Empty string should be quote

[antoyo]

Hello.
I think I found an issue with my pull request #39:
I think that the empty string should be quoted, because otherwise, it will be parsed as a Unit.
Thanks.

[chyh1990]

Will 2d6a83d be enough?

[antoyo]

I'll make some tests to check if trim() is needed.
Thanks.

[antoyo]

I made some tests and quotes are also needed for a string with only spaces.
So I don't know exactly how it is parsed, but perhaps quotes are also needed when there are spaces at the start/end of a string.
In any case, your commit is not sufficient:
the case of a string like " " will be emitted without quotes and the parser will try to parse it as a Unit.

[chyh1990]

I found a reference implementation here: https://github.com/adamkiss/LibYAML/blob/master/yaml/Escaper.php

We are also missing the single quoted part.

I think adding TAB and SPACE to the require quoted character is OK.

[antoyo]

I don't think adding SPACE to the required character is what we want.
For instance, if we have the string "my string", it can be emitted without quotes in YAML.
I don't know the precise rules about the spaces however. Do we need quotes when the string starts/ends with space?

[chyh1990]

Yeah, I get your point. But I think quoting something like "my string" is not a bad idea (the php version do this) and more robust. I'm not sure whether just quoting string starts/ends with space will introduce some corner cases?

[dtolnay]

I would strongly prefer not to quote strings unless necessary, even if it means we need to iterate on the heuristic a few times to get it right. Quoting for leading/trailing whitespace seems like a good start.

[chyh1990]

It looks good e52b058 ?

[dtolnay]

e52b058: No need to check for starts_with or ends_with '\t' because any string containing '\t' anywhere will be quoted. Just check for ' '.

[antoyo]

A style comment:
no need to use return in the last statement: just omit the semi-colon.

[chyh1990]

Closed by #46