Add VoidElement and VoidType to make sure that there is a canonical void type.

This fixes a wrong warning about void functions in which not all paths leads to return or throw statement.

TEST=added to type_checker_test
R=ngeoffray@google.com

Committed: https://code.google.com/p/dart/source/detail?r=7449

[ngeoffray, 2012-05-09 08:54:40]

LGTM

http://codereview.chromium.org/10387033/diff/1/frog/tests/leg/type_checker_te...
File frog/tests/leg/type_checker_test.dart (right):

http://codereview.chromium.org/10387033/diff/1/frog/tests/leg/type_checker_te...
frog/tests/leg/type_checker_test.dart:241: analyzeTopLevel("var foo() { if
(true) { return; } }");
var -> Dynamic. var at this position is not allowed AFAIK.

http://codereview.chromium.org/10387033/diff/1/lib/compiler/implementation/el...
File lib/compiler/implementation/elements/elements.dart (right):

http://codereview.chromium.org/10387033/diff/1/lib/compiler/implementation/el...
lib/compiler/implementation/elements/elements.dart:671: : super(Types.VOID,
ElementKind.VOID, enclosing);
Please add return types to the methods below.

http://codereview.chromium.org/10387033/diff/1/lib/compiler/implementation/ty...
File lib/compiler/implementation/typechecker.dart (right):

http://codereview.chromium.org/10387033/diff/1/lib/compiler/implementation/ty...
lib/compiler/implementation/typechecker.dart:597:
!types.isAssignable(expressionType, types.voidType)) {
Why this change? I think we followed Java's style conventions with the '&&' on
the new line.

[karlklose, 2012-05-09 10:32:41]

Thanks, Nicolas.

http://codereview.chromium.org/10387033/diff/1/frog/tests/leg/type_checker_te...
File frog/tests/leg/type_checker_test.dart (right):

http://codereview.chromium.org/10387033/diff/1/frog/tests/leg/type_checker_te...
frog/tests/leg/type_checker_test.dart:241: analyzeTopLevel("var foo() { if
(true) { return; } }");
Done, removed type.

http://codereview.chromium.org/10387033/diff/1/lib/compiler/implementation/el...
File lib/compiler/implementation/elements/elements.dart (right):

http://codereview.chromium.org/10387033/diff/1/lib/compiler/implementation/el...
lib/compiler/implementation/elements/elements.dart:671: : super(Types.VOID,
ElementKind.VOID, enclosing);
On 2012/05/09 08:54:40, ngeoffray wrote:
> Please add return types to the methods below.

Done.

http://codereview.chromium.org/10387033/diff/1/lib/compiler/implementation/ty...
File lib/compiler/implementation/typechecker.dart (right):

http://codereview.chromium.org/10387033/diff/1/lib/compiler/implementation/ty...
lib/compiler/implementation/typechecker.dart:597:
!types.isAssignable(expressionType, types.voidType)) {
We certainly do not follow it everywhere in our code. But I am fine with either.
Reverted.