cue/def: running def on the output creates increasingly nested results

[verdverm]

What version of CUE are you using (cue version)?

$ cue version
cue version v0.5.0-beta.5

go version go1.19.3
       -compiler gc
       -trimpath true
     CGO_ENABLED 0
          GOARCH amd64
            GOOS linux
         GOAMD64 v1

What did you do?

exec cue def 1.cue --outfile 2.cue
exec cue def 2.cue --outfile 3.cue
exec cue def 3.cue
cmp 3.cue golden.output

-- 1.cue --
package main

import "hof.io/repro/foo"

foo.#Foo

a: "A"

-- foo/foo.cue --
package foo

#Foo: {
	a: string
}

-- cue.mod/module.cue --
module: "hof.io/repro"

-- golden.output --
package main

import "hof.io/repro/foo"

foo.#Foo
a: "A"

What did you expect to see?

the final output is the same as the original

What did you see instead?

package main

import "hof.io/repro/foo"

_#def
_#def: {
        _#def
        foo.#Foo
        foo.#Foo
        _#def: {
                _#def
                _#def: {
                        foo.#Foo
                        a: "A"
                }
        }
        a: "A"
}

[mvdan]

Does this happen with v0.4.3? That's what the section about "latest release" in the bug template is for.

[verdverm]

With v0.4.3

package main

import "hof.io/repro/foo"

_#def
_#def: {
        _#def
        _#def: {
                _#def
                _#def: {
                        foo.#Foo
                        a: "A"
                }
        }
}

While cleaner, I would still consider this undesirable output

[myitcv]

@verdverm - just to confirm, is the intent behind embedding foo.#Foo into package main, to enforce that package main should then satisfy foo.#Foo?

If so, this gets close to needing what we want in #575 (or similar): a mechanism by which we can enforce that a package value satisfies a given schema. Because the problem with embedding (as in this case) is that closedness is relaxed during the embedding... which is almost certainly not what was intended.

The current behaviour of def is to apply some sort of heuristic that guesses what the user was trying to do. If we implement something like must() (bike shedding on name and semantics) that heuristic can go away entirely.