Support checked mode for return type.

Support checked mode for return type.
Committed: https://code.google.com/p/dart/source/detail?r=14518

[ngeoffray, 2012-11-02 12:47:55]

@Stephen: Please let me know if there are additional scripts I should update.

[kasperl, 2012-11-02 12:53:05]

LGTM. Can you cook up a reasonably simple test case?

https://codereview.chromium.org/11361060/diff/1/lib/compiler/implementation/l...
File lib/compiler/implementation/lib/js_helper.dart (right):

https://codereview.chromium.org/11361060/diff/1/lib/compiler/implementation/l...
lib/compiler/implementation/lib/js_helper.dart:1378: voidTypeCheck(value) =>
identical(value, null);
This may be what the spec says today, but I still think that's it's broken that
we allow code like this:

   void foo() => null;

That was never the intent.

https://codereview.chromium.org/11361060/diff/1/lib/compiler/implementation/s...
File lib/compiler/implementation/ssa/builder.dart (right):

https://codereview.chromium.org/11361060/diff/1/lib/compiler/implementation/s...
lib/compiler/implementation/ssa/builder.dart:928: DartType returnType;
Initialize to null for consistency or remove initialization for returnElement?

[sra1, 2012-11-02 20:13:51]

lgtm

https://codereview.chromium.org/11361060/diff/1/lib/compiler/implementation/l...
File lib/compiler/implementation/lib/js_helper.dart (right):

https://codereview.chromium.org/11361060/diff/1/lib/compiler/implementation/l...
lib/compiler/implementation/lib/js_helper.dart:1378: voidTypeCheck(value) =>
identical(value, null);
On 2012/11/02 12:53:05, kasperl wrote:
> This may be what the spec says today, but I still think that's it's broken
that
> we allow code like this:
> 
>    void foo() => null;
> 
> That was never the intent.

We *do* want to allow

   void foo() => bar();

This makes the delegate pattern look nice and uniform.
It is also nice to be able to write

   void foo() => throw UnimplementedError('No foo for you');

It is possible that

   void foo(a) => a + 1;

is correct, if perverse (operator+ declared as void).

What does the editor say?
If the editor does not already call this out, it could.  Any other literal will
give some kind of type warning, and any resolved invocation will warn if the
target is declared with a type other than dynamic.

I think the cure for trying to prevent your foo will be worse than the disease.

It follows from of bar returning null instead of some other marker value:

bar(){}

https://codereview.chromium.org/11361060/diff/5001/lib/compiler/implementatio...
File lib/compiler/implementation/lib/js_helper.dart (right):

https://codereview.chromium.org/11361060/diff/5001/lib/compiler/implementatio...
lib/compiler/implementation/lib/js_helper.dart:1379: if (identical(value, null))
return value;
value == null would be fine, since null is handled specially.

[ngeoffray, 2012-11-05 10:16:27]

Test added, and thanks Stephen for the review.

https://codereview.chromium.org/11361060/diff/5001/lib/compiler/implementatio...
File lib/compiler/implementation/lib/js_helper.dart (right):

https://codereview.chromium.org/11361060/diff/5001/lib/compiler/implementatio...
lib/compiler/implementation/lib/js_helper.dart:1379: if (identical(value, null))
return value;
On 2012/11/02 20:13:51, sra1 wrote:
> value == null would be fine, since null is handled specially.

Done.

[ngeoffray, 2012-11-05 10:17:05]

https://codereview.chromium.org/11361060/diff/1/lib/compiler/implementation/s...
File lib/compiler/implementation/ssa/builder.dart (right):

https://codereview.chromium.org/11361060/diff/1/lib/compiler/implementation/s...
lib/compiler/implementation/ssa/builder.dart:928: DartType returnType;
On 2012/11/02 12:53:05, kasperl wrote:
> Initialize to null for consistency or remove initialization for returnElement?

Done.