:help lib.nvim-logger

*lib.nvim-logger.txt*        Structured logging, diagnostics & crash dumps

lib.nvim.logger                                            *lib.nvim-logger*

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CONTENTS *lib.nvim-logger-contents*

  1. Introduction ......................... |lib.nvim-logger-intro|
  2. Creating a logger .................... |lib.nvim-logger-new|
  3. Logging .............................. |lib.nvim-logger-log|
  4. Switches (enable/disable, tags) ...... |lib.nvim-logger-switches|
  5. Crash capture ........................ |lib.nvim-logger-capture|
  6. File sink ............................ |lib.nvim-logger-file|
  7. Command .............................. |lib.nvim-logger-command|

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1. INTRODUCTION *lib.nvim-logger-intro*

lib.nvim.logger is a richer sibling of lib.nvim.notify. Next to a normal
notify it records a message plus a structured context table into a bounded
in-memory ring buffer, optionally streams JSONL to a file, and can dump that
ring when a guarded entrypoint fails.

It is designed so that logging — all of it, or only parts selected by level or
by tag — can be switched off with de-facto zero runtime cost, so a plugin can
ship with debug logging left in place.

Cross-platform: paths resolve through stdpath("log"); writes go through
lib.nvim.fs.write.append; no shell-outs.

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2. CREATING A LOGGER *lib.nvim-logger-new*

    local log = require("lib.nvim.logger").new({
      name         = "myplugin",  -- scope / prefix
      level        = "debug",     -- min level to RECORD
      notify_level = "warn",      -- min level to also vim.notify
      file         = nil,         -- nil=stdpath default, false=off, string=path
      capture      = true,        -- flush ring on VimLeavePre
      history      = 200,         -- ring-buffer size
      redact       = { "token" }, -- context keys to scrub
    })

Levels accept a number (|vim.log.levels|) or a name: "trace", "debug", "info",
"warn", "error", "off".

---

3. LOGGING *lib.nvim-logger-log*

    log.info("cache warm", { entries = 128, took_ms = 12 })
    log.warn("slow query", { ms = 340 })
    log.error("write failed", { path = p, err = err })
    log.debug("state", function() return expensive_snapshot() end) -- thunk
    log.info("tagged", { x = 1 }, { tags = { "net" } })            -- call opts

log.<level>(msg, ctx?, opts?) — ctx is a table OR a function returning one
(the thunk is only invoked when the level is active, so expensive context is
free when the level is off). opts is |lib.nvim-logger| CallOpts:
tags, to (per-call file override), notify (force/suppress).

Extras:

    log.once("k", "warn", "shown once")   -- log a key at most once
    local stop = log.timer("index build") -- returns stop() logging elapsed ms
    stop({ files = 42 })
    log.assert(cond, "must hold", ctx)    -- log + raise on falsy

---

4. SWITCHES *lib.nvim-logger-switches*

Global (affect every logger; the master switch is checked first in the hot
path, so a disabled logger costs one comparison):

    local L = require("lib.nvim.logger")
    L.set_enabled(false)          -- master kill switch (zero-cost when off)
    L.is_enabled()                -- current master-switch state
    L.set_level("warn")           -- global min-level override; nil clears
    L.disable_tag("net")          -- drop every record carrying tag "net"
    L.enable_tag("net")
    L.only_tags({ "cache" })      -- whitelist: keep only these tags; nil clears
    L.tags()                      -- { disabled = {...}, only = {...}|nil }
    L.setup({ level = "info" })   -- merge into every FUTURE logger's defaults
    L.loggers()                   -- every logger created so far (the registry)

setup(opts) also accepts enabled/min_level shorthand for the global
switches above; every other key becomes a new default merged into options
passed to future new() calls (does not touch already-created loggers).

Per-logger:

    log.set_enabled(false)
    log.is_enabled()
    log.set_level("error")

---

5. CRASH CAPTURE *lib.nvim-logger-capture*

There is no global "uncaught error" hook in Neovim, so capture combines:

  1. Synchronous file writes — every record (incl. errors) is durable the
     moment it is logged, so context survives a subsequent crash.
  2. guard()/wrap() — xpcall wrappers that log an ERROR with a traceback and
     flush the ring before re-raising (guard) or swallowing (wrap):

        vim.keymap.set("n", "<leader>x", log.guard(function() risky() end))
        M.run = log.wrap(M.run, "run")

  3. VimLeavePre flush — the ring is written to the file sink on exit.

log.flush() writes the whole ring to the file now; log.snapshot() returns
a copy; log.clear() empties it.

---

6. FILE SINK *lib.nvim-logger-file*

Records are appended as JSONL (one JSON object per line). Default location is
stdpath("log")/lib-logger/<name>.jsonl; pass file = "/path" to override, or
file = false to disable. Context tables are sanitized before encoding
(functions/userdata stringified, cycles broken, depth/width capped, redacted
keys scrubbed).

---

7. COMMAND *lib.nvim-logger-command*

:LibLogger is installed on the first logger.new() call:

    :LibLogger show [n]   open the n most recent records in a float
    :LibLogger on|off     global enable / disable
    :LibLogger level <l>  set the global min level
    :LibLogger dump       flush every logger's ring to its file
    :LibLogger clear      empty every ring buffer
    :LibLogger tags       show disabled / whitelisted tags