encoding/openapi: "unsupported op for number &" with ExpandReferences and default+bounded int

[berimbolo13]

Summary

openapi.Gen with ExpandReferences: true fails with unsupported op for number & when a definition contains a default value combined with a bounded integer conjunction.

Minimal reproduction

ctx := cuecontext.New()
v := ctx.CompileString(`#X: *20 | int & >=1 & <=100`)
_, err := openapi.Gen(v, &openapi.Generator{ExpandReferences: true})
// err: unsupported op for number &

What works vs what doesn't

Expression	ExpandReferences	Result
#X: *20 | int & >=1 & <=100	false	OK
#X: *20 | int & >=1 & <=100	true	FAILS
#X: *20 | int	true	OK
#X: int & >=1 & <=100	true	OK
#X: *20 | >=1	true	OK
#X: null | *20 | >=1 & <=100	true	OK

The combination of a default value (*20), a disjunction (|), and a conjunction of type+bounds (int & >=1 & <=100) is required to trigger the bug.

Where it fails

The error is produced at the default branch of the number() function:

cue/encoding/openapi/build.go

Lines 936 to 942 in 66ea772

	case cue.NoOp:
	// TODO: extract format from specific type.
	default:
	b.failf(v, "unsupported op for number %v", op)
	}
	}

number() handles individual constraint ops (>=, <=, <, >, !=, CallOp, NoOp) but has no case for AndOp. Normally conjunctions are decomposed before reaching number(), but with ExpandReferences: true the value arrives unsplit.

[berimbolo13]

Please let me know if there are any alternative ways to define both a default value and a range constraint

[mvdan]

The encoding/openapi package is rather old and buggy; going forward we're going to focus on the encoding/jsonschema package, which is already pretty good at decoding both JSON Schema and OpenAPI, and recently learned to generate JSON Schema (#929 (comment)). So the next chunk of work would be to teach it to generate the OpenAPI flavor as well.

So if generating JSON Schema is enough for you, give that a go instead; otherwise, I hope we'll have good news for you soon in terms of the new OpenAPI encoder.