tree cc40bbf2e11b65fd5d1abc6f5c8ef5c3bffc9836
parent e2107230e4343f5fd2e241bcd736fc99fce6eff3
author Paul Berry <paulberry@google.com> 1608233494 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1608233494 +0000

Flow analysis: do not treat null vars as equivalent to `null`.

When analyzing code like this with the
`allowLocalBooleanVarsToPromote` flag enabled, don't treat a variable
containing `null` as equivalent to a literal `null`.  For example:

    f(int? x) {
      var y = null;
      if (x != y) {
        print(x + 1); // ERROR: x must be null checked.
      }
    }

The rationale is that flow analysis doesn't promote variables that are
known to be `null` to the `Null` type, so it seems like it would be
inconsistent if we used the fact that they're `null` to promote other
variables.

Bug: https://github.com/dart-lang/language/issues/1274
Change-Id: Icfa14104936a26732353921e3a29a840c53d4d52
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/176560
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>