Netlify-cms: Validation Regex does not parse for all valid patterns

[dardub]

- Do you want to request a feature or report a bug?

Bug

- What is the current behavior?

Using a regular expression as outlined in documentation for pattern matching validation causes config.yml parsing to fail when special characters are used.

The documentation shows a very simple case without any special characters.

- If the current behavior is a bug, please provide the steps to reproduce.

Add a field to config.yml with a regex pattern that contains special characters (w, b, etc).

example

      - {label: URL Path, name: path, widget: string, pattern: ["\/news\/\S+", "Expects the form /news/your-path"]}

Returns the following error:

The config.yml file could not be loaded or failed to parse properly.
Error message: YAMLException: unknown escape sequence at line 23, column 29: pattern: ["\/news\/\S+", "Expects the form /news/you ... ^

To elaborate, it's currently not consistent with how to handle regex options:

This parses:
\/news\/\S+

This does not:
"\/news\/\S+"

This parses:
".{10,}"

This does not:
.{10,}

- What is the expected behavior?

Parsing of config.yml should not fail for any valid regex pattern.

JS-Yaml includes a type for javascript regex, but I'm not sure if it's implemented for this project.
https://github.com/nodeca/js-yaml#supported-yaml-types

- Please mention your CMS, node.js, and operating system version.

Netlify CMS version 0.4.6

[Benaiah]

This doesn't look to me like a problem with the CMS code - it looks like you're running into issues where your regex syntax is not being escaped correctly or is colliding with YAML syntax. First, when you put a \ in a string in YAML, you need to escape it or YAML will try to interpret it as a _string_ escape, not an escape in the regex you're trying to make. Does "\\/news\\/\\S+" or '\/news\/\S+' (YAML ignores backslash escapes in single-quote strings) parse correctly? If so, that's likely what you're running into.

As for the second example,{ and } have special meaning in YAML, so those need to be stored as a delimited string, not an implicit one. Again, the single-quote version ('.{10,}') is probably the best option.

Please let me know if these don't work.

[dardub]

Yes, using the "\\/news\\/\\S+" parses correctly.

Since escapes are ignored in single quotes, maybe it would be a good idea to update the example in the docs to use single quotes?

[Benaiah]

@dardub that's a great idea; thanks for the PR!

[NickStees]

This tripped me up even with the updated documentation, basically just use single quotes around complex regex patterns you get from regexr.com