allow double quotes for continuation, even if quote-type is ‘single’

[dato]

This is similar to #663, but not quite the same.

Consider:

$ cat cont.yaml
a: "b\
    c"

Comparing yamllint 1.35 to 1.37, I see an improvement, since quotes are allowed now:

$ yamllint --version && yamllint -d 'rules: {quoted-strings: {required: only-when-needed, quote-type: double}}' cont.yaml
yamllint 1.35.1
./cont.yaml
  1:4       error    string value is redundantly quoted with double quotes  (quoted-strings)

$ pip install yamllint==1.37.1
$ yamllint --version && yamllint -d 'rules: {quoted-strings: {required: only-when-needed, quote-type: double}}' cont.yaml
yamllint 1.37.1

However, if I change to using quote-type: single, yamllint complains that I’m using double quotes instead of single quotes:

$ yamllint --version && yamllint -d 'rules: {quoted-strings: {required: only-when-needed, quote-type: single}}' cont.yaml              
yamllint 1.37.1
cont.yaml
  1:4       error    string value is not quoted with single quotes  (quoted-strings)

(To the best of my knowledge, backslash-as-continuation-char only works with double quotes, not single quotes. The sample cont.yaml would typically be used for much longer strings, of course.)

Thanks for considering!

[adrienverge]

Hello @dato,

Thanks for this report.

I agree that double quotes " + backslashes \ at end of lines are the only way to break a long string if it doesn't contain spaces. (Note: I sometimes re-read this helpful post to remember multi-line strings features.)

E.g. we couldn't achieve the same without ":

# "bc"
- "b\
   c"

# "b\\ c"
- 'b\
   c'

# "b c"
- >-
    b
    c

# "b\nc"
- |-
    b
    c

So I agree that we could modify yamllint to avoid reporting such cases.

However, yamllint rules quoted-strings and line-length don't communicate, which means quoted-strings doesn't know whether the line needs to be broken in 2 lines or not.
In other words, while it's obvious that the following use case is valid and shouldn't be reported:

- "https://example.com/a/very/very/very/…/…/…/…/…/…/…/…/…/…/…/…/very/very\
   /long/URL"

… the following one could be written in only one line and use single quotes ('bc'), so we could argue it should be reported by rule quoted-strings:

- "b\
   c"

If we change yamllint to fix the problem you described, the side effect would be to stop reporting such "short" strings that don't need double quotes because they could fit in one line.

What do you think? Would that be OK for all users?

[NightTsarina]

[Note: I am a colleague of @dato, so I am also affected by this]

@adrienverge While I agree that the second case you describe should probably be written in a single line, I'd say that if the user is breaking lines in this manner they probably have a reason for it and should not be reported?

[dato]

Hello @adrienverge! Thanks for your detailed response.

I also agree with what @NightTsarina said above: it seems far more likely to use continuation lines to break long strings, so it makes sense to me to favor auto-detection there, at the cost of the shorter strings case.

Thanks again!

[adrienverge]

A better fix for this problem would probably be a new option rules: quoted-strings: {allow-double-quotes-for-escaping: true}}, like proposed in #777 (comment). @dato @NightTsarina what do you think?

[dato]

Sounds good to me, thanks!

[NightTsarina]

@adrienverge That'd be great, thanks!