Use child in fix?

[hobofan]

Hey there 👋

I'm trying to create a rule with a fix, that replaces the matched node with a child of the matched node. However, there doesn't seem to be a way (in the YAML syntax) to extract/select a child/field of a matched node. Is that correct?

I discovered the "transform" mechanism, which seems to take some steps towards that.

Concrete example

Goal: Lift up the object.(FooBar|BarFoo).iri to replace the matched object (pseudo-syntax)

Sample input:

const output = Thing.doThing(testInput, {
            known: [
                {
                    FooBar: {
                        iri: {
                            _type: 'IRI',
                            string: 'urn:abc',
                        },
                        annotations: [],
                    },
                },
                {
                    FooBar: {
                        iri: {
                            _type: 'IRI',
                            string: 'urn:cde',
                        },
                        annotations: [],
                    },
                },
                {
                    BarFoo: {
                        iri: someFn1(),
                        annotations: [],
                    },
                },
                {
                    FooBar: {
                        iri: someFn2(),
                        annotations: [],
                    },
                },
            ],
        })

Sample output:

const output = Thing.doThing(testInput, {
            known: [
                {
                    _type: 'IRI',
                    string: 'urn:abc',
                },
                {
                    _type: 'IRI',
                    string: 'urn:cde',
                },
                someFn1(),
                someFn2(),
            ],
        })

[HerringtonDarkholme]

Hi, thanks for using ast-grep. You can use relational rule to extract child.

rule:
  any:
    - pattern: '{FooBar: $CHILD}'
    - pattern: '{BarFoo: $CHILD}'
  has:
    pattern: '{ iri: $B, $$$ }'
    stopBy: end
fix: $B

link

[hobofan]

Ah, great! Thanks for the swift reply!

From most of the examples found in the docs, I was under the impression that only atomic rules would bind metavariables.

[HerringtonDarkholme]

Thanks for the suggestion! I will add it as a tip to the doc! ast-grep/ast-grep.github.io#161