fix: hunk header counts and the deleted-line check

lua/gitlab/hunks.lua

@@ -25,38 +25,26 @@ M.parse_possible_hunk_headers = function(line)
     --  @@ -41,0 +42,4 @@ ...
     local old_start, old_range, new_start, new_range = line:match("@@+ %-(%d+),?(%d*) %+(%d+),?(%d*) @@+")
 
+    -- Git omits the ",N" count when it is exactly 1, so an empty capture means 1,
+    -- while a captured "0" means a genuine zero-length range (pure insertion/deletion).
     return {
       old_line = tonumber(old_start),
-      old_range = tonumber(old_range) or 0,
+      old_range = tonumber(old_range) or 1,
       new_line = tonumber(new_start),
-      new_range = tonumber(new_range) or 0,
+      new_range = tonumber(new_range) or 1,
     }
   end
 end
 
 ---Return true if given line was removed in the MR.
+---The diff comes from `git.diff_files`, which runs with `--unified=0`. A hunk
+---therefore carries no context lines and its old range holds removed lines only,
+---so membership in that range already answers the question.
 ---@param linenr integer Line number in the old version of the file
 ---@param hunk Hunk A hunk candidate from the file's diff
----@param all_diff_output string[]
 ---@return boolean
-local line_was_removed = function(linenr, hunk, all_diff_output)
-  for matching_line_index, line in ipairs(all_diff_output) do
-    local found_hunk = M.parse_possible_hunk_headers(line)
-    if found_hunk ~= nil and vim.deep_equal(found_hunk, hunk) then
-      -- We found a matching hunk, now we need to iterate over the lines from the raw diff output
-      -- at that hunk until we reach the line we are looking for. When the indexes match we check
-      -- to see if that line is deleted or not.
-      for hunk_line_index = found_hunk.old_line, hunk.old_line + hunk.old_range, 1 do
-        local line_content = all_diff_output[matching_line_index + 1]
-        if hunk_line_index == linenr then
-          if string.match(line_content, "^%-") then
-            return true
-          end
-        end
-      end
-    end
-  end
-  return false
+local line_was_removed = function(linenr, hunk)
+  return linenr >= hunk.old_line and linenr < hunk.old_line + hunk.old_range
 end
 
 ---Return true if given line was added in the MR.
@@ -198,9 +186,8 @@ end
 ---@param old_line? integer The starting or ending line of the current selection in the old version
 ---@param new_line? integer The starting or ending line of the current selection in the new version
 ---@param hunks Hunk[]
----@param all_diff_output string[]
 ---@return ("deleted"|"unmodified")?
-local function get_modification_type_from_old_sha(old_line, new_line, hunks, all_diff_output)
+local function get_modification_type_from_old_sha(old_line, new_line, hunks)
   if old_line == nil then
     return nil
   end
@@ -210,7 +197,7 @@ local function get_modification_type_from_old_sha(old_line, new_line, hunks, all
     local new_line_end = hunk.new_line + hunk.new_range - (hunk.new_range > 0 and 1 or 0)
     local in_old_range = old_line >= hunk.old_line and old_line <= old_line_end
     local in_new_range = new_line >= hunk.new_line and new_line <= new_line_end
-    return (in_old_range or in_new_range) and line_was_removed(old_line, hunk, all_diff_output)
+    return (in_old_range or in_new_range) and line_was_removed(old_line, hunk)
   end) and "deleted" or "unmodified"
 end
 
@@ -236,7 +223,7 @@ function M.get_modification_type(old_line, new_line, new_sha_focused)
   local hunks = hunk_and_diff_data.hunks
   local all_diff_output = hunk_and_diff_data.all_diff_output
   return new_sha_focused and get_modification_type_from_new_sha(new_line, hunks, all_diff_output)
-    or get_modification_type_from_old_sha(old_line, new_line, hunks, all_diff_output)
+    or get_modification_type_from_old_sha(old_line, new_line, hunks)
 end
 
 ---Return the matching line number of a line in the new/old version of the file compared

tests/spec/hunks_spec.lua

@@ -0,0 +1,129 @@
+local hunks = require("gitlab.hunks")
+
+describe("gitlab/hunks.lua", function()
+  describe("parse_possible_hunk_headers", function()
+    it("treats an omitted old count as 1, keeping an explicit new count", function()
+      local got = hunks.parse_possible_hunk_headers("@@ -5 +5,3 @@")
+      local want = { old_line = 5, old_range = 1, new_line = 5, new_range = 3 }
+      assert.are.same(want, got)
+    end)
+
+    it("keeps an explicit old count of 0 as a genuine pure insertion", function()
+      local got = hunks.parse_possible_hunk_headers("@@ -5,0 +5,3 @@")
+      local want = { old_line = 5, old_range = 0, new_line = 5, new_range = 3 }
+      assert.are.same(want, got)
+    end)
+
+    it("treats both omitted counts as 1", function()
+      local got = hunks.parse_possible_hunk_headers("@@ -5 +5 @@")
+      local want = { old_line = 5, old_range = 1, new_line = 5, new_range = 1 }
+      assert.are.same(want, got)
+    end)
+
+    it("treats an omitted new count as 1, keeping an explicit old count", function()
+      local got = hunks.parse_possible_hunk_headers("@@ -5,3 +5 @@")
+      local want = { old_line = 5, old_range = 3, new_line = 5, new_range = 1 }
+      assert.are.same(want, got)
+    end)
+  end)
+
+  describe("get_modification_type", function()
+    local state = require("gitlab.state")
+
+    local function stub_diff(diff_text)
+      package.loaded["gitlab.git"] = {
+        diff_files = function()
+          return diff_text, nil
+        end,
+      }
+      package.loaded["gitlab.reviewer"] = {
+        get_current_file_oldpath = function()
+          return "file.txt"
+        end,
+        get_current_file_path = function()
+          return "file.txt"
+        end,
+      }
+    end
+
+    before_each(function()
+      state.INFO = { diff_refs = { base_sha = "base-sha" } }
+    end)
+
+    after_each(function()
+      state.INFO = nil
+      package.loaded["gitlab.git"] = nil
+      package.loaded["gitlab.reviewer"] = nil
+    end)
+
+    it("does not classify the unmodified context line above a single-line deletion as added", function()
+      stub_diff([[
+diff --git a/file.txt b/file.txt
+index 1111111..2222222 100644
+--- a/file.txt
++++ b/file.txt
+@@ -5 +4,0 @@
+-old content that was removed
+]])
+
+      local got = hunks.get_modification_type(4, 4, true)
+      assert.are_not.same("added", got)
+      assert.are.same("bad_file_unmodified", got)
+    end)
+
+    it("keeps classifying the context line above a two-line deletion as bad_file_unmodified", function()
+      stub_diff([[
+diff --git a/file.txt b/file.txt
+index 1111111..2222222 100644
+--- a/file.txt
++++ b/file.txt
+@@ -5,2 +4,0 @@
+-old line 5
+-old line 6
+]])
+
+      local got = hunks.get_modification_type(4, 4, true)
+      assert.are.same("bad_file_unmodified", got)
+    end)
+
+    it("treats a deleted line as deleted", function()
+      stub_diff([[
+diff --git a/file.txt b/file.txt
+index 1111111..2222222 100644
+--- a/file.txt
++++ b/file.txt
+@@ -5 +4,0 @@
+-old line 5
+]])
+
+      assert.are.same("deleted", hunks.get_modification_type(5, 4, false))
+    end)
+
+    it("treats the line below a single-line deletion as unmodified", function()
+      stub_diff([[
+diff --git a/file.txt b/file.txt
+index 1111111..2222222 100644
+--- a/file.txt
++++ b/file.txt
+@@ -5 +4,0 @@
+-old line 5
+]])
+
+      assert.are.same("unmodified", hunks.get_modification_type(6, 5, false))
+    end)
+
+    it("treats the line below a multi-line deletion as unmodified", function()
+      stub_diff([[
+diff --git a/file.txt b/file.txt
+index 1111111..2222222 100644
+--- a/file.txt
++++ b/file.txt
+@@ -5,2 +4,0 @@
+-old line 5
+-old line 6
+]])
+
+      assert.are.same("unmodified", hunks.get_modification_type(7, 5, false))
+    end)
+  end)
+end)