Fix incorrect parsing of placeholders that point to other tab stops.

[savetheclocktower]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions

Description of the Change

266 describes a regression with tab stop behavior when the placeholder contains a reference to another tab stop. This almost certainly happened as a result of #260, but there wasn't any test coverage for this particular usage.

Alternate Designs

The parser was incorrectly assuming that all the items it would receive for a particular rule would be represented as strings, and that it could thus join them all together. Tabstop references are represented as objects. So I wrote a couple of utility functions to ensure that adjacent strings would be merged together without incorrectly coercing objects.

If there's an easier way to do this with a PEG, I'm all for it. Parser grammars are not my strong suit.

Applicable Issues

266

[savetheclocktower]

I can merge this myself, but I'll leave it open for a couple days in case other maintainers have feedback.

[rsese]

Thanks @savetheclocktower, I'll ask the team to take a look in case anyone has feedback for you :bow:

[nathansobo]

@joefitzgerald can you give this a spin and see if it fixes things?

[joefitzgerald]

I have tested and can confirm that this restores the behavior that was present in v1.24.1.

[nathansobo]

:heart::heart: