Add support for python-dotenv at the config level

[PatrickAlphaC]

Overview

I'd love to see brownie support a .env file for environment variables. For new engineers, or a project that doesn't want to keep a ton of environment variables running, a .env file is a warm welcome. Truffle and Hardhat (the javascript smart contract frameworks) have really nice config files that allow them to work with .env files. A bit of a quality of life improvement.

Otherwise, we have to call in the .env file in all our script manually, seems pretty redundant to do so.

Specification

Not sure how this is normal done in yaml, but would like to see something like:
dotenv: true

And then they can load via a .env file. We could just use https://pypi.org/project/python-dotenv/ to load at the start of all the scripts.

Dependencies

https://pypi.org/project/python-dotenv/

What do we think?

[iamdefinitelyahuman]

I see no harm in checking for the existence of this file when loading a project, and processing it if it's found.

[omarish]

Would it make sense if the value of the dotenv key in the YAML config is a path instead of a boolean? That way you can specify if you're using a different dotenv.

[PatrickAlphaC]

Ooooo. That's much better

[omarish]

Cool. And @iamdefinitelyahuman, do you think the dotenv file should be a) auto-loaded, or b) loaded only if dotenv: is specified in the YAML config?

[PatrickAlphaC]

I vote for loading only if it's specified.

[skellet0r]

Loading only if explicitly opted in via the YAML config sounds better to me. Sort of how docker-compose allows one to load an env-file or multiple. Plus, security wise might be better to opt-in 🤔

https://docs.docker.com/compose/environment-variables/#the-env_file-configuration-option

[omarish]

I agree. I'd just like to get buy-in from @iamdefinitelyahuman before building something out.

When it comes to crypto projects, I'm an advocate for configuration over convention. Writing an extra line in a config file is a great price to pay, especially if it means avoiding unexpected configuration behavior.

[iamdefinitelyahuman]

Sounds good to me! I agree that the explicitness of adding a line to the config is better than potential accidentally... some config settings.

[omarish]

Excellent. Another realization is that this should probably support interpolating envvars in the config, like this:

.env:

DEFAULT_NETWORK=development

brownie-config.yaml:

dotenv: ./.env
networks:
  default: ${DEFAULT_NETWORK}

Double-checking that this makes sense to you, @iamdefinitelyahuman and @PatrickAlphaC?

[omarish]

@iamdefinitelyahuman I have something basic up, but 1) it's not quite working yet, and 2) I'm still thinking about what should be in charge of loading the env file. It seems like a responsibility of main.py. An earlier implementation I had done was loading it in the config container, but I don't think the config container should be in charge of something stateful like loading an env file.

That said, if we do want to support POSIX-style variable interpolation, we'd probably want access in the ConfigContainer level so that we only have to parse once.

Thoughts?

[PatrickAlphaC]

Excellent. Another realization is that this should probably support interpolating envvars in the config, like this:

.env:

DEFAULT_NETWORK=development

brownie-config.yaml:

dotenv: ./.env
networks:
  default: ${DEFAULT_NETWORK}

Double-checking that this makes sense to you, @iamdefinitelyahuman and @PatrickAlphaC?

Yes. 100%. This was something that I was surprised didn't work by default. This will be a massive improvement adding that to the yaml.

[gnattishness]

As I didn't see this mentioned previously, direnv is an alternative to having brownie process .env files on its own.

Its a tradeoff between suggesting users install a separate tool and increasing the amount of things brownie needs to do.
(Though I don't have a particular opinion either way)

[omarish]

Makes sense. I can add this in; should be pretty straightforward. Sorry for the delay, recently made the 2to3 family migration and just getting back into my routine now.

[PatrickAlphaC]

Congratulations!!