In this mode, javac AST and Symbol files are used during
Kotlin compilation instead of PSI / binary stuff.
Later, they are reused for Java file compilation.
javac in this mode is integrated into kotlinc.
The problem was that an overload of CodedOutputStream.newInstance
without size uses 4000 as a default value, thus allocating
a 4k-sized byte array.
At the same time the array remained effectively unused
in the most cases since it only used for storing data
for unknown fields.
Because such arrays are being created for each read of
protobuf message, during compilation of IntelliJ project
it was producing 25% of redundant memory traffic.
Of course these arrays were all in the young gen, but still
they have some effect on GC
Otherwise it might lead to the problems when reading class files
from the source scope (e.g. a groovy file or an already compiled java file)
Note that it may be reproduced only with Maven because in JPS
and Gradle we reading source java files even when they're shouldn't be
recompiled, while in Maven we read class files in the case
#KT-17897 Fixed
Backend: If kotlin class extends kotlin.collection.List
write it as it's super interface (light class mode only)
IDE: Provide wrapper classes to java resolve
that try to emulate backend behaviour
For example if kotlin class implements kotlin.collections.Map,
we provide a superinterface that has abstract 'getEntries' method
and 'entrySet' method that is considered default.
In reality all those methods are generated in the class itself.
In IDE supporting this case without hacks is not feasible performance-wise
since kotlin.collection.* may not be an immediate supertype and we need
to compute all supertypes just to calculate own methods of the class
baratynskiy