Add a clue for editors under "sops edit"

[rsrchboy]

Sometimes there are things we'd prefer our editors do differently when editing files with secrets in them: different configuration, disable certain plugins, etc. This change sets a clue in the launched editor's environment that can be used to easily and trivially determine if the editor was launched by sops edit.

[felixfontein]

Thanks for your contribution! I'm not sure that's a good idea though (are there other programs which do similar things? I'm not aware of any, but that doesn't mean there isn't). I think setting SOPS_EDITOR that will be introduced by #1611 is a better and more general solution.

[rsrchboy]

Correct me if I'm wrong, but the SOPS_EDITOR variable introduced in #1611 is set by the user, not sops itself, right? If that's the case, there's two problems for trying to use it in this PR's use case:

1. We cannot depend on SOPS_EDITOR always being set for editors invoked by sops, and
2. We cannot depend that SOPS_EDITOR being set means we're actually being run under sops, as it is the sort of thing likely to be set in one's ~/.bashrc / ~/.zshrc / etc.

SOPS_EDITOR in #1611 is not a solution to the problem being addressed by this PR: providing an unambiguous, reliable clue that we're in an editor launched by sops edit. These two PRs solve different problems.

[felixfontein]

Well, other programs can also set SOPS_IS_EDITING to true, so I don't see how the solution from this PR is better than the solution from the other PR for this problem.

[rsrchboy]

Well, other programs can also set SOPS_IS_EDITING to true, so I don't see how the solution from this PR is better than the solution from the other PR for this problem.

Because the work in the other PR is not a solution to this problem.

Nothing we do here can control other programs setting env variables. What we can control is ensuring a specific var will always be set in the editor's environment, for editors launched by sops edit. AFAICT #1611 does not do that with any var.

[felixfontein]

You use #1611 by pointing SOPS_EDITOR to a script that sets whatever env variable you need and then launches your editor. Then you have what this PR does in a way more general form.

Which editor is used and how that editor is configured is highly system dependent (and thus perfectly suited for system-wide or user-wide env variables). If you can control the use of SOPS_IS_EDITING, you can also control setting SOPS_EDITOR.

[rsrchboy]

You use #1611 by pointing SOPS_EDITOR to a script that sets whatever env variable you need and then launches your editor. Then you have what this PR does in a way more general form.

Ah, I see what you're saying now. Using SOPS_EDITOR to work around this problem is certainly feasible, but doesn't feel quite right, in a way I'm going to have to think about in order to be able to articulate. (Likely that with this PR I'd be depending on something I know sops would set and could just handle it entirely in my .vimrc.)