duplicate_ignore

The diagnostic '{0}' doesn't need to be ignored here because it's already being ignored.

The analyzer produces this diagnostic when a diagnostic name appears in an ignore comment, but the diagnostic is already being ignored, either because it's already included in the same ignore comment or because it appears in an ignore-in-file comment.

The following code produces this diagnostic because the diagnostic named unused_local_variable is already being ignored for the whole file so it doesn't need to be ignored on a specific line:

// ignore_for_file: unused_local_variable
void f() {
  // ignore: unused_local_variable
  var x = 0;
}

The following code produces this diagnostic because the diagnostic named unused_local_variable is being ignored twice on the same line:

void f() {
  // ignore: unused_local_variable, unused_local_variable
  var x = 0;
}

Remove the ignore comment, or remove the unnecessary diagnostic name if the ignore comment is ignoring more than one diagnostic:

// ignore_for_file: unused_local_variable
void f() {
  var x = 0;
}