Rollup merge of #80319 - jyn514:async-lifetimes, r=tmandry

Fix elided lifetimes shown as `'_` on async functions

Closes #63037.

r? `@tmandry` on the implementation, `@Darksonn` on the test cases.

src/librustdoc/clean/mod.rs

@@ -638,6 +638,18 @@ impl Clean<Generics> for hir::Generics<'_> {
  _ => false,
  }
  }
+ /// This can happen for `async fn`, e.g. `async fn f<'_>(&'_ self)`.
+ ///
+ /// See [`lifetime_to_generic_param`] in [`rustc_ast_lowering`] for more information.
+ ///
+ /// [`lifetime_to_generic_param`]: rustc_ast_lowering::LoweringContext::lifetime_to_generic_param
+ fn is_elided_lifetime(param: &hir::GenericParam<'_>) -> bool {
+ match param.kind {
+ hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Elided } => true,
+ _ => false,
+ }
+ }
+
  let impl_trait_params = self
  .params
  .iter()
@@ -656,7 +668,7 @@ impl Clean<Generics> for hir::Generics<'_> {
  .collect::<Vec<_>>();
 
  let mut params = Vec::with_capacity(self.params.len());
- for p in self.params.iter().filter(|p| !is_impl_trait(p)) {
+ for p in self.params.iter().filter(|p| !is_impl_trait(p) && !is_elided_lifetime(p)) {
  let p = p.clean(cx);
  params.push(p);
  }
@@ -1437,7 +1449,16 @@ impl Clean<Type> for hir::Ty<'_> {
  TyKind::Never => Never,
  TyKind::Ptr(ref m) => RawPointer(m.mutbl, box m.ty.clean(cx)),
  TyKind::Rptr(ref l, ref m) => {
- let lifetime = if l.is_elided() { None } else { Some(l.clean(cx)) };
+ // There are two times a `Fresh` lifetime can be created:
+ // 1. For `&'_ x`, written by the user. This corresponds to `lower_lifetime` in `rustc_ast_lowering`.
+ // 2. For `&x` as a parameter to an `async fn`. This corresponds to `elided_ref_lifetime in `rustc_ast_lowering`.
+ // See #59286 for more information.
+ // Ideally we would only hide the `'_` for case 2., but I don't know a way to distinguish it.
+ // Turning `fn f(&'_ self)` into `fn f(&self)` isn't the worst thing in the world, though;
+ // there's no case where it could cause the function to fail to compile.
+ let elided =
+ l.is_elided() || matches!(l.name, LifetimeName::Param(ParamName::Fresh(_)));
+ let lifetime = if elided { None } else { Some(l.clean(cx)) };
  BorrowedRef { lifetime, mutability: m.mutbl, type_: box m.ty.clean(cx) }
  }
  TyKind::Slice(ref ty) => Slice(box ty.clean(cx)),

src/test/rustdoc/async-fn.rs

@@ -1,3 +1,4 @@
+// ignore-tidy-linelength
 // edition:2018
 #![feature(min_const_generics)]
 
@@ -48,7 +49,50 @@ impl Foo {
  pub async fn mut_self(mut self, mut first: usize) {}
 }
 
+pub trait Pattern<'a> {}
+
 pub trait Trait<const N: usize> {}
 // @has async_fn/fn.const_generics.html
 // @has - '//pre[@class="rust fn"]' 'pub async fn const_generics<const N: usize>(_: impl Trait<N>)'
 pub async fn const_generics<const N: usize>(_: impl Trait<N>) {}
+
+// test that elided lifetimes are properly elided and not displayed as `'_`
+// regression test for #63037
+// @has async_fn/fn.elided.html
+// @has - '//pre[@class="rust fn"]' 'pub async fn elided(foo: &str) -> &str'
+pub async fn elided(foo: &str) -> &str {}
+// This should really be shown as written, but for implementation reasons it's difficult.
+// See `impl Clean for TyKind::Rptr`.
+// @has async_fn/fn.user_elided.html
+// @has - '//pre[@class="rust fn"]' 'pub async fn user_elided(foo: &str) -> &str'
+pub async fn user_elided(foo: &'_ str) -> &str {}
+// @has async_fn/fn.static_trait.html
+// @has - '//pre[@class="rust fn"]' 'pub async fn static_trait(foo: &str) -> Box<dyn Bar>'
+pub async fn static_trait(foo: &str) -> Box<dyn Bar> {}
+// @has async_fn/fn.lifetime_for_trait.html
+// @has - '//pre[@class="rust fn"]' "pub async fn lifetime_for_trait(foo: &str) -> Box<dyn Bar + '_>"
+pub async fn lifetime_for_trait(foo: &str) -> Box<dyn Bar + '_> {}
+// @has async_fn/fn.elided_in_input_trait.html
+// @has - '//pre[@class="rust fn"]' "pub async fn elided_in_input_trait(t: impl Pattern<'_>)"
+pub async fn elided_in_input_trait(t: impl Pattern<'_>) {}
+
+struct AsyncFdReadyGuard<'a, T> { x: &'a T }
+
+impl Foo {
+ // @has async_fn/struct.Foo.html
+ // @has - '//h4[@class="method"]' 'pub async fn complicated_lifetimes( &self, context: &impl Bar) -> impl Iterator<Item = &usize>'
+ pub async fn complicated_lifetimes(&self, context: &impl Bar) -> impl Iterator<Item = &usize> {}
+ // taken from `tokio` as an example of a method that was particularly bad before
+ // @has - '//h4[@class="method"]' "pub async fn readable<T>(&self) -> Result<AsyncFdReadyGuard<'_, T>, ()>"
+ pub async fn readable<T>(&self) -> Result<AsyncFdReadyGuard<'_, T>, ()> {}
+ // @has - '//h4[@class="method"]' "pub async fn mut_self(&mut self)"
+ pub async fn mut_self(&mut self) {}
+}
+
+// test named lifetimes, just in case
+// @has async_fn/fn.named.html
+// @has - '//pre[@class="rust fn"]' "pub async fn named<'a, 'b>(foo: &'a str) -> &'b str"
+pub async fn named<'a, 'b>(foo: &'a str) -> &'b str {}
+// @has async_fn/fn.named_trait.html
+// @has - '//pre[@class="rust fn"]' "pub async fn named_trait<'a, 'b>(foo: impl Pattern<'a>) -> impl Pattern<'b>"
+pub async fn named_trait<'a, 'b>(foo: impl Pattern<'a>) -> impl Pattern<'b> {}