If there are multiple copies of the same library on the classpath,
then ShadowedDeclarationsFilter becomes very slow because it
encounters many equal-signature declarations and thus has to resolve
a lot of calls in order to pick among them.
Having multiple copies of the same library on the classpath is
somewhat common in real-world projects. It occurs in the
JetBrains/intellij-kotlin project, for example. In that project,
ShadowedDeclarationsFilter ends up resolving thousands of calls,
accounting for around 80% of completion time when there are
many completion results (see KT-44276).
We can optimize ShadowedDeclarationsFilter by checking whether the
descriptors in an equal-signature group are structurally equivalent.
If they are, we can just pick one rather than running resolve.
Testing on a small project with Kotlin stdlib duplicated on the
classpath, this change reduces overhead in ShadowedDeclarationsFilter
from 1200 ms to 20 ms when running completion on the prefix 'a'.
End-to-end completion time is cut in half.
Test: JvmBasicCompletionTestGenerated.Common.Shadowing
Receiver of a function call '<receiver>.foo()' (where receiver is a
class/object/alias name) might be specified incorrectly - corresponding
[companion] object might not be declared.
Before this commit '<receiver>' was considered to be undefined (null).
As a consequence, import suggestion included all 'foo()' functions from
the search scope.
Now as a value of '<receiver>' we set class/object/alias itself
resulting in an empty import suggestion list.
See org/jetbrains/kotlin/idea/util/CallType.kt:307
(#extractReceiverTypeFrom(descriptor: ClassDescriptor)).
Matthew Gharrity