Template Regex Constraints

[cueckoo]

Originally opened by @khepin in cuelang/cue#659

When researching an answer to cuelang/cue#657 (restrict string length), I had the following regex:

#StrLen8: =~"^.{8}$"
{
    v: #StrLen8
}

Which works, but only for length 8. So, loosely inspired by the documentation at https://cuelang.org/docs/tutorials/tour/references/emit/ and https://cuelang.org/docs/tutorials/tour/types/templates/ I thought I could apply that to regexes and attempted:

#StrLen: [len=_]: =~"^.{\(len)}$"
{
    v: #StrLen : 8
}

... that does NOT work ;-) is there a way to template regexes like this?

[cueckoo]

Original reply by @mpvl in cuelang/cue#659 (comment)

See my answer in #657.

In this particular case, pattern constraints cannot match against numbers and must match against fields.

[cueckoo]

Original reply by @khepin in cuelang/cue#659 (comment)

So the suggestion in that answer is:

#StrLen: {
	=~"^.{\(#n)}$"
	#n: int
}
#StrLen8: { #StrLen, #n: 8 }

Which actually gives me an error:

#StrLen: can only embed structs (found string):
    ./test.cue:2:2