tree f25f394285ebfe57cdbcd56400897f1f7c50bd77
parent dfa661d4602a19abd5a854ffd99c0193fe47e3b2
author Paul Berry <paulberry@google.com> 1525390034 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1525390034 +0000

Don't infer types when there's an irreconcilable type mismatch.

Also fix the type inference algorithm so that when it explores
multiple alternatives (as a result of the use of FutureOr<>), if one
alternative generated some constraints but failed to produce a match,
it rewinds those constraints and tries the other alternative.
(Previously, it erroneously assumed that if any constraints were
generated, the alternative matched successfully).

Also add unit tests to verify the proper operation of the subtype
match algorithm.

Fixes #32305.

Change-Id: I060b5d6d5247a68d2b27bba78819bae172e43d97
Reviewed-on: https://dart-review.googlesource.com/53685
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Jenny Messerly <jmesserly@google.com>