How to use cuecontext.Context to compile definitions and concrete values in multiple passes

[yannk]

Using 0.4.0-rc.1 I'd like to load one cue file holding definitions, and then load cue instances from various sources (disk for instance). I can't find what's the right Go API to use to achieve that. I assumed that 'context' would retain the definitions already compiled.

But the second CompileString in the example below returns an bottom Value.

package main

import (
	"fmt"

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

func main() {

	ctx := cuecontext.New()

	def := ctx.CompileString(`
#Def: {
	id: string
    version: string
}`)

	val := ctx.CompileString(`
v: #Def & { id: "hi" }
	`)
	fmt.Printf("val: %v\n", val)

	root := cue.Path{}
	v := def.FillPath(root, val)
	fmt.Printf("%v\n", v.LookupPath(cue.ParsePath("v")))
}

outputs:

val: _|_ // 2:4: reference "#Def" not found
_|_ // field "v" not found

Of course it works when v and #Def are compiled at once.

package main

  import (
      "fmt"

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

 func main() {

      ctx := cuecontext.New()

      def := ctx.CompileString(`
  #Def: {
      id: string
      version: string
  }
  v: #Def & { id: "hi" }
      `)
      fmt.Printf("def: %v\n", def)

      fmt.Printf("%v\n", def.LookupPath(cue.ParsePath("v")))
  }

I'm still trying to wrap my head around how to best use Cue, since I'll import tool/exec, I was thinking about using vanilla cue scripts to load data validated against those definitions, then run processing on that validated data to finally output cue values back to storage. But I want context.Timeout that seems to be missing from tool/exec, so I ended up wanting to write a Go program to package that nicely but bumped into the problem above.

Thanks!

[mpvl]

The Context does not retain anything. The context just holds indices for mapping field names, builtins, etc. But there is no retention otherwise.

However, you can pass a "scope" which is used to resolve all unresolved identifiers:

	ctx := cuecontext.New()

	def := ctx.CompileString(`
#Def: {
	id: string
    version: string
}`)

	val := ctx.CompileString(`
v: #Def & { id: "hi" }
	`, cue.Scope(def)) // USE def to RESOLVE UNRESOLVED IDENTIFIERS, LIKE #Def

[yannk]

Awesome, thanks.

Do you recommend using CompileString / cue.Scope or something that seems more high-level: cue/load and friends?

Again, the goal is to load a schema once and do multiple, unrelated, data file loads that will be validated against it.

Thanks!

[myitcv]

Really whatever works best for you. The only constraint you need to be aware of however is that you need to use the same cue.Context when constructing cue.Value instances.

[cueckoo]

This discussion has been migrated to cue-lang/cue#988.

For more details about CUE's migration to a new home, please see cue-lang/cue#1078.