tree afb4fb216e5a0a2beeb0fa8b153a1366a232c6e1
parent 9a1f783007e2650640bc0eb52d9fbe14613833a5
author Kevin Millikin <kmillikin@google.com> 1536079851 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1536079851 +0000

Signal errors and warnings for invalid returns

Implement the feature spec for checking returns against inferred
function return types:

https://github.com/dart-lang/sdk/blob/master/docs/language/informal/invalid_returns.md

with the change that an invalid return without a subexpression is
a warning, not an error.  This is because it is a warning in the
analyzer and it would be a breaking change to turn it into an
error.

The check for valid returns is moved to exactly where we handle
returns, rather than in ensureAssignable which is used as a
helper in a lot of places. A bug in type inference was fixed: we
would use `void` for the type of return without a subexpression
instead of `null`.  To accommodate that we would use a
non-standard subtyping relation for returns.  This could lead to
us inferring a return type of `void` in cases where we should
not.

Change-Id: Iee9ece9c722f47efa305f49490d3022d0bbb9f44
Reviewed-on: https://dart-review.googlesource.com/72403
Commit-Queue: Kevin Millikin <kmillikin@google.com>
Reviewed-by: Aske Simon Christensen <askesc@google.com>