cmd/cue: trim cannot handle ellipsis and empty list value

[gisle]

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

$ cue version
cue version v0.8.2

go version go1.22.2
      -buildmode exe
       -compiler gc
       -trimpath true
     CGO_ENABLED 0
          GOARCH arm64
            GOOS darwin

Does this issue reproduce with the latest stable release?

I belive my version to be the latest stable release.

What did you do?

Ran 'cue trim' on this code:

package test

#Foo: {
	id: string
	...
}

foo: [ID=_]: #Foo & {
	id: ID
}

foo: X1: {
	id: "X1"
	alist: []
}

What did you expect to see?

No output from cue trim and that it removed the id field.

What did you see instead?

$ cue trim ./...:test
  {
      #Foo: {
      	id: string
      }
      foo: {
          X1: {
              id: "X1"
-             alist: []
          }
      }
  }
Aborting trim, output differs after trimming. This is a bug! Use -i to force trim.
You can file a bug here: https://cuelang.org/issues/new?assignees=&labels=NeedsInvestigation&template=bug_report.md&title=

[myitcv]

Thanks for the report. This appears to be something to do with the interaction between ... and the empty list value []:

# Keep a non-trimmed backup
cp config.cue config.cue.bak

# Working
exec cue trim working.cue config.cue
cmp config.cue config.cue.golden

# Broken
exec cue trim broken.cue config.cue
cmp config.cue config.cue.golden

-- working.cue --
package test

#Foo: {
	id:     string
	alist?: _
}

foo: [ID=_]: #Foo & {
	id: ID
}
-- broken.cue --
package test

#Foo: {
	id: string
	...
}

foo: [ID=_]: #Foo & {
	id: ID
}
-- config.cue --
foo: X1: {
	id: "X1"
	alist: []
}
-- config.cue.golden --
foo: X1: {
	alist: []
}

[NoamTD]

for the record, this can be further simplified to:

# Keep a non-trimmed backup
cp config.cue config.cue.golden

# Working
exec cue trim working.cue config.cue
cmp config.cue config.cue.golden

# Broken
exec cue trim broken.cue config.cue
cmp config.cue config.cue.golden

-- working.cue --
package test

#Foo: {
	alist?: _
	aStruct?: _
}

foo: #Foo & { }
-- broken.cue --
package test

#Foo: {...}

-- config.cue --
foo: X1: {
	alist: []
        astruct: {}
}

Also worth noting that this is equally broken in the case of an empty struct ({})