Tests check that allowed use of void is an error

[eernstg]

With dart-lang/sdk#30176, the treatment of void in Dart programs is updated such that several usages that used to be compile-time errors/warnings are now allowed. In particular, void can be an actual type argument and it can be the type annotation of a variable/parameter and the return type of a getter.

This calls for changes to the following co19 tests:

• Language/Types/Type_Void/syntax_t01: No longer an error.
• Language/Types/Type_Void/syntax_t02: No longer an error.
• Language/Types/Type_Void/syntax_t04: No longer an error.
• Language/Types/Type_Void/syntax_t09: The declaration void v is no longer an error, so the documentation should be updated, but print(v) is a compile-time error.
• Language/Classes/Getters/void_return_type_t01: No longer a static warning.

[sgrekhov]

Fixed in master and strong-mode branches

[eernstg]

Thanks! There are a couple of little things to think about here, though:

• The @assertion part and the @description part of these tests are now contradicting each other in some cases (e.g., in void_return_type_t01: 'It is a static warning..' vs. 'Check that no static warning is produced..'). We could change the description to say 'With generalized void, it is allowed..', which would indicate to readers how the extended language works, and also give a hint to readers who are unaware of the update.

• For syntax_t09.dart, it makes a subtle difference that print(v) is replaced by var x = v; print(x);. In Dart 1.x extended with generalized void, it is a compile-time error to evaluate v, hence var x = v; is a compile-time error, but print(x) is ok at compile-time because x has static type dynamic. However, in strong mode the type of x will be inferred, and with the static type void for x we will also have a static error at print(x). I'd suggest going back to print(v), and expecting that to be a compile-time error (1: that removes one little bump in the transition to strong-mode-only, and 2: the new form does not add anything of interest (Dart 1.x with generalized void: print(aDynamicValue) is tested elsewhere, strong mode: we just test twice that it is an error to use a void value)).

[sgrekhov]

Thank you! Fixed again according your notes in both branches