source: validate cursor before source lookup

changelog.txt

@@ -38,6 +38,7 @@ Template for new versions:
 - `caravan`: fix doubled "total value of items marked for trade" after toggling filter options, and keep item marks when switching between filter views in the ``Bring goods to depot`` overlay
 - `fix/loyaltycascade`: guard against citizens that are not historical figures and emit a warning.
 - `gui/siegemanager`: fix nil index if there are no siege engines on the map
+- `source`: report a useful error when no keyboard cursor is active
 
 ## Misc Improvements
 - `caravan`: the ``Bring goods to depot``, ``Trade``, and ``Assign items for display`` overlays now allow searching for items with non-ASCII characters in their description

source.lua

@@ -132,12 +132,12 @@ function main(args)
     end
 
     local targetPos = guidm.getCursorPos()
-    local index = find_liquid_source_at_pos(targetPos)
 
     if command == 'delete' then
         if not targetPos then
             qerror("Please place the cursor where there is a source to delete")
         end
+        local index = find_liquid_source_at_pos(targetPos)
         if index then
             delete_liquid_source(targetPos)
             print(('Deleted source at %s'):format(formatPos(targetPos)))

test/source.lua

@@ -0,0 +1,23 @@
+config = {
+    mode = 'fortress',
+    target = 'source',
+}
+
+local guidm = require('gui.dwarfmode')
+local source = reqscript('source')
+
+function test.delete_requires_cursor()
+    mock.patch(guidm, 'getCursorPos', function() end, function()
+        expect.error_match(
+            'Please place the cursor where there is a source to delete',
+            function() source.main{'delete'} end)
+    end)
+end
+
+function test.add_requires_cursor()
+    mock.patch(guidm, 'getCursorPos', function() end, function()
+        expect.error_match(
+            'Please place the cursor where you would like a source',
+            function() source.main{'add', 'water'} end)
+    end)
+end