feat: add log level highlighting

README.md

@@ -1,14 +1,16 @@
 # tail.nvim
 
 A minimal Neovim plugin that allows any buffer to follow appended lines—just like `tail -f`. It can
-optionally display a timestamp before each new line using virtual text.
+optionally display a timestamp before each new line using virtual text, and highlight log level
+keywords (ERROR, WARN, INFO, DEBUG, TRACE).
 
 ## Features
 
 - Auto-scrolls to the bottom of any buffer as new lines are added (if already at bottom)
 - Respects user scrolling: won't yank you back if you've moved up
 - Works on any buffer type: `nofile`, plugin buffers, etc. Your mileage may vary for writeable or "exotic" buffers like :terminal
 - Optional per-buffer timestamps: prefix newly inserted lines with the current time. The timestamp is drawn with virtual text, so it does not modify the file’s content.
+- Optional log level highlighting: colorize ERROR, WARN, INFO, DEBUG, TRACE keywords using Neovim's diagnostic highlight groups.
 - Does not move the cursor position on activation by default. Use neovim's move to end of buffer, default: Shift + g.
 
 ### Demo
@@ -44,12 +46,14 @@ Set up the plugin in your init.lua:
 
 ```lua
 require("tail").setup({
-  -- uncomment the next line to enable timestamps by default
-  -- timestamps = true,
+  -- enable timestamps by default
+  timestamps = false,
   -- customise the format (see `:help os.date`)
   timestamp_format = "%Y-%m-%d %H:%M:%S",
   -- customise the highlight group used for the timestamp
   timestamp_hl = "Comment",
+  -- enable log level highlighting by default
+  log_level_hl = false,
 })
 ```
 
@@ -61,12 +65,16 @@ Then, from any buffer enable, disable or toggle tailing behaviour:
 :TailToggle
 ```
 
-Similarily the timestamps are controlled:
+Similarly, timestamps and log level highlighting are controlled:
 
 ```vim
-:TailTimestampToggle
 :TailTimestampEnable
 :TailTimestampDisable
+:TailTimestampToggle
+
+:TailLogLevelHlEnable
+:TailLogLevelHlDisable
+:TailLogLevelHlToggle
 ```
 
 The actual following behavior might not directly work, as the cursor position is not changed
@@ -98,6 +106,10 @@ require("tail").timestamps_enable(bufnr, { backfill = true })
 require("tail").timestamps_disable(bufnr)
 require("tail").timestamps_toggle(bufnr, { backfill = false })
 
+-- Log level highlighting
+require("tail").log_level_hl_enable(bufnr, { backfill = true })
+require("tail").log_level_hl_disable(bufnr)
+require("tail").log_level_hl_toggle(bufnr, { backfill = false })
 ```
 
 ## License

lua/tail/init.lua

@@ -20,6 +20,17 @@ local default_config = {
 	timestamp_format = "%Y-%m-%d %H:%M:%S ",
 	-- highlight group used for the timestamp virtual text
 	timestamp_hl = "Comment",
+	-- enable log level highlighting by default for new buffers?
+	log_level_hl = false,
+	-- highlight groups for each log level keyword (uppercase only)
+	log_level_groups = {
+		TRACE = "DiagnosticHint",
+		DEBUG = "DiagnosticHint",
+		INFO = "DiagnosticInfo",
+		WARN = "DiagnosticWarn",
+		WARNING = "DiagnosticWarn",
+		ERROR = "DiagnosticError",
+	},
 }
 
 local config = vim.deepcopy(default_config)
@@ -37,6 +48,7 @@ local ns = vim.api.nvim_create_namespace("tail.nvim")
 -- buf_state[bufnr] = {
 --   enabled = bool,
 --   timestamps = bool,
+--   log_level_hl = bool,
 --   attached = bool,
 --   wins = {
 --     [winid] = { pinned = bool },
@@ -51,6 +63,7 @@ local function get_buf_state(bufnr)
 		s = {
 			enabled = false,
 			timestamps = config.timestamps,
+			log_level_hl = config.log_level_hl,
 			attached = false,
 			wins = {},
 		}
@@ -131,6 +144,59 @@ local function backfill_timestamps(bufnr)
 	end
 end
 
+-- ---------------------------------------------------------------------------
+-- Log level highlighting
+-- ---------------------------------------------------------------------------
+
+local ns_loglevel = vim.api.nvim_create_namespace("tail.nvim.loglevel")
+
+--- Highlight log level keywords in the given line range (1-based, inclusive)
+---@param bufnr number
+---@param start_line number 1-based start line
+---@param end_line number 1-based end line (inclusive)
+local function highlight_log_levels(bufnr, start_line, end_line)
+	if not is_valid_buf(bufnr) then
+		return
+	end
+
+	local lines = vim.api.nvim_buf_get_lines(bufnr, start_line - 1, end_line, false)
+
+	for i, line in ipairs(lines) do
+		local lnum = start_line + i - 1
+
+		for keyword, hl_group in pairs(config.log_level_groups) do
+			-- Use frontier pattern for word boundary matching (uppercase only)
+			local pattern = "%f[%w]" .. keyword .. "%f[%W]"
+			local search_start = 1
+
+			while true do
+				local match_start, match_end = line:find(pattern, search_start)
+				if not match_start then
+					break
+				end
+
+				vim.api.nvim_buf_set_extmark(bufnr, ns_loglevel, lnum - 1, match_start - 1, {
+					end_col = match_end,
+					hl_group = hl_group,
+				})
+
+				search_start = match_end + 1
+			end
+		end
+	end
+end
+
+local function backfill_log_levels(bufnr)
+	if not is_valid_buf(bufnr) then
+		return
+	end
+	vim.api.nvim_buf_clear_namespace(bufnr, ns_loglevel, 0, -1)
+	local line_count = vim.api.nvim_buf_line_count(bufnr)
+	if line_count > 0 then
+		highlight_log_levels(bufnr, 1, line_count)
+	end
+end
+
 -- ---------------------------------------------------------------------------
 -- Core: on_lines handler (tail + timestamps)
 -- ---------------------------------------------------------------------------
@@ -151,6 +217,12 @@ local function on_lines(_, bufnr, _changedtick, firstline, lastline_old, new_las
 		end
 	end
 
+	-- log level highlighting: only care if lines were added
+	if bs.log_level_hl and new_lastline > lastline_old then
+		local start = firstline + 1 -- convert 0-based to 1-based
+		highlight_log_levels(bufnr, start, new_lastline)
+	end
+
 	-- tail-following: only if the window was “pinned” *before* the change
 	local wins = vim.fn.win_findbuf(bufnr)
 	if not wins or #wins == 0 then
@@ -312,4 +384,42 @@ function M.timestamps_toggle(bufnr, opts)
 	end
 end
 
+-- ---------------------------------------------------------------------------
+-- Public API: log level highlighting
+-- ---------------------------------------------------------------------------
+
+function M.log_level_hl_enable(bufnr, opts)
+	bufnr = bufnr or vim.api.nvim_get_current_buf()
+	if not is_valid_buf(bufnr) then
+		return
+	end
+	local bs = get_buf_state(bufnr)
+	bs.log_level_hl = true
+
+	opts = opts or {}
+	if opts.backfill then
+		backfill_log_levels(bufnr)
+	end
+end
+
+function M.log_level_hl_disable(bufnr)
+	bufnr = bufnr or vim.api.nvim_get_current_buf()
+	if not is_valid_buf(bufnr) then
+		return
+	end
+	local bs = get_buf_state(bufnr)
+	bs.log_level_hl = false
+	vim.api.nvim_buf_clear_namespace(bufnr, ns_loglevel, 0, -1)
+end
+
+function M.log_level_hl_toggle(bufnr, opts)
+	bufnr = bufnr or vim.api.nvim_get_current_buf()
+	local bs = get_buf_state(bufnr)
+	if bs.log_level_hl then
+		M.log_level_hl_disable(bufnr)
+	else
+		M.log_level_hl_enable(bufnr, opts)
+	end
+end
+
 return M