boxes: Inform the user to use autocomplete on invalid recipients.

This commit modifies the `invalid_recipients_error` message to also
mention the keys used for autocompleting recipients, so the user is
able to quickly reach the valid form of the intended recipients.

Tests added.

Author: prah23

tests/ui_tools/test_boxes.py

@@ -143,6 +143,58 @@ def test_tidying_recipients_on_keypresses(
 
         assert write_box.to_write_box.edit_text == tidied_recipients
 
+    @pytest.mark.parametrize(
+        ["raw_recipients", "invalid_recipients"],
+        [
+            ("Human 1 <[email protected]>", "Human 1 <[email protected]>"),
+            ("[email protected]", "[email protected]"),
+            ("Human 1", "Human 1"),
+        ],
+        ids=["name_email_mismatch", "no_name_specified", "no_email_specified"],
+    )
+    @pytest.mark.parametrize(
+        "key",
+        keys_for_command("SEND_MESSAGE")
+        + keys_for_command("SAVE_AS_DRAFT")
+        + keys_for_command("CYCLE_COMPOSE_FOCUS"),
+    )
+    def test_footer_notification_on_invalid_recipients(
+        self,
+        write_box,
+        key,
+        mocker,
+        widget_size,
+        raw_recipients,
+        invalid_recipients,
+    ):
+
+        write_box.model.is_valid_private_recipient = mocker.Mock(return_value=False)
+        write_box.private_box_view()
+        write_box.focus_position = write_box.FOCUS_CONTAINER_HEADER
+        write_box.header_write_box.focus_col = write_box.FOCUS_HEADER_BOX_RECIPIENT
+
+        write_box.to_write_box.edit_text = raw_recipients
+        write_box.to_write_box.set_edit_pos(len(raw_recipients))
+        expected_lines = [
+            "Invalid recipient(s) - " + invalid_recipients,
+            " - Use ",
+            ("footer_contrast", primary_key_for_command("AUTOCOMPLETE")),
+            " or ",
+            ("footer_contrast", primary_key_for_command("AUTOCOMPLETE_REVERSE")),
+            " to autocomplete.",
+        ]
+
+        size = widget_size(write_box)
+        write_box.keypress(size, key)
+
+        self.view.controller.report_error.assert_called_once_with(expected_lines)
+        # If there are invalid recipients, we expect the focus
+        # to remain in the to_write_box.
+        assert write_box.focus_position == write_box.FOCUS_CONTAINER_HEADER
+        assert (
+            write_box.header_write_box.focus_col == write_box.FOCUS_HEADER_BOX_RECIPIENT
+        )
+
     @pytest.mark.parametrize(
         "text, state",
         [

zulipterminal/ui_tools/boxes.py

@@ -252,9 +252,17 @@ def tidy_valid_recipients_and_notify_invalid_ones(
         write_box.edit_pos = len(write_box.edit_text)
 
         if invalid_recipients:
-            invalid_recipients_error = (
-                f"Invalid recipient(s) - {', '.join(invalid_recipients)}"
-            )
+            invalid_recipients_error = [
+                "Invalid recipient(s) - " + ", ".join(invalid_recipients),
+                " - Use ",
+                ("footer_contrast", primary_key_for_command("AUTOCOMPLETE")),
+                " or ",
+                (
+                    "footer_contrast",
+                    primary_key_for_command("AUTOCOMPLETE" "_REVERSE"),
+                ),
+                " to autocomplete.",
+            ]
             self.view.controller.report_error(invalid_recipients_error)
             return False