Add equals sign to list of unsafe values for plain styling

[murtazajafferji]

According to this post and my use case, the strings with equals sign needs to be quoted:
https://stackoverflow.com/questions/19109912/do-i-need-quotes-for-strings-in-yaml
Use quotes if your value includes special characters, (e.g. :, {, }, [, ], ,, &, *, #, ?, |, -, <, >, =, !, %, @, ).

[puzrin]

Do you have a concrete sample with broken result? All such PRs should go with tests.

[puzrin]

This PR will be declined if no example of which error does it fix.

[murtazajafferji]

If equals signs are not quoted, yaml will not be read correctly by the ruamel.yaml library when safe load is on. However, it will be loaded correctly when equals signs are quoted.

>>> import sys
>>> from  ruamel.yaml import YAML
>>> yaml = YAML(typ='safe')
>>> yaml.dump(yaml.load("="), sys.stdout)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/ruamel/yaml/main.py", line 341, in load
    return constructor.get_single_data()
  File "/usr/local/lib/python2.7/dist-packages/ruamel/yaml/constructor.py", line 113, in get_single_data
    return self.construct_document(node)
  File "/usr/local/lib/python2.7/dist-packages/ruamel/yaml/constructor.py", line 118, in construct_document
    data = self.construct_object(node)
  File "/usr/local/lib/python2.7/dist-packages/ruamel/yaml/constructor.py", line 146, in construct_object
    data = self.construct_non_recursive_object(node)
  File "/usr/local/lib/python2.7/dist-packages/ruamel/yaml/constructor.py", line 181, in construct_non_recursive_object
    data = constructor(self, node)
  File "/usr/local/lib/python2.7/dist-packages/ruamel/yaml/constructor.py", line 743, in construct_undefined
    node.start_mark,
ruamel.yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:value'
  in "<byte string>", line 1, column 1
>>> yaml.dump(yaml.load("'='"), sys.stdout)
'='

[puzrin]

That example is invalid. First, this must be executable code, not something, from your browser console. Second, this code works as expected:

node -e 'console.log(require("./").load("="))'
=

in js-yaml folder.

[puzrin]

If problem is with ruamel.yaml library, fix should be sent there.

[murtazajafferji]

The example above and the one below is showing that the output of a safeDump from js-yaml will not be interpreted as valid yaml by the most popular yaml parsers for Python. This is for PyYAML:

>>> import yaml
>>> yaml.dump(yaml.load("="))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/yaml/__init__.py", line 114, in load
    return loader.get_single_data()
  File "/usr/local/lib/python2.7/dist-packages/yaml/constructor.py", line 45, in get_single_data
    return self.construct_document(node)
  File "/usr/local/lib/python2.7/dist-packages/yaml/constructor.py", line 49, in construct_document
    data = self.construct_object(node)
  File "/usr/local/lib/python2.7/dist-packages/yaml/constructor.py", line 94, in construct_object
    data = constructor(self, node)
  File "/usr/local/lib/python2.7/dist-packages/yaml/constructor.py", line 420, in construct_undefined
    node.start_mark)
yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:value'
  in "<string>", line 1, column 1:
    =
    ^
>>> yaml.dump(yaml.load("'='"))
"'='\n"

[puzrin]

Ok, since pyyaml is reference parser, supported by spec authors, compatibility with it may make sense.

See my code comments.

[murtazajafferji]

@puzrin I have addressed all the comments. Do you have any other suggestions or can we complete this PR?

[puzrin]

Hm, i don't know why my last note is invisible. Could you return those comments and locations back?

• https://github.com/nodeca/js-yaml/pull/519/files#diff-fff1647e8e19b34e8c0a153680cd8723R224
• https://github.com/nodeca/js-yaml/pull/519/files#diff-fff1647e8e19b34e8c0a153680cd8723R233

The only change should be added = to first one.

[murtazajafferji]

@puzrin Done! Btw, your comment was collapsed by default because the comment thread was marked as resolved. If you wanted it to be shown, you could press "Unresolve conversation."