Add --option CLI flag for overriding configuration options

[domenkozar]

It's common to be able to build matrix on CI jobs, so let's allow passing options via CLI:

devenv --option services.redis.enable:bool true test

cc @staticdev

[vetsin]

Given the task model, why not natively support the concept of matrix/parallel within devenv? E.g. in the interest of reproducibility I would want to run a 'matrix task' via devenv not require some sort of shell wrapper to reproduce locally

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[domenkozar]

Given the task model, why not natively support the concept of matrix/parallel within devenv? E.g. in the interest of reproducibility I would want to run a 'matrix task' via devenv not require some sort of shell wrapper to reproduce locally

I'd like to support matrix within devenv and has always been the plan, but this is more of a quick way to be able to write scripts using devenv and for testing quick changes.

[vetsin]

Then i may suggest ENV var support (alternatively/in-addition-to) than building cli arguments -- given that the expectation that it will be 'for CI' it's much easier/the default to set specific variables than deal with command construction imo.

I am also confused on how one may refer to the different package versions if they're not explicitly packaged via nixpkgs -- e.g. the normal way one has multiple versions may require overlays, say:

            (final: prev: {
                go_1_18 = (import (builtins.fetchGit {
                  name = "old-go-1.18";
                  url = "https://github.com/NixOS/nixpkgs/";
                  ref = "refs/heads/nixos-24.05";
                  rev = "20cb53203e8a00ceaa9b1017ced00f23af93a314";
                }) {}).go_1_18;
            })

What would the value of the pkg option be then?

[domenkozar]

I've changed the design to always require specifying the type:

devenv --option env.FOO:bool true

[Copilot]

Pull Request Overview

This PR introduces a new CLI flag (--option) to allow overriding configuration options for building matrix on CI jobs. Key changes include:

• Adding a sample YAML file in tests/cli-options for CLI options.
• Updating documentation in docs/basics.md with a new section on how to use the --option flag.
• Implementing the logic for parsing and writing CLI options in devenv/src/devenv.rs, along with corresponding updates to CLI parsing and file watching in cnix.rs and cli.rs.

Reviewed Changes

Copilot reviewed 5 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/cli-options/devenv.yaml	Added sample configuration inputs for testing CLI options.
docs/basics.md	Expanded documentation to include instructions for using the --option flag.
devenv/src/devenv.rs	Implemented CLI options processing and writing to cli-options.nix.
devenv/src/cnix.rs	Updated file watching to include cli-options.nix.
devenv/src/cli.rs	Added new CLI flag definition for --option.

Files not reviewed (3)

• devenv/src/flake.tmpl.nix: Language not supported
• tests/cli-options/.test.sh: Language not supported
• tests/cli-options/devenv.nix: Language not supported

Comments suppressed due to low confidence (1)

devenv/src/devenv.rs:895

• Using chunks_exact(2) may silently ignore a trailing CLI option if an odd number of values is provided. Consider validating that the total number of --option arguments is even before processing.

for chunk in self.global_options.option.chunks_exact(2) {