cue export nil pointer dereference

[bozaro]

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

$ cue version

cue version v0.6.0

go version go1.20.7
      -buildmode exe
       -compiler gc
     CGO_ENABLED 1
          GOARCH amd64
            GOOS linux
         GOAMD64 v1

Does this issue reproduce with the latest stable release?

Yes

What did you do?

cue export for file:

package example

#Bar1: {
	bar1: string
}

#Bar2: {
	bar2: string
}

#BarFromName: #Bar1 & {
	#name: string

	let env = #name
	if env != "production" {
		bar2: env
	}
}

#Foo: {
	foo: string
}

#FooConfig: #Foo & {
	#bar: #Bar2

	let env = #bar.cluster.env
	if env == "dev" {
		let _bar = #bar
		foo: _bar
	}
}

#FooConfig: #Foo & {
	#foo: string
	#bar: #BarFromName & {
		#name: #foo
	}
}

foo: #FooConfig & {
	#foo: "dev"
}

What did you expect to see?

Not panic

What did you see instead?

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x6ae012]

goroutine 1 [running]:
cuelang.org/go/cmd/cue/cmd.recoverError(0xc0007adeb8)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cmd/cue/cmd/root.go:318 +0x7b
panic({0xcb7760, 0x13e56b0})
	/usr/lib/go-1.20/src/runtime/panic.go:884 +0x213
cuelang.org/go/internal/core/adt.(*nodeContext).processComprehension(0xc000515800, 0xc0003a33b0, 0x0?)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/comprehension.go:400 +0x172
cuelang.org/go/internal/core/adt.(*nodeContext).injectComprehensions(0xc000515800, 0xa0?)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/comprehension.go:332 +0x9a
cuelang.org/go/internal/core/adt.(*nodeContext).expandOne(0xc000515800, 0xd8?)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/eval.go:2077 +0x89
cuelang.org/go/internal/core/adt.(*OpContext).unify(0xc0000d8900, 0xc0000cb7a0, 0x5)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/eval.go:265 +0x685
cuelang.org/go/internal/core/adt.(*nodeContext).completeArcs(0xc000514c00, 0x5)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/eval.go:794 +0x1d5
cuelang.org/go/internal/core/adt.(*nodeContext).postDisjunct(0xc000514c00, 0x0?)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/eval.go:581 +0x4d2
cuelang.org/go/internal/core/adt.(*nodeContext).expandDisjuncts(0xc000514c00, 0xe8?, 0xc000514c00, 0x0, 0x0, 0x1)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/disjunct.go:158 +0x445
cuelang.org/go/internal/core/adt.(*OpContext).unify(0xc0000d8900, 0xc0000cafc0, 0x5)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/eval.go:292 +0x7e5
cuelang.org/go/internal/core/adt.(*nodeContext).completeArcs(0xc000514800, 0x5)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/eval.go:794 +0x1d5
cuelang.org/go/internal/core/adt.(*nodeContext).postDisjunct(0xc000514800, 0x30?)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/eval.go:581 +0x4d2
cuelang.org/go/internal/core/adt.(*nodeContext).expandDisjuncts(0xc000514800, 0xe8?, 0xc000514800, 0x0, 0x0, 0x1)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/disjunct.go:158 +0x445
cuelang.org/go/internal/core/adt.(*OpContext).unify(0xc0000d8900, 0xc0000ca5a0, 0x5)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/eval.go:292 +0x7e5
cuelang.org/go/internal/core/adt.(*Vertex).Finalize(...)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/internal/core/adt/composite.go:638
cuelang.org/go/cue.newVertexRoot(0x7f07d87d7848?, 0xc0000d8900?, 0x100?)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cue/types.go:614 +0x72
cuelang.org/go/cue.newValueRoot(0xedb3f8?, 0xc000392e28?, {0xed9e80?, 0xc0000ca5a0?})
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cue/types.go:623 +0x4d
cuelang.org/go/cue.(*Context).make(0xc000392e28, 0x0?)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cue/context.go:253 +0x6c
cuelang.org/go/cue.(*Context).BuildInstances(0xc000392e28, {0xc00044cb10, 0x1, 0x0?})
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cue/context.go:152 +0x1f9
cuelang.org/go/cmd/cue/cmd.buildInstances(0xc0003b1230, {0xc00044cb10, 0x1, 0x140e5a0?}, 0x0)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cmd/cue/cmd/common.go:729 +0x52
cuelang.org/go/cmd/cue/cmd.(*buildPlan).instances(0xc0003fe9c0)
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cmd/cue/cmd/common.go:171 +0x4a
cuelang.org/go/cmd/cue/cmd.runExport(0xc0003b1230?, {0xc0003ea4c0, 0x1, 0x1})
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cmd/cue/cmd/export.go:113 +0x19a
cuelang.org/go/cmd/cue/cmd.mkRunE.func1(0xc0003f0300?, {0xc0003ea4c0, 0x1, 0x1})
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cmd/cue/cmd/root.go:87 +0xb3
github.com/spf13/cobra.(*Command).execute(0xc0003f0300, {0xc0003ea480, 0x1, 0x1})
	/home/bozaro/go/pkg/mod/github.com/spf13/[email protected]/command.go:940 +0x862
github.com/spf13/cobra.(*Command).ExecuteC(0xc000005200)
	/home/bozaro/go/pkg/mod/github.com/spf13/[email protected]/command.go:1068 +0x3bd
github.com/spf13/cobra.(*Command).Execute(...)
	/home/bozaro/go/pkg/mod/github.com/spf13/[email protected]/command.go:992
cuelang.org/go/cmd/cue/cmd.(*Command).Run(0xc0003b1230, {0x2?, 0x2?})
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cmd/cue/cmd/root.go:303 +0x6b
cuelang.org/go/cmd/cue/cmd.Main()
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cmd/cue/cmd/root.go:231 +0x79
main.main()
	/home/bozaro/go/pkg/mod/cuelang.org/[email protected]/cmd/cue/main.go:24 +0x19

[mvdan]

Out of curiosity, did you git bisect to see if this is a relatively recent regression?

[bozaro]

Out of curiosity, did you git bisect to see if this is a relatively recent regression?

I didn't do bisect. This bug has been around since at least April 26th 2023.

My colleague made this correction a long time ago, but without creating a PR: https://github.com/joomcode/cue/pull/11/commits/1b57363c14956cea8b6999e0777a5c840b5f1077

[mvdan]

Ah, thanks. So at least it wasn't a very recent regression.

Here is a significantly smaller reproducer, which you should use as a regression test in your PR for the sake of avoiding verbosity:

exec cue export in.cue

-- in.cue --
foo: string
bar: close({})

if bar.missing == "x" {
	let _bar = bar
	foo: _bar
}

[bozaro]

Yes. This example also reproduces the problem.
I will now replace testcase in PR.