tree e64a2f04ee5f1ffdec492fd4e60a54e5cd214944
parent 575c1d08174a7cfd4db03d7359efe49a812e0ecb
author Paul Berry <stereotype441@gmail.com> 1600103276 -0700
committer GitHub <noreply@github.com> 1600103276 -0700

Work around flow analysis bug (dart-lang/source_span#59)

Flow analysis currently has a bug preventing for-each loop variables
from being properly promoted in the presence of closures
(https://github.com/dart-lang/sdk/issues/43136); as a result of this
bug the source_span package had two non-null assertions that ought to
have been unnecessary.

I'm preparing a fix for that bug, however if I land it as is, it will
cause the front end to emit errors saying "Operand of null-aware
operation '!' has type '_Highlight' which excludes null"; this in turn
will cause SDK bot breakages (since source_span is imported into the
SDK repo).

So, in order to land the fix, we need to first update the source_span
package to work around the bug; this change does that by allocating a
temporary variable (which *is* promoted correctly).

Once the fix for https://github.com/dart-lang/sdk/issues/43136 lands,
I will make a follow-up change that deletes the temporary variable.