implement null aware ops, fixes #249

implement null aware ops, fixes #249

this also implements multitest support, which fixes #280

Fixes some other preexisting bugs:
* MetaLets did not simplify themselves correctly in some nested cases
* Library prefixed identifiers did not work as lvalues in opassign
* dsetindex/dput/[]= methods did not return a value
* checker did not correctly handle invalid constructor field initializers
* cascades did not correctly work with method invocations(?)
* postfix ++/-- did not correctly generate lvalues in some cases

The good news: because this reuses on our existing lvalue/metalet helpers, it managed to flush out a lot of bugs in other features that use them.

R=vsm@google.com

Committed: https://github.com/dart-lang/dev_compiler/commit/f46ecdc839d040f5828e3012792d66fa6121ba06

[Jennifer Messerly, 2015-08-25 20:46:46]

jmesserly@google.com changed reviewers:
+ vsm@google.com

[vsm, 2015-08-25 21:47:26]

lgtm!

https://codereview.chromium.org/1316723003/diff/20001/lib/src/checker/checker...
File lib/src/checker/checker.dart (left):

https://codereview.chromium.org/1316723003/diff/20001/lib/src/checker/checker...
lib/src/checker/checker.dart:378: DartType staticType =
rules.elementType(field.staticElement);
FWIW, I recently changed rules.elementType to return dynamicType if the arg is
null.  (It was breaking some tests under sdk - forget which one.)

https://codereview.chromium.org/1316723003/diff/20001/lib/src/codegen/js_code...
File lib/src/codegen/js_codegen.dart (right):

https://codereview.chromium.org/1316723003/diff/20001/lib/src/codegen/js_code...
lib/src/codegen/js_codegen.dart:2526: // code expansion: each `?.` becomes `, _
=> _`, plus one helper call.
Very nice!

https://codereview.chromium.org/1316723003/diff/20001/test/codegen_test.dart
File test/codegen_test.dart (right):

https://codereview.chromium.org/1316723003/diff/20001/test/codegen_test.dart#...
test/codegen_test.dart:138: //!!!if (testPathsToSkip.contains(filePath))
continue;
Delete or TODO

[Jennifer Messerly, 2015-08-25 22:13:11]

Thanks! Fixed & Rebased

https://codereview.chromium.org/1316723003/diff/20001/lib/src/checker/checker...
File lib/src/checker/checker.dart (left):

https://codereview.chromium.org/1316723003/diff/20001/lib/src/checker/checker...
lib/src/checker/checker.dart:378: DartType staticType =
rules.elementType(field.staticElement);
On 2015/08/25 21:47:26, vsm wrote:
> FWIW, I recently changed rules.elementType to return dynamicType if the arg is
> null.  (It was breaking some tests under sdk - forget which one.)

Nice! reverted this

https://codereview.chromium.org/1316723003/diff/20001/test/codegen_test.dart
File test/codegen_test.dart (right):

https://codereview.chromium.org/1316723003/diff/20001/test/codegen_test.dart#...
test/codegen_test.dart:138: //!!!if (testPathsToSkip.contains(filePath))
continue;
On 2015/08/25 21:47:26, vsm wrote:
> Delete or TODO

Done.

[Jennifer Messerly, 2015-08-25 22:13:22]

Committed patchset #3 (id:40001) manually as
f46ecdc839d040f5828e3012792d66fa6121ba06 (presubmit successful).