Cannot get the merge alias of a map

[mikefarah]

Discussed in #1937

^{Originally posted by qaisjp February 6, 2024}
I have the following YAML:

foo: &foo
  hello: world
bar:
  <<: *foo

And would like to compute the following values based on the "parent" of each object

foo: &foo
  parent: null
bar:
  parent: foo   # bar inherits from "foo", so the value of bar.parent should be "foo"

I've tried the following filters, but can't seem to figure it out!

filter attempt 1

the following queries:

with_entries(.value |= {
  "parent": . | alias
})

with_entries(.value |= {
  "parent": alias
})

produces

foo: &foo
  parent: ""
bar:
  parent: ""  # expected "foo"

filter attempt 2

with_entries(.value |= {
  "parent": .["<<"]
})

produces

foo: &foo
  parent: null
bar:
  parent: null

filter attempt 3

with_entries(.value |= {
  "parent": (.["<<"] | alias)
})

produces

foo: &foo
  parent: "null"
bar:
  parent: "null"

Note that it works fine with anchors

with_entries(.value |= {
  "anchor_name": . | anchor
})

produces

foo: &foo
  anchor_name: foo
bar:
  anchor_name: ""

<<: * is parsed correctly

When I just pipe my yaml through with the . filter, I get

foo: &foo
  hello: world
bar:
  !!merge <<: *foo

Which is correct — according to the docs it says:

yq supports merge aliases (like <<: *blah) however this is no longer in the standard yaml spec (1.2) and so yq will automatically add the !!merge tag to these nodes as it is effectively a custom tag.

(also mentioned at #680 (comment))

but why can't I read the merge alias at .["<<"]?

---

Any pointers? 🙁 Thanks!

[mikefarah]

Will fix in the next release :)

[mikefarah]

Fwiw - when fixed you can get the alias name by:

yq '.bar["<<"] | alias' file.yaml

[mikefarah]

Fixed in 4.41.1

[qaisjp]

Thanks!