This *almost* completes the job for #16440. The idea is that even if we do not know whether some closure type `C` implements `Fn` or `FnMut` (etc), we still know its argument and return types. So if we see an obligation `C : Fn(_0)`, we can unify `_0` with those argument types while still considering the obligation ambiguous and unsatisfied. This helps to make a lot of progress with type inference even before closure kind inference is done.
As part of this PR, the explicit `:` syntax is removed from the AST and completely ignored. We still infer the closure kind based on the expected type if that is available. There are several reasons for this. First, deciding the closure kind earlier is always better, as it allows us to make more progress. Second, this retains a (admittedly obscure) way for users to manually specify the closure kind, which is useful for writing tests if nothing else. Finally, there are still some cases where inference can fail, so it may be useful to have this manual override. (The expectation is that we will eventually revisit an explicit syntax for specifying the closure kind, but it will not be `:` and may be some sort of generalization of the `||` syntax to handle other traits as well.)
This commit does not *quite* fix#16640 because a snapshot is still needed to enable the obsolete syntax errors for explicit `&mut:` and friends.
r? @eddyb as he reviewed the prior patch in this direction
The extra check caused by the expect() call can, in general, not be
optimized away, because the length of the iterator is unknown at compile
time, causing a noticable slow-down. Since the check only triggers if
the element isn't actually found in the iterator, i.e. it isn't
guaranteed to trigger for ill-behaved ExactSizeIterators, it seems
reasonable to switch to an implementation that doesn't need the check
and just always returns None if the value isn't found.
Benchmark:
````rust
let v: Vec<u8> = (0..1024*65).map(|_| 0).collect();
b.iter(|| {
v.as_slice().iter().rposition(|&c| c == 1)
});
````
Before:
````
test rposition ... bench: 49939 ns/iter (+/- 23)
````
After:
````
test rposition ... bench: 33306 ns/iter (+/- 68)
````
`{` and `}` aren’t valid characters on ARM.
This also fixes a small bug where `)` (**r**ight **p**arenthesis) and `*`
(**r**aw **p**ointer) would both mangle to `$RP$`, making `)` show up as `*` in
backtraces.
Building over night, posting for review now. Presumably not much should need change.
I consider this necessary to move forward with a proper stabilization of the API.
r? @huonw
This commit is an implementation of [RFC 576][rfc] which adds back the `std::io`
module to the standard library. No functionality in `std::old_io` has been
deprecated just yet, and the new `std::io` module is behind the same `io`
feature gate.
[rfc]: https://github.com/rust-lang/rfcs/pull/576
A good bit of functionality was copied over from `std::old_io`, but many tweaks
were required for the new method signatures. Behavior such as precisely when
buffered objects call to the underlying object may have been tweaked slightly in
the transition. All implementations were audited to use composition wherever
possible. For example the custom `pos` and `cap` cursors in `BufReader` were
removed in favor of just using `Cursor<Vec<u8>>`.
A few liberties were taken during this implementation which were not explicitly
spelled out in the RFC:
* The old `LineBufferedWriter` is now named `LineWriter`
* The internal representation of `Error` now favors OS error codes (a
0-allocation path) and contains a `Box` for extra semantic data.
* The io prelude currently reexports `Seek` as `NewSeek` to prevent conflicts
with the real prelude reexport of `old_io::Seek`
* The `chars` method was moved from `BufReadExt` to `ReadExt`.
* The `chars` iterator returns a custom error with a variant that explains that
the data was not valid UTF-8.
This PR implements [path reform](https://github.com/rust-lang/rfcs/pull/474), and motivation and details for the change can be found there.
For convenience, the old path API is being kept as `old_path` for the time being. Updating after this PR is just a matter of changing imports to `old_path` (which is likely not needed, since the prelude entries still export the old path API).
This initial PR does not include additional normalization or platform-specific path extensions. These will be done in follow up commits or PRs.
[breaking-change]
Closes#20034Closes#12056Closes#11594Closes#14028Closes#14049Closes#10035
Implements [RFC 474](https://github.com/rust-lang/rfcs/pull/474); see
that RFC for details/motivation for this change.
This initial commit does not include additional normalization or
platform-specific path extensions. These will be done in follow up
commits or PRs.
Use the crates.io crate `rand` (version 0.1 should be a drop in
replacement for `std::rand`) and `rand_macros` (`#[derive_Rand]` should
be a drop-in replacement).
[breaking-change]
As part of [RFC 474](https://github.com/rust-lang/rfcs/pull/474), this
commit renames `std::path` to `std::old_path`, leaving the existing path
API in place to ease migration to the new one. Updating should be as
simple as adjusting imports, and the prelude still maps to the old path
APIs for now.
[breaking-change]
This commit is an implementation of [RFC 576][rfc] which adds back the `std::io`
module to the standard library. No functionality in `std::old_io` has been
deprecated just yet, and the new `std::io` module is behind the same `io`
feature gate.
[rfc]: https://github.com/rust-lang/rfcs/pull/576
A good bit of functionality was copied over from `std::old_io`, but many tweaks
were required for the new method signatures. Behavior such as precisely when
buffered objects call to the underlying object may have been tweaked slightly in
the transition. All implementations were audited to use composition wherever
possible. For example the custom `pos` and `cap` cursors in `BufReader` were
removed in favor of just using `Cursor<Vec<u8>>`.
A few liberties were taken during this implementation which were not explicitly
spelled out in the RFC:
* The old `LineBufferedWriter` is now named `LineWriter`
* The internal representation of `Error` now favors OS error codes (a
0-allocation path) and contains a `Box` for extra semantic data.
* The io prelude currently reexports `Seek` as `NewSeek` to prevent conflicts
with the real prelude reexport of `old_io::Seek`
* The `chars` method was moved from `BufReadExt` to `ReadExt`.
* The `chars` iterator returns a custom error with a variant that explains that
the data was not valid UTF-8.
This removes the `ByRef` iterator adaptor to stay in line with the changes to
`std::io`. The `by_ref` method instead just returns `&mut Self`.
This also removes the implementation of `Iterator for &mut Iterator` and instead
generalizes it to `Iterator for &mut I` where `I: Iterator + ?Sized`. The
`Box<I>` implementations were also updated.
This is a breaking change due to the removal of the `std::iter::ByRef` type. All
mentions of `ByRef<'a, T>` should be replaced with `&mut T` to migrate forward.
[breaking-change]
upgrade the inference based on expected type so that it is able to
infer the fn kind in isolation even if the full signature is not
available (and we could perhaps do better still in some cases, such as
extracting just the types of the arguments but not the return value).
closure kind, thereby detecting what happens if there are
mismatches. Simply removing the `:` annotations caused most of these
tests to pass or produce other errors, because the inference would
convert the closure into a more appropriate kind. (The ability to
override the inference by using the expected type is an important
backdoor partly for this reason.)
possible. There is some amount of duplication as a result (similar to
select) -- I am not happy about this but not sure how to fix it
without deeper rewrites.
The extra check caused by the expect() call can, in general, not be
optimized away, because the length of the iterator is unknown at compile
time, causing a noticable slow-down. Since the check only triggers if
the element isn't actually found in the iterator, i.e. it isn't
guaranteed to trigger for ill-behaved ExactSizeIterators, it seems
reasonable to switch to an implementation that doesn't need the check
and just always returns None if the value isn't found.
Benchmark:
````rust
let v: Vec<u8> = (0..1024*65).map(|_| 0).collect();
b.iter(|| {
v.as_slice().iter().rposition(|&c| c == 1)
});
````
Before:
````
test rposition ... bench: 49939 ns/iter (+/- 23)
````
After:
````
test rposition ... bench: 33306 ns/iter (+/- 68)
````
That is, when offering suggestions for unresolved method calls, avoid
suggesting traits for which implementing the trait for the receiver type
either makes little sense (e.g. type errors, or sugared unboxed
closures), or violates coherence.
The latter is approximated by ensuring that at least one of `{receiver
type, trait}` is local. This isn't precisely correct due to
multidispatch, but the error messages one encounters in such situation
are useless more often than not; it is better to be conservative and
miss some cases, than have overly many false positives (e.g. writing
`some_slice.map(|x| ...)` uselessly suggested that one should implement
`IteratorExt` for `&[T]`, while the correct fix is to call `.iter()`).
Closes#21420.
That is, when offering suggestions for unresolved method calls, avoid
suggesting traits for which implementing the trait for the receiver type
either makes little sense (e.g. type errors, or sugared unboxed
closures), or violates coherence.
The latter is approximated by ensuring that at least one of `{receiver
type, trait}` is local. This isn't precisely correct due to
multidispatch, but the error messages one encounters in such situation
are useless more often than not; it is better to be conservative and
miss some cases, than have overly many false positives (e.g. writing
`some_slice.map(|x| ...)` uselessly suggested that one should implement
`IteratorExt` for `&[T]`, while the correct fix is to call `.iter()`).
Closes#21420.
I’d kind of like to be able to use HashState in AnyMap, which I can’t do without a stability attribute on it. While I was at it I looked around and found a few more missing.
