Rollup of 5 pull requests #97347
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Rollup of 5 pull requests #97347
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this simplifies the code inside the `structure.each` closure argument and allows to remove the `vis` field from `FieldInfo`.
(with an intermediate raw ptr, not a direct transmute)
Modify MIR building to drop repeat expressions with length zero Closes rust-lang#74836 . Previously, when a user wrote `[foo; 0]` we used to simply leak `foo`. The goal is to fix that. This PR changes MIR building to make `[foo; 0]` equivalent to `{ drop(foo); [] }` in all cases. Of course, this is a breaking change (see below). A crater run did not indicate any regressions though, and given that the previous behavior was almost definitely not what any user wanted, it seems unlikely that anyone was relying on this. Note that const generics are in general unaffected by this. Inserting the extra `drop` is only meaningful/necessary when `foo` is of a non-`Copy` type, and array repeat expressions with const generic repetition count must always be `Copy`. Besides the obvious change to behavior associated with the additional drop, there are three categories of examples where this also changes observable behavior. In all of these cases, the new behavior is consistent with what you would get by replacing `[foo; 0]` with `{ drop(foo); [] }`. As such, none of these give the user new powers to express more things. **No longer allowed in const (breaking)**: ```rust const _: [String; 0] = [String::new(); 0]; ``` This compiles on stable today. Because we now introduce the drop of `String`, this no longer compiles as `String` may not be dropped in a const context. **Reduced dataflow (non-breaking)**: ```rust let mut x: i32 = 0; let r = &x; let a = [r; 0]; x = 5; let _b = a; ``` Borrowck rejects this code on stable because it believes there is dataflow between `a` and `r`, and so the lifetime of `r` has to extend to the last statement. This change removes the dataflow and the above code is allowed to compile. **More const promotion (non-breaking)**: ```rust let _v: &'static [String; 0] = &[String::new(); 0]; ``` This does not compile today because `String` having drop glue keeps it from being const promoted (despite that drop glue never being executed). After this change, this is allowed to compile. ### Alternatives A previous attempt at this tried to reduce breakage by various tricks. This is still a possibility, but given that crater showed no regressions it seems unclear why we would want to introduce this complexity. Disallowing `[foo; 0]` completely is also an option, but obviously this is more of a breaking change. I do not know how often this is actually used though. r? `@oli-obk`
…vidtwco Avoid double binding of subdiagnostics inside `#[derive(SessionDiagnostic)]` r? `@davidtwco`
…ylan-DPC Lifetime variance fixes for rustdoc rust-lang#97287 migrates rustc to a `Ty` type that is invariant over its lifetime `'tcx`, so I need to fix a bunch of places that assume that `Ty<'a>` and `Ty<'b>` can be unified by shortening both to some common lifetime. This is doable, since everything is already `'tcx`, so all this PR does is be a bit more explicit that elided lifetimes are actually `'tcx`. Split out from rust-lang#97287 so the rustdoc team can review independently.
…, r=davidtwco
Parse expression after `else` as a condition if followed by `{`
Fixes rust-lang#49361.
Two things:
1. This wording needs help. I can never find a natural/intuitive phrasing when I write diagnostics 😅
2. Do we even want to show the "wrap in braces" case? I would assume most of the time the "add an `if`" case is the right one.
explain how to turn integers into fn ptrs (with an intermediate raw ptr, not a direct transmute) Direct int2ptr transmute, under the semantics I am imagining, will produce a ptr with "invalid" provenance that is invalid to deref or call. We cannot give it the same semantics as int2ptr casts since those do [something complicated](https://www.ralfj.de/blog/2022/04/11/provenance-exposed.html). To my great surprise, that is already what the example in the `transmute` docs does. :) I still added a comment to say that that part is important, and I added a section explicitly talking about this to the `fn()` type docs. With rust-lang/miri#2151, Miri will start complaining about direct int-to-fnptr transmutes (in the sense that it is UB to dereference the resulting pointer).
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@bors r+ rollup=never p=5 |
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📌 Commit dd60378 has been approved by |
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⌛ Testing commit dd60378 with merge e71513c6d5a89d80bf4cc3a6117a8305cbaff755... |
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💔 Test failed - checks-actions |
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Failed by #95953 |
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Successful merges:
#[derive(SessionDiagnostic)]#97121 (Avoid double binding of subdiagnostics inside#[derive(SessionDiagnostic)])elseas a condition if followed by{#97298 (Parse expression afterelseas a condition if followed by{)Failed merges:
r? @ghost
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