Fix lifetime elision

 struct Concrete(u32); impl Concrete { fn m(self: &Box<Self>) -> &u32 { &self.0 } } resulted in a confusing error. impl Concrete { fn n(self: &Box<&Self>) -> &u32 { &self.0 } } resulted in no error or warning, despite apparent ambiguity over the elided lifetime. Fixes #117715

Author: adetaylor

compiler/rustc_resolve/src/late.rs

@@ -2090,13 +2090,15 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
  // Handle `self` specially.
  if index == 0 && has_self {
  let self_lifetime = self.find_lifetime_for_self(ty);
- if let Set1::One(lifetime) = self_lifetime {
+ elision_lifetime = match self_lifetime {
  // We found `self` elision.
- elision_lifetime = Elision::Self_(lifetime);
- } else {
+ Set1::One(lifetime) => Elision::Self_(lifetime),
+ // `self` itself had ambiguous lifetimes, e.g.
+ // &Box<&Self>
+ Set1::Many => Elision::Err,
  // We do not have `self` elision: disregard the `Elision::Param` that we may
  // have found.
- elision_lifetime = Elision::None;
+ Set1::Empty => Elision::None,
  }
  }
  debug!("(resolving function / closure) recorded parameter");
@@ -2120,6 +2122,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
  r: &'r Resolver<'a, 'tcx>,
  impl_self: Option<Res>,
  lifetime: Set1<LifetimeRes>,
+ self_found: bool,
  }
 
  impl SelfVisitor<'_, '_, '_> {
@@ -2143,9 +2146,11 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
  impl<'a> Visitor<'a> for SelfVisitor<'_, '_, '_> {
  fn visit_ty(&mut self, ty: &'a Ty) {
  trace!("SelfVisitor considering ty={:?}", ty);
- if let TyKind::Ref(lt, ref mt) = ty.kind
- && self.is_self_ty(&mt.ty)
- {
+ if self.is_self_ty(ty) {
+ trace!("SelfVisitor found Self");
+ self.self_found = true;
+ }
+ if let TyKind::Ref(lt, _) = ty.kind {
  let lt_id = if let Some(lt) = lt {
  lt.id
  } else {
@@ -2186,10 +2191,11 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
  Res::Def(DefKind::Struct | DefKind::Union | DefKind::Enum, _,) | Res::PrimTy(_)
  )
  });
- let mut visitor = SelfVisitor { r: self.r, impl_self, lifetime: Set1::Empty };
+ let mut visitor =
+ SelfVisitor { r: self.r, impl_self, lifetime: Set1::Empty, self_found: false };
  visitor.visit_ty(ty);
- trace!("SelfVisitor found={:?}", visitor.lifetime);
- visitor.lifetime
+ trace!("SelfVisitor found={:?}, self_found={:?}", visitor.lifetime, visitor.self_found);
+ if visitor.self_found { visitor.lifetime } else { Set1::Empty }
  }
 
  /// Searches the current set of local scopes for labels. Returns the `NodeId` of the resolved

tests/ui/self/elision/ref-self-multi.rs

@@ -0,0 +1,24 @@
+#![feature(arbitrary_self_types)]
+#![allow(non_snake_case)]
+
+use std::marker::PhantomData;
+use std::ops::Deref;
+use std::pin::Pin;
+
+struct Struct { }
+
+struct Wrap<T, P>(T, PhantomData<P>);
+
+impl<T, P> Deref for Wrap<T, P> {
+ type Target = T;
+ fn deref(&self) -> &T { &self.0 }
+}
+
+impl Struct {
+ fn ref_box_ref_Self(self: &Box<&Self>, f: &u32) -> &u32 {
+ f
+ //~^ ERROR missing lifetime specifier
+ }
+}
+
+fn main() { }

tests/ui/self/elision/ref-self-multi.stderr

@@ -0,0 +1,15 @@
+error[E0106]: missing lifetime specifier
+ --> $DIR/ref-self-multi.rs:18:56
+ |
+LL | fn ref_box_ref_Self(self: &Box<&Self>, f: &u32) -> &u32 {
+ | ----------- ---- ^ expected named lifetime parameter
+ |
+ = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from one of `self`'s 2 lifetimes or `f`
+help: consider introducing a named lifetime parameter
+ |
+LL | fn ref_box_ref_Self<'a>(self: &'a Box<&'a Self>, f: &'a u32) -> &'a u32 {
+ | ++++ ++ ++ ++ ++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0106`.

tests/ui/self/elision/ref-self.rs

@@ -53,6 +53,11 @@ impl Struct {
  f
  //~^ ERROR lifetime may not live long enough
  }
+
+ fn ref_box_Self(self: &Box<Self>, f: &u32) -> &u32 {
+ f
+ //~^ ERROR lifetime may not live long enough
+ }
 }
 
 fn main() { }

tests/ui/self/elision/ref-self.stderr

@@ -103,5 +103,20 @@ help: consider introducing a named lifetime parameter and update trait if needed
 LL | fn wrap_ref_Self_Self<'a>(self: Wrap<&'a Self, Self>, f: &'a u8) -> &u8 {
  | ++++ ++ ++
 
-error: aborting due to 7 previous errors
+error: lifetime may not live long enough
+ --> $DIR/ref-self.rs:58:9
+ |
+LL | fn ref_box_Self(self: &Box<Self>, f: &u32) -> &u32 {
+ | - - let's call the lifetime of this reference `'1`
+ | |
+ | let's call the lifetime of this reference `'2`
+LL | f
+ | ^ method was supposed to return data with lifetime `'2` but it is returning data with lifetime `'1`
+ |
+help: consider introducing a named lifetime parameter and update trait if needed
+ |
+LL | fn ref_box_Self<'a>(self: &'a Box<Self>, f: &'a u32) -> &u32 {
+ | ++++ ++ ++
+
+error: aborting due to 8 previous errors