Auto merge of #61207 - taiki-e:arbitrary_self_types-lifetime-elision-2, r=<try>

Allow lifetime elision in `Pin<&(mut) Self>`

This replaces #60944.

~~This PR changes elision rules to apply `self: &(mut) Self` elision rules even if nested in `Pin`.~~
This PR changes `self: &(mut) S` elision rules to instead visit the type of `self` and look for `&(mut) S` (where `is_self_ty(S)`) within it

Closes #52675

r? @eddyb
cc @cramertj @Centril @withoutboats @scottmcm

Author: bors

src/librustc/middle/resolve_lifetime.rs

@@ -2149,20 +2149,45 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
                 false
             };
 
-            if let hir::TyKind::Rptr(lifetime_ref, ref mt) = inputs[0].node {
-                if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.node {
-                    if is_self_ty(path.res) {
-                        if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
-                            let scope = Scope::Elision {
-                                elide: Elide::Exact(lifetime),
-                                s: self.scope,
-                            };
-                            self.with(scope, |_, this| this.visit_ty(output));
-                            return;
+            struct SelfVisitor<'a, F: FnMut(Res) -> bool> {
+                is_self_ty: F,
+                map: &'a NamedRegionMap,
+                lifetime: Option<Region>,
+            }
+
+            impl<'a, F: FnMut(Res) -> bool> Visitor<'a> for SelfVisitor<'a, F> {
+                fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'a> {
+                    NestedVisitorMap::None
+                }
+
+                fn visit_ty(&mut self, ty: &'a hir::Ty) {
+                    if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.node {
+                        if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.node
+                        {
+                            if (self.is_self_ty)(path.res) {
+                                self.lifetime = self.map.defs.get(&lifetime_ref.hir_id).copied();
+                                return;
+                            }
                         }
                     }
+                    intravisit::walk_ty(self, ty)
                 }
             }
+
+            let mut visitor = SelfVisitor {
+                is_self_ty,
+                map: self.map,
+                lifetime: None,
+            };
+            visitor.visit_ty(&inputs[0]);
+            if let Some(lifetime) = visitor.lifetime {
+                let scope = Scope::Elision {
+                    elide: Elide::Exact(lifetime),
+                    s: self.scope,
+                };
+                self.with(scope, |_, this| this.visit_ty(output));
+                return;
+            }
         }
 
         // Second, if there was exactly one lifetime (either a substitution or a

src/test/ui/self/arbitrary_self_types_pin_lifetime.rs

@@ -0,0 +1,60 @@
+// compile-pass
+
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+struct Foo;
+
+impl Foo {
+    fn pin_ref(self: Pin<&Self>) -> Pin<&Self> { self }
+
+    fn pin_mut(self: Pin<&mut Self>) -> Pin<&mut Self> { self }
+
+    fn pin_pin_pin_ref(self: Pin<Pin<Pin<&Self>>>) -> Pin<Pin<Pin<&Self>>> { self }
+
+    fn pin_ref_impl_trait(self: Pin<&Self>) -> impl Clone + '_ { self }
+
+    fn b(self: Pin<&Foo>, f: &Foo) -> Pin<&Foo> { self }
+}
+
+type Alias<T> = Pin<T>;
+impl Foo {
+    fn bar<'a>(self: Alias<&Self>, arg: &'a ()) -> Alias<&Self> { self }
+}
+
+struct Bar<T: Unpin, U: Unpin> {
+    field1: T,
+    field2: U,
+}
+
+impl<T: Unpin, U: Unpin> Bar<T, U> {
+    fn fields(self: Pin<&mut Self>) -> (Pin<&mut T>, Pin<&mut U>) {
+        let this = self.get_mut();
+        (Pin::new(&mut this.field1), Pin::new(&mut this.field2))
+    }
+}
+
+trait AsyncBufRead {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>)
+        -> Poll<std::io::Result<&[u8]>>;
+}
+
+struct Baz(Vec<u8>);
+
+impl AsyncBufRead for Baz {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>)
+        -> Poll<std::io::Result<&[u8]>>
+    {
+        Poll::Ready(Ok(&self.get_mut().0))
+    }
+}
+
+fn main() {
+    let mut foo = Foo;
+    { Pin::new(&foo).pin_ref() };
+    { Pin::new(&mut foo).pin_mut() };
+    { Pin::new(Pin::new(Pin::new(&foo))).pin_pin_pin_ref() };
+    { Pin::new(&foo).pin_ref_impl_trait() };
+    let mut bar = Bar { field1: 0u8, field2: 1u8 };
+    { Pin::new(&mut bar).fields() };
+}

src/test/ui/self/arbitrary_self_types_pin_lifetime_impl_trait.rs

@@ -0,0 +1,13 @@
+// compile-fail
+
+use std::pin::Pin;
+
+struct Foo;
+
+impl Foo {
+    fn f(self: Pin<&Self>) -> impl Clone { self } //~ ERROR cannot infer an appropriate lifetime
+}
+
+fn main() {
+    { Pin::new(&Foo).f() };
+}

src/test/ui/self/arbitrary_self_types_pin_lifetime_impl_trait.stderr

@@ -0,0 +1,20 @@
+error: cannot infer an appropriate lifetime
+  --> $DIR/arbitrary_self_types_pin_lifetime_impl_trait.rs:8:44
+   |
+LL |     fn f(self: Pin<&Self>) -> impl Clone { self }
+   |                               ----------   ^^^^ ...but this borrow...
+   |                               |
+   |                               this return type evaluates to the `'static` lifetime...
+   |
+note: ...can't outlive the anonymous lifetime #1 defined on the method body at 8:5
+  --> $DIR/arbitrary_self_types_pin_lifetime_impl_trait.rs:8:5
+   |
+LL |     fn f(self: Pin<&Self>) -> impl Clone { self }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: you can add a constraint to the return type to make it last less than `'static` and match the anonymous lifetime #1 defined on the method body at 8:5
+   |
+LL |     fn f(self: Pin<&Self>) -> impl Clone + '_ { self }
+   |                               ^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/self/arbitrary_self_types_pin_lifetime_mismatch.rs

@@ -0,0 +1,18 @@
+// compile-fail
+
+use std::pin::Pin;
+
+struct Foo;
+
+impl Foo {
+    fn a(self: Pin<&Foo>, f: &Foo) -> &Foo { f } //~ ERROR E0623
+
+    fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) } //~ ERROR E0623
+}
+
+type Alias<T> = Pin<T>;
+impl Foo {
+    fn bar<'a>(self: Alias<&Self>, arg: &'a ()) -> &() { arg } //~ ERROR E0623
+}
+
+fn main() {}

src/test/ui/self/arbitrary_self_types_pin_lifetime_mismatch.stderr

@@ -0,0 +1,26 @@
+error[E0623]: lifetime mismatch
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch.rs:8:46
+   |
+LL |     fn a(self: Pin<&Foo>, f: &Foo) -> &Foo { f }
+   |                              ----     ----   ^ ...but data from `f` is returned here
+   |                              |
+   |                              this parameter and the return type are declared with different lifetimes...
+
+error[E0623]: lifetime mismatch
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch.rs:10:76
+   |
+LL |     fn c(self: Pin<&Self>, f: &Foo, g: &Foo) -> (Pin<&Foo>, &Foo) { (self, f) }
+   |                               ----              -----------------          ^ ...but data from `f` is returned here
+   |                               |
+   |                               this parameter and the return type are declared with different lifetimes...
+
+error[E0623]: lifetime mismatch
+  --> $DIR/arbitrary_self_types_pin_lifetime_mismatch.rs:15:58
+   |
+LL |     fn bar<'a>(self: Alias<&Self>, arg: &'a ()) -> &() { arg }
+   |                                         ------     ---   ^^^ ...but data from `arg` is returned here
+   |                                         |
+   |                                         this parameter and the return type are declared with different lifetimes...
+
+error: aborting due to 3 previous errors
+

src/test/ui/self/self_lifetime.rs

@@ -0,0 +1,13 @@
+// compile-pass
+
+struct Foo<'a>(&'a ());
+impl<'a> Foo<'a> {
+    fn foo<'b>(self: &'b Foo<'a>) -> &() { self.0 }
+}
+
+type Alias = Foo<'static>;
+impl Alias {
+    fn bar<'a>(self: &Alias, arg: &'a ()) -> &() { arg }
+}
+
+fn main() {}