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>
When I moved these tests from front_end to _fe_analyzer_shared, I
forgot to move the corresponding entries in analysis_options to
exclude them from analysis, causing spurious analyzer errors in
_fe_analyzer_shared.
Change-Id: Ibd651cd893be262f388758d9b09bbf1423967021
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/123742
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
Previously such shared code was in the front_end package, but that
created problems because there is a lot of code in front_end that
isn't intended to be shared with the analyzer (including, notably, the
dependency on kernel).
This CL just moves over the flow_analysis logic to the new shared
package. Follow-up CLs will move over other shared logic and tests.
The end goal is that the analyzer package will no longer have a
dependency on front_end.
Change-Id: I5642d6565204422d79808ca47648462db85e442a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/123624
Reviewed-by: Jens Johansen <jensj@google.com>
Johnni Winther