FIR: skip return insertion for lambda w/ Unit return type

compiler/fir/analysis-tests/testData/extendedCheckers/RedundantReturnUnitTypeChecker.txt

@@ -60,7 +60,7 @@ FILE: RedundantReturnUnitTypeChecker.kt
 
         public final fun foo(): R|kotlin/Unit| {
             ^foo this@R|/B|.R|/B.run|<R|kotlin/Int|>(<L> = run@fun <anonymous>(): R|kotlin/Int| {
-                ^ this@R|/B|.R|/B.bar|()
+                this@R|/B|.R|/B.bar|()
             }
             )
         }
@@ -89,7 +89,7 @@ FILE: RedundantReturnUnitTypeChecker.kt
 
         public final fun goo(): R|kotlin/Unit| {
             ^goo (this@R|/B|, Int(1)).R|/B.let|<R|kotlin/Int|, R|kotlin/Int|>(<L> = let@fun <anonymous>(it: R|kotlin/Int|): R|kotlin/Int| {
-                ^ this@R|/B|.R|/B.bar|()
+                this@R|/B|.R|/B.bar|()
             }
             )
         }

compiler/fir/analysis-tests/testData/resolve/cfg/lambdas.txt

@@ -6,7 +6,7 @@ FILE: lambdas.kt
         when () {
             (R|<local>/x| is R|kotlin/Int|) ->  {
                 R|/run|(<L> = run@fun <anonymous>(): R|kotlin/Unit| <kind=UNKNOWN>  {
-                    ^ R|<local>/x|.R|kotlin/Int.inc|()
+                    R|<local>/x|.R|kotlin/Int.inc|()
                 }
                 )
             }

compiler/fir/analysis-tests/testData/resolve/expresssions/lambda.txt

@@ -9,7 +9,7 @@ FILE: lambda.kt
     }
     public final fun main(): R|kotlin/Unit| {
         R|/foo|(<L> = foo@fun <anonymous>(): R|kotlin/Unit| {
-            ^ String(This is test)
+            String(This is test)
         }
         )
         R|/bar|(<L> = bar@fun <anonymous>(): R|kotlin/String| {

compiler/fir/analysis-tests/testData/resolve/expresssions/lambdaWithReceiver.txt

@@ -35,7 +35,7 @@ FILE: lambdaWithReceiver.kt
         R|/complexLambda|(<L> = complexLambda@fun R|kotlin/Int|.<anonymous>(it: R|kotlin/String|): R|kotlin/Unit| {
             this@R|special/anonymous|.R|kotlin/Int.inc|()
             this@R|special/anonymous|.R|kotlin/Int.inc|()
-            ^ R|<local>/it|.R|kotlin/String.length|
+            R|<local>/it|.R|kotlin/String.length|
         }
         )
     }

compiler/fir/analysis-tests/testData/resolve/inference/lambdaInElvis.txt

@@ -9,13 +9,13 @@ FILE: lambdaInElvis.kt
     }
     public final fun bar1(w: R|kotlin/collections/List<kotlin/CharSequence>|): R|kotlin/collections/List<kotlin/CharSequence>?| {
         ^bar1 R|/foo|<R|kotlin/CharSequence|>(<L> = foo@fun <anonymous>(container: R|kotlin/collections/MutableList<kotlin/CharSequence>|): R|kotlin/Unit| {
-            ^ R|<local>/container|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
+            R|<local>/container|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
         }
         ) ?: R|<local>/w|
     }
     public final fun bar2(): R|kotlin/collections/List<kotlin/CharSequence>?| {
         ^bar2 R|/foo|<R|kotlin/CharSequence|>(<L> = foo@fun <anonymous>(container: R|kotlin/collections/MutableList<kotlin/CharSequence>|): R|kotlin/Unit| {
-            ^ R|<local>/container|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
+            R|<local>/container|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
         }
         ) ?: R|/listOf|<R|kotlin/CharSequence|>()
     }

compiler/fir/analysis-tests/testData/resolve/problems/complexLambdaWithTypeVariableAsExpectedType.txt

@@ -7,7 +7,7 @@ FILE: complexLambdaWithTypeVariableAsExpectedType.kt
     }
     public final fun test(): R|kotlin/Unit| {
         R|/select|<R|(kotlin/Int) -> kotlin/Unit|>(R|/id|<R|(kotlin/Int) -> kotlin/Int|>(<L> = id@fun <anonymous>(it: R|kotlin/Int|): R|kotlin/Int| {
-            ^ R|<local>/it|.R|kotlin/Int.inv|()
+            R|<local>/it|.R|kotlin/Int.inv|()
         }
         ), R|/id|<R|(kotlin/Int) -> kotlin/Unit|>(<L> = id@fun <anonymous>(it: R|kotlin/Int|): R|kotlin/Unit| {
             ^@id Unit

compiler/fir/analysis-tests/testData/resolve/samConversions/runnable.txt

@@ -1,11 +1,11 @@
 FILE: main.kt
     public final fun main(): R|kotlin/Unit| {
         Q|JavaClass|.R|/JavaClass.foo|(<L> = foo@fun <anonymous>(): R|kotlin/Unit| {
-            ^ String()
+            String()
         }
         )
         R|/JavaClass.JavaClass|().R|/JavaClass.bar|(<L> = bar@fun <anonymous>(): R|kotlin/Unit| {
-            ^ String()
+            String()
         }
         )
     }

compiler/fir/analysis-tests/testData/resolve/smartcasts/safeCalls/safeCalls.txt

@@ -21,7 +21,7 @@ FILE: safeCalls.kt
     }
     public final fun test_3(x: R|kotlin/Any|): R|kotlin/Unit| {
         (R|<local>/x| as? R|A|)?.{ $subj$.R|/A.bar|(R|<local>/x|) }?.{ $subj$.R|/foo|(R|<local>/x|.R|/A.bool|()) }?.{ $subj$.R|/let|(<L> = let@fun <anonymous>(): R|kotlin/Unit| {
-            ^ R|<local>/x|.R|/A.bool|()
+            R|<local>/x|.R|/A.bool|()
         }
         ) }
         R|<local>/x|.<Unresolved name: bool>#()

compiler/fir/analysis-tests/testData/resolveWithStdlib/addAllOnJavaCollection.txt

@@ -2,7 +2,7 @@ FILE: addAllOnJavaCollection.kt
     public final fun foo(): R|kotlin/Unit| {
         lval y: R|kotlin/collections/List<kotlin/String>| = R|kotlin/collections/listOf|<R|kotlin/String|>(vararg(String(Alpha), String(Beta)))
         lval x: R|java/util/LinkedHashSet<kotlin/String>| = R|java/util/LinkedHashSet.LinkedHashSet|<R|kotlin/String|>().R|kotlin/apply|<R|java/util/LinkedHashSet<kotlin/String>|>(<L> = apply@fun R|java/util/LinkedHashSet<kotlin/String>|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
-            ^ this@R|special/anonymous|.R|FakeOverride<java/util/LinkedHashSet.addAll: R|kotlin/Boolean|>|(R|<local>/y|)
+            this@R|special/anonymous|.R|FakeOverride<java/util/LinkedHashSet.addAll: R|kotlin/Boolean|>|(R|<local>/y|)
         }
         )
         lval z: R|java/util/ArrayList<kotlin/String>| = R|java/util/ArrayList.ArrayList|<R|kotlin/String|>()

compiler/fir/analysis-tests/testData/resolveWithStdlib/complexPostponedCfg.txt

@@ -7,9 +7,9 @@ FILE: complexPostponedCfg.kt
         lval firstCalls: R|kotlin/collections/List<FirFunctionCall>| = R|kotlin/with|<R|FirFunctionCall|, R|kotlin/collections/List<FirFunctionCall>|>((R|<local>/statements|.R|kotlin/collections/last|<R|FirBase|>() as R|FirFunctionCall|), <L> = setCall@fun R|FirFunctionCall|.<anonymous>(): R|kotlin/collections/List<FirFunctionCall>| <kind=EXACTLY_ONCE>  {
             ^ R|kotlin/collections/buildList|<R|FirFunctionCall|>(<L> = buildList@fun R|kotlin/collections/MutableList<FirFunctionCall>|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
                 this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(this@R|special/anonymous|)
-                ^ R|kotlin/with|<R|FirFunctionCall|, R|kotlin/Boolean|>((R|<local>/arguments|.R|kotlin/collections/last|<R|FirBase|>() as R|FirFunctionCall|), <L> = plusCall@fun R|FirFunctionCall|.<anonymous>(): R|kotlin/Boolean| <kind=EXACTLY_ONCE>  {
+                R|kotlin/with|<R|FirFunctionCall|, R|kotlin/Boolean|>((R|<local>/arguments|.R|kotlin/collections/last|<R|FirBase|>() as R|FirFunctionCall|), <L> = plusCall@fun R|FirFunctionCall|.<anonymous>(): R|kotlin/Boolean| <kind=EXACTLY_ONCE>  {
                     this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(this@R|special/anonymous|)
-                    ^ this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|((R|<local>/explicitReceiver| as R|FirFunctionCall|))
+                    this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|((R|<local>/explicitReceiver| as R|FirFunctionCall|))
                 }
                 )
             }

compiler/fir/analysis-tests/testData/resolveWithStdlib/contracts/fromLibrary/callsInPlace.txt

@@ -9,13 +9,13 @@ FILE: callsInPlace.kt
     }
     public final fun test_2(): R|kotlin/Unit| {
         R|kotlin/repeat|(Int(10), <L> = repeat@fun <anonymous>(it: R|kotlin/Int|): R|kotlin/Unit| <kind=UNKNOWN>  {
-            ^ String(test_2)
+            String(test_2)
         }
         )
     }
     public final fun test_3(): R|kotlin/Unit| {
         R|kotlin/repeat|(action = repeat@fun <anonymous>(it: R|kotlin/Int|): R|kotlin/Unit| <kind=UNKNOWN>  {
-            ^ String(test_3)
+            String(test_3)
         }
         , times = Int(10))
     }
@@ -39,19 +39,19 @@ FILE: callsInPlace.kt
     }
     public final fun test_6(): R|kotlin/Unit| {
         R|/myRun|(myRun@fun <anonymous>(): R|kotlin/Unit| <kind=UNKNOWN>  {
-            ^ String(test_6_1)
+            String(test_6_1)
         }
         , <L> = myRun@fun <anonymous>(): R|kotlin/Unit| <kind=UNKNOWN>  {
-            ^ String(test_6_2)
+            String(test_6_2)
         }
         )
     }
     public final fun test_7(): R|kotlin/Unit| {
         R|/myRun|(block2 = myRun@fun <anonymous>(): R|kotlin/Unit| <kind=UNKNOWN>  {
-            ^ String(test_7_2)
+            String(test_7_2)
         }
         , block1 = myRun@fun <anonymous>(): R|kotlin/Unit| <kind=UNKNOWN>  {
-            ^ String(test_7_1)
+            String(test_7_1)
         }
         )
     }
@@ -60,7 +60,7 @@ FILE: callsInPlace.kt
     }
     public final fun test_8(): R|kotlin/Unit| {
         R|/myDummyRun|(<L> = myDummyRun@fun <anonymous>(): R|kotlin/Unit| {
-            ^ String(test_8)
+            String(test_8)
         }
         )
     }

compiler/fir/analysis-tests/testData/resolveWithStdlib/hashTableWithForEach.txt

@@ -15,7 +15,7 @@ FILE: hashTableWithForEach.kt
                     R|/DEBUG| ->  {
                         ^ Q|java/util/Collections|.R|java/util/Collections.unmodifiableSet|<R|ft<kotlin/collections/MutableMap.MutableEntry<K, V>, kotlin/collections/MutableMap.MutableEntry<K, V>?>!|>(R|kotlin/collections/mutableSetOf|<R|kotlin/collections/MutableMap.MutableEntry<K, V>|>().R|kotlin/apply|<R|kotlin/collections/MutableSet<kotlin/collections/MutableMap.MutableEntry<K, V>>|>(<L> = apply@fun R|kotlin/collections/MutableSet<kotlin/collections/MutableMap.MutableEntry<K, V>>|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
                             this@R|/SomeHashTable|.R|/SomeHashTable.forEach|(<L> = forEach@fun <anonymous>(key: R|K|, value: R|V|): R|kotlin/Unit| {
-                                ^ this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableSet.add: R|kotlin/Boolean|>|(R|/SomeHashTable.Entry.Entry|<R|K|, R|V|>(R|<local>/key|, R|<local>/value|))
+                                this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableSet.add: R|kotlin/Boolean|>|(R|/SomeHashTable.Entry.Entry|<R|K|, R|V|>(R|<local>/key|, R|<local>/value|))
                             }
                             )
                         }

compiler/fir/analysis-tests/testData/resolveWithStdlib/inference/builderInference.txt

@@ -6,7 +6,7 @@ FILE: builderInference.kt
     }
     public final fun test(): R|kotlin/Unit| {
         lval s: R|kotlin/String| = R|/foo|<R|kotlin/String|>(<L> = foo@fun R|kotlin/collections/MutableList<kotlin/String>|.<anonymous>(): R|kotlin/Unit| {
-            ^ this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
+            this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
         }
         )
         R|/takeString|(R|<local>/s|)

compiler/fir/analysis-tests/testData/resolveWithStdlib/inference/builderInferenceFromStdlib.txt

@@ -1,14 +1,14 @@
 FILE: builderInferenceFromStdlib.kt
     public final fun test_1(): R|kotlin/Unit| {
         lval list: R|kotlin/collections/List<kotlin/String>| = R|kotlin/collections/buildList|<R|kotlin/String|>(<L> = buildList@fun R|kotlin/collections/MutableList<kotlin/String>|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
-            ^ this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
+            this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
         }
         )
         R|/takeList|(R|<local>/list|)
     }
     public final fun test_2(): R|kotlin/Unit| {
         lval list: R|kotlin/collections/List<kotlin/String>| = R|/myBuildList|<R|kotlin/String|>(<L> = myBuildList@fun R|kotlin/collections/MutableList<kotlin/String>|.<anonymous>(): R|kotlin/Unit| {
-            ^ this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
+            this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.add: R|kotlin/Boolean|>|(String())
         }
         )
         R|/takeList|(R|<local>/list|)

compiler/fir/analysis-tests/testData/resolveWithStdlib/j+k/MyMap.txt

@@ -9,7 +9,7 @@ FILE: test.kt
         R|<local>/map|.R|FakeOverride</MyMap.forEach: R|kotlin/Unit|>|(<L> = forEach@fun <anonymous>(key: R|ft<kotlin/String, kotlin/String?>!|, value: R|ft<kotlin/String, kotlin/String?>!|): R|kotlin/Unit| {
             R|kotlin/io/println|(<strcat>(R|<local>/key|.R|kotlin/Any.toString|(), String(: ), R|<local>/value|.R|kotlin/Any.toString|()))
             R|<local>/key|.R|kotlin/String.length|
-            ^ R|<local>/value|.R|kotlin/String.length|
+            R|<local>/value|.R|kotlin/String.length|
         }
         )
         R|<local>/map|.R|kotlin/collections/forEach|<R|ft<kotlin/String, kotlin/String?>!|, R|ft<kotlin/String, kotlin/String?>!|>(<L> = forEach@fun <anonymous>(<destruct>: R|kotlin/collections/Map.Entry<ft<kotlin/String, kotlin/String?>!, ft<kotlin/String, kotlin/String?>!>|): R|kotlin/Unit| <kind=UNKNOWN>  {
@@ -17,7 +17,7 @@ FILE: test.kt
             lval value: R|ft<kotlin/String, kotlin/String?>!| = R|<local>/<destruct>|.R|kotlin/collections/component2|<R|ft<kotlin/String, kotlin/String?>!|, R|ft<kotlin/String, kotlin/String?>!|>()
             R|kotlin/io/println|(<strcat>(R|<local>/key|.R|kotlin/Any.toString|(), String(: ), R|<local>/value|.R|kotlin/Any.toString|()))
             R|<local>/key|.R|kotlin/String.length|
-            ^ R|<local>/value|.R|kotlin/String.length|
+            R|<local>/value|.R|kotlin/String.length|
         }
         )
     }
@@ -31,7 +31,7 @@ FILE: test.kt
         R|<local>/map|.R|FakeOverride<kotlin/collections/MutableMap.forEach: R|kotlin/Unit|>|(<L> = forEach@fun <anonymous>(key: R|ft<kotlin/String, kotlin/String?>!|, value: R|ft<kotlin/String, kotlin/String?>!|): R|kotlin/Unit| {
             R|kotlin/io/println|(<strcat>(R|<local>/key|.R|kotlin/Any.toString|(), String(: ), R|<local>/value|.R|kotlin/Any.toString|()))
             R|<local>/key|.R|kotlin/String.length|
-            ^ R|<local>/value|.R|kotlin/String.length|
+            R|<local>/value|.R|kotlin/String.length|
         }
         )
         R|<local>/map|.R|kotlin/collections/forEach|<R|kotlin/String|, R|kotlin/String|>(<L> = forEach@fun <anonymous>(<destruct>: R|kotlin/collections/Map.Entry<kotlin/String, kotlin/String>|): R|kotlin/Unit| <kind=UNKNOWN>  {
@@ -39,7 +39,7 @@ FILE: test.kt
             lval value: R|kotlin/String| = R|<local>/<destruct>|.R|kotlin/collections/component2|<R|kotlin/String|, R|kotlin/String|>()
             R|kotlin/io/println|(<strcat>(R|<local>/key|.R|kotlin/Any.toString|(), String(: ), R|<local>/value|.R|kotlin/Any.toString|()))
             R|<local>/key|.R|kotlin/String.length|
-            ^ R|<local>/value|.R|kotlin/String.length|
+            R|<local>/value|.R|kotlin/String.length|
         }
         )
     }

compiler/fir/analysis-tests/testData/resolveWithStdlib/j+k/SyntheticWithForEach.txt

@@ -2,12 +2,12 @@ FILE: test.kt
     public final fun <D : R|kotlin/Any|> R|Call<D>|.testForEach(): R|kotlin/Unit| {
         this@R|/testForEach|.R|/Call.arguments|.R|FakeOverride<kotlin/collections/MutableMap.forEach: R|kotlin/Unit|>|(<L> = forEach@fun <anonymous>(key: R|ft<kotlin/String, kotlin/String?>!|, value: R|ft<kotlin/String, kotlin/String?>!|): R|kotlin/Unit| {
             R|<local>/key|.R|kotlin/String.length|
-            ^ R|<local>/value|.R|kotlin/String.length|
+            R|<local>/value|.R|kotlin/String.length|
         }
         )
         this@R|/testForEach|.R|/Call.arguments|.R|kotlin/collections/forEach|<R|ft<kotlin/String, kotlin/String?>!|, R|ft<kotlin/String, kotlin/String?>!|>(<L> = forEach@fun <anonymous>(it: R|kotlin/collections/Map.Entry<ft<kotlin/String, kotlin/String?>!, ft<kotlin/String, kotlin/String?>!>|): R|kotlin/Unit| <kind=UNKNOWN>  {
             R|<local>/it|.R|FakeOverride<kotlin/collections/Map.Entry.key: R|ft<kotlin/String, kotlin/String?>!|>|.R|kotlin/String.length|
-            ^ R|<local>/it|.R|FakeOverride<kotlin/collections/Map.Entry.value: R|ft<kotlin/String, kotlin/String?>!|>|.R|kotlin/String.length|
+            R|<local>/it|.R|FakeOverride<kotlin/collections/Map.Entry.value: R|ft<kotlin/String, kotlin/String?>!|>|.R|kotlin/String.length|
         }
         )
     }

compiler/fir/analysis-tests/testData/resolveWithStdlib/mapList.txt

@@ -7,7 +7,7 @@ FILE: mapList.kt
         )
         R|<local>/u|.R|/applyX|<R|kotlin/collections/List<kotlin/Int>|>(<L> = applyX@fun R|kotlin/collections/List<kotlin/Int>|.<anonymous>(): R|kotlin/Unit| <kind=UNKNOWN>  {
             this@R|special/anonymous|.R|FakeOverride<kotlin/collections/List.contains: R|kotlin/Boolean|>|(Int(1))
-            ^ this@R|special/anonymous|.R|FakeOverride<kotlin/collections/List.contains: R|kotlin/Boolean|>|(Int(1))
+            this@R|special/anonymous|.R|FakeOverride<kotlin/collections/List.contains: R|kotlin/Boolean|>|(Int(1))
         }
         )
     }

compiler/fir/analysis-tests/testData/resolveWithStdlib/noneWithForEach.txt

@@ -11,7 +11,7 @@ FILE: noneWithForEach.kt
         }
         ).R|kotlin/collections/forEach|<R|kotlin/String|, R|kotlin/collections/List<Diagnostic>|>(<L> = forEach@fun <anonymous>(it: R|kotlin/collections/Map.Entry<kotlin/String, kotlin/collections/List<Diagnostic>>|): R|kotlin/Unit| <kind=UNKNOWN>  {
             lval diagnostics: R|kotlin/collections/List<Diagnostic>| = R|<local>/it|.R|FakeOverride<kotlin/collections/Map.Entry.value: R|kotlin/collections/List<Diagnostic>|>|
-            ^ R|<local>/filtered|.R|FakeOverride<java/util/ArrayList.addAll: R|kotlin/Boolean|>|(R|<local>/diagnostics|.R|kotlin/collections/filter|<R|Diagnostic|>(<L> = filter@fun <anonymous>(me: R|Diagnostic|): R|kotlin/Boolean| <kind=UNKNOWN>  {
+            R|<local>/filtered|.R|FakeOverride<java/util/ArrayList.addAll: R|kotlin/Boolean|>|(R|<local>/diagnostics|.R|kotlin/collections/filter|<R|Diagnostic|>(<L> = filter@fun <anonymous>(me: R|Diagnostic|): R|kotlin/Boolean| <kind=UNKNOWN>  {
                 ^ R|<local>/diagnostics|.R|kotlin/collections/none|<R|Diagnostic|>(<L> = none@fun <anonymous>(other: R|Diagnostic|): R|kotlin/Boolean| <kind=UNKNOWN>  {
                     ^ !=(R|<local>/me|, R|<local>/other|)
                 }

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

@@ -748,6 +748,12 @@ open class FirDeclarationsResolveTransformer(transformer: FirBodyResolveTransfor
     }
 
     private fun FirAnonymousFunction.addReturn(): FirAnonymousFunction {
+        // If this lambda's resolved, expected return type is Unit, we don't need an explicit return statement.
+        // During conversion (to backend IR), the last expression will be coerced to Unit if needed.
+        // As per KT-41005, we should not force coercion to Unit for nullable return type, though.
+        if (returnTypeRef.isUnit && body?.typeRef?.isMarkedNullable == false) {
+            return this
+        }
         val lastStatement = body?.statements?.lastOrNull()
         val returnType = (body?.typeRef as? FirResolvedTypeRef) ?: return this
         val returnNothing = returnType.isNothing || returnType.isUnit

compiler/fir/tree/src/org/jetbrains/kotlin/fir/types/FirTypeUtils.kt

@@ -35,15 +35,21 @@ val FirTypeRef.isArrayType: Boolean
         isBuiltinType(StandardClassIds.Array, false) ||
                 StandardClassIds.primitiveArrayTypeByElementType.values.any { isBuiltinType(it, false) }
 
-private fun FirTypeRef.isBuiltinType(classId: ClassId, isNullable: Boolean): Boolean {
+private val FirTypeRef.classLikeTypeOrNull: ConeClassLikeType?
-    val type = when (this) {
+    get() = when (this) {
         is FirImplicitBuiltinTypeRef -> type
-        is FirResolvedTypeRef -> type as? ConeClassLikeType ?: return false
+        is FirResolvedTypeRef -> type as? ConeClassLikeType
-        else -> return false
+        else -> null
     }
+
+private fun FirTypeRef.isBuiltinType(classId: ClassId, isNullable: Boolean): Boolean {
+    val type = this.classLikeTypeOrNull ?: return false
     return type.lookupTag.classId == classId && type.isNullable == isNullable
 }
 
+val FirTypeRef.isMarkedNullable: Boolean?
+    get() = classLikeTypeOrNull?.isMarkedNullable
+
 val FirFunctionTypeRef.parametersCount: Int
     get() = if (receiverTypeRef != null)
         valueParameters.size + 1

compiler/testData/codegen/box/coroutines/coercionToUnit.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // WITH_RUNTIME
 // WITH_COROUTINES
 // COMMON_COROUTINES_TEST

compiler/testData/codegen/box/coroutines/controlFlow/throwInTryWithHandleResult.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // WITH_RUNTIME
 // WITH_COROUTINES
 // COMMON_COROUTINES_TEST

compiler/testData/codegen/box/coroutines/handleResultNonUnitExpression.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // WITH_RUNTIME
 // WITH_COROUTINES
 // COMMON_COROUTINES_TEST

compiler/testData/codegen/box/coroutines/lastStatementInc.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // WITH_RUNTIME
 // WITH_COROUTINES
 // COMMON_COROUTINES_TEST

compiler/testData/diagnostics/tests/inference/completion/postponedArgumentsAnalysis/basic.fir.kt

@@ -142,8 +142,8 @@ fun main() {
     val x18: (C) -> Unit = select(id { <!DEBUG_INFO_EXPRESSION_TYPE("C")!>it<!> }, { <!DEBUG_INFO_EXPRESSION_TYPE("C")!>it<!> }, id<(B) -> Unit> { x -> x })
 
     // Resolution of extension/non-extension functions combination
-    val x19: String.() -> Unit = select(<!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function1<kotlin.String, kotlin.Unit>")!>id { <!DEBUG_INFO_EXPRESSION_TYPE("ERROR CLASS: Unresolved this@null"), DEBUG_INFO_EXPRESSION_TYPE("kotlin.Nothing")!>this<!> }<!>, <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function1<kotlin.String, kotlin.Unit>")!>id(fun(x: String) {})<!>)
+    val x19: String.() -> Unit = select(<!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function1<kotlin.String, kotlin.Unit>")!>id { <!DEBUG_INFO_EXPRESSION_TYPE("ERROR CLASS: Unresolved this@null"), DEBUG_INFO_EXPRESSION_TYPE("ERROR CLASS: Unresolved this@null")!>this<!> }<!>, <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function1<kotlin.String, kotlin.Unit>")!>id(fun(x: String) {})<!>)
-    val x20: String.() -> Unit = select(<!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function1<kotlin.String, kotlin.Unit>")!>{ <!DEBUG_INFO_EXPRESSION_TYPE("ERROR CLASS: Unresolved this@null"), DEBUG_INFO_EXPRESSION_TYPE("kotlin.Nothing")!>this<!> }<!>, (fun(x: String) {}))
+    val x20: String.() -> Unit = select(<!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function1<kotlin.String, kotlin.Unit>")!>{ <!DEBUG_INFO_EXPRESSION_TYPE("ERROR CLASS: Unresolved this@null"), DEBUG_INFO_EXPRESSION_TYPE("ERROR CLASS: Unresolved this@null")!>this<!> }<!>, (fun(x: String) {}))
     val x21: String.() -> Unit = select(<!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function1<kotlin.String, kotlin.Unit>")!>id(fun(x: String) {})<!>, <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function1<kotlin.String, kotlin.Unit>")!>id(fun(x: String) {})<!>)
     select(id<String.() -> Unit>(fun(x: String) {}), <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function1<kotlin.String, kotlin.Unit>")!>id(fun(x: String) {})<!>)
     select(<!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function2<kotlin.String, kotlin.String, kotlin.Unit>")!>id(fun String.(x: String) {})<!>, <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Function2<kotlin.String, kotlin.String, kotlin.Unit>")!>id(fun(x: String, y: String) {})<!>)

compiler/testData/ir/irText/types/coercionToUnitInLambdaReturnValue.fir.txt

@@ -1,12 +0,0 @@
-FILE fqName:<root> fileName:/coercionToUnitInLambdaReturnValue.kt
-  FUN name:use visibility:public modality:FINAL <> (fn:kotlin.Function0<kotlin.Unit>) returnType:kotlin.Unit
-    VALUE_PARAMETER name:fn index:0 type:kotlin.Function0<kotlin.Unit>
-    BLOCK_BODY
-  FUN name:test visibility:public modality:FINAL <> () returnType:kotlin.Unit
-    BLOCK_BODY
-      CALL 'public final fun use (fn: kotlin.Function0<kotlin.Unit>): kotlin.Unit declared in <root>' type=kotlin.Unit origin=null
-        fn: FUN_EXPR type=kotlin.Function0<kotlin.Unit> origin=LAMBDA
-          FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> () returnType:kotlin.Unit
-            BLOCK_BODY
-              RETURN type=kotlin.Nothing from='local final fun <anonymous> (): kotlin.Unit declared in <root>.test'
-                CONST Int type=kotlin.Int value=42

compiler/testData/ir/irText/types/coercionToUnitInLambdaReturnValue.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !LANGUAGE: +NewInference
 
 fun use(fn: () -> Unit) {}