Add support for `const unsafe? extern fn`
This works just as you might expect - an `const extern fn` is a `const fn` that is callable from foreign code.
Currently, panicking is not allowed in `const`s. When https://github.com/rust-lang/rfcs/pull/2345 (https://github.com/rust-lang/rust/issues/51999) is stabilized, then panicking in an `const extern fn` will produce a compile-time error when invoked at compile time, and an abort when invoked at runtime.
Since this is extending the language (we're allowing the `const` keyword in a new context), I believe that this will need an FCP. However, it's a very minor change, so I didn't think that filing an RFC was necessary.
This will allow libc (and other FFI crates) to make many functions `const`, without having to give up on making them `extern` as well.
Tracking issue: https://github.com/rust-lang/rust/issues/64926.
This commit improves the suggestions provided when function parameters
do not have types:
- A new suggestion is added for arbitrary self types, which suggests
adding `self: ` before the type.
- Existing suggestions are now provided when a `<` is found where a `:`
was expected (previously only `,` and `)` or trait items), this gives
suggestions in the case where the unnamed parameter type is generic
in a free function.
- The suggestion that a type name be provided (e.g. `fn foo(HashMap<u32>)`
-> `fn foo(HashMap: TypeName<u32>)`) will no longer occur when a `<` was
found instead of `:`.
- The ident will not be used for recovery when a `<` was found instead
of `:`.
Signed-off-by: David Wood <david@davidtw.co>
This works just as you might expect - an 'extern const fn' is a 'const
fn' that is callable from foreign code.
Currently, panicking is not allowed in consts. When RFC 2345 is
stabilized, then panicking in an 'extern const fn' will produce a
compile-time error when invoked at compile time, and an abort when
invoked at runtime.
Since this is extending the language (we're allowing the `const` keyword
in a new context), I believe that this will need an FCP. However, it's a
very minor change, so I didn't think that filing an RFC was necessary.
This will allow libc (and other FFI crates) to make many functions
`const`, without having to give up on making them `extern` as well.
Remove blanket check for existence of other errors before emitting
"type annotation needed" errors, and add some eager checks to avoid
adding obligations when they refer to types that reference
`[type error]` in order to reduce unneded errors.
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.
Unfortunately, the diagnotic machinery does not cope well with an empty
span which can happen if the crate is empty, in which case we merely set
a spanless note.
Bail out when encountering likely missing turbofish in parser
When encountering a likely intended turbofish without `::`, bubble
up the diagnostic instead of emitting it to allow the parser to recover
more gracefully and avoid uneccessary type errors that are likely to be
wrong.
Fix#61329.
When encountering a likely intended turbofish without `::`, bubble
up the diagnostic instead of emitting it to allow the parser to recover
more gracefully and avoid uneccessary type errors that are likely to be
wrong.
Change opaque type syntax from `existential type` to type alias `impl Trait`
This implements a new feature gate `type_alias_impl_trait` (this is slightly different from the originally proposed feature name, but matches what has been used in discussion since), deprecating the old `existential_types` feature.
The syntax for opaque types has been changed. In addition, the "existential" terminology has been replaced with "opaque", as per previous discussion and the RFC.
This makes partial progress towards implementing https://github.com/rust-lang/rust/issues/63063.
r? @Centril
Implement RFC 2707 + Parser recovery for range patterns
Implement https://github.com/rust-lang/rfcs/pull/2707.
- Add a new basic syntactic pattern form `ast::PatKind::Rest` (parsed as `..` or `DOTDOT`) and simplify `ast::PatKind::{Slice, Tuple, TupleStruct}` as a result.
- Lower `ast::PatKind::Rest` in combination with the aforementioned `PatKind` variants as well as `PatKind::Ident`. The HIR remains unchanged for now (may be advisable to make slight adjustments later).
- Refactor `parser.rs` wrt. parsing sequences and lists of things in the process.
- Add parser recovery for range patterns of form `X..`, `X..=`, `X...`, `..Y`, `..=Y`, and `...Y`.
This should make it easy to actually support these patterns semantically later if we so desire.
cc https://github.com/rust-lang/rust/issues/62254
r? @petrochenkov
