How to run nvim (without user interaction) and export a realistic stats().startuptime?

[NonlinearFruit]

Background
I frequently have a slow neovim startup time and I would love to test the startup time via a script. The goal would be to script:

• start neovim a few times
• take the average
• start neovim with minimal lazy config a few times
• take the average
• print something like

  nvim: 100ms +/- 10ms
  basline: 25ms +/- 2ms
  difference: 75ms
  

The part I am stuck on is programmatically getting an accurate nvim startup time.

Question
Is it possible to run neovim (without user interaction) and get lazy.nvim to export a realistic startup time?

Attempts
This is what I've iterated to so far, but startuptime is always 0 and I think I'm missing significant parts of the startup process since there isn't a UIEnter in times. UIEnter might require removing the --headless but when --headless is removed there is no output.

$ nvim --headless +'lua =require("lazy.stats").stats()' +q
{
  count = 46,
  loaded = 27,
  real_cputime = true,
  startuptime = 0,
  times = {
    LazyDone = 59.0021,
    LazyStart = 4.8092
  }
}

[NonlinearFruit]

Solution

Here is what I've found:

$ nvim -s - /dev/null <<EOF
> :redir >> output.txt
> :lua =require('lazy.stats').stats()
> ZQ
> EOF

Explanation

• -s usually points to a file that nvim treats as keyboard input
• -s - tells nvim to read the file from stdin
• open /dev/null as a blank file (to avoid the dashboard plugin I use 👀)
• <<EOF is a "heredoc" and basically pipes multi-line input to stdin
• :redir >> output.txt tells nvim to append command-line mode output to output.txt
• :lua =require('lazy.stats').stats() prints the lazy.nvim stats
• ZQ quit nvim without checking for changes
• EOF end the heredoc

Output

Then you can cat the output like so:

$ cat output.txt
{
  count = 46,
  loaded = 27,
  real_cputime = true,
  startuptime = 43.1625,
  times = {
    LazyDone = 41.249,
    LazyStart = 5.2174,
    UIEnter = 43.1625
  }
}

Results

Here is a nushell script that uses this solution to analyze startup time (script).

Script output

╭───┬───────────────┬───────────────┬────────────────┬─────────────┬──────┬──────┬──────┬──────┬────────╮
│ # │      vim      │ total_plugins │ loaded_plugins │ sample_size │ avg  │ dev  │ max  │ min  │ median │
├───┼───────────────┼───────────────┼────────────────┼─────────────┼──────┼──────┼──────┼──────┼────────┤
│ 0 │ nvim-baseline │             1 │              1 │          10 │ 7.03 │ 0.37 │ 7.91 │ 6.61 │   6.95 │
╰───┴───────────────┴───────────────┴────────────────┴─────────────┴──────┴──────┴──────┴──────┴────────╯
╭───┬──────┬───────────────┬────────────────┬─────────────┬───────┬──────┬───────┬───────┬────────╮
│ # │ vim  │ total_plugins │ loaded_plugins │ sample_size │  avg  │ dev  │  max  │  min  │ median │
├───┼──────┼───────────────┼────────────────┼─────────────┼───────┼──────┼───────┼───────┼────────┤
│ 1 │ nvim │            46 │             27 │          10 │ 38.50 │ 1.69 │ 41.29 │ 36.28 │  37.96 │
╰───┴──────┴───────────────┴────────────────┴─────────────┴───────┴──────┴───────┴───────┴────────╯