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Tasks

New in version 1.2

Tasks allow you to form dependencies between code, executed in parallel.

Defining tasks

devenv.nix
{ pkgs, ... }:

{
  tasks."myapp:hello" = {
    exec = ''echo "Hello, world!"'';
  };
}

$ devenv tasks run myapp:hello
Running tasks     myapp:hello
Succeeded         myapp:hello         9ms
1 Succeeded                           10.14ms

enterShell / enterTest

If you'd like the tasks to run as part of the enterShell or enterTest:

devenv.nix
{ pkgs, lib, config, ... }:

{
  tasks = {
    "bash:hello" = {
      exec = "echo 'Hello world from bash!'";
      before = [ "devenv:enterShell" "devenv:enterTest" ];
    };
  };
}

$ devenv shell
...
Running tasks     devenv:enterShell
Succeeded         devenv:pre-commit:install 25ms
Succeeded         bash:hello                 9ms
Succeeded         devenv:enterShell         13ms
3 Succeeded                                 28.14ms

Using your favourite language

Tasks can also use another package for execution, for example when entering the shell:

devenv.nix
{ pkgs, lib, config, ... }:

{
  tasks = {
    "python:hello"" = {
      exec = ''
        print("Hello world from Python!")
      '';
      package = config.languages.python.package;
    };
  };
}

Avoiding running expensive exec via status check

If you define a status command, it will be executed first and if it returns 0, exec will be skipped.

devenv.nix
{ pkgs, lib, config, ... }:

{
  tasks = {
    "myapp:migrations" = {
      exec = "db-migrate";
      status = "db-needs-migrations";
    };
  };
}

Inputs / Outputs

Tasks support passing inputs and produce outputs, both as JSON objects:

  • $DEVENV_TASK_INPUT: JSON object of tasks."myapp:mytask".input.
  • $DEVENV_TASKS_OUTPUTS: JSON object with dependent tasks as keys and their outputs as values.
  • $DEVENV_TASK_OUTPUT_FILE: a writable file with tasks' outputs in JSON.
devenv.nix
{ pkgs, lib, config, ... }:

{
  tasks = {
    "myapp:mytask" = {
      exec = ''
        echo $DEVENV_TASK_INPUTS> $DEVENV_ROOT/input.json
        echo '{ "output" = 1; }' > $DEVENV_TASK_OUTPUT_FILE
        echo $DEVENV_TASKS_OUTPUTS > $DEVENV_ROOT/outputs.json
      '';
      input = {
        value = 1;
      };
    };
  };
}

SDK using Task Server Protocol

See Task Server Protocol for a proposal how defining tasks in your favorite language would look like.