cue/def: wrapping code in `_#def`

[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 input.cue
cmp stdout golden.stdout

-- input.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.stdout --
package main

import "hof.io/repro/foo"

foo.#Foo
a: "A"

What did you expect to see?

PASS and that the code looks the same before & after

What did you see instead?

The original code, wrapped in _#def

> exec cue def input.cue
[stdout]
package main

import "hof.io/repro/foo"

_#def
_#def: {
        foo.#Foo
        a: "A"
}
> cmp stdout golden.stdout
--- stdout
+++ golden.stdout
@@ -1,9 +0,0 @@
-package main
-
-import "hof.io/repro/foo"
-
-_#def
-_#def: {
-       foo.#Foo
-       a: "A"
-}

FAIL: /tmp/testscript3051149263/repro.txt/script.txtar:2: stdout and golden.stdout differ
error running repro.txt in /tmp/testscript3051149263/repro.txt

[myitcv]

Linking to response in #2251 (comment).

[mpvl]

I'm in favor of getting rid of the _#def mechanism altogether. But we need an alternative. To address #2251 and this partially, we could add some heuristic to prevent wrapping when it is not necessary.

But the plan is to do something more principled altogether, such as using must or some explicit schema directive/builtin.