Clean up new highlight_group config option code

Makes some overall cleanup for the highlight_group work:

* Adds highlight_group to the Opts type
* Adds tests ensuring it works and the default is respected
* Adds more descriptive commenting to readme

README.md

@@ -40,10 +40,20 @@ The swap commands intelligently swap nodes, including comments and attributes/de
 ```lua
 {
   "aaronik/treewalker.nvim",
+
+  -- The following options are the defaults.
+  -- Treewalker aims for sane defaults, so these are each individually optional,
+  -- and the whole opts block is optional as well.
   opts = {
-    highlight = true, -- Whether to briefly highlight the node after jumping to it
-    highlight_duration = 250, -- How long should above highlight last (in ms)
-    highlight_group = "ColorColumn", -- Highlight group 
+    -- Whether to briefly highlight the node after jumping to it
+    highlight = true,
+
+    -- How long should above highlight last (in ms)
+    highlight_duration = 250,
+
+    -- The color of the above highlight. Must be a valid vim highlight group.
+    -- (see :h highlight-group)
+    highlight_group = "ColorColumn",
   }
 }
 ```

lua/treewalker/init.lua

@@ -1,10 +1,9 @@
-local util = require('treewalker.util')
 local movement = require('treewalker.movement')
 local swap = require('treewalker.swap')
 
 local Treewalker = {}
 
----@alias Opts { highlight: boolean, highlight_duration: integer }
+---@alias Opts { highlight: boolean, highlight_duration: integer, highlight_group: string }
 
 -- Default setup() options
 ---@type Opts
@@ -14,6 +13,7 @@ Treewalker.opts = {
   highlight_group = "ColorColumn",
 }
 
+-- This does not need to be called for Treewalker to work. The defaults are preinitialized and aim to be sane.
 ---@param opts Opts | nil
 function Treewalker.setup(opts)
   if opts then

lua/treewalker/ops.lua

@@ -10,10 +10,10 @@ local M = {}
 ---Flash a highlight over the given range
 ---@param range Range4
 ---@param duration integer
-function M.highlight(range, duration)
+---@param hl_group string
+function M.highlight(range, duration, hl_group)
   local start_row, start_col, end_row, end_col = range[1], range[2], range[3], range[4]
   local ns_id = vim.api.nvim_create_namespace("")
-  local hl_group = require("treewalker").opts.highlight_group
 
   for row = start_row, end_row do
     if row == start_row and row == end_row then
@@ -46,7 +46,8 @@ function M.jump(row, node)
   if require("treewalker").opts.highlight then
     local range = nodes.range(node)
     local duration = require("treewalker").opts.highlight_duration
-    M.highlight(range, duration)
+    local hl_group = require("treewalker").opts.highlight_group
+    M.highlight(range, duration, hl_group)
   end
 end
 

tests/treewalker/highlight_spec.lua

@@ -71,6 +71,20 @@ describe("Highlights in a regular lua file: ", function()
     assert.equal(duration, duration_arg)
   end)
 
+  it("respects default highlight_group", function()
+    tw.setup({ highlight = true, highlight_duration = 250 })
+    tw.move_down()
+    local hl_group_arg = highlight_stub.calls[1].refs[3]
+    assert.equal("ColorColumn", hl_group_arg)
+  end)
+
+  it("respects highlight_group config option", function()
+    tw.setup({ highlight = true, highlight_duration = 50, highlight_group = "DiffAdd" })
+    tw.move_down()
+    local hl_group_arg = highlight_stub.calls[1].refs[3]
+    assert.equal("DiffAdd", hl_group_arg)
+  end)
+
   it("highlights whole functions", function()
     vim.fn.cursor(10, 1)
     tw.move_down()