Conflicting options: 'override' and 'cascade'

[llovett2]

The override option introduced in #87 by @jfairley conflicts with the cascade option when both are used together.

Example

.env

MY_NAME=Bob

.env.local

MY_NAME=Joe

Command

> dotenv -c -- bash -c 'echo $MY_NAME'
Joe
> dotenv -co -- bash -c 'echo $MY_NAME'
Bob

I would expect Joe from .env.local to override Bob from .env based on how cascade works, but when the override option is present Bob prevails because .env is processed last (see here and here).

[jfairley]

That's interesting. You raise a valid point, but I'm not sure how to easily make both work together. The problem is dotenv doesn't support "cascade" natively. There's probably no way to avoid edge cases without dotenv supporting cascade natively.

[llovett2]

What if we reversed the paths array if override is set before iterating through it? I'm trying to think if that will cause any negative side effects.

[entropitor]

Yeah, there was an earlier discussion: #63 (comment)

I think it's just incompatible. Feel free to make a PR to update the README to document this but this is not really solvable.

I think the best solution is just erroring out if using override together with multiple files, ...

[jfairley]

Ooh man, this one bit me in the butt the other day.

Like @llovett2 found, when you run override with cascade, the order of files is effectively inverted such that values in .env will override .env.test.

We need to do something about this, because of the potential impact. In my case, a dev on my team ran unit tests that blew away our QA database.

I'm available to submit a new pull-request, but @entropitor, I'm looking to discover what you're likely to accept, considering this issue was closed before.

1. Invert the files array when argv.c && argv.o.
   • I actually believe this is a pretty simple and readable change. I have it ready to go locally. fix: invert file order for override+cascade #92
2. Prevent "cascade with override".
   • Literally throw a runtime error if argv.c && argv.o saying it's not supported.

[entropitor]

I think it's best to throw. I knew this was a problem when merging that's why I pushed back so hard on cascade. The other solution has a problem with expanding variables so I don't think that's valid either. I guess throwing is the most elegant solution! Happy to merge such a pr