Implement the `loop_break_value` feature.
This implements RFC 1624, tracking issue #37339.
- `FnCtxt` (in typeck) gets a stack of `LoopCtxt`s, which store the
currently deduced type of that loop, the desired type, and a list of
break expressions currently seen. `loop` loops get a fresh type
variable as their initial type (this logic is stolen from that for
arrays). `while` loops get `()`.
- `break {expr}` looks up the broken loop, and unifies the type of
`expr` with the type of the loop.
- `break` with no expr unifies the loop's type with `()`.
- When building MIR, loops no longer construct a `()` value at
termination of the loop; rather, the `break` expression assigns the
result of the loop.
- ~~I have also changed the loop scoping in MIR-building so that the test
of a while loop is not considered to be part of that loop. This makes
the rules consistent with #37360. The new loop scopes in typeck also
follow this rule. That means that `loop { while (break) {} }` now
terminates instead of looping forever. This is technically a breaking
change.~~
- ~~On that note, expressions like `while break {}` and `if break {}` no
longer parse because `{}` is interpreted as an expression argument to
`break`. But no code except compiler test cases should do that anyway
because it makes no sense.~~
- The RFC did not make it clear, but I chose to make `break ()` inside
of a `while` loop illegal, just in case we wanted to do anything with
that design space in the future.
This is my first time dealing with this part of rustc so I'm sure
there's plenty of problems to pick on here ^_^
On unix like systems, the underlying file corresponding to any given path may
change at any time. This function makes it possible to set the permissions of
the a file corresponding to a `File` object even if its path changes.
Make Peekable remember peeking a None
Peekable should remember if a None has been seen in the `.peek()` method.
It ensures that `.peek(); .peek();` or `.peek(); .next();` only advances the
underlying iterator at most once. This does not by itself make the iterator
fused.
Thanks to @s3bk for the code in `fn peek()` itself.
Fixes#37784
This implements RFC 1624, tracking issue #37339.
- `FnCtxt` (in typeck) gets a stack of `LoopCtxt`s, which store the
currently deduced type of that loop, the desired type, and a list of
break expressions currently seen. `loop` loops get a fresh type
variable as their initial type (this logic is stolen from that for
arrays). `while` loops get `()`.
- `break {expr}` looks up the broken loop, and unifies the type of
`expr` with the type of the loop.
- `break` with no expr unifies the loop's type with `()`.
- When building MIR, `loop` loops no longer construct a `()` value at
termination of the loop; rather, the `break` expression assigns the
result of the loop. `while` loops are unchanged.
- `break` respects contexts in which expressions may not end with braced
blocks. That is, `while break { break-value } { while-body }` is
illegal; this preserves backwards compatibility.
- The RFC did not make it clear, but I chose to make `break ()` inside
of a `while` loop illegal, just in case we wanted to do anything with
that design space in the future.
This is my first time dealing with this part of rustc so I'm sure
there's plenty of problems to pick on here ^_^
parser: simplify directory ownership semantics
This PR simplifies the semantics of "directory ownership". After this PR,
- a non-inline module without a `#[path]` attribute (e.g. `mod foo;`) is allowed iff its parent module/block (whichever is nearer) is a directory owner,
- an non-inline module is a directory owner iff its corresponding file is named `mod.rs` (c.f. [comment](https://github.com/rust-lang/rust/issues/32401#issuecomment-201021902)),
- a block is never a directory owner (c.f. #31534), and
- an inline module is a directory owner iff either
- its parent module/block is a directory owner (again, c.f. #31534), or
- it has a `#[path]` attribute (c.f. #36789).
These semantics differ from today's in three orthogonal ways:
- `#[path = "foo.rs"] mod foo;` is no longer a directory owner. This is a [breaking-change].
- #36789 is generalized to apply to modules that are not directory owners in addition to blocks.
- A macro-expanded non-inline module is only allowed where an ordinary non-inline module would be allowed. Today, we incorrectly allow macro-expanded non-inline modules in modules that are not directory owners (but not in blocks). This is a [breaking-change].
Fixes#32401.
r? @nikomatsakis
Change HirVec<P<T>> to HirVec<T> in hir:: Expr.
This PR changes data structures like this:
```
[ ExprArray | 8 | P ]
|
v
[ P | P | P | P | P | P | P | P ]
|
v
[ ExprTup | 2 | P ]
|
v
[ P | P ]
|
v
[ Expr ]
```
to this:
```
[ ExprArray | 8 | P ]
|
v
[ [ ExprTup | 2 | P ] | ... ]
|
v
[ Expr | Expr ]
```
I thought this would be a win for #36799, and on a cut-down version of that workload this reduces the peak heap size (as measured by Massif) from 885 MiB to 875 MiB. However, the peak RSS as measured by `-Ztime-passes` and by `/usr/bin/time` increases by about 30 MiB.
I'm not sure why. Just look at the picture above -- the second data structure clearly takes up less space than the first. My best idea relates to unused elements in the slices. `HirVec<Expr>` is a typedef for `P<[Expr]>`. If there were any unused excess elements then I could see that memory usage would increase, because those excess elements are larger in `HirVec<Expr>` than in `HirVec<P<Expr>>`. But AIUI there are no such excess elements, and Massif's measurements corroborate that.
However, the two main creation points for these data structures are these lines from `lower_expr`:
```rust
ExprKind::Vec(ref exprs) => {
hir::ExprArray(exprs.iter().map(|x| self.lower_expr(x)).collect())
}
ExprKind::Tup(ref elts) => {
hir::ExprTup(elts.iter().map(|x| self.lower_expr(x)).collect())
}
```
I suspect what is happening is that temporary excess elements are created within the `collect` calls. The workload from #36799 has many 2-tuples and 3-tuples and when `Vec` gets doubled it goes from a capacity of 1 to 4, which would lead to excess elements. Though, having said that, `Vec::with_capacity` doesn't create excess AFAICT. So I'm not sure. What goes on inside `collect` is complex.
Anyway, in its current form this PR is a memory consumption regression and so not worth landing but I figured I'd post it in case anyone has additional insight.
This changes structures like this:
```
[ ExprArray | 8 | P ]
|
v
[ P | P | P | P | P | P | P | P ]
|
v
[ ExprTup | 2 | P ]
|
v
[ P | P ]
|
v
[ Expr ]
```
to this:
```
[ ExprArray | 8 | P ]
|
v
[ [ ExprTup | 2 | P ] | ... ]
|
v
[ Expr | Expr ]
```
libstd: support creation of anonymous pipe on WinXP/2K3
`PIPE_REJECT_REMOTE_CLIENTS` flag is not supported on Windows < VISTA, and every invocation of `anon_pipe` including attempts to pipe `std::process::Child`'s stdio fails.
This PR should work around this issue by performing a runtime check of windows version and conditionally omitting this flag on "XP and friends".
Getting the version should be probably moved out of the function `anon_pipe` itself (the OS version does not often change during runtime :) ), but:
- I didn't find any precedent for this and assuming there's not much overhead (I hope windows does not perform any heuristics to find out it's own version, just fills couple of fields in the struct).
- the code path is not especially performance sensitive anyway.
Clean up `ast::Attribute`, `ast::CrateConfig`, and string interning
This PR
- removes `ast::Attribute_` (changing `Attribute` from `Spanned<Attribute_>` to a struct),
- moves a `MetaItem`'s name from the `MetaItemKind` variants to a field of `MetaItem`,
- avoids needlessly wrapping `ast::MetaItem` with `P`,
- moves string interning into `syntax::symbol` (`ast::Name` is a reexport of `symbol::Symbol` for now),
- replaces `InternedString` with `Symbol` in the AST, HIR, and various other places, and
- refactors `ast::CrateConfig` from a `Vec` to a `HashSet`.
r? @eddyb
Improve .chars().count()
Use a simpler loop to count the `char` of a string: count the
number of non-continuation bytes. Use `count += <conditional>` which the
compiler understands well and can apply loop optimizations to.
benchmark descriptions and results for two configurations:
- ascii: ascii text
- cy: cyrillic text
- jp: japanese text
- words ascii: counting each split_whitespace item from the ascii text
- words jp: counting each split_whitespace item from the jp text
```
x86-64 rustc -Copt-level=3
name orig_ ns/iter cmov_ ns/iter diff ns/iter diff %
count_ascii 1,453 (1755 MB/s) 1,398 (1824 MB/s) -55 -3.79%
count_cy 5,990 (856 MB/s) 2,545 (2016 MB/s) -3,445 -57.51%
count_jp 3,075 (1169 MB/s) 1,772 (2029 MB/s) -1,303 -42.37%
count_words_ascii 4,157 (521 MB/s) 1,797 (1205 MB/s) -2,360 -56.77%
count_words_jp 3,337 (1071 MB/s) 1,772 (2018 MB/s) -1,565 -46.90%
x86-64 rustc -Ctarget-feature=+avx -Copt-level=3
name orig_ ns/iter cmov_ ns/iter diff ns/iter diff %
count_ascii 1,444 (1766 MB/s) 763 (3343 MB/s) -681 -47.16%
count_cy 5,871 (874 MB/s) 1,527 (3360 MB/s) -4,344 -73.99%
count_jp 2,874 (1251 MB/s) 1,073 (3351 MB/s) -1,801 -62.67%
count_words_ascii 4,131 (524 MB/s) 1,871 (1157 MB/s) -2,260 -54.71%
count_words_jp 3,253 (1099 MB/s) 1,331 (2686 MB/s) -1,922 -59.08%
```
I briefly explored a more involved blocked algorithm (looking at 8 or more bytes at a time),
but the code in this PR was always winning `count_words_ascii` in particular (counting
many small strings); this solution is an improvement without tradeoffs.
