If constraint_message includes a ${} reference and no translations, expanded XPath path should be in <output>

[lognaturel]

Software and hardware versions

pyxform v1.x.x, Python v1.2.0

Problem description

If a form only uses one language and has a constraint_message with a ${} reference, no output is generated. This is a side effect of https://github.com/XLSForm/pyxform/issues/285.

Steps to reproduce the problem

1. Build a single-language form with a constraint message that has a ${} reference in it:

type	name	label	constraint	constraint_message
select_one fruits	Q1	Select the fruit that you like the most:
select_one fruits	Q2	Select (again) the (same) fruit that you like the most (that you selected in Q1):	.=${Q1}	You chose ${Q1} in Q1 but now it's different!

1. Convert it and see that the constraint message is set to jr:constraintMsg="You chose /data/Q1 in Q1 but now it's different!". This means the /data/Q1 reference is not evaluated by clients.

Expected behavior

/data/Q1 gets evaluated by clients.

Other information

A form design workaround is to set a language for the constraint_message column to force the generation of an itext block. I think the only approach we could take is detect whether there's a ${} reference in a constraint_message and if so generate itext for it.

[lognaturel]

The same almost certainly also applies to required_message.

[MartijnR]

I think the only approach we could take is detect whether there's a ${} reference in a constraint_message and if so generate itext for it.

That seems like the only solution indeed.