cmd/cue: def emits invalid output with multiple list conjuncts

[vikstrous2]

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

The web based emulator https://cuelang.org/play/#cue@export@yaml

Does this issue reproduce with the latest release?

No, this is a bug reproducible only in the web based emulator.

What did you do?

https://cuelang.org/play/?id=B2-EGA_qicy#cue@export@yaml

l: [...]
l: ["a",...]
l: ["a","b",...]

What did you expect to see?

l: ["a", "b"]

What did you see instead?

When output is set to yaml in the cloud emulator, this produces an error:

failed to encode: l: conflicting values ["a","b",...] and {} (mismatched types list and struct)

Weirdly, this actually works if the list is at the top level (not inside l):

[...]
["a",...]
["a","b",...]

This is a weirdly specific bug. There must be something special about the way the emulator runs. I can't reproduce it locally with any version of cue.

[antong]

This is not limited to the playground. I managed a kind of repro with v0.4.0. With the original input, cue def outputs: l: [...] & ["a", ...] & ["a", "b", ...] & {}. So it makes up an extra conjunct "{}" of type struct, which break things. Perhaps the playground does some extra round of cue def, which triggers this.

Here is a txtar/testscript repro with v0.4.0 (@myitcv , did I finally get this right ? ;-)

exec cue def x.cue
stdin stdout
exec cue export -

-- x.cue --
l: [...]
l: ["a",...]
l: ["a","b",...]

Gives:

l: [...] & ["a", ...] & ["a", "b", ...] & {}
> stdin stdout
> exec cue export -
[stderr]
l: conflicting values ["a","b",...] and {} (mismatched types list and struct):
    -:1:25
    -:1:43
[exit status 1]

[myitcv]

Here is a txtar/testscript repro with v0.4.0 (@myitcv , did I finally get this right ? ;-)

🎉 great work! Just to check, do you use cmd/testscript to validate them? I tweeted recently about some means by which we could (in an ideal world) have this be integrated as part of the issue tracker/discussions.

This issue really falls in the same bucket as #1340, but will keep separate for now because I'm not totally clear they are one and the same "issue".

[antong]

Just to check, do you use cmd/testscript to validate them?

I installed github.com/rogpeppe/go-internal/cmd/testscript, ran it, and fed it the input (txtar). Then I copy pasted the interesting part from the output to the comment/description.