[FIR] Fix building fir for += with complex rhs

Also fix choosing candidate for assignment operator call

compiler/fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/BaseFirBuilder.kt

@@ -463,22 +463,6 @@ abstract class BaseFirBuilder<T>(val session: FirSession, val context: Context =
                 statements += arraySet.apply { lValue = FirSimpleNamedReference(psiArrayExpression?.toFirSourceElement(), name, null) }
             }
         }
-        if (operation != FirOperation.ASSIGN &&
-            tokenType != REFERENCE_EXPRESSION && tokenType != THIS_EXPRESSION &&
-            ((tokenType != DOT_QUALIFIED_EXPRESSION && tokenType != SAFE_ACCESS_EXPRESSION) || this.selectorExpression?.elementType != REFERENCE_EXPRESSION)
-        ) {
-            return FirBlockImpl(this.getSourceOrNull()).apply {
-                val name = Name.special("<complex-set>")
-                statements += generateTemporaryVariable(
-                    this@BaseFirBuilder.session, this@generateAssignment.getSourceOrNull(), name,
-                    this@generateAssignment?.convert()
-                        ?: FirErrorExpressionImpl(this.getSourceOrNull(), FirSimpleDiagnostic("No LValue in assignment", DiagnosticKind.Syntax))
-                )
-                statements += FirVariableAssignmentImpl(source, false, value, operation).apply {
-                    lValue = FirSimpleNamedReference(this.getSourceOrNull(), name, null)
-                }
-            }
-        }
 
         if (operation in FirOperation.ASSIGNMENTS && operation != FirOperation.ASSIGN) {
             return FirOperatorCallImpl(source, operation).apply {

compiler/fir/psi2fir/testData/rawBuilder/expressions/lambda.txt

@@ -64,11 +64,10 @@ FILE: lambda.kt
     public? final? fun test(list: List<Int>): R|kotlin/Unit| {
         lval map: <implicit> = mutableMapOf#<Int, String>()
         list#.forEach#(<L> = forEach@fun <implicit>.<anonymous>(): <implicit> {
-            lval <complex-set>: <implicit> = map#.getOrPut#(it#, getOrPut@fun <implicit>.<anonymous>(): <implicit> {
+            +=(map#.getOrPut#(it#, getOrPut@fun <implicit>.<anonymous>(): <implicit> {
                 mutableListOf#()
             }
-            )
+            ), String())
-            <complex-set># += String()
         }
         )
     }

compiler/fir/psi2fir/testData/rawBuilder/expressions/modifications.txt

@@ -11,6 +11,5 @@ FILE: modifications.kt
         +=(this#, String(Omega))
     }
     public? final? fun Any.modify(): R|kotlin/Unit| {
-        lval <complex-set>: <implicit> = (this# as List<Int>)
+        +=((this# as List<Int>), Int(42))
-        <complex-set># += Int(42)
     }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/diagnostics/FirDiagnostics.kt

@@ -37,6 +37,10 @@ class FirOperatorAmbiguityError(val candidates: Collection<AbstractFirBasedSymbo
     override val reason: String get() = "Operator overload ambiguity. Compatible candidates: ${candidates.map { describeSymbol(it) }}"
 }
 
+class FirVariableExpectedError : FirDiagnostic() {
+    override val reason: String get() = "Variable expected"
+}
+
 private fun describeSymbol(symbol: AbstractFirBasedSymbol<*>): String {
     return when (symbol) {
         is FirClassLikeSymbol<*> -> symbol.classId.asString()

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/diagnostics/collectors/components/ErrorNodeDiagnosticCollectorComponent.kt

@@ -56,6 +56,7 @@ class ErrorNodeDiagnosticCollectorComponent(collector: AbstractDiagnosticCollect
             is FirInapplicableCandidateError -> FirErrors.INAPPLICABLE_CANDIDATE.onSource(source, diagnostic.candidates)
             is FirAmbiguityError -> FirErrors.AMBIGUITY.onSource(source, diagnostic.candidates)
             is FirOperatorAmbiguityError -> FirErrors.ASSIGN_OPERATOR_AMBIGUITY.onSource(source, diagnostic.candidates)
+            is FirVariableExpectedError -> Errors.VARIABLE_EXPECTED.onSource(source)
             is FirSimpleDiagnostic -> diagnostic.getFactory().onSource(source)
             FirEmptyDiagnostic -> null
             else -> throw IllegalArgumentException("Unsupported diagnostic type: ${diagnostic.javaClass}")

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt

@@ -7,7 +7,9 @@ package org.jetbrains.kotlin.fir.resolve.transformers.body.resolve
 
 import org.jetbrains.kotlin.fir.BuiltinTypes
 import org.jetbrains.kotlin.fir.FirCallResolver
+import org.jetbrains.kotlin.fir.declarations.FirProperty
 import org.jetbrains.kotlin.fir.declarations.FirTypeParametersOwner
+import org.jetbrains.kotlin.fir.declarations.FirVariable
 import org.jetbrains.kotlin.fir.diagnostics.DiagnosticKind
 import org.jetbrains.kotlin.fir.diagnostics.FirSimpleDiagnostic
 import org.jetbrains.kotlin.fir.expressions.*
@@ -26,13 +28,14 @@ import org.jetbrains.kotlin.fir.resolve.*
 import org.jetbrains.kotlin.fir.resolve.calls.ConeInferenceContext
 import org.jetbrains.kotlin.fir.resolve.calls.candidate
 import org.jetbrains.kotlin.fir.resolve.diagnostics.FirOperatorAmbiguityError
-import org.jetbrains.kotlin.fir.resolve.diagnostics.FirUnresolvedReferenceError
+import org.jetbrains.kotlin.fir.resolve.diagnostics.FirVariableExpectedError
 import org.jetbrains.kotlin.fir.resolve.transformers.InvocationKindTransformer
 import org.jetbrains.kotlin.fir.resolve.transformers.StoreReceiver
 import org.jetbrains.kotlin.fir.resolvedTypeFromPrototype
 import org.jetbrains.kotlin.fir.scopes.impl.withReplacedConeType
 import org.jetbrains.kotlin.fir.symbols.StandardClassIds
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
 import org.jetbrains.kotlin.fir.symbols.invoke
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.types.impl.ConeClassTypeImpl
@@ -200,13 +203,13 @@ class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransformer) :
     }
 
     override fun transformOperatorCall(operatorCall: FirOperatorCall, data: ResolutionMode): CompositeTransformResult<FirStatement> {
-        val result = if (operatorCall.operation in FirOperation.BOOLEANS) {
+        if (operatorCall.operation in FirOperation.BOOLEANS) {
-            (operatorCall.transformChildren(transformer, ResolutionMode.ContextIndependent) as FirOperatorCall).also {
+            val result = (operatorCall.transformChildren(transformer, ResolutionMode.ContextIndependent) as FirOperatorCall).also {
                 it.resultType = builtinTypes.booleanType
             }
-        } else {
+            dataFlowAnalyzer.exitOperatorCall(result)
-            transformExpression(operatorCall, data).single
+            return result.compose()
-        } as FirOperatorCall
+        }
 
         if (operatorCall.operation in FirOperation.ASSIGNMENTS) {
             require(operatorCall.operation != FirOperation.ASSIGN)
@@ -230,20 +233,24 @@ class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransformer) :
             val assignOperatorCall = createFunctionCall(assignmentOperatorName)
             val resolvedAssignCall = assignOperatorCall.transformSingle(this, ResolutionMode.ContextIndependent)
             val assignCallReference = resolvedAssignCall.toResolvedCallableReference()
-            // x + y
+            val assignIsError = resolvedAssignCall.typeRef is FirErrorTypeRef
+            // x = x + y
             val simpleOperatorName = FirOperationNameConventions.ASSIGNMENTS_TO_SIMPLE_OPERATOR.getValue(operatorCall.operation)
             val simpleOperatorCall = createFunctionCall(simpleOperatorName)
             val resolvedOperatorCall = simpleOperatorCall.transformSingle(this, ResolutionMode.ContextIndependent)
             val operatorCallReference = resolvedOperatorCall.toResolvedCallableReference()
 
-            val property = (leftArgument.toResolvedCallableSymbol() as? FirPropertySymbol)?.fir
+            val lhsReference = leftArgument.toResolvedCallableReference()
+            val lhsIsVar = (lhsReference?.resolvedSymbol as? FirVariableSymbol<*>)?.fir?.isVar == true
             return when {
-                operatorCallReference == null || property?.isVal == true -> resolvedAssignCall.compose()
+                operatorCallReference == null || (!lhsIsVar && !assignIsError) -> resolvedAssignCall.compose()
                 assignCallReference == null -> {
                     val assignment =
                         FirVariableAssignmentImpl(operatorCall.source, false, resolvedOperatorCall, FirOperation.ASSIGN).apply {
-                            lValue = (leftArgument as? FirQualifiedAccess)?.calleeReference
+                            lValue = if (lhsIsVar)
-                                ?: FirErrorNamedReferenceImpl(null, FirUnresolvedReferenceError())
+                                lhsReference!!
+                            else
+                                FirErrorNamedReferenceImpl(operatorCall.arguments.first().source, FirVariableExpectedError())
                         }
                     assignment.transform(transformer, ResolutionMode.ContextIndependent)
                 }
@@ -254,8 +261,7 @@ class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransformer) :
             }
         }
 
-        dataFlowAnalyzer.exitOperatorCall(result)
+        throw IllegalArgumentException(operatorCall.render())
-        return result.compose()
     }
 
     override fun transformTypeOperatorCall(typeOperatorCall: FirTypeOperatorCall, data: ResolutionMode): CompositeTransformResult<FirStatement> {

compiler/fir/resolve/testData/resolve/arguments/fieldPlusAssign.kt

@@ -0,0 +1,10 @@
+var x: Int = 1
+    set(value) {
+        field += value
+    }
+
+val y: Int = 1
+    get() {
+        <!VARIABLE_EXPECTED!>field<!> += 1
+        return 1
+    }

compiler/fir/resolve/testData/resolve/arguments/fieldPlusAssign.txt

@@ -0,0 +1,11 @@
+FILE: fieldPlusAssign.kt
+    public final var x: R|kotlin/Int| = Int(1)
+        public get(): R|kotlin/Int|
+        public set(value: R|kotlin/Int|): R|kotlin/Unit| {
+            F|/x| = F|/x|.R|kotlin/Int.plus|(R|<local>/value|)
+        }
+    public final val y: R|kotlin/Int| = Int(1)
+        public get(): R|kotlin/Int| {
+            <Variable expected># = F|/y|.R|kotlin/Int.plus|(Int(1))
+            ^ Int(1)
+        }

compiler/fir/resolve/testData/resolve/stdlib/listPlusAssign.kt

@@ -0,0 +1,19 @@
+fun List<String>.modify() {
+    <!VARIABLE_EXPECTED!>this<!> += "Alpha"
+    <!VARIABLE_EXPECTED!>this<!> += "Omega"
+}
+
+fun Any.modify() {
+    (<!VARIABLE_EXPECTED!>this as List<Int><!>) += 42
+}
+
+operator fun <T> Set<T>.plusAssign(x: T) {}
+
+fun Set<String>.modify() {
+    this += "Alpha"
+    this += "Omega"
+}
+
+fun Any.modifySet() {
+    (this as Set<Int>) += 42
+}

compiler/fir/resolve/testData/resolve/stdlib/listPlusAssign.txt

@@ -0,0 +1,17 @@
+FILE: listPlusAssign.kt
+    public final fun R|kotlin/collections/List<kotlin/String>|.modify(): R|kotlin/Unit| {
+        <Variable expected># = this@R|/modify|.R|kotlin/collections/plus|<R|kotlin/String|>(String(Alpha))
+        <Variable expected># = this@R|/modify|.R|kotlin/collections/plus|<R|kotlin/String|>(String(Omega))
+    }
+    public final fun R|kotlin/Any|.modify(): R|kotlin/Unit| {
+        <Variable expected># = (this@R|/modify| as R|kotlin/collections/List<kotlin/Int>|).R|kotlin/collections/plus|<R|kotlin/Int|>(Int(42))
+    }
+    public final operator fun <T> R|kotlin/collections/Set<T>|.plusAssign(x: R|T|): R|kotlin/Unit| {
+    }
+    public final fun R|kotlin/collections/Set<kotlin/String>|.modify(): R|kotlin/Unit| {
+        this@R|/modify|.R|/plusAssign|<R|kotlin/String|>(String(Alpha))
+        this@R|/modify|.R|/plusAssign|<R|kotlin/String|>(String(Omega))
+    }
+    public final fun R|kotlin/Any|.modifySet(): R|kotlin/Unit| {
+        (this@R|/modifySet| as R|kotlin/collections/Set<kotlin/Int>|).R|/plusAssign|<R|kotlin/Int|>(Int(42))
+    }

compiler/fir/resolve/tests/org/jetbrains/kotlin/fir/FirDiagnosticsTestGenerated.java

@@ -230,6 +230,11 @@ public class FirDiagnosticsTestGenerated extends AbstractFirDiagnosticsTest {
             runTest("compiler/fir/resolve/testData/resolve/arguments/default.kt");
         }
 
+        @TestMetadata("fieldPlusAssign.kt")
+        public void testFieldPlusAssign() throws Exception {
+            runTest("compiler/fir/resolve/testData/resolve/arguments/fieldPlusAssign.kt");
+        }
+
         @TestMetadata("invoke.kt")
         public void testInvoke() throws Exception {
             runTest("compiler/fir/resolve/testData/resolve/arguments/invoke.kt");

compiler/fir/resolve/tests/org/jetbrains/kotlin/fir/FirDiagnosticsWithStdlibTestGenerated.java

@@ -98,6 +98,11 @@ public class FirDiagnosticsWithStdlibTestGenerated extends AbstractFirDiagnostic
         runTest("compiler/fir/resolve/testData/resolve/stdlib/implicitReceiverOrder.kt");
     }
 
+    @TestMetadata("listPlusAssign.kt")
+    public void testListPlusAssign() throws Exception {
+        runTest("compiler/fir/resolve/testData/resolve/stdlib/listPlusAssign.kt");
+    }
+
     @TestMetadata("mapList.kt")
     public void testMapList() throws Exception {
         runTest("compiler/fir/resolve/testData/resolve/stdlib/mapList.kt");

compiler/testData/ir/irText/expressions/augmentedAssignmentWithExpression.fir.txt

@@ -40,15 +40,13 @@ FILE fqName:<root> fileName:/augmentedAssignmentWithExpression.kt
         x: CONST Int type=kotlin.Int value=1
   FUN name:test3 visibility:public modality:FINAL <> () returnType:kotlin.Unit
     BLOCK_BODY
-      VAR IR_TEMPORARY_VARIABLE name:tmp_0 type:<root>.Host [val]
+      CALL 'public final fun plusAssign (x: kotlin.Int): kotlin.Unit declared in <root>.Host' type=kotlin.Unit origin=null
-        CALL 'public final fun foo (): <root>.Host declared in <root>' type=<root>.Host origin=null
+        $this: CALL 'public final fun foo (): <root>.Host declared in <root>' type=<root>.Host origin=null
-      SET_VAR 'val tmp_0: <root>.Host [val] declared in <root>.test3' type=<root>.Host origin=null
+        x: CONST Int type=kotlin.Int value=1
-        CONST Int type=<root>.Host value=1
   FUN name:test4 visibility:public modality:FINAL <> (a:kotlin.Function0<<root>.Host>) returnType:kotlin.Unit
     VALUE_PARAMETER name:a index:0 type:kotlin.Function0<<root>.Host>
     BLOCK_BODY
-      VAR IR_TEMPORARY_VARIABLE name:tmp_1 type:<root>.Host [val]
+      CALL 'public final fun plusAssign (x: kotlin.Int): kotlin.Unit declared in <root>.Host' type=kotlin.Unit origin=null
-        CALL 'public abstract fun invoke (): <root>.Host declared in kotlin.Function0' type=<root>.Host origin=null
+        $this: CALL 'public abstract fun invoke (): <root>.Host declared in kotlin.Function0' type=<root>.Host origin=null
           $this: GET_VAR 'a: kotlin.Function0<<root>.Host> declared in <root>.test4' type=kotlin.Function0<<root>.Host> origin=null
-      SET_VAR 'val tmp_1: <root>.Host [val] declared in <root>.test4' type=<root>.Host origin=null
+        x: CONST Int type=kotlin.Int value=1
-        CONST Int type=<root>.Host value=1

compiler/testData/ir/irText/expressions/javaSyntheticPropertyAccess.fir.txt

@@ -10,4 +10,4 @@ FILE fqName:<root> fileName:/javaSyntheticPropertyAccess.kt
           $this: GET_VAR 'j: <root>.J declared in <root>.test' type=<root>.J origin=null
       ERROR_CALL 'Unresolved reference: R|/J.foo|' type=IrErrorType
       GET_VAR 'val tmp_0: kotlin.Int [val] declared in <root>.test' type=kotlin.Int origin=null
-      ERROR_CALL 'Unresolved reference: R|/J.foo|' type=IrErrorType
+      ERROR_CALL 'Unresolved reference: <Variable expected>#' type=IrErrorType

compiler/testData/ir/irText/expressions/kt30020.fir.txt

@@ -28,61 +28,58 @@ FILE fqName:<root> fileName:/kt30020.kt
         $receiver: CALL 'public abstract fun <get-xs> (): kotlin.collections.MutableList<kotlin.Any> declared in <root>.X' type=kotlin.collections.MutableList<kotlin.Any> origin=null
           $this: GET_VAR 'x: <root>.X declared in <root>.test' type=<root>.X origin=null
         element: CONST Int type=kotlin.Int value=1
-      VAR IR_TEMPORARY_VARIABLE name:tmp_0 type:kotlin.collections.MutableList<kotlin.Any> [val]
+      CALL 'public final fun plusAssign (element: T of <uninitialized parent>): kotlin.Unit [inline] declared in kotlin.collections' type=kotlin.Unit origin=null
-        CALL 'public abstract fun f (): kotlin.collections.MutableList<kotlin.Any> declared in <root>.X' type=kotlin.collections.MutableList<kotlin.Any> origin=null
+        $receiver: CALL 'public abstract fun f (): kotlin.collections.MutableList<kotlin.Any> declared in <root>.X' type=kotlin.collections.MutableList<kotlin.Any> origin=null
           $this: GET_VAR 'x: <root>.X declared in <root>.test' type=<root>.X origin=null
-      SET_VAR 'val tmp_0: kotlin.collections.MutableList<kotlin.Any> [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Any> origin=null
+        element: CONST Int type=kotlin.Int value=2
-        CONST Int type=kotlin.collections.MutableList<kotlin.Any> value=2
+      CALL 'public final fun plusAssign (element: T of <uninitialized parent>): kotlin.Unit [inline] declared in kotlin.collections' type=kotlin.Unit origin=null
-      VAR IR_TEMPORARY_VARIABLE name:tmp_1 type:kotlin.collections.MutableList<kotlin.Int> [val]
+        $receiver: TYPE_OP type=kotlin.collections.MutableList<kotlin.Int> origin=CAST typeOperand=kotlin.collections.MutableList<kotlin.Int>
-        TYPE_OP type=kotlin.collections.MutableList<kotlin.Int> origin=CAST typeOperand=kotlin.collections.MutableList<kotlin.Int>
+          CALL 'public abstract fun <get-xs> (): kotlin.collections.MutableList<kotlin.Any> declared in <root>.X' type=kotlin.collections.MutableList<kotlin.Int> origin=null
-          CALL 'public abstract fun <get-xs> (): kotlin.collections.MutableList<kotlin.Any> declared in <root>.X' type=kotlin.collections.MutableList<kotlin.Any> origin=null
             $this: GET_VAR 'x: <root>.X declared in <root>.test' type=<root>.X origin=null
-      SET_VAR 'val tmp_1: kotlin.collections.MutableList<kotlin.Int> [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
+        element: CONST Int type=kotlin.Int value=3
-        CONST Int type=kotlin.collections.MutableList<kotlin.Int> value=3
+      CALL 'public final fun plusAssign (element: T of <uninitialized parent>): kotlin.Unit [inline] declared in kotlin.collections' type=kotlin.Unit origin=null
-      VAR IR_TEMPORARY_VARIABLE name:tmp_2 type:kotlin.collections.MutableList<kotlin.Int> [val]
+        $receiver: TYPE_OP type=kotlin.collections.MutableList<kotlin.Int> origin=CAST typeOperand=kotlin.collections.MutableList<kotlin.Int>
-        TYPE_OP type=kotlin.collections.MutableList<kotlin.Int> origin=CAST typeOperand=kotlin.collections.MutableList<kotlin.Int>
           CALL 'public abstract fun f (): kotlin.collections.MutableList<kotlin.Any> declared in <root>.X' type=kotlin.collections.MutableList<kotlin.Any> origin=null
             $this: GET_VAR 'x: <root>.X declared in <root>.test' type=<root>.X origin=null
-      SET_VAR 'val tmp_2: kotlin.collections.MutableList<kotlin.Int> [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
+        element: CONST Int type=kotlin.Int value=4
-        CONST Int type=kotlin.collections.MutableList<kotlin.Int> value=4
+      CALL 'public final fun plusAssign (element: T of <uninitialized parent>): kotlin.Unit [inline] declared in kotlin.collections' type=kotlin.Unit origin=null
-      VAR IR_TEMPORARY_VARIABLE name:tmp_3 type:kotlin.collections.MutableList<kotlin.Int> [val]
+        $receiver: BLOCK type=kotlin.collections.MutableList<kotlin.Int> origin=EXCLEXCL
-        BLOCK type=kotlin.collections.MutableList<kotlin.Int> origin=EXCLEXCL
+          VAR IR_TEMPORARY_VARIABLE name:tmp_0 type:kotlin.collections.MutableList<kotlin.Int> [val]
-          VAR IR_TEMPORARY_VARIABLE name:tmp_4 type:kotlin.collections.MutableList<kotlin.Int> [val]
             CALL 'public abstract fun <get-xs> (): kotlin.collections.MutableList<kotlin.Any> declared in <root>.X' type=kotlin.collections.MutableList<kotlin.Int> origin=null
               $this: GET_VAR 'nx: <root>.X? declared in <root>.test' type=<root>.X? origin=null
           WHEN type=kotlin.collections.MutableList<kotlin.Int> origin=EXCLEXCL
             BRANCH
               if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
-                arg0: GET_VAR 'val tmp_4: kotlin.collections.MutableList<kotlin.Int> [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
+                arg0: GET_VAR 'val tmp_0: kotlin.collections.MutableList<kotlin.Int> [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
                 arg1: CONST Null type=kotlin.Nothing? value=null
               then: THROW type=kotlin.Nothing
                 CONSTRUCTOR_CALL 'public constructor <init> () declared in kotlin.KotlinNullPointerException' type=kotlin.KotlinNullPointerException origin=null
             BRANCH
               if: CONST Boolean type=kotlin.Boolean value=true
-              then: GET_VAR 'val tmp_4: kotlin.collections.MutableList<kotlin.Int> [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
+              then: GET_VAR 'val tmp_0: kotlin.collections.MutableList<kotlin.Int> [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
-      SET_VAR 'val tmp_3: kotlin.collections.MutableList<kotlin.Int> [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
+        element: CONST Int type=kotlin.Int value=5
-        CONST Int type=kotlin.collections.MutableList<kotlin.Int> value=5
+      CALL 'public final fun plusAssign (element: T of <uninitialized parent>): kotlin.Unit [inline] declared in kotlin.collections' type=kotlin.Unit origin=null
-      VAR IR_TEMPORARY_VARIABLE name:tmp_5 type:kotlin.collections.MutableList<kotlin.Int> [val]
+        $receiver: BLOCK type=kotlin.collections.MutableList<kotlin.Int> origin=EXCLEXCL
-        BLOCK type=kotlin.collections.MutableList<kotlin.Int> origin=EXCLEXCL
+          VAR IR_TEMPORARY_VARIABLE name:tmp_1 type:kotlin.collections.MutableList<kotlin.Any>? [val]
-          VAR IR_TEMPORARY_VARIABLE name:tmp_6 type:kotlin.collections.MutableList<kotlin.Any>? [val]
             CALL 'public abstract fun f (): kotlin.collections.MutableList<kotlin.Any> declared in <root>.X' type=kotlin.collections.MutableList<kotlin.Any>? origin=null
               $this: GET_VAR 'nx: <root>.X? declared in <root>.test' type=<root>.X origin=null
           WHEN type=kotlin.collections.MutableList<kotlin.Int> origin=EXCLEXCL
             BRANCH
               if: CALL 'public final fun EQEQ (arg0: kotlin.Any?, arg1: kotlin.Any?): kotlin.Boolean declared in kotlin.internal.ir' type=kotlin.Boolean origin=EQEQ
-                arg0: GET_VAR 'val tmp_6: kotlin.collections.MutableList<kotlin.Any>? [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Any>? origin=null
+                arg0: GET_VAR 'val tmp_1: kotlin.collections.MutableList<kotlin.Any>? [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Any>? origin=null
                 arg1: CONST Null type=kotlin.Nothing? value=null
               then: THROW type=kotlin.Nothing
                 CONSTRUCTOR_CALL 'public constructor <init> () declared in kotlin.KotlinNullPointerException' type=kotlin.KotlinNullPointerException origin=null
             BRANCH
               if: CONST Boolean type=kotlin.Boolean value=true
-              then: GET_VAR 'val tmp_6: kotlin.collections.MutableList<kotlin.Any>? [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
+              then: GET_VAR 'val tmp_1: kotlin.collections.MutableList<kotlin.Any>? [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
-      SET_VAR 'val tmp_5: kotlin.collections.MutableList<kotlin.Int> [val] declared in <root>.test' type=kotlin.collections.MutableList<kotlin.Int> origin=null
+        element: CONST Int type=kotlin.Int value=6
-        CONST Int type=kotlin.collections.MutableList<kotlin.Int> value=6
   FUN name:testExtensionReceiver visibility:public modality:FINAL <> ($receiver:kotlin.collections.MutableList<kotlin.Any>) returnType:kotlin.Unit
     $receiver: VALUE_PARAMETER name:<this> type:kotlin.collections.MutableList<kotlin.Any>
     BLOCK_BODY
-      ERROR_EXPR 'Operator overload ambiguity. Compatible candidates: [kotlin/collections/plus, kotlin/collections/plusAssign]' type=IrErrorType
+      CALL 'public final fun plusAssign (element: T of <uninitialized parent>): kotlin.Unit [inline] declared in kotlin.collections' type=kotlin.Unit origin=null
+        $receiver: GET_VAR '<this>: kotlin.collections.MutableList<kotlin.Any> declared in <root>.testExtensionReceiver' type=kotlin.collections.MutableList<kotlin.Any> origin=null
+        element: CONST Int type=kotlin.Int value=100
   CLASS CLASS name:AML modality:ABSTRACT visibility:public superTypes:[kotlin.collections.MutableList<kotlin.Int>]
     $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.AML
     CONSTRUCTOR visibility:public <> () returnType:<root>.AML [primary]
@@ -92,7 +89,9 @@ FILE fqName:<root> fileName:/kt30020.kt
     FUN name:testExplicitThis visibility:public modality:FINAL <> ($this:<root>.AML) returnType:kotlin.Unit
       $this: VALUE_PARAMETER name:<this> type:<root>.AML
       BLOCK_BODY
-        ERROR_EXPR 'Operator overload ambiguity. Compatible candidates: [kotlin/collections/plus, kotlin/collections/plusAssign]' type=IrErrorType
+        CALL 'public final fun plusAssign (element: T of <uninitialized parent>): kotlin.Unit [inline] declared in kotlin.collections' type=kotlin.Unit origin=null
+          $receiver: GET_VAR '<this>: <root>.AML declared in <root>.AML' type=<root>.AML origin=null
+          element: CONST Int type=kotlin.Int value=200
     CLASS CLASS name:Inner modality:FINAL visibility:public [inner] superTypes:[kotlin.Any]
       $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.AML.Inner
       CONSTRUCTOR visibility:public <> () returnType:<root>.AML.Inner [primary]
@@ -102,7 +101,9 @@ FILE fqName:<root> fileName:/kt30020.kt
       FUN name:testOuterThis visibility:public modality:FINAL <> ($this:<root>.AML.Inner) returnType:kotlin.Unit
         $this: VALUE_PARAMETER name:<this> type:<root>.AML.Inner
         BLOCK_BODY
-          ERROR_EXPR 'Operator overload ambiguity. Compatible candidates: [kotlin/collections/plus, kotlin/collections/plusAssign]' type=IrErrorType
+          CALL 'public final fun plusAssign (element: T of <uninitialized parent>): kotlin.Unit [inline] declared in kotlin.collections' type=kotlin.Unit origin=null
+            $receiver: GET_VAR '<this>: <root>.AML declared in <root>.AML' type=<root>.AML origin=null
+            element: CONST Int type=kotlin.Int value=300
       FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($this:kotlin.Any, other:kotlin.Any?) returnType:kotlin.Boolean [fake_override]
         overridden:
           public open fun equals (other: kotlin.Any?): kotlin.Boolean declared in kotlin.Any