Paul Berry
a42244f73b
This CL implements the core flow analysis infrastructure for tracking
reasons why an expression was not promoted. It supports the following
reasons:
- Expression was a property access
- Expression has been written to since it was promoted
I expect to add support for other non-promotion reasons in the future,
for example:
- `this` cannot be promoted
- Expression has been write captured
- Expression was a reference to a static field or top level variable
These non-promotion reasons are plumbed through to the CFE and
analyzer for the purpose of making errors easier for the user to
understand. For example, given the following code:
class C {
int? i;
f() {
if (i == null) return;
print(i.isEven);
}
}
The front end now prints:
../../tmp/test.dart:5:13: Error: Property 'isEven' cannot be accessed on 'int?' because it is potentially null.
Try accessing using ?. instead.
print(i.isEven);
^^^^^^
Context: 'i' refers to a property so it could not be promoted.
Much work still needs to be done to round out this feature, for example:
- Currently the analyzer only shows the new "why not promoted"
messages when the "--verbose" flag is specified; this means the
feature is unlikely to be noticed by users.
- Currently the analyzer doesn't show a "why not promoted" message
when the non-promotion reason is that the expression is a property
access.
- We need one or more web pages explaining non-promotion reasons in
more detail so that the error messages can contain pointers to them.
- The analyzer and front end currently only show non-promotion reasons
for expressions of the form `x.y` where `x` fails to be promoted to
non-nullable. There are many other scenarios that should be
handled.
Change-Id: I0a12df74d0fc6274dfb3cb555abea81a75884231
Bug: https://github.com/dart-lang/sdk/issues/38773
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/181741
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@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