`approve` plugin makes assumptions about OWNERS file implementation

[cjwagner]

The approve plugin is not working with regex filtering because it makes a bunch of undocumented assumptions about the implementation of the repoowners package which aren't necessarily true for regex filtered OWNERS files (thats what I get for copying code from mungegithub...)
Some invalid assumptions that are not provided by the interface:

• Approvers in OWNERS files are able to approve any file in the directory or subdirectories.
• OWNERS files contain one set of approvers.
• Files in the same directory have the same approvers.

The approve plugin will need a pretty significant rewrite to support regex filtering. It was due for one anyways; it is very inefficient and excessively complex, but I don't think I'll have the cycles to do this in the near future.

Other OWNERS file based plugins (blunderbuss, owners-label) are unaffected by this problem and should work properly with regexp filtering.

Sorry for the trouble Jeff ☹️

/kind bug
/area prow
cc @ixdy @rmmh

[fejta-bot]

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/lifecycle stale

[nikhita]

/remove-lifecycle stale

[spiffxp]

/lifecycle frozen
Also a note to self: this is the issue to link when describing why OWNERS regex filters don't work for approvers

[cblecker]

Is there clear enough direction here for this to be help wanted, @cjwagner?

[cjwagner]

Is there clear enough direction here for this to be help wanted, @cjwagner?

Definitely not. It is unclear how approver suggestions and the list of files that still need approval should work with regexp filtering.