Fix ICE in return_type_impl_trait

src/librustc/ty/context.rs

@@ -17,7 +17,7 @@ use session::Session;
 use session::config::{BorrowckMode, OutputFilenames};
 use session::config::CrateType;
 use middle;
-use hir::{TraitCandidate, HirId, ItemLocalId, Node};
+use hir::{TraitCandidate, HirId, ItemKind, ItemLocalId, Node};
 use hir::def::{Def, Export};
 use hir::def_id::{CrateNum, DefId, DefIndex, LOCAL_CRATE};
 use hir::map as hir_map;
@@ -1602,6 +1602,20 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         &self,
         scope_def_id: DefId,
     ) -> Option<Ty<'tcx>> {
+        // HACK: `type_of_def_id()` will fail on these (#55796), so return None
+        let node_id = self.hir.as_local_node_id(scope_def_id).unwrap();
+        match self.hir.get(node_id) {
+            Node::Item(item) => {
+                match item.node {
+                    ItemKind::Fn(..) => { /* type_of_def_id() will work */ }
+                    _ => {
+                        return None;
+                    }
+                }
+            }
+            _ => { /* type_of_def_id() will work or panic */ }
+        }
+
         let ret_ty = self.type_of(scope_def_id);
         match ret_ty.sty {
             ty::FnDef(_, _) => {

src/test/ui/issues/issue-55796.rs

@@ -0,0 +1,22 @@
+pub trait EdgeTrait<N> {
+    fn target(&self) -> N;
+}
+
+pub trait Graph<'a> {
+    type Node;
+    type Edge: EdgeTrait<Self::Node>;
+    type NodesIter: Iterator<Item = Self::Node> + 'a;
+    type EdgesIter: Iterator<Item = Self::Edge> + 'a;
+
+    fn nodes(&'a self) -> Self::NodesIter;
+    fn out_edges(&'a self, u: &Self::Node) -> Self::EdgesIter;
+    fn in_edges(&'a self, u: &Self::Node) -> Self::EdgesIter;
+
+    fn out_neighbors(&'a self, u: &Self::Node) -> Box<Iterator<Item = Self::Node>> {
+        Box::new(self.out_edges(u).map(|e| e.target()))
+    }
+
+    fn in_neighbors(&'a self, u: &Self::Node) -> Box<Iterator<Item = Self::Node>> {
+        Box::new(self.in_edges(u).map(|e| e.target()))
+    }
+}

src/test/ui/issues/issue-55796.stderr

@@ -0,0 +1,50 @@
+error[E0601]: `main` function not found in crate `issue_55796`
+   |
+   = note: consider adding a `main` function to `$DIR/issue-55796.rs`
+
+error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
+  --> $DIR/issue-55796.rs:16:9
+   |
+LL |         Box::new(self.out_edges(u).map(|e| e.target()))
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: first, the lifetime cannot outlive the lifetime 'a as defined on the trait at 5:17...
+  --> $DIR/issue-55796.rs:5:17
+   |
+LL | pub trait Graph<'a> {
+   |                 ^^
+note: ...so that the type `std::iter::Map<<Self as Graph<'a>>::EdgesIter, [closure@$DIR/issue-55796.rs:16:40: 16:54]>` will meet its required lifetime bounds
+  --> $DIR/issue-55796.rs:16:9
+   |
+LL |         Box::new(self.out_edges(u).map(|e| e.target()))
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: but, the lifetime must be valid for the static lifetime...
+   = note: ...so that the expression is assignable:
+           expected std::boxed::Box<(dyn std::iter::Iterator<Item=<Self as Graph<'a>>::Node> + 'static)>
+              found std::boxed::Box<dyn std::iter::Iterator<Item=<Self as Graph<'a>>::Node>>
+
+error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
+  --> $DIR/issue-55796.rs:20:9
+   |
+LL |         Box::new(self.in_edges(u).map(|e| e.target()))
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: first, the lifetime cannot outlive the lifetime 'a as defined on the trait at 5:17...
+  --> $DIR/issue-55796.rs:5:17
+   |
+LL | pub trait Graph<'a> {
+   |                 ^^
+note: ...so that the type `std::iter::Map<<Self as Graph<'a>>::EdgesIter, [closure@$DIR/issue-55796.rs:20:39: 20:53]>` will meet its required lifetime bounds
+  --> $DIR/issue-55796.rs:20:9
+   |
+LL |         Box::new(self.in_edges(u).map(|e| e.target()))
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: but, the lifetime must be valid for the static lifetime...
+   = note: ...so that the expression is assignable:
+           expected std::boxed::Box<(dyn std::iter::Iterator<Item=<Self as Graph<'a>>::Node> + 'static)>
+              found std::boxed::Box<dyn std::iter::Iterator<Item=<Self as Graph<'a>>::Node>>
+
+error: aborting due to 3 previous errors
+
+Some errors occurred: E0495, E0601.
+For more information about an error, try `rustc --explain E0495`.