Fix invalid link generation for type alias methods

src/librustdoc/html/render/write_shared.rs

@@ -568,18 +568,14 @@ fn get(
                         if let Some(ret) = &mut ret {
                             ret.aliases.push(type_alias_fqp);
                         } else {
-                            let target_did = impl_
-                                .inner_impl()
-                                .trait_
-                                .as_ref()
-                                .map(|trait_| trait_.def_id())
-                                .or_else(|| impl_.inner_impl().for_.def_id(&cx.shared.cache));
+                            let target_trait_did =
+                                impl_.inner_impl().trait_.as_ref().map(|trait_| trait_.def_id());
                             let provided_methods;
-                            let assoc_link = if let Some(target_did) = target_did {
+                            let assoc_link = if let Some(target_trait_did) = target_trait_did {
                                 provided_methods =
                                     impl_.inner_impl().provided_trait_methods(cx.tcx());
                                 AssocItemLink::GotoSource(
-                                    ItemId::DefId(target_did),
+                                    ItemId::DefId(target_trait_did),
                                     &provided_methods,
                                 )
                             } else {

tests/rustdoc-gui/src/test_docs/lib.rs

@@ -786,3 +786,13 @@ pub fn bar() -> Vec<u8> {
         Vec::new()
     }
 }
+
+pub mod tyalias {
+    pub struct X<T>(pub T);
+
+    impl<T: std::fmt::Debug> X<T> {
+        pub fn blob(&self) {}
+    }
+
+    pub type Y = X<u8>;
+}

tests/rustdoc-gui/type-alias.goml

@@ -0,0 +1,7 @@
+// This test ensures that we correctly generate links to methods on type aliases.
+go-to: "file://" + |DOC_PATH| + "/test_docs/tyalias/type.Y.html"
+
+// It's generated with JS so we need to wait for it to be done generating.
+wait-for: "#implementations"
+// We check that it's "#method." and not "#tymethod.".
+assert-text: ('#method\.blob a.fn[href="#method.blob"]', "blob")