substituted variables from `.env` are not expanded

[fdnt7]

Describe the bug
When using dotenv.enable = true; in devenv.nix, variables that have substitutions are parsed literally without any expansion.

To reproduce

1. Run devenv init in an empty directory
2. Add dotenv.enable = true; in devenv.nix
3. Create an .env file like so:

A=0
B=1
C=$A+$B

The C=$A+$B line is interchangable with C=${A}+${B}.
4. Enter the development shell, either via devenv shell or automatically if nix-direnv is present
5. Run echo $C. It should output 0+1, but it outputs $A+$B instead

Additional context:

• I am not sure if this is intentional or not (as some parsers are deliberately made simple), but considering that in other tools I used (Docker, Docker Compose, Rust's sqlx and dotenvy) they are expanded, I figured it's worth reporting about this behaviour.
• If this is intentional, please treat this as a feature request instead; Maybe a boolean like dotenv.expand as an option.

Version
devenv 1.9.0 (x86_64-linux)

[domenkozar]

dotenv implementation is basic, in general that's one of the reason we wrote https://devenv.sh/integrations/secretspec/

[fdnt7]

I figured so; after I tried secretspec instead, the substitution works. Does this mean that dotenv will be deprecated / phased out in the future? (so I can close this issue as "not planned")

[domenkozar]

I don't see us working on that (secretspec.dev has way more potential), but if someone does I'm happy to merge it.