Order matters for if expressions - cannot add field..was already used error

[cueckoo]

Originally opened by @KostasKgr in cuelang/cue#1075

Hello all, I wasn't sure if the right place for this is here, or in slack or in issues. Let me know!

I've been trying to model our multi customer configuration and whilst trying it I saw a behaviour that I didn't expect.

I'm trying to understand if it is an issue or not, but it definitely breaks composition of different files for the approach I was trying.

So to showcase this, i have two files:

feature_definitions.cue

package config

features: {
    myFeature: *false | bool
}

if features.myFeature {
    myService: {
        config: {
            replicas: 4
        }
    }    
}

regional_configs.cue

package config

region: "US"
if region == "US" {
    features: myFeature: true
}

If I include feature definitions before regional configs then I get an error, If i do it the other way around I get the intended outcome.

15:41 $ cue eval -c feature_definitions.cue regional_configs.cue 
cannot add field myFeature: was already used:
    ./regional_configs.cue:5:15

15:46 $ cue eval -c regional_configs.cue feature_definitions.cue 
region: "US"
features: {
    myFeature: true
}
myService: {
    config: {
        replicas: 4
    }
}

Does using expressions limit splitting out the definitions across multiple files and thus in random composition?
Is this an issue or the intended outcome?

Thank you!

[cueckoo]

Original reply by @verdverm in cuelang/cue#1075 (comment)

Given CUE is order agnostic, this does seem like a bug to me. Note this behavior is the same across eval, export, and def.

Can you open an issue following the guidelines here: https://github.com/cuelang/cue/wiki/Creating-test-or-performance-reproducers

[KostasKgr]

Raised #1083

How can I accept this as the answer?