try-catch + ascii_downcase fails in "catch" condition

[Gursewak Mangat]

I see an error when we run a jq statement using try-catch and ascii_downcase. If it has a match, it doesn't error out but when it needs to take the catch path, it errors out.
This issue was seen after upgrading the jq from jq 1.6-17.fc39 -> jq-1.7.1-1.fc40
OS I am runnning on: Fedora CoreOS-Rawhide.

Steps to Reproduce:

1. Run jq -r 'map(select(try .baz catch "" | ascii_downcase == ""))' <<< '[{"foo":"bar"}]'

Actual results:
jq: error (at <stdin>:1): explode input must be a string
Expected results:

[
  {
    "foo": "bar"
  }
]

[Emanuele Torre]

@gursewak1997
I cannot reproduce that command not failing in jq 1.6.
The exception is triggered by {"foo":"bar"} | .baz returning null succesfully (since there is not a "baz" key in the object), and then null | ascii_downcase being called, and ascii_downcase is not in a try block.
ascii_downcase errors for non-string inputs in both jq 1.6, jq 1.7, and jq 1.7.1.
{"foo":"bar"} | .baz retruns null in both jq 1.6, jq 1.7, and jq 1.7.1. .baz would only error if the input is neither null nor an object. If the specified key is missing from the input object, or if the input is null, it just returns null in all versions of jq, it does not error.

[Emanuele Torre]

I don't get what is the point of using ascii_downcase == "" either.

[Emanuele Torre]

Nevermind, I can reproduce it now, I was using the wrong binary; sorry! ^^
Anyway, I think this was only not erroring because try was bugged in many ways in jq 1.6. Especially when used in combination with foreach which was very annoying. :-(
If you try null | ascii_downcase even in jq 1.6 it will error. And in that command, it is supposed to error.

I am not sure I understand what the intent of that jq command is supposed to be.
If you want to only keep the objects that either don't contain .baz or that have a .baz equal to null or "", I suggest using this instead:

jq 'del(.[] | select(.baz | IN(null, "") | not))'
# alternatively
jq 'del(.[] | select((.baz // "") != ""))'
jq 'map(select(.baz | IN(null, "")))'
jq 'map(select((.baz // "") == ""))'

If you want to only remove objects that contain a "baz" in general, you can use:

jq 'del(.[] | select(has("baz")))'
# or, if you want to also keep objects with {"baz":null}
jq 'del(.[] | select(.baz != null))'

[itchyny]

See #1859, #2750. This is working as intended in 1.7. In 1.6 try catches the error of ascii_downcase but it should not.

[Jonathan Lebon]

@emanuele6 For posterity, note the example here is just a minimal reproducer. The real world use case it was boiled down from can be seen in coreos/fedora-coreos-config#2797 (where we worked around it).