From 38ca560b9c5ef46f59f3adcdd1cba9f181be4218 Mon Sep 17 00:00:00 2001
From: "Pey Lian Lim (Github)" <2090236+pllim@users.noreply.github.com>
Date: Fri, 30 Sep 2022 14:38:57 -0400
Subject: [PATCH] Disable Line Lists when there is no data

---
 CHANGES.rst                                            |  3 +++
 .../configs/default/plugins/line_lists/line_lists.py   | 10 ++++++++++
 .../plugins/line_lists/tests/test_line_lists.py        |  6 ++++++
 3 files changed, 19 insertions(+)

diff --git a/CHANGES.rst b/CHANGES.rst
index 77a4e87b54..9b9026b8c8 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -114,6 +114,9 @@ Mosviz
 Specviz
 ^^^^^^^
 
+- Line Lists plugin now disabled if no data is loaded instead of letting user
+  load a list list and crash. [#1691]
+
 Specviz2d
 ^^^^^^^^^
 
diff --git a/jdaviz/configs/default/plugins/line_lists/line_lists.py b/jdaviz/configs/default/plugins/line_lists/line_lists.py
index f1c3341163..550e750ce7 100644
--- a/jdaviz/configs/default/plugins/line_lists/line_lists.py
+++ b/jdaviz/configs/default/plugins/line_lists/line_lists.py
@@ -114,6 +114,14 @@ def __init__(self, *args, **kwargs):
         self._viewer.state.add_callback("x_max",
                                         lambda x_max: self._on_spectrum_viewer_limits_changed())
 
+        self._disable_if_no_data()
+
+    def _disable_if_no_data(self):
+        if len(self.app.data_collection) == 0:
+            self.disabled_msg = 'Line Lists unavailable when no data is loaded'
+        else:
+            self.disabled_msg = ''
+
     def _on_viewer_data_changed(self, msg=None):
         """
         Callback method for when data is added or removed from a viewer, or
@@ -131,6 +139,8 @@ def _on_viewer_data_changed(self, msg=None):
         msg : `glue.core.Message`
             The glue message passed to this callback method.
         """
+        self._disable_if_no_data()
+
         self._viewer_id = self.app._viewer_item_by_reference(
             'spectrum-viewer').get('id')
 
diff --git a/jdaviz/configs/default/plugins/line_lists/tests/test_line_lists.py b/jdaviz/configs/default/plugins/line_lists/tests/test_line_lists.py
index 560861beb7..e15ece58de 100644
--- a/jdaviz/configs/default/plugins/line_lists/tests/test_line_lists.py
+++ b/jdaviz/configs/default/plugins/line_lists/tests/test_line_lists.py
@@ -45,9 +45,15 @@ def test_line_lists(specviz_helper):
 
 
 def test_redshift(specviz_helper, spectrum1d):
+    # Also test that plugin is disabled before data is loaded.
+    plg = specviz_helper.plugins['Line Lists']
+    assert plg._obj.disabled_msg
+
     label = "Test 1D Spectrum"
     specviz_helper.load_spectrum(spectrum1d, data_label=label)
 
+    assert not plg._obj.disabled_msg
+
     lt = QTable()
     lt['linename'] = ['O III', 'Halpha']
     lt['rest'] = [5007, 6563]*u.AA