use_raw_strings  
            
            Use raw string to avoid escapes.
This rule is available as of Dart 2.8.1.
This rule has a quick fix available.
Details
A raw string can be used to avoid escaping only backslashes and dollars.
BAD:
var s = 'A string with only \\ and \$';
GOOD:
var s = r'A string with only \ and $';
Usage
To enable the use_raw_strings rule,
add use_raw_strings under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - use_raw_strings