Analyzer: Mixed returns is not an error any more

[eernstg]

Consider the following library:

import 'dart:async';

Future<void> foo(bool b) async {
  if (b) return;
  return null;
}

As of 54011e5, dartanalyzer reports errors for this library:

ERROR|STATIC_WARNING|MIXED_RETURN_TYPES|/usr/local/google/home/eernst/lang/dart/scratch/201911/n045.dart|4|10|6|Functions can't include return statements both with and without values.
ERROR|STATIC_WARNING|MIXED_RETURN_TYPES|/usr/local/google/home/eernst/lang/dart/scratch/201911/n045.dart|5|3|6|Functions can't include return statements both with and without values.

The language specification used to have a rule saying that it is a compile-time error to have both return; and return e; in the same function, but this is no longer the case. The change occurred in SDK commit 9388cb3, and it was a consequence of integrating the feature specification invalid-returns.md into the specification. So the analyzer should stop checking and reporting mixed_return_types. The current spec text is here.

[bwilkerson]

Fixed by https://dart-review.googlesource.com/c/sdk/+/125927.

@eernstg The test co19_2/Language/Statements/Return/many_return_statements_t01 appears to be based on the old spec. Could you please double check and follow up with the co19 team if necessary?

[eernstg]

I created an issue in the co19 repo for that, thanks!