Expand is_uninhabited
This allows code such as this to compile:
``` rust
let x: ! = ...;
match x {};
let y: (u32, !) = ...;
match y {};
```
@eddyb You were worried about making this change. Do you have any idea about what could break? Are there any special tests that need to be written for it?
Add some internal docs links for Args/ArgsOs
In many places the docs link to other sections and I noticed it was lacking here. Not sure if there is a standard for if inter-linking is appropriate.
Clarify the reference's status.
The former wording only gave part of the picture, we want to be crystal
clear about this.
/cc @petrochenkov, who had concerns about https://github.com/rust-lang/rust/pull/37820
Type walker small vector
These two changes avoid allocations on some hot paths and speed up a few workloads (some from rustc-benchmarks, as well as the workload from #36799) by 1--2%.
Provide hint when cast needs a dereference
For a given code:
``` rust
vec![0.0].iter().map(|s| s as i16).collect::<Vec<i16>>();
```
display:
``` nocode
error: casting `&f64` as `i16` is invalid
--> file3.rs:2:35
|
2 | vec![0.0].iter().map(|s| s as i16).collect::<Vec<i16>>();
| - ^^^
| |
| did you mean `*s`?
```
instead of:
``` nocode
error: casting `&f64` as `i16` is invalid
--> <anon>:2:30
|
2 | vec![0.0].iter().map(|s| s as i16).collect();
| ^^^^^^^^
|
= help: cast through a raw pointer first
```
Fixes#37338.
Add a method for setting permissions directly on an open file.
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.
@retep998, what's the best way to do this on Windows? I looked into `SetFileInformationByHandle` but couldn't find a way to do it atomically risking clobbering access time information.
This is a first step towards fixing #37885. This function doesn't *have* to be public but this is useful functionality that should probably be exposed.
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.
