dart analyze mistake (Unnecessary cast) on int to num cast with var declaration about sdk

[eernstg]

You might just as well use an explicit type annotation in the variable declaration:

void main() {
  num varNum = 0;
  varNum = 2.3;
  print(varNum);
}

The cast had no other purpose than changing the inferred type of the variable, and that's just a more complex way to make it a num variable. You could just write it directly.

Also note that a type cast is dangerous in general: Nothing will prevent typos/thinkos from causing failures at run time:

void main() {
  var varNum = 'Hello, world!' as num; // No errors/warnings, but throws at run time.
  varNum = 2.3;
  print(varNum);
}

[siahlooei]

A similar mistake occurs in these below commands:

dart fix --apply
dart fix --dry-run
dart fix --apply --code=unnecessary_cast

, and it is fixed incorrectly. In the fix made, this cast is removed wrongly and caused compile error.

[bwilkerson]

A similar mistake occurs in these below commands ...

That's because dart fix uses the diagnostics produced by dart analyze to determine what needs to be fixed. It assumes that those diagnostics are correct, which is not true in this case.