commit e610dd47d9294ccec68a25d320543814c5217ea4
author Paul Berry <paulberry@google.com> Fri Nov 12 00:41:01 2021 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> Fri Nov 12 00:41:01 2021 +0000
tree 9666955bc97fa0a2b74146da15add866bcb5e408
parent d21897b88d7349f08ae718ef2865c53e72e383b9

Migration: handle the multiple variable declarations in one line.

When the source code contains a declaration like `var x = ..., y =
...;`, and the variables need to be given different explicit types,
there's no easy way to do so because replacing the `var` with a type
causes the same type to be applied to *all* variables in the
declaration.

In an ideal world, the migration tool would split the declaration up
into several declarations and give each one the proper type.  But
doing so would require a lot of coding effort, and the problem is
extremely rare in practice (as witnessed by the fact that the issue
hasn't been reported until now).  So we opt for the much simpler fix
of introducing an `as` cast to the initializer of each variable whose
type needs to be changed.  This is less ideal (since the `as`
expressions bypass compile-time type safety), but considering how
rarely this problem crops up it seems like a worthwhile tradeoff.

Since the `as` expressions that are introduced are not downcasts, they
will show up near the top of the list of changes in the migration
tool's UI, so hopefully this will encourage the user to manually split
up the declaration into multiple lines and replace the casts with
explicit types.

Fixes #47669.

Bug: https://github.com/dart-lang/sdk/issues/47669
Change-Id: Idd7620cb5bb682c5fe235a4b088b94cd2208ebbd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/220060
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>