Fix downwards inference for async and generator functions.

Fix strong mode downwards inference for async and generator functions.

Downwards inference pushes the declared return type of a function down into the body in order to infer types for the returned or yielded values.  The asynchronous and generator cases were not being fully handled correctly.

This CL changes the return context stack kept by the inference context to contain the type expected to be returned or yielded (rather than the declared return type).  At each return/yield statement, this return/yield type is used to infer types for the returned/yielded expression.  At each yield* statement, the return/yield type is wrapped into the appropriate stream/iterable type.

This CL also adds future flattening when doing downwards inference on awaited expressions to avoid inferring nested future types.

BUG=
R=rnystrom@google.com

Committed: https://github.com/dart-lang/sdk/commit/a5addef3181bcf2576629d334aa6eb6a1322b425

[Leaf, 2015-12-29 22:31:56]

Description was changed from

==========
Fix downwards inference for async and generator functions.

BUG=
==========

to

==========
Fix strong mode downwards inference for async and generator functions.

Downwards inference pushes the declared return type of a function down into the
body in order to infer types for the returned or yielded values.  The
asynchronous and generator cases were not being fully handled correctly.

This CL changes the return context stack kept by the inference context to
contain the type expected to be returned or yielded (rather than the declared
return type).  At each return/yield statement, this return/yield type is used to
infer types for the returned/yielded expression.  At each yield* statement, the
return/yield type is wrapped into the appropriate stream/iterable type.

This CL also adds future flattening when doing downwards inference on awaited
expressions to avoid inferring nested future types.

BUG=
==========

[Leaf, 2015-12-29 22:31:56]

leafp@google.com changed reviewers:
+ rnystrom@google.com

[Bob Nystrom, 2015-12-30 01:03:39]

lgtm

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
File pkg/analyzer/lib/src/generated/resolver.dart (right):

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:5435: (_returnStack.isNotEmpty) ?
_returnStack.last : null;
Nit: the parentheses aren't needed here.

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:9401: DartType declaredType,
isGenerator, isAsynchronous) {
Type annotate isGenerator and isAsynchronous?

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:9407: if (declaredType is
InterfaceType) {
You could avoid a little indentation by flipping this:

if (declaredType is! InterfaceType) return null;

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:9409: InterfaceType wrapperD =
isAsynchronous
What does "D" mean here? "dynamic"? How about "rawType"?

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:9413: List<DartType> targs =
If "targs" isn't used much elsewhere, I'd use "typeArgs" to be a bit more
readable.

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/test/gener...
File pkg/analyzer/test/generated/resolver_test.dart (right):

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/test/gener...
pkg/analyzer/test/generated/resolver_test.dart:11887: // This should be int when
we handle the implicit Future<T> | T union
File a tracking bug and link to it here?

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/test/gener...
pkg/analyzer/test/generated/resolver_test.dart:11943: Asserter<InterfaceType>
assertFutureOfInt = isFutureOf([_isInt]);
You could hoist these variables up to the top level and share them between the
tests.

[Leaf, 2015-12-30 18:28:07]

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
File pkg/analyzer/lib/src/generated/resolver.dart (right):

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:5435: (_returnStack.isNotEmpty) ?
_returnStack.last : null;
On 2015/12/30 01:03:39, Bob Nystrom wrote:
> Nit: the parentheses aren't needed here.

Done.

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:9401: DartType declaredType,
isGenerator, isAsynchronous) {
On 2015/12/30 01:03:39, Bob Nystrom wrote:
> Type annotate isGenerator and isAsynchronous?

Done.

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:9407: if (declaredType is
InterfaceType) {
On 2015/12/30 01:03:39, Bob Nystrom wrote:
> You could avoid a little indentation by flipping this:
> 
> if (declaredType is! InterfaceType) return null;

Done.

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:9409: InterfaceType wrapperD =
isAsynchronous
On 2015/12/30 01:03:39, Bob Nystrom wrote:
> What does "D" mean here? "dynamic"? How about "rawType"?

Done.

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/lib/src/ge...
pkg/analyzer/lib/src/generated/resolver.dart:9413: List<DartType> targs =
On 2015/12/30 01:03:39, Bob Nystrom wrote:
> If "targs" isn't used much elsewhere, I'd use "typeArgs" to be a bit more
> readable.

Done.

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/test/gener...
File pkg/analyzer/test/generated/resolver_test.dart (right):

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/test/gener...
pkg/analyzer/test/generated/resolver_test.dart:11887: // This should be int when
we handle the implicit Future<T> | T union
On 2015/12/30 01:03:39, Bob Nystrom wrote:
> File a tracking bug and link to it here?

https://github.com/dart-lang/sdk/issues/25322

https://codereview.chromium.org/1555603002/diff/40001/pkg/analyzer/test/gener...
pkg/analyzer/test/generated/resolver_test.dart:11943: Asserter<InterfaceType>
assertFutureOfInt = isFutureOf([_isInt]);
On 2015/12/30 01:03:39, Bob Nystrom wrote:
> You could hoist these variables up to the top level and share them between the
> tests.

Done.

[Leaf, 2015-12-30 18:35:37]

Description was changed from

==========
Fix strong mode downwards inference for async and generator functions.

Downwards inference pushes the declared return type of a function down into the
body in order to infer types for the returned or yielded values.  The
asynchronous and generator cases were not being fully handled correctly.

This CL changes the return context stack kept by the inference context to
contain the type expected to be returned or yielded (rather than the declared
return type).  At each return/yield statement, this return/yield type is used to
infer types for the returned/yielded expression.  At each yield* statement, the
return/yield type is wrapped into the appropriate stream/iterable type.

This CL also adds future flattening when doing downwards inference on awaited
expressions to avoid inferring nested future types.

BUG=
==========

to

==========
Fix strong mode downwards inference for async and generator functions.

Downwards inference pushes the declared return type of a function down into the
body in order to infer types for the returned or yielded values.  The
asynchronous and generator cases were not being fully handled correctly.

This CL changes the return context stack kept by the inference context to
contain the type expected to be returned or yielded (rather than the declared
return type).  At each return/yield statement, this return/yield type is used to
infer types for the returned/yielded expression.  At each yield* statement, the
return/yield type is wrapped into the appropriate stream/iterable type.

This CL also adds future flattening when doing downwards inference on awaited
expressions to avoid inferring nested future types.

BUG=
R=rnystrom@google.com

Committed:
https://github.com/dart-lang/sdk/commit/a5addef3181bcf2576629d334aa6eb6a1322b425
==========

[Leaf, 2015-12-30 18:35:38]

Committed patchset #4 (id:60001) manually as
a5addef3181bcf2576629d334aa6eb6a1322b425 (presubmit successful).