A GNU Emacs library which uses the direnv tool
to determine per-directory/project environment variables and then set
those environment variables on a per-buffer basis. This means that when you
work across multiple projects which have .envrc files, all processes
launched from the buffers "in" those projects will be executed with
the environment variables specified in those files. This allows
different versions of linters and other tools to be used in each
project if desired.
direnv.el repeatedly
changes the global Emacs environment, based on tracking what buffer
you're working on.
Instead, envrc.el simply sets and stores the right environment in
each buffer, as a buffer-local variable.
From a user perspective, both are well tested and typically work fine,
but the envrc.el approach feels cleaner to me.
Installable packages are available via MELPA: do
M-x package-install RET envrc RET.
Alternatively, download
the latest release or clone the repository, and install
envrc.el with M-x package-install-file.
Add a snippet like the following at the bottom of your init.el:
(envrc-global-mode)or
(add-hook 'after-init-hook 'envrc-global-mode)or, if you're a use-package fan:
(use-package envrc
:hook (after-init . envrc-global-mode))Why must you enable the global mode late in your startup sequence like this?
You normally want envrc-mode to be initialized in each buffer before
other minor modes like flycheck-mode which might look for
executables. Counter-intuitively, this means that envrc-global-mode
should be enabled after other global minor modes, since each
prepends itself to various hooks.
The global mode will only have an effect if direnv is installed and
available in the default Emacs exec-path. (There is a local minor
mode envrc-mode, but you should not try to enable this granularly,
e.g. for certain modes or projects, because compilation and other
buffers might not get set up with the right environment.)
Regarding interaction with the mode, see envrc-mode-map, and the
commands envrc-reload, envrc-allow and envrc-deny. (There's also
envrc-reload-all as a "nuclear" reset, for now!)
In particular, you can enable keybindings for the above commands by
binding your preferred prefix to envrc-command-map in
envrc-mode-map, e.g.
(with-eval-after-load 'envrc
(define-key envrc-mode-map (kbd "C-c e") 'envrc-command-map))If you find that a particular Emacs command isn't picking up the
environment of your current buffer, and you're sure that envrc-mode
is active in that buffer, then it's possible you've found code that
runs a process in a temp buffer and neglects to propagate your
environment to that buffer before doing so.
A couple of common Emacs commands that suffer from this defect are also
patched directly via advice in envrc.el — shell-command-to-string
is a prominent example!
The inheritenv package was designed to handle this case in general.
By default, Emacs has a single global set of environment variables
used for all subprocesses, stored in the process-environment
variable. direnv.el switches that global environment using values
from direnv when the user performs certain actions, such as
switching between buffers in different projects.
In practice, this is simple and mostly works very well. But there are some quirks, and it feels wrong to me to mutate the global environment in order to support per-directory environments.
Now, in Emacs we can also set process-environment locally in a
buffer. If this value could be correctly maintained in all buffers
based on their various respective .envrc files, then buffers across
multiple projects could simultaneously be "connected" to the
environments of their corresponding project directories. I wrote
envrc.el to explore this approach.
envrc.el uses a global minor mode (envrc-global-mode) to hook into
practically every buffer created by Emacs, including hidden and
temporary ones. When a buffer is found to be "inside" an
.envrc-managed project, process-environment is set buffer-locally
by running direnv, the results of which are also cached indefinitely
so that this is not too costly overall. Each buffer has a local minor
mode (envrc-mode) with an indicator which displays whether or not a
direnv is in effect in that buffer. (Hooking into every buffer is
important, rather than just those with certain major modes, since
separate temporary, compilation and repl buffers are routinely used
for executing processes.)
This approach also has some trade-offs:
-
Buffers like
*Help*will haveenvrc-modeenabled based on the directory of the buffer which caused them to be created initially, and then those buffers often live for a long time. If you launch programs from such buffers while working on a different project, the results might not be what you expect. I might exclude certain modes to minimise confusion, but users will always have to be aware of the fact that environments are buffer-specific. -
There's a (very small) overhead every time a buffer is created, and that happens quite a lot.
-
direnvupdates are not automatic.direnv.elre-executesdirenvwhen switching between buffers that visit files in different directories, whereasenvrc-modecaches the environment until the user refreshes it explicitly withenvrc-reload.
Overall this approach works well in practice, and feels cleaner than trying to strategically modify the global environment.
It's also possible that there's a way to call direnv more
aggressively by allowing it to see values of DIRENV_* obtained
previously such that it becomes a no-op.
💝 Support this project and my other Open Source work via Patreon