internal/core/toposort: panic involving IndexToString

[mvdan]

exec cue eval input.cue

exec cue def input.cue

-- input.cue --
package p

import "list"

_cfg: {
	[VN=string]: {
		active: true
		name: VN
	}
	cfg0: {
		index: 1
	}
}
_topics: [
	"foo1", 
	"foo2", 
	"foo3", 
	"foo4", 
	"foo5", 
	"foo6", 
	"foo7", 
	"foo8", 
	"foo9", 
	"foo10", 
]

out: list.FlattenN([
	for _ in _cfg.cfg0 for topic in _topics {
		[
			{f: "a-\(topic)"},
			{f: "b-\(topic)"},
			{f: "c-\(topic)"},
			{f: "d-\(topic)"},
			{f: "e-\(topic)" },
			{f: "f-\(topic)" },
		]
	},
], 1)

As of 17c5d0b:

> exec cue eval input.cue
[stderr]
panic: runtime error: index out of range [121] with length 121

goroutine 1 gp=0xc000002380 m=8 mp=0xc000580008 [running]:
panic({0x1028580?, 0xc00003a498?})
	/home/mvdan/tip/src/runtime/panic.go:806 +0x168 fp=0xc00051e4a8 sp=0xc00051e3f8 pc=0x47a628
runtime.goPanicIndex(0x79, 0x79)
	/home/mvdan/tip/src/runtime/panic.go:115 +0x74 fp=0xc00051e4e8 sp=0xc00051e4a8 pc=0x43fdb4
cuelang.org/go/internal/core/runtime.(*index).IndexToString(0xc00051e548?, 0x478651?)
	/home/mvdan/src/c/cue/internal/core/runtime/index.go:94 +0xaa fp=0xc00051e520 sp=0xc00051e4e8 pc=0x7a8d6a
cuelang.org/go/internal/core/runtime.(*Runtime).IndexToString(0x5d?, 0xc00051e640?)
	/home/mvdan/src/c/cue/internal/core/runtime/index.go:25 +0x16 fp=0xc00051e540 sp=0xc00051e520 pc=0x7a86d6
cuelang.org/go/internal/core/adt.(*OpContext).IndexToString(0xc0001517d0?, 0xc00051e5e0?)
	<autogenerated>:1 +0x24 fp=0xc00051e560 sp=0xc00051e540 pc=0x745484
cuelang.org/go/internal/core/adt.Feature.RawString(0x2ac980?, {0x124ebe8?, 0xc0003730e0?})
	/home/mvdan/src/c/cue/internal/core/adt/feature.go:130 +0x37 fp=0xc00051e580 sp=0xc00051e560 pc=0x72e5f7
cuelang.org/go/internal/core/toposort.VertexFeatures(0xc0003730e0, 0xc00021a0a0)
	/home/mvdan/src/c/cue/internal/core/toposort/vertex.go:396 +0x45 fp=0xc00051e8f8 sp=0xc00051e580 pc=0x760be5
cuelang.org/go/internal/core/export.VertexFeatures(0xc00051e978?, 0x417d8f?)
	/home/mvdan/src/c/cue/internal/core/export/toposort.go:33 +0x19 fp=0xc00051e918 sp=0xc00051e8f8 pc=0x777e99
cuelang.org/go/internal/core/export.(*exporter).structComposite(0xc0000e0370, 0xc00021a0a0, {0x0, 0x0, 0x104d200?})
	/home/mvdan/src/c/cue/internal/core/export/value.go:427 +0x348 fp=0xc00051eaa8 sp=0xc00051e918 pc=0x77c888
[...]
> exec cue def input.cue
[stdout]
package p

import "list"
[...]

[cuematthew]

A smaller repro is:

import "list"
list.Repeat([{x: 5}], 1000)