Fix goto definition for type alias type parameters

closes https://github.com/rust-analyzer/rust-analyzer/issues/5042

crates/ra_hir/src/semantics.rs

@@ -485,6 +485,7 @@ impl<'db> SemanticsImpl<'db> {
             ChildContainer::ModuleId(it) => it.resolver(self.db.upcast()),
             ChildContainer::EnumId(it) => it.resolver(self.db.upcast()),
             ChildContainer::VariantId(it) => it.resolver(self.db.upcast()),
+            ChildContainer::TypeAliasId(it) => it.resolver(self.db.upcast()),
             ChildContainer::GenericDefId(it) => it.resolver(self.db.upcast()),
         };
         SourceAnalyzer::new_for_resolver(resolver, src)

crates/ra_hir/src/semantics/source_to_def.rs

@@ -194,6 +194,10 @@ impl SourceToDefCtx<'_, '_> {
                         let def = self.const_to_def(container.with_value(it))?;
                         DefWithBodyId::from(def).into()
                     },
+                    ast::TypeAliasDef(it) => {
+                        let def = self.type_alias_to_def(container.with_value(it))?;
+                        def.into()
+                    },
                     _ => continue,
                 }
             };
@@ -246,6 +250,7 @@ pub(crate) enum ChildContainer {
     ImplId(ImplId),
     EnumId(EnumId),
     VariantId(VariantId),
+    TypeAliasId(TypeAliasId),
     /// XXX: this might be the same def as, for example an `EnumId`. However,
     /// here the children generic parameters, and not, eg enum variants.
     GenericDefId(GenericDefId),
@@ -258,6 +263,7 @@ impl_froms! {
     ImplId,
     EnumId,
     VariantId,
+    TypeAliasId,
     GenericDefId
 }
 
@@ -271,6 +277,7 @@ impl ChildContainer {
             ChildContainer::ImplId(it) => it.child_by_source(db),
             ChildContainer::EnumId(it) => it.child_by_source(db),
             ChildContainer::VariantId(it) => it.child_by_source(db),
+            ChildContainer::TypeAliasId(_) => DynMap::default(),
             ChildContainer::GenericDefId(it) => it.child_by_source(db),
         }
     }

crates/ra_ide/src/goto_definition.rs

@@ -856,4 +856,14 @@ impl Foo {
 "#,
         );
     }
+
+    #[test]
+    fn goto_def_for_type_alias_generic_parameter() {
+        check(
+            r#"
+type Alias<T> = T<|>;
+         //^
+"#,
+        )
+    }
 }