fix: handle line codes with an empty line number

lua/gitlab/actions/common.lua

@@ -262,10 +262,10 @@ M.get_line_numbers_for_range = function(old_line, new_line, start_line_code, end
   local old_start_line, new_start_line = indicators_common.parse_line_code(start_line_code)
   local old_end_line, new_end_line = indicators_common.parse_line_code(end_line_code)
   if old_line ~= nil and old_start_line ~= 0 then
-    local range = old_end_line - old_start_line
+    local range = (old_start_line and old_end_line) and (old_end_line - old_start_line) or 0
     return (old_line - range), old_line, false
   elseif new_line ~= nil then
-    local range = new_end_line - new_start_line
+    local range = (new_start_line and new_end_line) and (new_end_line - new_start_line) or 0
     -- Force start_line to be greater than 0
     -- TODO: use `math.max(new_line - range, 1)` instead
     local start_line = (new_line - range > 0) and (new_line - range) or 1

lua/gitlab/indicators/common.lua

@@ -53,15 +53,14 @@ M.filter_placeable_discussions = function()
 end
 
 ---Parse old and new line from a line code like "3f454a98e586d1aa0d322e19afd5e67e08f2d3c8_10_44".
----@param line_code string A SHA hash of the file name and line numbers before and after change
----@return integer The line number before the change
----@return integer The line number after the change
+---GitLab leaves a number empty when the line has no counterpart, e.g. "3f454a98...__44".
+---@param line_code? string A SHA hash of the file name and line numbers before and after change
+---@return integer? The line number before the change
+---@return integer? The line number after the change
 M.parse_line_code = function(line_code)
-  local line_code_regex = "%w+_(%d+)_(%d+)"
-  local old_line, new_line = line_code:match(line_code_regex)
-  old_line = tonumber(old_line) --[[@as integer]]
-  new_line = tonumber(new_line) --[[@as integer]]
-  return old_line, new_line
+  local line_code_regex = "%w+_(%d*)_(%d*)"
+  local old_line, new_line = (line_code or ""):match(line_code_regex)
+  return tonumber(old_line), tonumber(new_line)
 end
 
 ---Return true if discussion/draft belongs to the old file, otherwise false.

tests/spec/line_code_spec.lua

@@ -0,0 +1,45 @@
+local indicators_common = require("gitlab.indicators.common")
+local actions_common = require("gitlab.actions.common")
+
+local sha = "3f454a98e586d1aa0d322e19afd5e67e08f2d3c8"
+
+describe("indicators/common.parse_line_code", function()
+  it("Parses both line numbers", function()
+    assert.are.same({ 10, 44 }, { indicators_common.parse_line_code(sha .. "_10_44") })
+  end)
+
+  it("Returns nil for an empty old line number", function()
+    assert.are.same({ nil, 44 }, { indicators_common.parse_line_code(sha .. "__44") })
+  end)
+
+  it("Returns nil for an empty new line number", function()
+    assert.are.same({ 10, nil }, { indicators_common.parse_line_code(sha .. "_10_") })
+  end)
+
+  it("Returns nil for a missing line code", function()
+    assert.are.same({ nil, nil }, { indicators_common.parse_line_code(nil) })
+  end)
+end)
+
+describe("actions/common.get_line_numbers_for_range", function()
+  it("Computes a range on the new SHA", function()
+    assert.are.same(
+      { 40, 44, true },
+      { actions_common.get_line_numbers_for_range(nil, 44, sha .. "_1_40", sha .. "_1_44") }
+    )
+  end)
+
+  it("Falls back to a single line when a line code has an empty number", function()
+    assert.are.same(
+      { 44, 44, true },
+      { actions_common.get_line_numbers_for_range(nil, 44, sha .. "__40", sha .. "_1_") }
+    )
+  end)
+
+  it("Falls back to a single line on the old SHA when a line code has an empty number", function()
+    assert.are.same(
+      { 12, 12, false },
+      { actions_common.get_line_numbers_for_range(12, nil, sha .. "_10_", sha .. "__5") }
+    )
+  end)
+end)