How does process-environment get initialized and why would it be different from initial-environment?

Question

I'm trying to troubleshoot an issue with my exec-path. It contains a couple of paths prepended to it that I don't want. initial-environment contains the paths that match what I see when I echo $PATH in xterm but process-environment contains a couple extra and I can't figure out how they are getting there.

I've tried setting a watcher withdebug-on-variable-change at the start of my init.el file, but by the time the watcher gets triggered, process-environment already has those 2 garbage entries. Can I set that watch before Emacs launches?

Answer 1

The C function set_initial_environment in callproc.c populates process-environment and initial-environment together. Subsequent calls to setenv are the usual way of modifying process-environment (but noting that it's very common to be doing that in only a temporary dynamic scope). Obviously it's just a list though, so other manipulations are also entirely possible.

Is there a way to watch a variable and enter a debugger when it is changed?

Yes, see: C-hig (elisp)Watching Variables

Can I set that watch before Emacs launches?

There is nothing to set or watch before Emacs launches.

Answer 2

The answer is related to Doom Emacs. I should have included in my original question that I was using a Doom config.

The reason my initial attempt at putting a debug-on-variable-change in my init.el didn't work was because I was putting it in .doom.d/init.el which is loaded late in the initialization process. After reading the Doom docs about the initialization order, I saw that it starts with .emacs.d/init.el (of course). I put the debug-on-variable-change in there and saw it was happening in the function (doom-load-envvars-file "~/.emacs.d/.local/env") which gets called as part of Doom's initialization.

# -*- mode: sh -*-
# Generated from a /bin/zsh shell environent
# ---------------------------------------------------------------------------
# This file was auto-generated by `doom env'. It contains a list of environment
# variables scraped from your default shell (excluding variables blacklisted
# in doom-env-ignored-vars).
#
# It is NOT safe to edit this file. Changes will be overwritten next time you
# run 'doom sync'. To create a safe-to-edit envvar file use:
#
#   doom env -o ~/.doom.d/myenv
#
# And load it with (doom-load-envvars-file "~/.doom.d/myenv").
# ---------------------------------------------------------------------------

I just needed to run doom sync from a terminal that had the environment that I wanted.