Add test for issue rust-lang#70304

Author: marmeladema

src/test/ui/generic-associated-types/issue-70304.rs

@@ -0,0 +1,63 @@
+#![allow(incomplete_features)]
+#![feature(generic_associated_types)]
+
+trait Document {
+    type Cursor<'a>: DocCursor<'a>;
+
+    fn cursor(&self) -> Self::Cursor<'_>;
+}
+
+struct DocumentImpl {}
+
+impl Document for DocumentImpl {
+    type Cursor<'a> = DocCursorImpl<'a>;
+
+    fn cursor(&self) -> Self::Cursor<'_> {
+        DocCursorImpl {
+            document: &self,
+        }
+    }
+}
+
+
+trait DocCursor<'a> {}
+
+struct DocCursorImpl<'a> {
+    document: &'a DocumentImpl,
+}
+
+impl<'a> DocCursor<'a> for DocCursorImpl<'a> {}
+
+struct Lexer<'d, Cursor>
+where
+    Cursor: DocCursor<'d>,
+{
+    cursor: Cursor,
+    _phantom: std::marker::PhantomData<&'d ()>,
+}
+
+
+impl<'d, Cursor> Lexer<'d, Cursor>
+where
+    Cursor: DocCursor<'d>,
+{
+    pub fn from<Doc>(document: &'d Doc) -> Lexer<'d, Cursor>
+    where
+        Doc: Document<Cursor<'d> = Cursor>,
+    {
+        Lexer {
+            cursor: document.cursor(),
+            _phantom: std::marker::PhantomData,
+        }
+    }
+}
+
+fn create_doc() -> impl Document<Cursor<'_> = DocCursorImpl<'_>> {
+                                       //~^ ERROR: missing lifetime specifier
+    DocumentImpl {}
+}
+
+pub fn main() {
+    let doc = create_doc();
+    let lexer: Lexer<'_, DocCursorImpl<'_>> = Lexer::from(&doc);
+}

src/test/ui/generic-associated-types/issue-70304.stderr

@@ -0,0 +1,15 @@
+error[E0106]: missing lifetime specifier
+  --> $DIR/issue-70304.rs:55:41
+   |
+LL | fn create_doc() -> impl Document<Cursor<'_> = DocCursorImpl<'_>> {
+   |                                         ^^ expected named lifetime parameter
+   |
+   = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
+help: consider using the `'static` lifetime
+   |
+LL | fn create_doc() -> impl Document<Cursor<'static> = DocCursorImpl<'_>> {
+   |                                         ^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0106`.