Add a "quote-percent" option to the "quoted-strings" rule

[leofeyer]

I really like the new required: only-when-needed option that has been added to the quoted-strings rule in version 1.21.0. Thank you for that.

When linting Symfony configuration files, there is a kind of false-positive though: Symfony requires placeholders such as %kernel.project_dir% or %env(DATABASE_URL)% to be quoted. Now even though this deviates from the YAML standard, it would be nice if yamllint would support this somehow.

This PR outlines a possible solution by adding a quote-percent option to the quoted-strings rule. Tests are still missing, because I wanted to discuss the implementation first. WDYT?

[coveralls]

Coverage decreased (-0.09%) to 97.786% when pulling b41de1d on leofeyer:patch-1 into 542ae75 on adrienverge:master.

[adrienverge]

Hello @leofeyer, thanks for your proposal.

I'm against features specific to one program (including Symfony), and I think quote-percent usage is too narrow to be a good addition to yamllint.

However, we could imagine something more general, like a new option needed-extra-regex (or any better wording)?

Then for Symfony you could use:

quoted-strings:
  required: only-when-needed
  needed-extra-regex: ^%.*%$

If you like the idea, feel free to open a new PR!

[leofeyer]

What about making START_TOKENS configurable?

CONF = {'quote-type': ('any', 'single', 'double'),
        'required': (True, False, 'only-when-needed'),
        'start-tokens': set()}
DEFAULT = {'quote-type': 'any',
           'required': True,
           'start-tokens': {'#', '*', '!', '?', '@', '`', '&', ',', '-', '{', '}', '[', ']', ':'}}

I am not familiar with Python, so no idea if that is the correct syntax.

[adrienverge]

It wouldn't be a general solution. What if I want to quote strings that look like phone numbers, for example? A regex would be more configurable.

[leofeyer]

I agree. 👍 As I said, I am not familiar with Python, but I will try my best to create a PR that implements the needed-extra-regex option.

[adrienverge]

Cool!

I recommend starting by writing tests in tests/rules/test_quoted_strings.py. Write exactly what you expect from the rule (including corner cases), then it will be easy to check your feature while you write it (using python3 -m unittest tests.rules.test_quoted_strings).

[leofeyer]

See #246. 🎉