Rollup of 9 pull requests
Successful merges:
- #63907 (Add explanation to type mismatch involving type params and assoc types)
- #64615 (rustbuild: Turn down compression on exe installers)
- #64617 (rustbuild: Turn down compression on msi installers)
- #64618 (rustbuild: Improve output of `dist` step)
- #64619 (Fixes#63962. Hint about missing tuple parentheses in patterns)
- #64634 (Update to LLVM 9.0.0)
- #64635 (Allow using fn pointers in const fn with unleash miri)
- #64660 (unify errors for tuple/struct variants)
- #64664 (fully remove AstBuilder)
Failed merges:
r? @ghost
Allow using fn pointers in const fn with unleash miri
This allows using function pointers in const fns when `-Zunleash-the-miri-within-you` is enabled.
If the call to the `const fn` happens in a `const`-context, the function pointer is required to point to a `const fn`:
```rust
fn non_const_fn() -> i32 { 42 }
const fn const_fn() -> i32 { 42 }
const fn foo(x: fn() -> i32) -> i32 { x() }
let x: i32 = foo(non_const_fn_ptr); // OK
let y: i32 = foo(const_fn_ptr); // OK
const X: i32 = foo(non_const_fn_ptr); // ERROR: `non_const_fn` is not `const fn`
const Y: i32 = foo(const_fn_ptr); // OK
```
r? @oli-obk
rustbuild: Improve output of `dist` step
* Pass `/Q` to `iscc` on Windows to supress the thousands of lines of
output about compressing documentation.
* Print out what's happening before long steps
* Use `timeit` to print out timing information for long-running
installer assemblies.
* Try to scope output of `Dist ...` to not also encompass actual build steps
rustbuild: Turn down compression on msi installers
This is the same as #64615 except applied to our MSI installers. The
same fix is applied effectively bringing these installers in line with
the gz tarball installers, which are about 3x faster to produce locally
and likely much faster to produce on CI.
rustbuild: Turn down compression on exe installers
The Windows dist builders are the slowest builders right now, and the
distribution phase of them is enormously slow clocking in at around 20
minutes to build all the related installers. This commit starts to
optimize these by turning down the compression level in the `exe`
installers. These aren't super heavily used so there's no great need for
them to be so ultra-compressed, so let's dial back the compression
parameters to get closer to the rest of our xz archives. This brings the
installer in line with the gz tarball installer locally, and also brings
the compression settings on par with the rest of our xz installers.
Rollup of 9 pull requests
Successful merges:
- #64010 (Stabilize `param_attrs` in Rust 1.39.0)
- #64136 (Document From trait for LhsExpr in parser)
- #64342 (factor out pluralisation remains after #64280)
- #64347 (Add long error explanation for E0312)
- #64621 (Add Compatibility Notes to RELEASES.md for 1.38.0)
- #64632 (remove the extra comma after the match arm)
- #64640 (No home directory on vxWorks)
- #64641 (Exempt extern "Rust" from improper_ctypes)
- #64642 (Fix the span used to suggest avoiding for-loop moves)
Failed merges:
r? @ghost
Fix the span used to suggest avoiding for-loop moves
It was using the snippet from the "use" span, which often renders the
same, but with closures that snippet is on the start of the closure
where the value is captured. We should be using the snippet from the
span where it was moved into the `for` loop, which is `move_span`.
Fixes#64559.
Document From trait for LhsExpr in parser
Add doc for From trait for converting P<Expr> and Option<ThinVec<Attribute>> to LhsExpr
As part of issue rust-lang#51430 (cc @skade).
Both of these should just be moving an address and setting a discriminant in an enum. The main thing I'm not sure about is whether it's worth documenting the branch in the From<Option<ThinVec<Attribute>>. As far as I can tell it doesn't seem like it is optimized away (although if the discriminant happened to work out you could just copy the pointer and the discriminant which might be cheaper, but that's not guaranteed). So it seems like if it's being called often, it's doubling the number of possible branch mispredictions on this Option, which could be a significant cost.
Let me know if there's anything that needs fixing and I'll get to it as soon as possible!
Stabilize `param_attrs` in Rust 1.39.0
# Stabilization proposal
I propose that we stabilize `#![feature(param_attrs)]`.
Tracking issue: #60406
Version: 1.39 (2019-09-26 => beta, 2019-11-07 => stable).
## What is stabilized
It is now possible to add outer attributes like `#[cfg(..)]` on formal parameters of functions, closures, and function pointer types. For example:
```rust
fn len(
#[cfg(windows)] slice: &[u16],
#[cfg(not(windows))] slice: &[u8],
) -> usize {
slice.len()
}
```
## What isn't stabilized
* Documentation comments like `/// Doc` on parameters.
* Code expansion of a user-defined `#[proc_macro_attribute]` macro used on parameters.
* Built-in attributes other than `cfg`, `cfg_attr`, `allow`, `warn`, `deny`, and `forbid`. Currently, only the lints `unused_variables` and `unused_mut` have effect and may be controlled on parameters.
## Motivation
The chief motivations for stabilizing `param_attrs` include:
* Finer conditional compilation with `#[cfg(..)]` and linting control of variables.
* Richer macro DSLs created by users.
* External tools and compiler internals can take advantage of the additional information that the parameters provide.
For more examples, see the [RFC][rfc motivation].
## Reference guide
In the grammar of function and function pointer, the grammar of variadic tails (`...`) and parameters are changed respectively from:
```rust
FnParam = { pat:Pat ":" }? ty:Type;
VaradicTail = "...";
```
into:
```rust
FnParam = OuterAttr* { pat:Pat ":" }? ty:Type;
VaradicTail = OuterAttr* "...";
```
The grammar of a closure parameter is changed from:
```rust
ClosureParam = pat:Pat { ":" ty:Type }?;
```
into:
```rust
ClosureParam = OuterAttr* pat:Pat { ":" ty:Type }?;
```
More generally, where there's a list of formal (value) parameters separated or terminated by `,` and delimited by `(` and `)`. Each parameter in that list may optionally be prefixed by `OuterAttr+`.
Note that in all cases, `OuterAttr*` applies to the whole parameter and not just the pattern. This distinction matters in pretty printing and in turn for macros.
## History
* On 2018-10-15, @Robbepop proposes [RFC 2565][rfc], "Attributes in formal function parameter position".
* On 2019-04-30, [RFC 2565][rfc] is merged and the tracking issue is made.
* On 2019-06-12, a partial implementation was completed. The implementation was done in [#60669][60669] by @c410-f3r and the PR was reviewed by @petrochenkov and @Centril.
* On 2019-07-29, [#61238][61238] was fixed in [#61856][61856]. The issue fixed was that lint attributes on function args had no effect. The PR was written by @c410-f3r and reviewed by @matthewjasper, @petrochenkov, and @oli-obk.
* On 2019-08-02, a bug [#63210][63210] was filed wherein the attributes on formal parameters would not be passed to macros. The issue was about forgetting to call the relevant method in `fn print_arg` in the pretty printer. In [#63212][63212], written by @Centril on 2019-08-02 and reviewed by @davidtwco, the issue aforementioned was fixed.
* This PR stabilizes `param_attrs`.
## Tests
* [On Rust 2018, attributes aren't permitted on function parameters without a pattern in trait definitions.](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2565-param-attrs/param-attrs-2018.rs)
* [All attributes that should be allowed. This includes `cfg`, `cfg_attr`, and lints check attributes.](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2565-param-attrs/param-attrs-allowed.rs)
* [Built-in attributes, which should be forbidden, e.g., `#[test]`, are.](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2565-param-attrs/param-attrs-builtin-attrs.rs)
* [`cfg` and `cfg_attr` are properly evaluated.](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2565-param-attrs/param-attrs-cfg.rs)
* [`unused_mut`](46f405ec4d/src/test/ui/rfc-2565-param-attrs/param-attrs-cfg.rs) and [`unused_variables`](https://github.com/rust-lang/rust/blob/master/src/test/ui/lint/lint-unused-variables.rs) are correctly applied to parameter patterns.
* [Pretty printing takes formal parameter attributes into account.](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2565-param-attrs/param-attrs-pretty.rs)
## Possible future work
* Custom attributes inside function parameters aren't currently supported but it is something being worked on internally.
* Since documentation comments are syntactic sugar for `#[doc(...)]`, it is possible to allow literal `/// Foo` comments on function parameters.
[rfc motivation]: https://github.com/rust-lang/rfcs/blob/master/text/2565-formal-function-parameter-attributes.md#motivation
[rfc]: https://github.com/rust-lang/rfcs/pull/2565
[60669]: https://github.com/rust-lang/rust/pull/60669
[61856]: https://github.com/rust-lang/rust/pull/61856
[63210]: https://github.com/rust-lang/rust/issues/63210
[61238]: https://github.com/rust-lang/rust/issues/61238
[63212]: https://github.com/rust-lang/rust/pull/63212
This report is a collaborative work with @Centril.
Add `cmp::{min_by, min_by_key, max_by, max_by_key}`
This adds the following functions to `core::cmp`:
- `min_by`
- `min_by_key`
- `max_by`
- `max_by_key`
`min_by` and `max_by` are somewhat trivial to implement, but not entirely because `min_by` returns the first value in case the two are equal (and `max_by` the second). `min` and `max` can be implemented in terms of `min_by` and `max_by`, but not as easily the other way around.
To give an example of why I think these functions could be useful: the `Iterator::{min_by, min_by_key, max_by, max_by_key}` methods all currently hard-code the behavior mentioned above which is an ever so small duplication of logic. If we delegate them to `cmp::{min_by, max_by}` methods instead, we get the correct behavior for free. (edit: this is now included in the PR)
I added `min_by_key` / `max_by_key` for consistency's sake but I wouldn't mind removing them. I don't have a particular use case in mind for them, and `min_by` / `max_by` seem to be more useful.
Tracking issue: #64460
It was using the snippet from the "use" span, which often renders the
same, but with closures that snippet is on the start of the closure
where the value is captured. We should be using the snippet from the
span where it was moved into the `for` loop, which is `move_span`.
