IR: do not inherit IrFakeOverride* from IrFunction/IrProperty

This will help to reduce boilerplate after making the latter classes.

Without this change, IrFunctionCommonImpl would not be able to be a
class because it would introduce a diamond class hierarchy, and thus
that would require copying all its contents to IrFunctionImpl and
IrFakeOverrideFunctionImpl.

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrFactoryImpl.kt

@@ -185,7 +185,7 @@ object IrFactoryImpl : IrFactory {
         isDelegated: Boolean,
         isExternal: Boolean,
         isExpect: Boolean,
-    ): IrFakeOverrideProperty =
+    ): IrProperty =
         IrFakeOverridePropertyImpl(
             startOffset, endOffset, origin, name, visibility, modality,
             isVar, isConst, isLateinit, isDelegated, isExternal, isExpect,

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrFunctionImpl.kt

@@ -104,10 +104,11 @@ class IrFakeOverrideFunctionImpl(
         get() = _symbol?.descriptor ?: WrappedSimpleFunctionDescriptor()
 
     @OptIn(ObsoleteDescriptorBasedAPI::class)
-    override fun acquireSymbol(symbol: IrSimpleFunctionSymbol) {
+    override fun acquireSymbol(symbol: IrSimpleFunctionSymbol): IrSimpleFunction {
         assert(_symbol == null) { "$this already has symbol _symbol" }
         _symbol = symbol
         symbol.bind(this)
         (symbol.descriptor as? WrappedSimpleFunctionDescriptor)?.bind(this)
+        return this
     }
 }

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt

@@ -103,10 +103,11 @@ class IrFakeOverridePropertyImpl(
         get() = _symbol?.descriptor ?: WrappedPropertyDescriptor()
 
     @OptIn(ObsoleteDescriptorBasedAPI::class)
-    override fun acquireSymbol(symbol: IrPropertySymbol) {
+    override fun acquireSymbol(symbol: IrPropertySymbol): IrProperty {
         assert(_symbol == null) { "$this already has symbol _symbol" }
         _symbol = symbol
         symbol.bind(this)
         (symbol.descriptor as? WrappedPropertyDescriptor)?.bind(this)
+        return this
     }
 }

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrFactory.kt

@@ -189,7 +189,7 @@ object PersistentIrFactory : IrFactory {
         isDelegated: Boolean,
         isExternal: Boolean,
         isExpect: Boolean,
-    ): IrFakeOverrideProperty =
+    ): IrProperty =
         PersistentIrFakeOverrideProperty(
             startOffset, endOffset, origin, name, visibility, modality,
             isVar, isConst, isLateinit, isDelegated, isExternal, isExpect,

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrFunction.kt

@@ -133,10 +133,11 @@ internal class PersistentIrFakeOverrideFunction(
         get() = _symbol?.descriptor ?: WrappedSimpleFunctionDescriptor()
 
     @OptIn(ObsoleteDescriptorBasedAPI::class)
-    override fun acquireSymbol(symbol: IrSimpleFunctionSymbol) {
+    override fun acquireSymbol(symbol: IrSimpleFunctionSymbol): IrSimpleFunction {
         assert(_symbol == null) { "$this already has symbol _symbol" }
         _symbol = symbol
         symbol.bind(this)
         (symbol.descriptor as? WrappedSimpleFunctionDescriptor)?.bind(this)
+        return this
     }
 }

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrProperty.kt

@@ -140,10 +140,11 @@ internal class PersistentIrFakeOverrideProperty(
         get() = _symbol?.descriptor ?: WrappedPropertyDescriptor()
 
     @OptIn(ObsoleteDescriptorBasedAPI::class)
-    override fun acquireSymbol(symbol: IrPropertySymbol) {
+    override fun acquireSymbol(symbol: IrPropertySymbol): IrProperty {
         assert(_symbol == null) { "$this already has symbol _symbol" }
         _symbol = symbol
         symbol.bind(this)
         (symbol.descriptor as? WrappedPropertyDescriptor)?.bind(this)
+        return this
     }
 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFactory.kt

@@ -160,7 +160,7 @@ interface IrFactory {
         isDelegated: Boolean,
         isExternal: Boolean,
         isExpect: Boolean,
-    ): IrFakeOverrideProperty
+    ): IrProperty
 
     fun createTypeAlias(
         startOffset: Int,

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFakeOverrideFunction.kt

@@ -8,8 +8,8 @@ package org.jetbrains.kotlin.ir.declarations
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
 
-interface IrFakeOverrideFunction : IrSimpleFunction {
-    override var modality: Modality
+interface IrFakeOverrideFunction : IrSymbolDeclaration<IrSimpleFunctionSymbol> {
+    var modality: Modality
 
-    fun acquireSymbol(symbol: IrSimpleFunctionSymbol)
+    fun acquireSymbol(symbol: IrSimpleFunctionSymbol): IrSimpleFunction
 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFakeOverrideProperty.kt

@@ -8,8 +8,10 @@ package org.jetbrains.kotlin.ir.declarations
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.ir.symbols.IrPropertySymbol
 
-interface IrFakeOverrideProperty : IrProperty {
-    override var modality: Modality
+interface IrFakeOverrideProperty : IrSymbolDeclaration<IrPropertySymbol> {
+    var modality: Modality
+    var getter: IrSimpleFunction?
+    var setter: IrSimpleFunction?
 
-    fun acquireSymbol(symbol: IrPropertySymbol)
+    fun acquireSymbol(symbol: IrPropertySymbol): IrProperty
 }

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/overrides/FakeOverrides.kt

@@ -17,7 +17,6 @@
 package org.jetbrains.kotlin.backend.common.overrides
 
 import org.jetbrains.kotlin.backend.common.serialization.signature.IdSignatureSerializer
-import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.descriptors.WrappedPropertyDescriptor
@@ -31,9 +30,6 @@ import org.jetbrains.kotlin.ir.types.IrTypeProjection
 import org.jetbrains.kotlin.ir.types.extractTypeParameters
 import org.jetbrains.kotlin.ir.types.getClass
 import org.jetbrains.kotlin.ir.util.SymbolTable
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
-import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
-import org.jetbrains.kotlin.ir.visitors.acceptVoid
 import org.jetbrains.kotlin.types.Variance
 
 interface PlatformFakeOverrideClassFilter {
@@ -124,7 +120,6 @@ class FakeOverrideBuilder(
 
         symbolTable.declareSimpleFunctionFromLinker(WrappedSimpleFunctionDescriptor(), signature) {
             declaration.acquireSymbol(it)
-            declaration
         }
     }
 
@@ -136,7 +131,7 @@ class FakeOverrideBuilder(
         // To break this loop we use temp symbol in correspondingProperty.
 
         val tempSymbol = IrPropertySymbolImpl(WrappedPropertyDescriptor()).also {
-            it.bind(declaration)
+            it.bind(declaration as IrProperty)
         }
         declaration.getter?.let {
             it.correspondingPropertySymbol = tempSymbol
@@ -149,7 +144,6 @@ class FakeOverrideBuilder(
 
         symbolTable.declarePropertyFromLinker(WrappedPropertyDescriptor(), signature) {
             declaration.acquireSymbol(it)
-            declaration
         }
 
         declaration.getter?.let {