yq -i does not work on empty files with comments

[Yann-J]

Describe the bug

yq -i seems to return an empty file when there are no values in the original file, even losing any original comments.

Version of yq: 4.9.6
Operating system: mac
Installed via: homebrew

Input Yaml

test.yaml:

# comment

Command
The command you ran:

yq eval '.key = "value"' test.yaml -i

Actual behavior

File is empty

Expected behavior

# comment
key: value

Additional context

It works when an empty object is specified in JSON format:

$ echo "{}" > test.yaml
$ yq eval '.key = "value"' test.yaml -i
$ cat test.yaml
{key: value}

[mikefarah]

Yeah that's a known issue - though I hadn't considered empty yaml docs with comments. That is annoying.

[mikefarah]

Unfortunately there's not much I can do in yq to solve this - the underlying go-yaml parser returns io.EOF when reading a yaml file with no yaml contents (even if that file has valid yaml comments)

[mikefarah]

as a workaround, you could put in an empty object {} like you had along with the comments

# interesting comment
{}

[Yann-J]

OK understood...

I don't think that's a huge issue of course, but just to be clear my issue is not about the comments, but rather that yq -i will essentially be a noop on an empty file. Comments or not, any new value you're trying to insert will not be present in the output. The use case I provided in example will also fail on an empty file without comments:

touch test.yaml
yq eval '.key = "value"' test.yaml -i
cat test.yaml

The (minor) problem I have with starting with an {} empty object is that:

• We need to know about this workaround :)
• It will cause the output file to use the compact JSON format (in my script I have a final step to reformat it)

[mikefarah]

Good call, I've added it to 'Known Issues' - I'm going to have another look when I get more time and see if I can fix it so it just works.

[mikefarah]

I've made some changes in yq in 4.11.0 to workaround go-yaml and to process empty files with comments as you'd expect, let me know how it works for you :)

[Yann-J]

Working fine for me!
Thanks!