Bug in deletion through an anchor?

[ransford]

Hello! Thanks for this elegant and useful tool. I'm wondering whether I've tickled a bug or am just holding yq wrong. I'm trying to delete array elements whose parents' parents match a wildcard, but running into surprising behavior when some of those parents are aliases of others.

Example:

$ cat foo.yaml
a:
  b.ext: &b
    things:
      - a
      - b
  c.ext: *b

$ yq 'del(.a.["*.ext"].things.[] | select(. == "a"))' foo.yaml
a:
  b.ext: &b
    things: []
  c.ext: *b

I expected .a."b.ext".things to still contain a single element "b".

If I add a third element "c" to that array, del deletes two elements as before but leaves the third:

$ cat foo3.yaml
a:
  b.ext: &b
    things:
      - a
      - b
      - c
  c.ext: *b

$ yq 'del(.a.["*.ext"].things.[] | select(. == "a"))' foo3.yaml
a:
  b.ext: &b
    things:
      - c
  c.ext: *b

I can see why del might want to delete the 0th element of a."b.ext".things twice, once for b.ext and once for c.ext through its alias:

$ cat foo.yaml
a:
  b.ext: &b
    things:
      - a
      - b
  c.ext: *b

$ yq '.a.["*.ext"].things.[] | select(. == "a") | path' foo.yaml
- a
- b.ext
- things
- 0
- a
- b.ext
- things
- 0

... but it's still surprising to see an element deleted that doesn't match . == "a".

Workaround

I can interpose select(alias == "") to avoid traversing aliases:

$ yq 'del(.a.["*.ext"] | select(alias != "") | .things.[] | select(. == "a"))' foo.yaml
a:
  b.ext: &b
    things:
      - b
  c.ext: *b