[Yaml] Mappings with multiline keys are not supported while the documentation explicitly mentions it to work

[ampaze]

In a Yaml file used for translations, I want to use a multiline key using the folded style.

The Yaml Documentation first describes the folded style for multiline text under the section scalar and then goes on to say

In a mapping, a key can be any valid scalar.

But it just results in parsing error. Is this a bug or is the documentation wrong?
In any case I think especially in translation files this would be very good to have.

[stof]

Multiline keys are not supported by the Symfony parser (it does not support using booleans or floats as key either as these are not valid keys in PHP, and will be converted to strings)

[xabbuh]

Actually, I am not sure if that really is justified by the specs. @ampaze Can you give an example of such a valid YAML file that we currently do not support?

[ampaze]

Yes, something like this.

? |
    This is a key
    that has multiple lines
: and this is its value

[xabbuh]

I think this is an edge case which is not worth to add to the parser given the amount of code that would be needed for this feature.

@symfony/deciders What do you think?

[fabpot]

👎 for supporting this.

[javiereguiluz]

@xabbuh knows the Yaml component well. If he estimates that this feature could require a lot of code and given that this is not a commonly used feature, my vote is 👎 too.

Given that some Symfony Core members have downvoted this proposal, I'm closing this as "won't fix". thank you all for the discussion.

[ampaze]

That still leaves the documentation as misleading / wrong.

[javiereguiluz]

@ampaze you are right. I've created symfony/symfony-docs#6730 to improve Yaml docs. Thanks!

[towc]

This PR is one of the top google results for "yaml multiline key", and the top one that worked properly for me. To the people who ended up here and are getting discouraged by the comments, what @ampaze suggested does currently work!

🆗 🟢

? |
    This is a key
    that has multiple lines
: and this is its value

🆗 🟢