feat(hunks)!: highlight inline overlay diffs

BREAKING CHANGE: rename :GitDiffOverlay to :GitHunkOverlay and <Plug>(git-diff-overlay) to <Plug>(git-hunk-overlay).

test/git/hunks_test.lua

@@ -64,6 +64,19 @@ local function find_float()
     end
 end
 
+---@param hl string|string[]?
+---@param group string
+---@return boolean
+local function has_hl(hl, group)
+    if hl == group then
+        return true
+    end
+    if type(hl) == "table" then
+        return vim.tbl_contains(hl, group)
+    end
+    return false
+end
+
 t.test("pure add: hunk shape and add signs", function()
     local _, buf, state = setup("a\nd\n", "a\nb\nc\nd\n")
     t.eq(#state.hunks, 1, "one hunk for a pure addition")
@@ -173,7 +186,19 @@ t.test("overlay: change hunk shows deletion and addition", function()
         vim.startswith(piece[1], "b"),
         "deleted line shows the old content"
     )
-    t.eq(piece[2], "GitHunkDeleteLine")
+    t.truthy(has_hl(piece[2], "GitHunkDeleteLine"))
+    t.truthy(has_hl(piece[2], "DiffText"))
+    local seen_inline = false
+    for _, m in ipairs(detailed_marks(buf, "ow.git.hunks.overlay")) do
+        local d = assert(m[4])
+        if d.hl_group == "DiffText" then
+            seen_inline = true
+            t.eq(m[2], 1, "inline addition highlight is on the changed line")
+            t.eq(m[3], 0, "inline addition starts at the changed byte")
+            t.eq(d.end_col, 1, "inline addition ends after the changed byte")
+        end
+    end
+    t.truthy(seen_inline, "the added side gets an inline highlight")
 end)
 
 t.test("overlay: delete hunk shows only deletion lines", function()