two nested loops output doesn't meet expectation

[cueckoo]

Originally opened by @zzxwill in cuelang/cue#632

Here are two nested loops.

envValueFrom: {
	env:
	[ for c in parameter.configRef {
		[ for k in c.keys {
			name: k
			valueFrom: {
				secretKeyRef: {
					name: c.name
					key:  k
				}
			}
		},
		]
	}]

}

parameter: {
	configRef: [
		{name: "rds-config", keys: ["db_name", "db_host"]},
		{name: "oss-config", keys: ["bucket_name"]},
	]
}

It generates envValueFrom as below.

envValueFrom: {
    env: [[{
        name: "db_name"
        valueFrom: {
            secretKeyRef: {
                name: "rds-config"
                key:  "db_name"
            }
        }
    }, {
        name: "db_host"
        valueFrom: {
            secretKeyRef: {
                name: "rds-config"
                key:  "db_host"
            }
        }
    }], [{
        name: "bucket_name"
        valueFrom: {
            secretKeyRef: {
                name: "oss-config"
                key:  "bucket_name"
            }
        }
    }]]
}

But env should be the list with all inner items as below. Did I miss anything? Thanks.

envValueFrom: {
    env: [{
        name: "db_name"
        valueFrom: {
            secretKeyRef: {
                name: "rds-config"
                key:  "db_name"
            }
        }
    }, 
    {
        name: "db_host"
        valueFrom: {
            secretKeyRef: {
                name: "rds-config"
                key:  "db_host"
            }
        }
    }, 
    {
        name: "bucket_name"
        valueFrom: {
            secretKeyRef: {
                name: "oss-config"
                key:  "bucket_name"
            }
        }
    }]
}

[cueckoo]

Original reply by @verdverm in cuelang/cue#632 (comment)

You have nested list comprehensions, so the list of lists is expected.

What you want to add is a list.FlattenN([[]], 1) around your nested list comp.

https://pkg.go.dev/cuelang.org/[email protected]/pkg/list#FlattenN

[cueckoo]

Original reply by @zzxwill in cuelang/cue#632 (comment)

Great, thanks.

[cueckoo]

Original reply by @mpvl in cuelang/cue#632 (comment)

Instead of using flatten, you can also drop the inner square brackets.

[cueckoo]

Original reply by @zzxwill in cuelang/cue#632 (comment)

Yes, that's exactly what I need. How can I drop the brackets?

[cueckoo]

Original reply by @verdverm in cuelang/cue#632 (comment)

You should just be able to remove the inner [] brackets. You then comprehend a list of comprehensions, which will each comprehend some objects, and can avoid the flatten call. I keep forgetting that a list of comprehensions is now available...