Don't mark unknown type as implementing every notable trait

Because the new solver, will return "yes" for them (which is a good thing).

crates/ide/src/hover.rs

@@ -483,6 +483,12 @@ fn notable_traits<'db>(
     db: &'db RootDatabase,
     ty: &hir::Type<'db>,
 ) -> Vec<(hir::Trait, Vec<(Option<hir::Type<'db>>, hir::Name)>)> {
+    if ty.is_unknown() {
+        // The trait solver returns "yes" to the question whether the error type
+        // impls any trait, and we don't want to show it as having any notable trait.
+        return Vec::new();
+    }
+
     db.notable_traits_in_deps(ty.krate(db).into())
         .iter()
         .flat_map(|it| &**it)

crates/ide/src/hover/tests.rs

@@ -11097,3 +11097,26 @@ impl Enum<'_, Borrowed> {
         "#]],
     );
 }
+
+#[test]
+fn unknown_should_not_implement_notable_traits() {
+    check(
+        r#"
+//- minicore: future, iterator
+fn foo() {
+    let x$0;
+}
+    "#,
+        expect![[r#"
+            *x*
+
+            ```rust
+            let x: {unknown}
+            ```
+
+            ---
+
+            no Drop
+        "#]],
+    );
+}