The issue was that when rendering declarations in
the `CONFLICTING_KLIB_SIGNATURES_DATA` diagnostics, we sort them using
`MemberComparator`. That comparator falls back to comparing
declarations' renders if all previous checks were unsuccessful
(and in case of almost identical properties they are). The renderer that
the comparator uses also renders the properties' backing field
annotations, for which it calls `PropertyDescriptor#getBackingField`.
That method wasn't implemented in IR-based descriptors.
This is fixed by returning an instance of the new
`IrBasedBackingFieldDescriptor` class from that method.
^KT-65551 Fixed
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
Sergej Jaskiewicz