files: fix use of onChange with directory source

[rycee]

Description

Previously, the comparison would not handle directory comparison correctly, always finding that the source and target differed. This would trigger the onChange script on each activation.

Fixes #2004

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

[berbiche]

Author approved the change here: #2004 (comment)

[rycee]

@berbiche Thanks for the ping! Merged now.

[bb010g]

@rycee Why was the recursive assertion added?

[rycee]

The existing code doesn't handle onChange in a reasonable way when recursive = true so I figured it would be best to stop allowing its use. To do it properly one would have to compare the included files one by one. Perhaps something like

find $sourceDir -type l -printf '%P\n' | xargs -i cmp --quiet "$sourceDir/{}" "$targetDir/{}"

But yeah, I guess it should be safe to remove the assertion anyway. It'll always run the onChange as before, which shouldn't be a problem, since it should be idempotent. I'll make a PR for it.