One test added. and compared against libYAML operation. Sorry about the mess in commits.

The list of commits in your branch seems to be a mess.

@crayner can you please rebase+squash on branch 3.4? That should clean the git history.

HI @nicolas-grekas , I tried to do the rebase-squash as suggested. Result may now be worse. Let me know. Happy to close request and rebuild form scratch given < 10 lines of code.

@crayner It looks like you merged instead of rebasing (one great thing about rebasing is that it removes the merge commits, which prevent us from merging a pull request). You can find more information here: https://symfony.com/doc/current/contributing/code/pull_requests.html#rebase-your-pull-request

If you want to, I will happily do it for you.

Thanks @fabpot , I will have another go, as that is how one learns.

Tried again, with a lot of errors at the git rebase --continue as there were NO changes. Do not know what I was doing wrong.

but: tried PHPStorm script and it seemed to work? If it has not work as expected, please go ahead and rebase squash.

what if this kind of structure does not appear as top-level ?

Thanks @xabbuh

@stof This will still fail in the existing parser code. A different fix?

what if this kind of structure does not appear as top-level ?

In the past we decided not to support the JSON syntax in the YAML parser (see for example #18968). I would agree on a PR throwing a (more) meaningful exception when we detect such structures, but I am against supporting it only partially.

@crayner can you do the PR ?

Not sure I agree, therefore would like to see other opinions! What do you think @ylixir. This is not really a JSON fix, but a whitespace issue, IMHO.

I think four things:

1. yes, it is clearly a whitespace issue
2. This is a very basic example, not some weird edge case. Standards matter. If we aren't making a yaml parser maybe don't call it a yaml parser.
3. The fact that this continues to come up in multiple issues means it's a real problem. In my case it's machine generated yaml, so it's not like i can just tweak the syntax
4. If this thing isn't a yaml parser, then whatever this thing can and can't parse should be documented. If this bug isn't going to be fixed, then the pr should be a documentation update instead of a bug fix.

I have spent some time on parsing the inline notation when it spans mutliple lines (see #33658). That PR would land as a new feature in Symfony 4.4. I suggest to close here in favour of the new PR.

Closing in favor of #33658 as suggested by @xabbuh