Provided that the iterator has finite length and does not trigger user-provided code, this is safe.
What follows is a full list of the DoubleEndedIterators in liballoc/libcore and whether this optimization is safe, and if not, why not.
src/liballoc/boxed.rs
Box: Pass through to avoid defeating optimization of the underlying DoubleIterator implementation. This has no correctness impact.
src/liballoc/collections/binary_heap.rs
Iter: Pass through to avoid defeating optimizations on slice::Iter
IntoIter: Not safe, changes Drop order
Drain: Not safe, changes Drop order
src/liballoc/collections/btree/map.rs
Iter: Safe to call next_back, invokes no user defined code.
IterMut: ditto
IntoIter: Not safe, changes Drop order
Keys: Safe to call next_back, invokes no user defined code.
Values: ditto
ValuesMut: ditto
Range: ditto
RangeMut: ditto
src/liballoc/collections/btree/set.rs
Iter: Safe to call next_back, invokes no user defined code.
IntoIter: Not safe, changes Drop order
Range: Safe to call next_back, invokes no user defined code.
src/liballoc/collections/linked_list.rs
Iter: Safe to call next_back, invokes no user defined code.
IterMut: ditto
IntoIter: Not safe, changes Drop order
src/liballoc/collections/vec_deque.rs
Iter: Safe to call next_back, invokes no user defined code.
IterMut: ditto
IntoIter: Not safe, changes Drop order
Drain: ditto
src/liballoc/string.rs
Drain: Safe because return type is a primitive (char)
src/liballoc/vec.rs
IntoIter: Not safe, changes Drop order
Drain: ditto
Splice: ditto
src/libcore/ascii.rs
EscapeDefault: Safe because return type is a primitive (u8)
src/libcore/iter/adapters/chain.rs
Chain: Not safe, invokes user defined code (Iterator impl)
src/libcore/iter/adapters/flatten.rs
FlatMap: Not safe, invokes user defined code (Iterator impl)
Flatten: ditto
FlattenCompat: ditto
src/libcore/iter/adapters/mod.rs
Rev: Not safe, invokes user defined code (Iterator impl)
Copied: ditto
Cloned: Not safe, invokes user defined code (Iterator impl and T::clone)
Map: Not safe, invokes user defined code (Iterator impl + closure)
Filter: ditto
FilterMap: ditto
Enumerate: Not safe, invokes user defined code (Iterator impl)
Skip: ditto
Fuse: ditto
Inspect: ditto
src/libcore/iter/adapters/zip.rs
Zip: Not safe, invokes user defined code (Iterator impl)
src/libcore/iter/range.rs
ops::Range: Not safe, changes Drop order, but ALREADY HAS SPECIALIZATION
ops::RangeInclusive: ditto
src/libcore/iter/sources.rs
Repeat: Not safe, calling last should iloop.
Empty: No point, iterator is at most one item long.
Once: ditto
OnceWith: ditto
src/libcore/option.rs
Item: No point, iterator is at most one item long.
Iter: ditto
IterMut: ditto
IntoIter: ditto
src/libcore/result.rs
Iter: No point, iterator is at most one item long
IterMut: ditto
IntoIter: ditto
src/libcore/slice/mod.rs
Split: Not safe, invokes user defined closure
SplitMut: ditto
RSplit: ditto
RSplitMut: ditto
Windows: Safe, already has specialization
Chunks: ditto
ChunksMut: ditto
ChunksExact: ditto
ChunksExactMut: ditto
RChunks: ditto
RChunksMut: ditto
RChunksExact: ditto
RChunksExactMut: ditto
src/libcore/str/mod.rs
Chars: Safe, already has specialization
CharIndices: ditto
Bytes: ditto
Lines: Safe to call next_back, invokes no user defined code.
LinesAny: Deprecated
Everything that is generic over P: Pattern: Not safe because Pattern invokes user defined code.
SplitWhitespace: Safe to call next_back, invokes no user defined code.
SplitAsciiWhitespace: ditto
Revert "Set test flag when rustdoc is running with --test option"
Reverts https://github.com/rust-lang/rust/pull/59940.
It caused doctests in this repository to no longer be tested including all of the core crate.
Add suggestion for missing `.await` keyword
This commit adds a suggestion diagnostic for missing `.await`. In order to do this, the trait `Future` is promoted to a lang item.
Compiling code of the form:
```rust
#![feature(async_await)]
fn take_u32(x: u32) {}
async fn make_u32() -> u32 {
22
}
async fn foo() {
let x = make_u32();
take_u32(x)
}
fn main() {}
```
Will now result in the suggestion:
```
error[E0308]: mismatched types
--> src/main.rs:11:18
|
11 | take_u32(x)
| ^
| |
| expected u32, found opaque type
| help: consider using `.await` here: `x.await`
|
= note: expected type `u32`
found type `impl std::future::Future`
```
This commit does not cover chained expressions and therefore only covers the case originally pointed out in #61076. Cases I can think of that still need to be covered:
- [ ] Return places for functions
- [ ] Field access
- [ ] Method invocation
I'm planning to submit PRs for each of these separately as and when I have figured them out.
Fix meta-variable binding errors in macros
The errors are either:
- The meta-variable used in the right-hand side is not bound (or defined) in the
left-hand side.
- The meta-variable used in the right-hand side does not repeat with the same
kleene operator as its binder in the left-hand side. Either it does not repeat
enough, or it uses a different operator somewhere.
This change should have no semantic impact.
Found by https://github.com/rust-lang/rust/pull/62008
The errors are either:
- The meta-variable used in the right-hand side is not bound (or defined) in the
left-hand side.
- The meta-variable used in the right-hand side does not repeat with the same
kleene operator as its binder in the left-hand side. Either it does not repeat
enough, or it uses a different operator somewhere.
This change should have no semantic impact.
Remove the default type of `Rem::Output`
Associated type defaults are not yet stable, and `Rem` is the only trait that specifies a default. Let's see what breaks when it's removed.
cc https://github.com/rust-lang/rust/pull/61812#issuecomment-502394566
cc @Centril
@bors try
Implement nth_back for slice::{Iter, IterMut}
Part of #54054.
I implemented `nth_back` as straightforwardly as I could, and then slightly changed `nth` to match `nth_back`. I believe I did so correctly, but please double-check 🙂
I also added the helper methods `zst_shrink`, `next_unchecked`, and `next_back_unchecked` to get rid of some duplicated code. These changes hopefully make this code easier to understand for new contributors like me.
I noticed the `is_empty!` and `len!` macros which sole purpose seems to be inlining, according to the comment right above them, but the `is_empty` and `len` methods are already marked with `#[inline(always)]`. Does that mean we could replace these macros with method calls, without affecting anything? I'd love to get rid of them.
Rollup of 11 pull requests
Successful merges:
- #61505 (Only show methods that appear in `impl` blocks in the Implementors sections of trait doc pages)
- #61701 (move stray run-pass const tests into const/ folder)
- #61748 (Tweak transparent enums and unions diagnostic spans)
- #61802 (Make MaybeUninit #[repr(transparent)])
- #61839 (ci: Add a script for generating CPU usage graphs)
- #61842 (Remove unnecessary lift calls)
- #61843 (Turn down the myriad-closures test)
- #61896 (rustc_typeck: correctly compute `Substs` for `Res::SelfCtor`.)
- #61898 (syntax: Factor out common fields from `SyntaxExtension` variants)
- #61938 (create an issue for miri even in status test-fail)
- #61941 (Preserve generator and yield source for error messages)
Failed merges:
r? @ghost
Refactor C FFI variadics to more closely match their C counterparts, and add Clone implementation
We had to make some changes to expose `va_copy` and `va_end` directly to users (mainly for C2Rust, but not exclusively):
- redefine the Rust variadic structures to more closely correspond to C: `VaList` now matches `va_list`, and `VaListImpl` matches `__va_list_tag`
- add `Clone` for `VaListImpl`
- add explicit `as_va_list()` conversion function from `VaListImpl` to `VaList`
- add deref coercion from `VaList` to `VaListImpl`
- add support for the `asmjs` target
All these changes were needed for use cases like:
```Rust
let mut ap2 = va_copy(ap);
vprintf(fmt, ap2);
va_end(&mut ap2);
```
Help LLVM better optimize slice::Iter(Mut)::len
r? @RalfJung
I've included a codegen test that fails without this change as a demonstration of usefulness.
Change `...` to `..=` where applicable
This is mainly to fix#61816, but I decided to manually check a few thousand `...` throughout the code base to check for any other cases. I think I found a documentation bug in `src\libsyntax\ast.rs` where both `1..` and `1...` where mentioned. If there is internal support for both `1..` and `1..=` (that can exist before error handling gets to it), then I can add that back.
There were some other cases that look like `// struct Closure<'l0...'li, T0...Tj, CK, CS, U0...Uk> {`, `// <P0 as Trait<P1...Pn>>::Foo: 'a`, and `assert!(min <= max, "discriminant range is {}...{}", min, max);`, but I am not sure if I should change those.
There are a bunch of cases in the `/test/` directory that could be changed, but I presume I should just leave those be.
