Migration tool should call out inserted casts of function literals as questionable.

[stereotype441]

As of https://dart-review.googlesource.com/c/sdk/+/134504, there are certain situations where the migration tool may insert a type cast that is guaranteed to fail. For example:

void f(int/*!*/ Function(int) callback) {
  callback(null);
}
int g(int x) => x;
void test() {
  f(g);
}

gets migrated to:

void f(int/*!*/ Function(int?) callback) {
  callback(null);
}
int? g(int? x) => x;
void test() {
  f(g as int Function(int?)); // BAD
}

In this sort of situation, user intervention is required to figure out how the code should be migrated. The tool should either highlight the cast as questionable.

Alternatively, we could either:

• change the migration tool so that it doesn't generate the questionable cast, and the user is alerted to the problem by the fact that the migrated code has a compile-time error, OR
• change the migration tool so that it inserts a function literal with a null check, i.e. f((x) => g(x)!); in this example.

[stereotype441]

As of 1c7fe71, the null safety migration tool has been removed from active development and retired. No further work on the tool is planned.

If you still need help, or you believe this issue has been closed in error, please feel free to reopen.