YQ gives invalid/useless error description while processing an invalid yaml document

[sk4zuzu]

Describe the bug

YQ gives invalid/useless error description while processing an invalid yaml document.

version of yq:

$ yq -V
yq version 3.4.0

operating system: linux amd64, the yq binary was installed from github releases manually

Input Yaml

An invalid document:

aaa:
  bbb: x
  ccc: "["y":1]"

Command

So far we tried:

$ yq r test.yml aaa.bbb

and

$ yq w test.yml aaa.bbb test

Actual behavior

$ yq r test.yml aaa.bbb
Error: yaml: line 1: did not find expected key

$ yq w test.yml aaa.bbb test
Error: Error reading document at index 0, yaml: line 1: did not find expected key: yaml: line 1: did not find expected key
Usage:
  yq write [yaml_file] [path_expression] [value] [flags]

Aliases:
  write, w

Examples:

yq write things.yaml 'a.b.c' true
yq write things.yaml 'a.*.c' true
yq write things.yaml 'a.**' true
yq write things.yaml 'a.(child.subchild==co*).c' true
yq write things.yaml 'a.b.c' --tag '!!str' true # force 'true' to be interpreted as a string instead of bool
yq write things.yaml 'a.b.c' --tag '!!float' 3
yq write --inplace -- things.yaml 'a.b.c' '--cat' # need to use '--' to stop processing arguments as flags
yq w -i things.yaml 'a.b.c' cat
yq w -i -s update_script.yaml things.yaml
yq w things.yaml 'a.b.d[+]' foo # appends a new node to the 'd' array
yq w --doc 2 things.yaml 'a.b.d[+]' foo # updates the 3rd document of the yaml file


Flags:
      --anchorName string   anchor name
  -d, --doc string          process document index number (0 based, * for all documents) (default "0")
  -f, --from string         yaml file for updating yaml (as-is)
  -h, --help                help for write
  -i, --inplace             update the yaml file inplace
      --makeAlias           create an alias using the value as the anchor name
  -s, --script string       yaml script for updating yaml
      --style string        formatting style of the value: single, double, folded, flow, literal, tagged
  -t, --tag string          set yaml tag (e.g. !!int)

Global Flags:
  -C, --colors        print with colors
  -I, --indent int    sets indent level for output (default 2)
  -P, --prettyPrint   pretty print
  -j, --tojson        output as json. By default it prints a json document in one line, use the prettyPrint flag to print a formatted doc.
  -v, --verbose       verbose mode

Expected behavior

Possibly an error message with some line number indicating where the syntax error is? 🤔

Additional context

This has some nice potential for wasting unaware user's time 👍😇. This happened to my colleague. We get it that the document was incorrect, but yq didn't help us... 😭

Thanks for the great tool! 😍

[j-zimnowoda]

Yes, and please do not print the Usage sting if provided file has invalid content.
The Usage string should be only printed if a command arguments are invalid or missing.