The reason #1 for this feature is that we want to test IdSignatures
generated for declarations. Currently, there is no (easy) way to ensure
that a change in the signature building logic doesn't cause any breaking
changes wrt klibs.
Now, most IdSignatures include hashed mangled names in them, so even if
we catch a regression where the included hash changes, there would be no
way of knowing immediately what caused it, unless we'd also have mangled
names in the expectations.
The reason #2 is to test the manglers themselves. Currently, there are
no tests for them. They heavily duplicate each other, this is already
causing issues (see KT-57427) that would be very hard to catch without
these tests.
^KT-58238 Fixed
tl;dr the current design of klibs does not allow to properly deserialize
the list of sealed subclasses in a sound way. It is possible that
a subclass of a sealed class is declared in a different file, AND is
private in that file.
A more detailed explanation:
Right now we don't serialize file signatures at all.
However, a private declaration's signature must necessarily include
the file signature.
How do we serialize a private declaration's signature into a klib
and deserialize it later?
**Serialization** is simple: we just serialize the file signature as
an empty protobuf message.
When we are **deserializing** a private declaration, we look at the file
that is being deserialized right now, and construct the file signature
based on that.
This logic, however, doesn't always work. An example is KT-54028.
Basically, if we have a sealed interface with a private implementor
declared in a different file, this breaks:
1. We are deserializing the sealed interface. The deserializer knows
that we are now in the file in which the sealed interface is declared.
2. As part of deserializing the interface, we deserialize its sealed
subclasses.
3. Naturally, we come to deserializing the private implementor that is
declared in another file, but the deserializer still thinks that we are
in the file in which the interface is declared. A wrong signature is
created, which leads to linkage failure.
We *could* fix this by properly serializing the file signature,
i.e. instead of an empty protobuf message we could write the file path
and its package to the klib. However, there a problems with this
approach:
- The current design of signatures allows a situation where two
different files can have the same relative path
(for example, with the help of the `-Xklib-relative-path-base` compiler
flag) *and* the same package, which would introduce ambiguity during
linkage.
- Most importantly, this appoach won't work well with incremental
compilation of klibs. Currently we rely on the assumption that all
cross-file references are handled with public signatures, and private
signatures are only used inside a single file. This allows to move
declarations across files without recompiling it's use sites.
It has been decided to apply the following hacky solution: we just don't
deserialize the list of sealed subclasses from klibs.
The list of sealed subclasses is not used in lowerings, so it should be
safe.
#KT-54028 Fixed
We are going to deprecate `WITH_RUNTIME` directive. The main reason
behind this change is that `WITH_STDLIB` directive better describes
its meaning, specifically it will add kotlin stdlib to test's classpath.
Kirill Rakhman