Rollup of 7 pull requests
Successful merges:
- #80185 (Fix ICE when pointing at multi bytes character)
- #80260 (slightly more typed interface to panic implementation)
- #80311 (Improvements to NatVis support)
- #80337 (Use `desc` as a doc-comment for queries if there are no doc comments)
- #80381 (Revert "Cleanup markdown span handling")
- #80492 (remove empty wraps, don't return Results from from infallible functions)
- #80509 (where possible, pass slices instead of &Vec or &String (clippy::ptr_arg))
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
remove empty wraps, don't return Results from from infallible functions
This makes code easier to understand because it is more obvious when a function actually can't fail (return Err or None)
Make functions that only ever return Some(x), return x directly
Remove return type from functions that return Option<(), Err> but would only ever return Ok(()).
Found with `clippy::unnecessary_wraps`
Revert "Cleanup markdown span handling"
Reverts rust-lang/rust#80244. This caused a diagnostic regression, originally it was:
```
warning: unresolved link to `std::process::Comman`
--> link.rs:3:10
|
3 | //! [a]: std::process::Comman
| ^^^^^^^^^^^^^^^^^^^^ no item named `Comman` in module `process`
|
= note: `#[warn(broken_intra_doc_links)]` on by default
```
but after that PR rustdoc now displays
```
warning: unresolved link to `std::process::Comman`
--> link.rs:1:14
|
1 | //! Links to [a] [link][a]
| ^^^ no item named `Comman` in module `process`
|
= note: `#[warn(broken_intra_doc_links)]` on by default
```
which IMO is much less clear.
cc `@bugadani,` thanks for catching this in https://github.com/rust-lang/rust/pull/77859.
r? `@GuillaumeGomez`
Improvements to NatVis support
NatVis files describe how to display types in some Windows debuggers,
such as Visual Studio, WinDbg, and VS Code.
This commit makes several improvements:
* Adds visualizers for Rc<T>, Weak<T>, and Arc<T>.
* Changes [size] to [len], for consistency with the Rust API.
Visualizers often use [size] to mirror the size() method on C++ STL
collections.
* Several visualizers used the PVOID and ULONG typedefs. These are part
of the Windows API; they are not guaranteed to always be defined in a
pure Rust DLL/EXE. I converted PVOID to `void*` and `ULONG` to
`unsigned long`.
* Cosmetic change: Removed {} braces around the visualized display
for `Option` types. They now display simply as `Some(value)` or
`None`, which reflects what is written in source code.
* The visualizer for `alloc::string::String` makes assumptions about
the layout of `String` (it casts `String*` to another type), rather
than using symbolic expressions. This commit changes the visualizer
so that it simply uses symbolic expressions to access the string
data and string length.
* The visualizers for `str` and `String` now place the character data
array under a synthetic `[chars]` node. When expanding a `String`
node, users rarely want to see an array of characters. This just places
them behind one expansion node / level.
remove unused return type of dropck::check_drop_obligations()
don't wrap return type in Option in get_macro_by_def_id() since we would always return Some(..)
remove redundant return type of back::write::optimize()
don't Option-wrap return type of compute_type_parameters() since we always return Some(..)
don't return empty Result in assemble_generator_candidates()
don't return empty Result in assemble_closure_candidates()
don't return empty result in assemble_fn_pointer_candidates()
don't return empty result in assemble_candidates_from_impls()
don't return empty result in assemble_candidates_from_auto_impls()
don't return emtpy result in assemble_candidates_for_trait_alias()
don't return empty result in assemble_builtin_bound_candidates()
don't return empty results in assemble_extension_candidates_for_traits_in_scope() and assemble_extension_candidates_for_trait()
remove redundant wrapping of return type of StripItem::strip() since it always returns Some(..)
remove unused return type of assemble_extension_candidates_for_all_traits()
Use sans-serif font for the "all items" page links
The "all items" pages' links aren't using a sans-serif font unlike the rest of equivalent items in the other module pages. ``@Nemo157`` reported me this issue so here is the fix!
r? ``@Nemo157``
Add llvm-libunwind change to bootstrap CHANGELOG
From #77703.
This doesn't need a `changelog-seen` version bump because the old values aren't accepted anymore, meaning anyone who was using this had to change it already.
r? ``@Mark-Simulacrum``
Lint on redundant trailing semicolon after item
We now lint on code like this:
```rust
fn main() {
fn foo() {};
struct Bar {};
}
```
Previously, this caused warnings in Cargo, so it was disabled.
[rustdoc] Box ItemKind to reduce the size of `Item`
This brings the size of `Item` from
```
[src/librustdoc/lib.rs:103] std::mem::size_of::<Item>() = 536
```
to
```
[src/librustdoc/lib.rs:103] std::mem::size_of::<Item>() = 136
```
This is an alternative to https://github.com/rust-lang/rust/pull/79967; I don't think it makes sense to make both changes.
Helps with #79103.
NatVis files describe how to display types in some Windows debuggers,
such as Visual Studio, WinDbg, and VS Code.
This commit makes several improvements:
* Adds visualizers for Rc<T>, Weak<T>, and Arc<T>.
* Changes [size] to [len], for consistency with the Rust API.
Visualizers often use [size] to mirror the size() method on C++ STL
collections.
* Several visualizers used the PVOID and ULONG typedefs. These are part
of the Windows API; they are not guaranteed to always be defined in a
pure Rust DLL/EXE. I converted PVOID to `void*` and `ULONG` to
`unsigned long`.
* Cosmetic change: Removed {} braces around the visualized display
for `Option` types. They now display simply as `Some(value)` or
`None`, which reflects what is written in source code.
* The visualizer for `alloc::string::String` makes assumptions about
the layout of `String` (it casts `String*` to another type), rather
than using symbolic expressions. This commit changes the visualizer
so that it simply uses symbolic expressions to access the string
data and string length.
Add regression test for #80375
This will also make sure that #80375 is handled if #79135 has to be reverted (which won't happen 🤞).
Closes#80375.
r? `@lcnr`
Add links to the source for the rustc and rustdoc books.
This adds a little icon in the upper-right corner of the books so that readers can find the source if they want to make changes or file issues. This is already included in several of the other books.
bootstrap: put the component name in the tarball temp dir path
This should not matter right now, but if we ever parallelize rustbuild this will avoid tarball contents being merged together.
r? `@Mark-Simulacrum`
Suggest fn ptr rather than fn item and suggest to use `Fn` trait bounds rather than the unique closure type in E0121
Previously, using `_` as a return type in a function that returned a function/closure would provide a diagnostic that would cause a papercut. For example:
```rust
fn f() -> i32 { 0 }
fn fn_ptr() -> _ { f }
fn closure() -> _ { || 0 }
```
would result in this diagnostic:
```rust
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> <anon>:2:16
|
2 | fn fn_ptr() -> _ { f }
| ^
| |
| not allowed in type signatures
| help: replace with the correct return type: `fn() -> i32 {f}`
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> <anon>:3:17
|
3 | fn closure() -> _ { || 0 }
| ^
| |
| not allowed in type signatures
| help: replace with the correct return type: `[closure@<anon>:3:21: 3:25]`
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0121`.
```
As can be seen, it was suggested to use the function definition return type `fn() -> i32 { f }` which is not valid syntax as a return type. Additionally, closures cause a papercut as unique closure types (notated in this case as `[closure@<anon>:3:21: 3:25]`) are not valid syntax either.
Instead, this PR implements this version of the diagnostic (this example is for the same code featured above):
```rust
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> <anon>:2:16
|
2 | fn fn_ptr() -> _ { f }
| ^
| |
| not allowed in type signatures
| help: replace with the correct return type: `fn() -> i32`
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> <anon>:3:17
|
3 | fn closure() -> _ { || 0 }
| ^ not allowed in type signatures
|
= help: consider using an `Fn`, `FnMut`, or `FnOnce` trait bound
= note: for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0121`.
```
As can be seen in this diagnostic, the papercut for returning a function item is fixed by suggesting the usage of a function pointer as the return type. As for closures, it's suggested to use an `Fn`, `FnMut`, or `FnOnce` trait bound (with further reading on closures and `Fn` traits in *The Book* for beginners). I did not implement a suggestion to use `impl Fn() -> i32` syntax as that was out-of-scope for my abilities at the moment, therefore someone in the future may want to implement that. Also, it's possible to use either `impl Trait` syntax, generics, or generics with a `where` clause, and some users may not want to use `impl Trait` syntax for their own reasons.
This PR fixes#80179.
Fix intra-doc links for non-path primitives
This does *not* currently work for associated items that are
auto-implemented by the compiler (e.g. `never::eq`), because they aren't
present in the source code. I plan to fix this in a follow-up PR.
Fixes https://github.com/rust-lang/rust/issues/63351 using the approach mentioned in https://github.com/rust-lang/rust/issues/63351#issuecomment-683352130.
r? `@Manishearth`
cc `@petrochenkov` - this makes `rustc_resolve::Res` public, is that ok? I'd just add an identical type alias in rustdoc if not, which seems a waste.
rustdoc: stabilise --default-theme command line option
As discussed in #77213, this seems like it has bedded in and can be safely and usefully made stable.
(rustdoc already has other stable options that interact quite intimately with the rustdoc-supplied CSS, and also an option for supplying entirely different CSS, so exposing the theme names this way seems a very minor step.)
There is also a commit to do some minor grammar fixes to the help message.
stabilize `#![feature(min_const_generics)]` in 1.51
*A new Kind*
*A Sort long Prophesized*
*Once Fragile, now Eternal*
blocked on #79073.
# Stabilization report
This is the stabilization report for `#![feature(min_const_generics)]` (tracking issue #74878), a subset of `#![feature(const_generics)]` (tracking issue #44580), based on rust-lang/rfcs#2000.
The [version target](https://forge.rust-lang.org/#current-release-versions) is ~~1.50 (2020-12-31 => beta, 2021-02-11 => stable)~~ 1.51 (2021-02-111 => beta, 2021-03-25 => stable).
This report is a collaborative effort of `@varkor,` `@shepmaster` and `@lcnr.`
## Summary
It is currently possible to parameterize functions, type aliases, types, traits and implementations by types and lifetimes.
With `#![feature(min_const_generics)]`, it becomes possible, in addition, to parameterize these by constants.
This is done using the syntax `const IDENT: Type` in the parameter listing. Unlike full const generics, `min_const_generics` is limited to parameterization by integers, and constants of type `char` or `bool`.
We already use `#![feature(min_const_generics)]` on stable to implement many common traits for arrays. See [the documentation](https://doc.rust-lang.org/nightly/std/primitive.array.html) for specific examples.
Generic const arguments, for now, are not permitted to involve computations depending on generic parameters. This means that const parameters may only be instantiated using either:
1. const expressions that do not depend on any generic parameters, e.g. `{ foo() + 1 }`, where `foo` is a `const fn`
1. standalone const parameters, e.g. `{N}`
### Example
```rust
#![feature(min_const_generics)]
trait Foo<const N: usize> {
fn method<const M: usize>(&mut self, arr: [[u8; M]; N]);
}
struct Bar<T, const N: usize> {
inner: [T; N],
}
impl<const N: usize> Foo<N> for Bar<u8, N> {
fn method<const M: usize>(&mut self, arr: [[u8; M]; N]) {
for (elem, s) in self.inner.iter_mut().zip(arr.iter()) {
for &x in s {
*elem &= x;
}
}
}
}
fn function<const N: u16>() -> u16 {
// Const parameters can be used freely inside of functions.
(N + 1) / 2 * N
}
fn main() {
let mut bar = Bar { inner: [0xff; 3] };
// This infers the value of `M` from the type of the function argument.
bar.method([[0b11_00, 0b01_00], [0b00_11, 0b00_01], [0b11_00, 0b00_11]]);
assert_eq!(bar.inner, [0b01_00, 0b00_01, 0b00_00]);
// You can also explicitly specify the value of `N`.
assert_eq!(function::<17>(), 153);
}
```
## Motivation
Rust has the built-in array type, which is parametric over a constant. Without const generics, this type can be quite cumbersome to use as it is not possible to generically implement a trait for arrays of different lengths. For example, this meant that, for a long time, the standard library only contained trait implementations for arrays up to a length of 32. This restriction has since been lifted through the use of const generics.
Const parameters allow users to naturally specify variants of a generic type which are more naturally parameterized by values, rather than by types. For example, using const generics, many of the uses of the crate [typenum](https://crates.io/crates/typenum) may now be replaced with const parameters, improving compilation time as well as code readability and diagnostics.
The subset described by `min_const_generics` is self-contained, but extensive enough to help with the most frequent issues: implementing traits for arrays and using arbitrarily-sized arrays inside of other types. Furthermore, it extends naturally to full `const_generics` once the remaining design and implementation questions have been resolved.
## In-depth feature description
### Declaring const parameters
*Const parameters* are allowed in all places where types and lifetimes are supported. They use the syntax `const IDENT: Type`. Currently, const parameters must be declared after lifetime and type parameters. Their scope is equal to the scope of other generic parameters. They live in the value namespace.
`Type` must be one of `u8`, `u16`, `u32`, `u64`, `u128`, `usize`, `i8`, `i16`, `i32`, `i64`, `i128`, `isize`, `char` and `bool`. This restriction is implemented in two places:
1. during name resolution, where we forbid generic parameters
1. during well-formedness checking, where we only allow the types listed above
The updated syntax of parameter listings is:
```
GenericParams:
(OuterAttr* LifetimeParam),* (OuterAttr* TypeParam),* (OuterAttr* ConstParam),*
OuterAttr: '#[' ... ']'
LifetimeParam: ...
TypeParam: ...
ConstParam: 'const' IDENT ':' Type
```
Unlike type and lifetime parameters, const parameters of types can be used without being mentioned inside of a parameterized type because const parameters do not have issues concerning variance. This means that the following types are allowed:
```rust
struct Foo<const N: usize>;
enum Bar<const M: usize> { A, B }
```
### Const arguments
Const parameters are instantiated using *const arguments*. Any concrete const expression or const parameter as a standalone argument can be used. When applying an expression as const parameter, most expressions must be contained within a block, with two exceptions:
1. literals and single-segment path expressions
1. array lengths
This syntactic restriction is necessary to avoid ambiguity, or requiring infinite lookahead when parsing an expression as a generic argument.
In the cases where a generic argument could be resolved as either a type or const argument, we always interpret it as a type. This causes the following test to fail:
```rust
type N = u32;
struct Foo<const N: usize>;
fn foo<const N: usize>() -> Foo<N> { todo!() } // ERR
```
To circumvent this, the user may wrap the const parameter with braces, at which point it is unambiguously accepted.
```rust
type N = u32;
struct Foo<const N: usize>;
fn bar<const N: usize>() -> Foo<{ N }> { todo!() } // ok
```
Operations depending on generic parameters are **not** allowed, which is enforced during well-formedness checking. Allowing generic unevaluated constants would require a way to check if they would always evaluate successfully to prevent errors that are not caught at declaration time. This ability forms part of `#![feature(const_evaluatable_checked)]`, which is not yet being stabilised.
Since we are not yet stabilizing `#![feature(lazy_normalization_consts)]`, we must not supply the parent generics to anonymous constants except for repeat expressions. Doing so can cause cycle errors for arrays used in `where`-bounds. Not supplying the parent generics can however lead to ICEs occurring before well-formedness checking when trying to use a generic parameter. See #56445 for details.
Since we expect cases like this to occur more frequently once `min_const_generics` is stabilized, we have chosen to forbid generic parameters in anonymous constants during name resolution. While this changes the ICE in the situation above to an ordinary error, this is theoretically a breaking change, as early-bound lifetimes were previously permitted in repeat expressions but now are disallowed, causing the following snippet to break:
```rust
fn late_bound<'a>() {
let _ = [0; {
let _: &'a (); // ICE ==> ERR
3
}];
}
fn early_bound<'a>() where &'a (): Sized {
let _ = [0; {
let _: &'a (); // ok ==> ERR
3
}];
}
```
### Using const parameters
Const parameters can be used almost everywhere ordinary constants are allowed, except that they may not be used in the construction of consts, statics, functions, or types inside a function body and are subject to the generic argument restrictions mentioned above.
Expressions containing const parameters are eligible for promotion:
```rust
fn test<const N: usize>() -> &'static usize {
&(3 + N)
}
```
### Symbol mangling
See the [Rust symbol name mangling RFC](https://rust-lang.github.io/rfcs/2603-rust-symbol-name-mangling-v0.html) for an overview. Generic const parameters take the form `K[type][value]` when the value is known, or `Kp` where the value is not known, where:
- `[type]` is any integral type, `bool`, or `char`.
- `[value]` is the unsigned hex value for integers, preceded by `n` when negative; is `0` or `1` for `bool`; is the hex value for `char`.
### Exhaustiveness checking
We do not check the exhaustiveness of impls, meaning that the following example does **not** compile:
```rust
struct Foo<const B: bool>;
trait Bar {}
impl Bar for Foo<true> {}
impl Bar for Foo<false> {}
fn needs_bar(_: impl Bar) {}
fn generic<const B: bool>() {
let v = Foo::<B>;
needs_bar(v);
}
```
### Type inference
The value of const parameters can be inferred during typeck. One interesting case is the length of generic arrays, which can also be inferred from patterns (implemented in #70562). Practical usage of this can be seen in #76825.
### Equality of constants
`#![feature(min_const_generics)]` only permits generic parameters to be used as standalone generic arguments. We compare two parameters to be equal if they are literally the same generic parameter.
### Associated constants
Associated constants can use const parameters without restriction, see https://github.com/rust-lang/rust/pull/79135#issuecomment-748299774 for more details.
## Future work
As this is a limited subset of rust-lang/rfcs#2000, there are quite a few extensions we will be looking into next.
### Lazy normalization of constants
Stabilizing `#![feature(lazy_normalization_consts)]` (tracking issue #72219) will remove some special cases that are currently necessary for `min_const_generics`, and unblocks operations on const parameters.
### Relaxing ordering requirements between const and type parameters
We currently restrict the order of generic parameters so that types must come before consts. We could relax this, as is currently done with `const_generics`. Without this it is not possible to use both type defaults and const parameters at the same time.
Unrestricting the order will require us to improve some diagnostics that expect there to be a strict order between type and const parameters.
### Allowing more parameter types
We would like to support const parameters of more types, especially`&str` and user-defined types. Both are blocked on [valtrees]. There are also open questions regarding the design of `structural_match` concerning the latter. Supporting generic const parameter types such as `struct Foo<T, const N: T>` will be a lot harder and is unlikely to be implemented in the near future.
### Default values of const parameters
We do not yet support default values for const parameters. There is work in progress to enable this on nightly (see https://github.com/rust-lang/rust/pull/75384).
### Generic const operations
With `#![feature(min_const_generics)]`, only concrete const expressions and parameters as standalone arguments are allowed in types and repeat expressions. However, supporting generic const operations, such as `N + 1` or `std::mem::size_of::<T>()` is highly desirable. This feature is in early development under `#![feature(const_evaluatable_checked)]`.
## Implementation history
Many people have contributed to the design and implementation of const generics over the last three years. See https://github.com/rust-lang/rust/issues/44580#issuecomment-728913127 for a summary. Once again thank you to everybody who helped out here!
[valtrees]: https://github.com/rust-lang/rust/issues/72396
---
r? `@varkor`
lint-docs: Warn on missing lint when documenting.
In #79522, I missed converting one of the errors to a warning, in the situation where a lint is missing. This was unearthed by the renaming of overlapping-patterns (#78242). This will still be validated during the test phase.
