Auto merge of #115429 - compiler-errors:assoc-ct-lt-fallthrough, r=cjgillot

Fall through when resolving elided assoc const lifetimes

`@QuineDot` makes a good point in https://github.com/rust-lang/rust/issues/115010#issuecomment-1702127634 that we probably should not accept *more* code due to #115011 even though that code will eventually become a forbid-warning in a few versions (https://github.com/rust-lang/rust/issues/115010#issuecomment-1701598067).

Fall through when walking thru the `AnonymousWarnToStatic` (renamed to `AnonymousWarn`) rib so that we can resolve as a fresh lifetime like we did before.

compiler/rustc_resolve/src/late.rs

@@ -313,7 +313,7 @@ enum LifetimeRibKind {
 
     /// Resolves elided lifetimes to `'static`, but gives a warning that this behavior
     /// is a bug and will be reverted soon.
-    AnonymousWarnToStatic(NodeId),
+    AnonymousWarn(NodeId),
 
     /// Signal we cannot find which should be the anonymous lifetime.
     ElisionFailure,
@@ -1154,7 +1154,7 @@ impl<'a: 'ast, 'ast, 'tcx> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast,
                             }
                             LifetimeRibKind::AnonymousCreateParameter { .. }
                             | LifetimeRibKind::AnonymousReportError
-                            | LifetimeRibKind::AnonymousWarnToStatic(_)
+                            | LifetimeRibKind::AnonymousWarn(_)
                             | LifetimeRibKind::Elided(_)
                             | LifetimeRibKind::ElisionFailure
                             | LifetimeRibKind::ConcreteAnonConst(_)
@@ -1522,7 +1522,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                                     // lifetime would be illegal.
                                     LifetimeRibKind::Item
                                     | LifetimeRibKind::AnonymousReportError
-                                    | LifetimeRibKind::AnonymousWarnToStatic(_)
+                                    | LifetimeRibKind::AnonymousWarn(_)
                                     | LifetimeRibKind::ElisionFailure => Some(LifetimeUseSet::Many),
                                     // An anonymous lifetime is legal here, and bound to the right
                                     // place, go ahead.
@@ -1585,7 +1585,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                 | LifetimeRibKind::Generics { .. }
                 | LifetimeRibKind::ElisionFailure
                 | LifetimeRibKind::AnonymousReportError
-                | LifetimeRibKind::AnonymousWarnToStatic(_) => {}
+                | LifetimeRibKind::AnonymousWarn(_) => {}
             }
         }
 
@@ -1625,8 +1625,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                     self.record_lifetime_res(lifetime.id, res, elision_candidate);
                     return;
                 }
-                LifetimeRibKind::AnonymousWarnToStatic(node_id) => {
-                    self.record_lifetime_res(lifetime.id, LifetimeRes::Static, elision_candidate);
+                LifetimeRibKind::AnonymousWarn(node_id) => {
                     let msg = if elided {
                         "`&` without an explicit lifetime name cannot be used here"
                     } else {
@@ -1642,7 +1641,6 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                             span: lifetime.ident.span,
                         },
                     );
-                    return;
                 }
                 LifetimeRibKind::AnonymousReportError => {
                     let (msg, note) = if elided {
@@ -1840,7 +1838,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                     //     impl Foo for std::cell::Ref<u32> // note lack of '_
                     //     async fn foo(_: std::cell::Ref<u32>) { ... }
                     LifetimeRibKind::AnonymousCreateParameter { report_in_path: true, .. }
-                    | LifetimeRibKind::AnonymousWarnToStatic(_) => {
+                    | LifetimeRibKind::AnonymousWarn(_) => {
                         let sess = self.r.tcx.sess;
                         let mut err = rustc_errors::struct_span_err!(
                             sess,
@@ -2936,9 +2934,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                         kind: LifetimeBinderKind::ConstItem,
                     },
                     |this| {
-                        this.with_lifetime_rib(
-                            LifetimeRibKind::AnonymousWarnToStatic(item.id),
-                            |this| {
+                        this.with_lifetime_rib(LifetimeRibKind::AnonymousWarn(item.id), |this| {
                             // If this is a trait impl, ensure the const
                             // exists in trait
                             this.check_trait_item(
@@ -2961,8 +2957,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                                 // not used as part of the type system, this is far less surprising.
                                 this.resolve_const_body(expr, None);
                             }
-                            },
-                        );
+                        });
                     },
                 );
             }

tests/ui/associated-consts/double-elided.rs

@@ -0,0 +1,12 @@
+struct S;
+
+impl S {
+    const C: &&str = &"";
+    //~^ WARN `&` without an explicit lifetime name cannot be used here
+    //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    //~| WARN `&` without an explicit lifetime name cannot be used here
+    //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    //~| ERROR in type `&&str`, reference has a longer lifetime than the data it references
+}
+
+fn main() {}

tests/ui/associated-consts/double-elided.stderr

@@ -0,0 +1,47 @@
+warning: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/double-elided.rs:4:14
+   |
+LL |     const C: &&str = &"";
+   |              ^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #115010 <https://github.com/rust-lang/rust/issues/115010>
+   = note: `#[warn(elided_lifetimes_in_associated_constant)]` on by default
+help: use the `'static` lifetime
+   |
+LL |     const C: &'static &str = &"";
+   |               +++++++
+
+warning: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/double-elided.rs:4:15
+   |
+LL |     const C: &&str = &"";
+   |               ^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #115010 <https://github.com/rust-lang/rust/issues/115010>
+help: use the `'static` lifetime
+   |
+LL |     const C: &&'static str = &"";
+   |                +++++++
+
+error[E0491]: in type `&&str`, reference has a longer lifetime than the data it references
+  --> $DIR/double-elided.rs:4:5
+   |
+LL |     const C: &&str = &"";
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: the pointer is valid for the anonymous lifetime as defined here
+  --> $DIR/double-elided.rs:4:14
+   |
+LL |     const C: &&str = &"";
+   |              ^
+note: but the referenced data is only valid for the anonymous lifetime as defined here
+  --> $DIR/double-elided.rs:4:14
+   |
+LL |     const C: &&str = &"";
+   |              ^
+
+error: aborting due to previous error; 2 warnings emitted
+
+For more information about this error, try `rustc --explain E0491`.