Fix check for RIGHT_ATTRS in dep matcher

[polm]

If a non-anchor node does not have RIGHT_ATTRS, the dep matcher throws
an E100, which says that non-anchor nodes must have LEFT_ID, REL_OP, and
RIGHT_ID. It specifically does not say RIGHT_ATTRS is required.

An empty dict for RIGHT_ATTRS is also valid, and patterns with one will be
accepted. While not normal, sometimes a REL_OP is enough to specify a
non-anchor node - maybe you just want the head of another node
unconditionally, for example.

This change just sets RIGHT_ATTRS to {} if not present. Alternatively
changing E100 to state RIGHT_ATTRS is required could also be reasonable.

Became aware of this issue while looking at #8803.

Description

Types of change

Bug fix?

Checklist

• I have submitted the spaCy Contributor Agreement.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[svlandeg]

I personally think that E100 should just be updated and mention RIGHT_ATTRS specifically. This does seem to be the original intention, as there is an explicit unit test checking for this error to be thrown when RIGHT_ATTRS is missing.

Alternatively, a slightly different error msg could be given for each missing attribute, mentioning the exact one that's missing and potentially also a default value that can be used (instead of setting this implicitely in code).

[polm]

Sounds good to me. I changed the error message to list missing attributes.

It would be good to suggest default values, but I wasn't sure how to add that without making the error too verbose.