Caused by over-zealous doom-switch-window-hook.
For my own sanity (and if you're curious), I'll break it down here:
1. Doom has a `doom-switch-window-hook` hook. It triggers when window
focus is changed.
2. We use `buffer-list-update-hook` to trigger
`doom-switch-window-hook`. (That may sound weird, but this hook is
reliably executed when window focus is changed -- there are
safeguards to prevent this from triggering too often)
3. `buffer-list-update-hook` triggers whenever a buffer is created, but
`doom-switch-window-hook` only triggers if the created buffer is in
a new window.
4. The use of `with-temp-buffer` in `centaur-tabs-line-format` counts as
"buffer creation" in a "new window".
5. `+vc-gutter-update-h` is in `doom-switch-window-hook`. This refreshes
git-gutter, which initiates a redraw of Emacs.
6. When Emacs redraws, it recalculates its mode and header lines. which
triggers `doom-switch-window-hook` once, which triggers
`+vc-gutter-update-h`, which redraws the screen, then Emacs recalculates
the header line, running `centaur-tabs-line-format`...
Infinite loop ensues
Hopefully fixes:
- hlissner/doom-emacs#2436
- ema2159/centaur-tabs#18
- ema2159/centaur-tabs#88
eb69073578