feat: add log level highlighting #1

S1M0N38 · 2026-01-05T16:11:19Z

Summary

Add support for highlighting log level keywords (TRACE, DEBUG, INFO, WARN, WARNING, ERROR) using Neovim's diagnostic highlight groups.

Features

Highlights uppercase log level keywords with word-boundary matching
Uses diagnostic highlight groups by default (DiagnosticError, DiagnosticWarn, DiagnosticInfo, DiagnosticHint)
Customizable highlight groups via log_level_groups config
Disabled by default (opt-in via log_level_hl = true in setup)
Works for both regular buffers and file-based tailing

New Commands

:TailLogLevelHlEnable
:TailLogLevelHlDisable
:TailLogLevelHlToggle

New Lua API

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 })

Configuration

require("tail").setup({
  log_level_hl = true,  -- enable by default
  log_level_groups = {  -- customize highlight groups
    TRACE = "DiagnosticHint",
    DEBUG = "DiagnosticHint",
    INFO = "DiagnosticInfo",
    WARN = "DiagnosticWarn",
    WARNING = "DiagnosticWarn",
    ERROR = "DiagnosticError",
  },
})

- Add log_level_hl and log_level_groups to default config - Add highlight_log_levels() function with word-boundary matching - Add backfill_log_levels() for existing buffer content - Track log_level_hl state per buffer - Hook into on_lines callback to highlight new lines - Add public API: log_level_hl_enable/disable/toggle Supports uppercase keywords: TRACE, DEBUG, INFO, WARN, WARNING, ERROR Uses Neovim's diagnostic highlight groups by default.

- Add highlight_log_levels() function for file-tail buffers - Add file_log_level_hl_enable/disable functions - Hook highlighting into file poller callback - Add commands: TailLogLevelHlEnable/Disable/Toggle

- Update description and features list - Add log_level_hl config option to setup example - Document new commands and Lua API functions

Copilot

Pull request overview

This PR adds support for highlighting log level keywords (TRACE, DEBUG, INFO, WARN, WARNING, ERROR) in tail.nvim buffers. The feature is opt-in and uses Neovim's diagnostic highlight groups by default, with support for customization.

Key Changes:

Implements log level highlighting using frontier patterns for word boundary matching
Adds new configuration options (log_level_hl and log_level_groups)
Provides new commands and Lua API functions for controlling the feature at runtime

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
plugin/tail.lua	Adds log level highlighting implementation for file-based tail buffers, including namespace creation, highlighting logic, enable/disable functions, and new user commands
lua/tail/init.lua	Implements log level highlighting for non-file buffers with configuration support, integrates with the on_lines handler, and exposes public API functions
README.md	Documents the new log level highlighting feature, including usage examples and API reference

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Copilot · 2026-01-05T16:14:56Z

plugin/tail.lua

+		cfg = {
+			follow       = true,
+			ts_enabled   = false,
+			ts_format    = "%Y-%m-%d %H:%M:%S ",


The default config created here is missing the ts_hl field which is present in other similar initializations (see line 204 and file_timestamps_enable around line 356). This inconsistency could lead to bugs if code expects ts_hl to be present. The field should be initialized to maintain consistency with other config initializations.

Suggested change

ts_format = "%Y-%m-%d %H:%M:%S ",

ts_format = "%Y-%m-%d %H:%M:%S ",

ts_hl = false,

Copilot · 2026-01-05T16:14:57Z

README.md

 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,
 })


The README documentation is incomplete. According to the PR description, users should be able to customize highlight groups via the log_level_groups config option, but this is not documented in the setup example. Consider adding documentation showing users how to customize the highlight groups, similar to how the PR description shows this feature.

Copilot · 2026-01-05T16:14:57Z

plugin/tail.lua

+local log_level_groups = {
+	TRACE = "DiagnosticHint",
+	DEBUG = "DiagnosticHint",
+	INFO = "DiagnosticInfo",
+	WARN = "DiagnosticWarn",
+	WARNING = "DiagnosticWarn",
+	ERROR = "DiagnosticError",
+}


The highlight groups are hardcoded here in plugin/tail.lua but should respect the user's configuration from tail.opts.log_level_groups. Currently, if a user configures custom highlight groups via setup(), they will work for non-file buffers but not for file-based tail buffers because this local table is not reading from the config. Consider accessing tail.opts.log_level_groups instead.

Copilot · 2026-01-05T16:14:57Z

plugin/tail.lua

+local ns_loglevel = vim.api.nvim_create_namespace("tail-loglevel")
+
+-- default log level highlight groups (same as init.lua)
+local log_level_groups = {
+	TRACE = "DiagnosticHint",
+	DEBUG = "DiagnosticHint",
+	INFO = "DiagnosticInfo",
+	WARN = "DiagnosticWarn",
+	WARNING = "DiagnosticWarn",
+	ERROR = "DiagnosticError",
+}
+
+--- 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 vim.api.nvim_buf_is_valid(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(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


This function is duplicated in lua/tail/init.lua (lines 157-187). The two implementations are nearly identical, which creates a maintainability issue. Consider extracting this to a shared utility module to avoid code duplication and ensure consistent behavior across file and non-file buffers.

Suggested change

local ns_loglevel = vim.api.nvim_create_namespace("tail-loglevel")

-- default log level highlight groups (same as init.lua)

local log_level_groups = {

TRACE = "DiagnosticHint",

DEBUG = "DiagnosticHint",

INFO = "DiagnosticInfo",

WARN = "DiagnosticWarn",

WARNING = "DiagnosticWarn",

ERROR = "DiagnosticError",

}

--- 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 vim.api.nvim_buf_is_valid(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(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

-- re-use the namespace from the core tail module if available, so highlights stay consistent

local ns_loglevel = tail.ns_loglevel or vim.api.nvim_create_namespace("tail-loglevel")

--- Highlight log level keywords in the given line range (1-based, inclusive)

--- Delegates to the implementation in the core `tail` module to avoid code duplication.

---@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 the core module exposes a shared implementation, delegate to it.

if type(tail.highlight_log_levels) == "function" then

return tail.highlight_log_levels(bufnr, start_line, end_line)

end

-- Fallback: keep behavior safe (no-op) if the shared implementation is not available.

if not vim.api.nvim_buf_is_valid(bufnr) then

return

end

S1M0N38 · 2026-01-05T16:20:10Z

The code and this PR were AI-generated. I’m testing this new feature locally, and it works nicely so far. This PR can be used:

as a reference for a manual implementation
to showcase the idea of diagnostic highlight groups to highlight common log levels

Alternatively, it can be closed without additional comments if it falls outside the scope of this plugin.

S1M0N38 added 3 commits January 5, 2026 17:09

feat(plugin): add log level highlighting for file-based tailing

db2f13d

- Add highlight_log_levels() function for file-tail buffers - Add file_log_level_hl_enable/disable functions - Hook highlighting into file poller callback - Add commands: TailLogLevelHlEnable/Disable/Toggle

docs: document log level highlighting feature

0cf009d

- Update description and features list - Add log_level_hl config option to setup example - Document new commands and Lua API functions

Copilot AI review requested due to automatic review settings January 5, 2026 16:11

Copilot started reviewing on behalf of S1M0N38 January 5, 2026 16:11 View session

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	ts_format = "%Y-%m-%d %H:%M:%S ",
	ts_format = "%Y-%m-%d %H:%M:%S ",
	ts_hl = false,

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S1M0N38 commented Jan 5, 2026

Summary

Features

New Commands

New Lua API

Configuration

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