Properly handle circular references among constants in the task model.

Properly handle circular references among constants in the task model.

Tasks may now override the getter "handlesDependencyCycles" to return
true to indicate that they can deal with circular dependencies.  Most
tasks will not have to do this, since outside of constant evaluation
circular dependencies among tasks should only be possible due to an
analyzer bug.

Any task that handles dependency cycles can detect that a cycle has
occurred by consulting AnalysisTask.dependencyCycle inside its
internalPerform() method.  The ComputeConstantValueTask uses this to
determine which constants are involved in the cycle.

This required modifying the TaskInputBuilder classes so that if the
current input can't be evaluated due to a circularity, they can
continue on to evaluate other inputs.  This allows the circularity to
be reported on the whole strongly connected component, rather than
just the firs cycle that was noticed (which would be
nondeterministic).

R=brianwilkerson@google.com, scheglov@google.com

Committed: https://github.com/dart-lang/sdk/commit/a9982b0e0247b79ef10e6bab9847377f4c794923

[Paul Berry, 2015-05-19 16:48:48]

paulberry@google.com changed reviewers:
+ brianwilkerson@google.com, scheglov@google.com

[Brian Wilkerson, 2015-05-19 19:25:17]

LGTM

[scheglov, 2015-05-19 19:25:42]

lgtm

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
File pkg/analyzer/test/src/task/dart_test.dart (right):

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/dart_test.dart:1465: }).variable;
You could use unit.element.topLevelVariables directly.

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
File pkg/analyzer/test/src/task/inputs_test.dart (right):

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/inputs_test.dart:206: expect(list.length, 1);
expect(list, hasLength(1));

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/inputs_test.dart:207: expect(list[0], value3);
or maybe even just this statement only:
expect(list, orderedEquals([value3]));

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/inputs_test.dart:400: expect(inputValue.length, 1);
expect(inputValue, hasLength(1));

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/inputs_test.dart:785: expect(inputs.length, 1);
hasLength(1)

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
File pkg/analyzer/test/src/task/test_support.dart (right):

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/test_support.dart:40: this.handlesDependencyCycles:
false})
Please keep these parameters sorted by name.

[Paul Berry, 2015-05-19 19:36:11]

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
File pkg/analyzer/test/src/task/dart_test.dart (right):

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/dart_test.dart:1465: }).variable;
On 2015/05/19 19:25:41, scheglov wrote:
> You could use unit.element.topLevelVariables directly.

Done.

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
File pkg/analyzer/test/src/task/inputs_test.dart (right):

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/inputs_test.dart:207: expect(list[0], value3);
On 2015/05/19 19:25:42, scheglov wrote:
> or maybe even just this statement only:
> expect(list, orderedEquals([value3]));

Done.

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/inputs_test.dart:400: expect(inputValue.length, 1);
On 2015/05/19 19:25:41, scheglov wrote:
> expect(inputValue, hasLength(1));

Done.

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/inputs_test.dart:785: expect(inputs.length, 1);
On 2015/05/19 19:25:41, scheglov wrote:
> hasLength(1)

Done.

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
File pkg/analyzer/test/src/task/test_support.dart (right):

https://codereview.chromium.org/1147853002/diff/1/pkg/analyzer/test/src/task/...
pkg/analyzer/test/src/task/test_support.dart:40: this.handlesDependencyCycles:
false})
On 2015/05/19 19:25:42, scheglov wrote:
> Please keep these parameters sorted by name.

Done.

[Paul Berry, 2015-05-19 19:43:33]

Committed patchset #1 (id:1) manually as
a9982b0e0247b79ef10e6bab9847377f4c794923 (presubmit successful).