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Auto merge of #116447 - oli-obk:gen_fn, r=compiler-errors

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Implement `gen` blocks in the 2024 edition

Coroutines tracking issue https://github.com/rust-lang/rust/issues/43122
`gen` block tracking issue https://github.com/rust-lang/rust/issues/117078

This PR implements `gen` blocks that implement `Iterator`. Most of the logic with `async` blocks is shared, and thus I renamed various types that were referring to `async` specifically.

An example usage of `gen` blocks is

```rust
fn foo() -> impl Iterator<Item = i32> {
    gen {
        yield 42;
        for i in 5..18 {
            if i.is_even() { continue }
            yield i * 2;
        }
    }
}
```

The limitations (to be resolved) of the implementation are listed in the tracking issue
This commit is contained in:
bors 2023-10-29 00:03:52 +00:00
commit 2cad938a81
75 changed files with 1096 additions and 148 deletions
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12
compiler/rustc_trait_selection/src/solve/assembly/mod.rs
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@ -201,7 +201,15 @@ pub(super) trait GoalKind<'tcx>:
goal: Goal<'tcx, Self>,
) -> QueryResult<'tcx>;
/// A coroutine (that doesn't come from an `async` desugaring) is known to
/// A coroutine (that comes from a `gen` desugaring) is known to implement
/// `Iterator<Item = O>`, where `O` is given by the generator's yield type
/// that was computed during type-checking.
fn consider_builtin_iterator_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
) -> QueryResult<'tcx>;
/// A coroutine (that doesn't come from an `async` or `gen` desugaring) is known to
/// implement `Coroutine<R, Yield = Y, Return = O>`, given the resume, yield,
/// and return types of the coroutine computed during type-checking.
fn consider_builtin_coroutine_candidate(
@ -554,6 +562,8 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
G::consider_builtin_pointee_candidate(self, goal)
} else if lang_items.future_trait() == Some(trait_def_id) {
G::consider_builtin_future_candidate(self, goal)
} else if lang_items.iterator_trait() == Some(trait_def_id) {
G::consider_builtin_iterator_candidate(self, goal)
} else if lang_items.gen_trait() == Some(trait_def_id) {
G::consider_builtin_coroutine_candidate(self, goal)
} else if lang_items.discriminant_kind_trait() == Some(trait_def_id) {