Support serialization of strings to literal and folded scalars

[spenserblack]

Apologies if this feature already exists, but I didn't see it in the documentation.

Info

the literal scalar | can be used in YAML to break up a string to multiple lines, treating the line breaks literally.

the folded scalar > also can be used to break up a string into multiple lines, but it treats line breaks as spaces.

Request

When serializing a value containing a multiline string, it seems to always serialize that string to a single line with line breaks represented as \n (reproduction)
I think that there should be some way to specify how you want your string to be serialized (single line, folded scalar, literal scalar).

Scalar Examples

Literal: |

Input

key: |
  line 1
  line 2

Output (JSON)

{ "key": "line 1\nline 2\n" }

Folded: >

Input

key: >
  word1
  word2

Output (JSON)

{ "key": "word1 word2" }

[emmanueltouzery]

I'm also interested in this feature, and several others, but this would have to be implemented by the underlying library used by serde-yaml.

Currently, that is yaml-rust, which is not really maintained. There are three unanswered pull requests for yaml-rust to add the feature:

• Add support for multiline string output chyh1990/yaml-rust#137
• Emit multi-line string values as block scalars chyh1990/yaml-rust#136
• Add flag to emit multiline strings chyh1990/yaml-rust#132

There isn't much that can be done from serde-yaml I'm afraid.

[spenserblack]

I see... I was worried that that was the case 😞

Hopefully when those PRs are addressed or a fork is created, this issue can be addressed.

Thanks for your answer!

[jhoobergs]

@dtolnay Is this something that you would want in this library? Or should I use my own fork(s) if I want this? The main problem does lay at https://github.com/chyh1990/yaml-rust I guess?

[dtolnay]

To the extent that this issue is asking to expose choice over the string representation at the granularity of individual fields, that is not something I would accept in this library.

If it is asking just for prettier defaults, such as serializing to literal scalar if a string value contains newlines, I am open to that but this crate is not where that code lives.

[jhoobergs]

@dtolnay yaml-rust doesn't seem so active. Where do you stand on using an on-crates-published-fork (like https://github.com/davvid/yaml-rust) which implements these prettier defaults? (it basically equals yaml-rust but with chyh1990/yaml-rust#137 merged and working CI)

[dtolnay]

I wouldn't do that. It would be good to drop the dependency on yaml-rust entirely though, in favor of the backend style described in dtolnay/request-for-implementation#9.

[spenserblack]

If it is asking just for prettier defaults, such as serializing to literal scalar if a string value contains newlines

That is actually what I initially wanted, but was worried that it was too opinionated 😆

this crate is not where that code lives.

If/when possible, could this issue be transferred to the relevant repo?