devenv
⚠️ Notice: This extension is forked from direnv/direnv-vscode and has
been rewritten for devenv using an LLM coding agent. Use with appropriate
caution and review the source before deploying in production environments.
devenv is a tool for creating fast, declarative, reproducible, and composable
developer environments using Nix.
This extension adds devenv support to Visual Studio Code
by loading environment variables from devenv.nix for the workspace root.
Features
Custom Environment
This extension automatically loads the custom environment
devenv provides for the workspace by running devenv print-dev-env.
When devenv.nix, devenv.yaml, devenv.lock, or local override files are
modified, the extension automatically reloads the environment.
The custom environment is available in integrated terminals,
in custom tasks of type shell,
and in environment variable substitutions (${env:VAR}).
Commands
"devenv: Open devenv.nix file"
opens an editor with the devenv.nix file for the workspace root.
"devenv: Reload environment"
reloads the custom environment for the workspace.
"devenv: Reset and reload environment"
resets the custom environment for the workspace, then reloads it.
Status Item
The extension displays a status icon
that indicates whether it is currently working or has succeeded or failed.
Clicking the status item will also reload the custom environment.
Requirements
This extension requires devenv to be installed.
See the devenv installation guide for details.
Settings
| Setting |
Default |
Description |
devenv.path.executable |
devenv |
Path to the devenv executable. Set this to an absolute path if devenv is not on the PATH that VS Code sees. |
devenv.path.nixBinPaths |
[] |
Extra directories to prepend to PATH when running devenv. The extension already adds the standard Nix profile directories and common system paths; use this only for non-standard install locations. |
devenv.extraEnv |
{} |
Environment variables to set before running devenv. |
devenv.watchForChanges |
true |
Automatically reload the environment when devenv.nix, devenv.yaml, devenv.lock, or local override files change. |
devenv.status.showChangesCount |
true |
Show the count of added/changed/removed variables in the status bar. |
devenv.restart.automatic |
false |
Automatically restart the extension host after the environment changes (instead of prompting). |
Known Issues
Custom tasks with type process don't pick up on the modified environment.
Several task provider extensions provide these kinds of tasks.
When devenv unsets an environment variable that already existed before devenv loaded,
then in the terminal it will be set to empty (what POSIX calls null)
rather than truly unset.
VSCode does not provide API to unset environment variables for the terminal.
Variables that were not present before devenv loaded are handled correctly
and will remain absent in the terminal.
The difference between null and unset variables is mostly academic
but some programs insist on treating them distinctly.
devenv evaluates Nix expressions so this extension requires trusted workspaces.
Virtual Environments and Background Tasks
This extension determines your environment by running devenv print-dev-env --json in the background. This command is fast and purely evaluates your Nix derivations without executing heavy shell tasks.
Because of this, if your devenv.nix contains configurations that require a shell task to physically build (such as languages.python.venv.enable = true in devenv 2.x), the extension will not automatically build the .venv directory for you in the background when you edit the file. Doing so could cause unexpected CPU spikes, network downloads, and hide installation errors from you.
To build or update your virtual environment:
- Open a terminal and run
devenv shell (or use direnv). This will execute the required tasks and build your virtual environment.
- The extension will automatically detect that the
.devenv/state/venv folder now exists, and it will safely inject the VIRTUAL_ENV variable and prepend .venv/bin into your VS Code PATH.
