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unnecessary-trailing-comma

added in: 1.2.0
style
⚙️🛠
Pro+
preset: recommended

Checks for unnecessary trailing commas for arguments, parameters, enum values and collections.

Removing those commas results in dart format producing code that fits on one line.

⚙️ Config​

Set max-width (default is 80) to configure a custom max line width.

Set multiline (default is false) to highlight an unnecessary comma for arguments that take more than one line and are last (example).

Set trailing-lists (default is false) to highlight an unnecessary comma for list, set or map literals that are the last argument of an invocation (example).

analysis_options.yaml
dart_code_metrics:
  rules:
    - unnecessary-trailing-comma:
        max-width: 80
        multiline: false
        trailing-lists: false

Example​

❌ Bad:

void function(
  String first,
  String second, // LINT: Avoid unnecessary trailing comma. Try removing it.
) {
  return;
}

✅ Good:

void function(String first, String second) {
  return;
}

Example with "multiline"​

Config
analysis_options.yaml
dart_code_metrics:
  rules:
    - unnecessary-trailing-comma:
        multiline: true

❌ Bad:

Invocation().thisOrAncestorMatching(
  (someObject) => someObject is List<int>
      ? someObject.length
      : int.tryParse(someObject.toString()), // LINT: Avoid unnecessary trailing comma. Try removing it.
);

✅ Good:

Invocation().thisOrAncestorMatching((someObject) => someObject is List<int>
        ? someObject.length
        : int.tryParse(someObject.toString()));

Example with "trailing-lists"​

Config
analysis_options.yaml
dart_code_metrics:
  rules:
    - unnecessary-trailing-comma:
        trailing-lists: true

❌ Bad:

withNamedList(
  name: '',
  values: [
    true,
    false,
  ], // LINT: Avoid unnecessary trailing comma. Try removing it.
);

✅ Good:

withNamedList( name: '', values: [
  true,
  false,
]);