duplicate_rest_element_in_pattern

At most one rest element is allowed in a list or map pattern.

The analyzer produces this diagnostic when there's more than one rest pattern in either a list or map pattern. A rest pattern will capture any values unmatched by other subpatterns, making subsequent rest patterns unnecessary because there's nothing left to capture.

The following code produces this diagnostic because there are two rest patterns in the list pattern:

void f(List<int> x) {
  if (x case [0, ..., ...]) {}
}

Remove all but one of the rest patterns:

void f(List<int> x) {
  if (x case [0, ...]) {}
}