Can you retrieve via a go API the type information and validation that are defined in a cue file ?

[cueckoo]

Originally opened by @ymolists in cuelang/cue#1056

I am trying to read cue files that contain type information and validation only

[cueckoo]

Original reply by @myitcv in cuelang/cue#1056 (comment)

Yes, everything can be done via the https://pkg.go.dev/cuelang.org/[email protected]/cue API:

-- go.mod --
module mod.com

go 1.16

require cuelang.org/go v0.4.0
-- main.go --
package main

import (
	"fmt"

	"cuelang.org/go/cue"
	"cuelang.org/go/cue/cuecontext"
	"cuelang.org/go/cue/load"
)

func main() {
	ctx := cuecontext.New()
	bps := load.Instances([]string{"."}, nil)
	v := ctx.BuildInstance(bps[0])
	schema := v.LookupPath(cue.ParsePath("#Schema"))
	fmt.Printf("%!v(MISSING)\n", schema)
}
-- schema.cue --
package x

#Schema: {
	Name: string
	Age:  >100
}

[cueckoo]

Original reply by @ymolists in cuelang/cue#1056 (comment)

At this point all i need is to disregard the value when it is a validation in a deterministic way. something like isValidation that returns true or false.

[cueckoo]

Original reply by @verdverm in cuelang/cue#1056 (comment)

What is a "validation"? I suspect the answer may vary from user to user. What if I want to ensure that a particular field has an exact value? Is that a validation?

Both int and >100 are "constraints" on a field. Conjunctions (&) can also constrain a value. Actual values can constrain structs as well.

Sometimes it helps to describe what you are trying to achieve, examples are helpful. There may be other ways to reach your goal. In this case, why do you want to separate out ≥100?

[cueckoo]

Original reply by @ymolists in cuelang/cue#1056 (comment)

@verdverm I need to filter anything that is not an actual value. If a field is not assigned a value then i cannot use it.

a: 10 // isConstraint() returns false. isActualValue() returns true
a: <100 // isConstraint() returns true. isActualValue() returns false
a: >9 // isConstraint() returns true. isActualValue() returns false

1. if the first line is missing from above what happens if i want to retrieve the value of a?
2. lets say I am looping over the fields of a struct how would i go about implementing an isConstraint() bool or isActualValue() bool for a given field that returns true or false in a deterministic way ?

[cueckoo]

Original reply by @eonpatapon in cuelang/cue#1056 (comment)

You can check if a cue Value is concrete with v.Validate(cue.Concrete(true)).

If you want to use default values use v.Default() first.

[mpvl]

Also look at these methods on Value:

• IncompleteKind: indicates the possible types of a Value as a bitmask.
• Expr: dissects a constraint into the operation and values of the expression for further inspection.

The Struct method is deprecated.