Paul Berry
5afdebf219
Previously, we treated cast patterns as a simple type-check, relying
on promotion machinery to supply the correct matched value type for
the inner pattern. In other words `P as T` was analyzed like `T() &&
P`. This had two unforunate consequences:
(1) If the type `T` was not a subtype of the matched value type, no
promotion occurred. So for example, if `x` had type `int?`, then
`if (x case var y as String?)` caused `y` to get an inferred type
of `int?` (which is clearly not what the user wants).
(2) Any promotions triggered inside the inner pattern would propagate
to the outer pattern. So for example, if `x` had the type
`Object?`, then `if (x case int _ as num)` caused `x` to be
promoted first to `num` and then to `int`. Although this was
sound, it seemed to me that it was strange and unexpected
behaviour, because the typical user expectation when performing a
cast is that only the type being cast to should be used for
promotion.
The solution to both of these is simple: we analyze the inner pattern
as though its matched value is distinct from the matched value
supplied to the cast, and has a static type of the cast type. Even
though in reality we know that the two values are the same, it's sound
for flow analysis to ignore that information.
Fixing this made it possible to add tests of some other patterns flow
analysis behaviours that weren't previously testable, so I've included
several tests in this CL that aren't strictly testing the change.
Bug: https://github.com/dart-lang/sdk/issues/50419
Change-Id: I8cf864c3bf20f55406cfd74aeb8891d8e81f93e2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/280207
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Package validation
The packages in pkg/ are automatically validated on the LUCI CI bots. The
validation is largely done by the tools/package_deps package; it can be tested
locally via:
dart tools/package_deps/bin/package_deps.dart
Packages which are published
There are several packages developed in pkg/ which are published to pub.
Validation of these packages is particularly important because the pub tools are
not used for these packages during development; we get our dependency versions
from the DEPS file. Its very easy for the dependencies specified in a package's
pubspec file to get out of date wrt the packages and versions actually used.
In order to better ensure we're publishing correct packages, we validate some properties of the pubspec files on our CI system. These validations include:
- that the dependencies listed in the pubspec are used in the package
- that all the packages used by the source are listed in the pubspec
- that we don't use relative path deps to pkg/ or third_party/ packages
Packages which are not published
For packages in pkg/ which we do not intend to be published, we put the following comment in the pubspec.yaml file:
# This package is not intended for consumption on pub.dev. DO NOT publish.
publish_to: none
These pubspecs are still validated by the package validation tool. The contents are more informational as the pubspecs for these packages are not consumed by the pub tool or ecosystem.
We validate:
- that the dependencies listed in the pubspec are used in the package
- that all the packages used by the source are listed in the pubspec
- that a reference to a pkg/ package is done via a relative path dependency