Move some field extraction logic onto a method on Node

compiler/rustc_hir/src/hir.rs

@@ -3743,6 +3743,29 @@ impl<'hir> Node<'hir> {
         }
     }
 
+    /// Get the type for constants, assoc types, type aliases and statics.
+    pub fn ty(self) -> Option<&'hir Ty<'hir>> {
+        match self {
+            Node::Item(it) => match it.kind {
+                ItemKind::TyAlias(ty, _) | ItemKind::Static(ty, _, _) | ItemKind::Const(ty, _) => {
+                    Some(ty)
+                }
+                _ => None,
+            },
+            Node::TraitItem(it) => match it.kind {
+                TraitItemKind::Const(ty, _) => Some(ty),
+                TraitItemKind::Type(_, ty) => ty,
+                _ => None,
+            },
+            Node::ImplItem(it) => match it.kind {
+                ImplItemKind::Const(ty, _) => Some(ty),
+                ImplItemKind::Type(ty) => Some(ty),
+                _ => None,
+            },
+            _ => None,
+        }
+    }
+
     pub fn alias_ty(self) -> Option<&'hir Ty<'hir>> {
         match self {
             Node::Item(Item { kind: ItemKind::TyAlias(ty, ..), .. }) => Some(ty),

compiler/rustc_ty_utils/src/opaque_types.rs

@@ -177,13 +177,9 @@ fn opaque_types_defined_by<'tcx>(tcx: TyCtxt<'tcx>, item: LocalDefId) -> &'tcx [
                     }
                 }
                 DefKind::AssocTy | DefKind::AssocConst => {
-                    let span = match tcx.hir().get_by_def_id(item) {
+                    let span = match tcx.hir().get_by_def_id(item).ty() {
-                        rustc_hir::Node::ImplItem(it) => match it.kind {
+                        Some(ty) => ty.span,
-                            rustc_hir::ImplItemKind::Const(ty, _) => ty.span,
+                        _ => tcx.def_span(item),
-                            rustc_hir::ImplItemKind::Type(ty) => ty.span,
-                            other => span_bug!(tcx.def_span(item), "{other:#?}"),
-                        },
-                        other => span_bug!(tcx.def_span(item), "{other:#?}"),
                     };
                     collector.visit_spanned(span, tcx.type_of(item).subst_identity());
                 }