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Auto merge of #109010 - compiler-errors:rtn, r=eholk

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Initial support for return type notation (RTN)

See: https://smallcultfollowing.com/babysteps/blog/2023/02/13/return-type-notation-send-bounds-part-2/

1. Only supports `T: Trait<method(): Send>` style bounds, not `<T as Trait>::method(): Send`. Checking validity and injecting an implicit binder for all of the late-bound method generics is harder to do for the latter.
    * I'd add this in a follow-up.
3. ~Doesn't support RTN in general type position, i.e. no `let x: <T as Trait>::method() = ...`~
    * I don't think we actually want this.
5. Doesn't add syntax for "eliding" the function args -- i.e. for now, we write `method(): Send` instead of `method(..): Send`.
    * May be a hazard if we try to add it in the future. I'll probably add it in a follow-up later, with a structured suggestion to change `method()` to `method(..)` once we add it.
7. ~I'm not in love with the feature gate name 😺~
    * I renamed it to `return_type_notation` ✔️

Follow-up PRs will probably add support for `where T::method(): Send` bounds. I'm not sure if we ever want to support return-type-notation in arbitrary type positions. I may also make the bounds require `..` in the args list later.

r? `@ghost`
This commit is contained in:
bors 2023-03-31 18:04:12 +00:00
commit 7402519c63
49 changed files with 880 additions and 174 deletions
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16
compiler/rustc_ast/src/ast.rs
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@ -167,6 +167,9 @@ pub enum GenericArgs {
AngleBracketed(AngleBracketedArgs),
/// The `(A, B)` and `C` in `Foo(A, B) -> C`.
Parenthesized(ParenthesizedArgs),
/// Associated return type bounds, like `T: Trait<method(..): Send>`
/// which applies the `Send` bound to the return-type of `method`.
ReturnTypeNotation(Span),
}
impl GenericArgs {
@ -178,6 +181,7 @@ impl GenericArgs {
match self {
AngleBracketed(data) => data.span,
Parenthesized(data) => data.span,
ReturnTypeNotation(span) => *span,
}
}
}
@ -231,15 +235,15 @@ impl AngleBracketedArg {
}
}
impl Into<Option<P<GenericArgs>>> for AngleBracketedArgs {
fn into(self) -> Option<P<GenericArgs>> {
Some(P(GenericArgs::AngleBracketed(self)))
impl Into<P<GenericArgs>> for AngleBracketedArgs {
fn into(self) -> P<GenericArgs> {
P(GenericArgs::AngleBracketed(self))
}
}
impl Into<Option<P<GenericArgs>>> for ParenthesizedArgs {
fn into(self) -> Option<P<GenericArgs>> {
Some(P(GenericArgs::Parenthesized(self)))
impl Into<P<GenericArgs>> for ParenthesizedArgs {
fn into(self) -> P<GenericArgs> {
P(GenericArgs::Parenthesized(self))
}
}