camel_case_extensions

Name extensions using UpperCamelCase.

From Effective Dart:

DO name extensions using UpperCamelCase.

Extensions should capitalize the first letter of each word (including the first word), and use no separators.

GOOD:

extension MyFancyList<T> on List<T> {
  // ...
}
​
extension SmartIterable<T> on Iterable<T> {
  // ...
}

To enable the camel_case_extensions rule, add camel_case_extensions under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - camel_case_extensions

If you're instead using the YAML map syntax to configure linter rules, add camel_case_extensions: true under linter > rules:

linter:
  rules:
    camel_case_extensions: true