If we encounter a declaration in the current module whose signature
is the same as that of a declaration in another module which we happen
to also reference from the current module, don't report any errors,
just like we don't do it in Kotlin/JVM. This leaves the user in the KLIB
hell situation, but this is intentional, because otherwise a legitimate
change like moving a declaration to another module and marking
the original one as `@Deprecated("", level = DeprecationLevel.HIDDEN)`
would lead to a error, and we don't want that.
Also, don't try to show the diagnostics on a declaration that doesn't
have an IrFile.
^KT-65063 Fixed
Now, we detect clashing signatures during serialization to KLIB and
report a compiler error if two or more declarations have the same
`IdSignature`
For example, for the following code:
```kotlin
@Deprecated("", level = DeprecationLevel.HIDDEN)
fun foo(): String = ""
fun foo(): Int = 0
```
the compiler will produce this diagnostic:
```
e: main.kt:1:1 Platform declaration clash: The following declarations
have the same KLIB signature (/foo|foo(){}[0]):
fun foo(): String defined in root package
fun foo(): Int defined in root package
e: main.kt:4:1 Platform declaration clash: The following declarations
have the same KLIB signature (/foo|foo(){}[0]):
fun foo(): String defined in root package
fun foo(): Int defined in root package
```
Note that we report this diagnostic during serialization and not earlier
(e.g., in fir2ir) for more robustness, so ensure that we check
exactly the signatures that will be written to a KLIB.
If we later introduce some annotation for customizing a declaration's
signature (e.g., for preserving binary compatibility), this
diagnostic will continue to work as expected.
^KT-63670 Fixed
Objective-C has a special type, "instancetype". Generally, it is a type
that matches the method receiver type. So, if `Foo.foo` method returns
`instancetype`, then `Foo.foo()` would be of type `Foo`, while
`Bar.foo()` would be of type `Bar` (where `Bar` is a subclass of `Foo`).
Surprisingly, `instancetype` can be used not only as a return type, but
also somewhere inside a return type. cinterop wasn't ready for this.
This commit expands implementation of `instancetype` in cinterop to
cover more cases.
^KT-59597 Fixed
Vladimir Sukharev