Properly type infer for-in loops when the iterator type is a type parameter.

Properly type infer for-in loops when the iterator type is a type parameter.

Also, fix a minor bug in variable declaration inference that was
preventing a local variable without an initializer from having its
type properly "inferred" as `dynamic`.

R=sigmund@google.com

Committed: https://github.com/dart-lang/sdk/commit/348b42c98bc23ec5332fd2ca62302e76192889ec

[Paul Berry, 2017-06-21 20:35:04]

paulberry@google.com changed reviewers:
+ sigmund@google.com

[Siggi Cherem (dart-lang), 2017-06-21 21:05:09]

lgtm

[Siggi Cherem (dart-lang), 2017-06-21 21:12:10]

https://codereview.chromium.org/2949093002/diff/1/pkg/front_end/lib/src/fasta...
File pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart (right):

https://codereview.chromium.org/2949093002/diff/1/pkg/front_end/lib/src/fasta...
pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart:2060: resolved =
resolveOneStep(hare);
random optional idea here - it took me some time to see that this is doing a
2-step and 1-step walk side by side (I wasn't as familiar with the algorithm), I
wonder if it helps to rename "resolved" here, maybe add a couple locals that
don't escape the loop body.

For example:

while (true) {
  if (identical(...)) stop;

  // hare takes 2 steps
  var step1 = resolveOneStep(hare);
  if (step1 == null) return hare;
  var step2 = resolveOneStep(step1);
  if (step2 == null) return step1;
  hare = step2;

  // toirtoise takes one step:
  type = resolveOneStep(type);

[Paul Berry, 2017-06-21 21:44:16]

https://codereview.chromium.org/2949093002/diff/1/pkg/front_end/lib/src/fasta...
File pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart (right):

https://codereview.chromium.org/2949093002/diff/1/pkg/front_end/lib/src/fasta...
pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart:2060: resolved =
resolveOneStep(hare);
On 2017/06/21 21:12:10, Siggi Cherem (dart-lang) wrote:
> random optional idea here - it took me some time to see that this is doing a
> 2-step and 1-step walk side by side (I wasn't as familiar with the algorithm),
I
> wonder if it helps to rename "resolved" here, maybe add a couple locals that
> don't escape the loop body.
> 
> For example:
> 
> while (true) {
>   if (identical(...)) stop;
> 
>   // hare takes 2 steps
>   var step1 = resolveOneStep(hare);
>   if (step1 == null) return hare;
>   var step2 = resolveOneStep(step1);
>   if (step2 == null) return step1;
>   hare = step2;
> 
>   // toirtoise takes one step:
>   type = resolveOneStep(type);

I like it!  Thanks

[Paul Berry, 2017-06-21 21:47:00]

Description was changed from

==========
Properly type infer for-in loops when the iterator type is a type parameter.

Also, fix a minor bug in variable declaration inference that was
preventing a local variable without an initializer from having its
type properly "inferred" as `dynamic`.
==========

to

==========
Properly type infer for-in loops when the iterator type is a type parameter.

Also, fix a minor bug in variable declaration inference that was
preventing a local variable without an initializer from having its
type properly "inferred" as `dynamic`.

R=sigmund@google.com

Committed:
https://github.com/dart-lang/sdk/commit/348b42c98bc23ec5332fd2ca62302e76192889ec
==========

[Paul Berry, 2017-06-21 21:47:01]

Committed patchset #1 (id:1) manually as
348b42c98bc23ec5332fd2ca62302e76192889ec (presubmit successful).