camel_case_extensions

Name extensions using UpperCamelCase.

This rule is available as of Dart 2.6.0.

Rule sets: core, recommended, flutter

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