invocation_of_extension_without_call

The extension '{0}' doesn't define a 'call' method so the override can't be used in an invocation.

The analyzer produces this diagnostic when an extension override is used to invoke a function but the extension doesn't declare a call method.

The following code produces this diagnostic because the extension E doesn't define a call method:

extension E on String {}
​
void f() {
  E('')();
}

If the extension is intended to define a call method, then declare it:

extension E on String {
  int call() => 0;
}
​
void f() {
  E('')();
}

If the extended type defines a call method, then remove the extension override.

If the call method isn't defined, then rewrite the code so that it doesn't invoke the call method.