` cc rust-lang#123076 `@rustbot` label A-edition-2024 A-patterns
5 participants
r? @Nadrieril
cc #123076
@rustbot label A-edition-2024 A-patterns