Use initial system for completion if common one is effectively empty

Otherwise we can get unsubstituted type variables as expected types and
 then write wrong information for assertions

 #KT-41470 Fixed

compiler/fir/fir2ir/tests/org/jetbrains/kotlin/codegen/ir/FirBlackBoxCodegenTestGenerated.java

@@ -12652,6 +12652,11 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
             runTest("compiler/testData/codegen/box/inference/manyFlexibleTypeParametersFromJavaAndConversions.kt");
         }
 
+        @TestMetadata("mapCollectChainWithNullResult.kt")
+        public void testMapCollectChainWithNullResult() throws Exception {
+            runTest("compiler/testData/codegen/box/inference/mapCollectChainWithNullResult.kt");
+        }
+
         @TestMetadata("noCoercionToUniForNullableLambdaReturnType.kt")
         public void testNoCoercionToUniForNullableLambdaReturnType() throws Exception {
             runTest("compiler/testData/codegen/box/inference/noCoercionToUniForNullableLambdaReturnType.kt");

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/inference/CoroutineInferenceSession.kt

@@ -174,8 +174,13 @@ class CoroutineInferenceSession(
         diagnosticsHolder: KotlinDiagnosticsHolder,
     ): Map<TypeConstructor, UnwrappedType>? {
         val (commonSystem, effectivelyEmptyConstraintSystem) = buildCommonSystem(initialStorage)
+        val initialStorageSubstitutor = initialStorage.buildResultingSubstitutor(commonSystem, transformTypeVariablesToErrorTypes = false)
         if (effectivelyEmptyConstraintSystem) {
-            updateCalls(lambda, commonSystem)
+            updateCalls(
+                lambda,
+                initialStorageSubstitutor,
+                commonSystem.errors
+            )
             return null
         }
 
@@ -188,7 +193,9 @@ class CoroutineInferenceSession(
             diagnosticsHolder
         )
 
-        updateCalls(lambda, commonSystem)
+        val resultingSubstitutor =
+            ComposedSubstitutor(initialStorageSubstitutor, commonSystem.buildCurrentSubstitutor() as NewTypeSubstitutor)
+        updateCalls(lambda, resultingSubstitutor, commonSystem.errors)
 
         return commonSystem.fixedTypeVariables.cast() // TODO: SUB
     }
@@ -289,23 +296,22 @@ class CoroutineInferenceSession(
         )
     }
 
-    private fun updateCalls(lambda: ResolvedLambdaAtom, commonSystem: NewConstraintSystemImpl) {
+    private fun updateCalls(lambda: ResolvedLambdaAtom, substitutor: NewTypeSubstitutor, errors: List<ConstraintSystemError>) {
         val nonFixedToVariablesSubstitutor = createNonFixedTypeToVariableSubstitutor()
-        val commonSystemSubstitutor = commonSystem.buildCurrentSubstitutor() as NewTypeSubstitutor
 
-        val nonFixedTypesToResult = nonFixedToVariablesSubstitutor.map.mapValues { commonSystemSubstitutor.safeSubstitute(it.value) }
-        val nonFixedTypesToResultSubstitutor = ComposedSubstitutor(commonSystemSubstitutor, nonFixedToVariablesSubstitutor)
+        val nonFixedTypesToResult = nonFixedToVariablesSubstitutor.map.mapValues { substitutor.safeSubstitute(it.value) }
+        val nonFixedTypesToResultSubstitutor = ComposedSubstitutor(substitutor, nonFixedToVariablesSubstitutor)
 
         val atomCompleter = createResolvedAtomCompleter(nonFixedTypesToResultSubstitutor, topLevelCallContext)
 
         for (completedCall in commonCalls) {
             updateCall(completedCall, nonFixedTypesToResultSubstitutor, nonFixedTypesToResult)
-            reportErrors(completedCall, completedCall.resolvedCall, commonSystem.errors)
+            reportErrors(completedCall, completedCall.resolvedCall, errors)
         }
 
         for (callInfo in partiallyResolvedCallsInfo) {
             val resolvedCall = completeCall(callInfo, atomCompleter) ?: continue
-            reportErrors(callInfo, resolvedCall, commonSystem.errors)
+            reportErrors(callInfo, resolvedCall, errors)
         }
 
         for (simpleCall in simpleCommonCalls) {

compiler/testData/codegen/box/inference/mapCollectChainWithNullResult.kt

@@ -0,0 +1,38 @@
+// WITH_RUNTIME
+
+@file:OptIn(kotlin.experimental.ExperimentalTypeInference::class)
+
+interface Flow<out T> {
+    fun collect(collector: FlowCollector<T>)
+}
+
+interface FlowCollector<in T> {
+    fun emit(value: T)
+}
+
+fun <T> flow(block: FlowCollector<T>.() -> Unit): Flow<T> =
+    object : Flow<T> {
+        override fun collect(collector: FlowCollector<T>) = collector.block()
+    }
+
+fun <T> Flow<T>.collect(action: (value: T) -> Unit): Unit =
+    collect(object : FlowCollector<T> {
+        override fun emit(value: T) = action(value)
+    })
+
+fun <T, R> Flow<T>.transform(@BuilderInference transform: FlowCollector<R>.(T) -> Unit): Flow<R> =
+    flow { collect { transform(it) } }
+
+fun <T, R> Flow<T>.map(transform: (T) -> R): Flow<R> =
+    transform { emit(transform(it)) }
+
+var result: Any? = "not null"
+
+fun main() {
+    flow<Int> { emit(1) }.map { null }.collect { result = it }
+}
+
+fun box(): String {
+    main()
+    return if (result == null) "OK" else "fail: $result"
+}

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -13877,6 +13877,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/inference/manyFlexibleTypeParametersFromJavaAndConversions.kt");
         }
 
+        @TestMetadata("mapCollectChainWithNullResult.kt")
+        public void testMapCollectChainWithNullResult() throws Exception {
+            runTest("compiler/testData/codegen/box/inference/mapCollectChainWithNullResult.kt");
+        }
+
         @TestMetadata("noCoercionToUniForNullableLambdaReturnType.kt")
         public void testNoCoercionToUniForNullableLambdaReturnType() throws Exception {
             runTest("compiler/testData/codegen/box/inference/noCoercionToUniForNullableLambdaReturnType.kt");

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -13877,6 +13877,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/inference/manyFlexibleTypeParametersFromJavaAndConversions.kt");
         }
 
+        @TestMetadata("mapCollectChainWithNullResult.kt")
+        public void testMapCollectChainWithNullResult() throws Exception {
+            runTest("compiler/testData/codegen/box/inference/mapCollectChainWithNullResult.kt");
+        }
+
         @TestMetadata("noCoercionToUniForNullableLambdaReturnType.kt")
         public void testNoCoercionToUniForNullableLambdaReturnType() throws Exception {
             runTest("compiler/testData/codegen/box/inference/noCoercionToUniForNullableLambdaReturnType.kt");

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -12652,6 +12652,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/inference/manyFlexibleTypeParametersFromJavaAndConversions.kt");
         }
 
+        @TestMetadata("mapCollectChainWithNullResult.kt")
+        public void testMapCollectChainWithNullResult() throws Exception {
+            runTest("compiler/testData/codegen/box/inference/mapCollectChainWithNullResult.kt");
+        }
+
         @TestMetadata("noCoercionToUniForNullableLambdaReturnType.kt")
         public void testNoCoercionToUniForNullableLambdaReturnType() throws Exception {
             runTest("compiler/testData/codegen/box/inference/noCoercionToUniForNullableLambdaReturnType.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/es6/semantics/IrJsCodegenBoxES6TestGenerated.java

@@ -10827,6 +10827,11 @@ public class IrJsCodegenBoxES6TestGenerated extends AbstractIrJsCodegenBoxES6Tes
             runTest("compiler/testData/codegen/box/inference/lastExpressionOfLambdaWithNothingConstraint.kt");
         }
 
+        @TestMetadata("mapCollectChainWithNullResult.kt")
+        public void testMapCollectChainWithNullResult() throws Exception {
+            runTest("compiler/testData/codegen/box/inference/mapCollectChainWithNullResult.kt");
+        }
+
         @TestMetadata("noCoercionToUniForNullableLambdaReturnType.kt")
         public void testNoCoercionToUniForNullableLambdaReturnType() throws Exception {
             runTest("compiler/testData/codegen/box/inference/noCoercionToUniForNullableLambdaReturnType.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java

@@ -10827,6 +10827,11 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/inference/lastExpressionOfLambdaWithNothingConstraint.kt");
         }
 
+        @TestMetadata("mapCollectChainWithNullResult.kt")
+        public void testMapCollectChainWithNullResult() throws Exception {
+            runTest("compiler/testData/codegen/box/inference/mapCollectChainWithNullResult.kt");
+        }
+
         @TestMetadata("noCoercionToUniForNullableLambdaReturnType.kt")
         public void testNoCoercionToUniForNullableLambdaReturnType() throws Exception {
             runTest("compiler/testData/codegen/box/inference/noCoercionToUniForNullableLambdaReturnType.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -10892,6 +10892,11 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/inference/lastExpressionOfLambdaWithNothingConstraint.kt");
         }
 
+        @TestMetadata("mapCollectChainWithNullResult.kt")
+        public void testMapCollectChainWithNullResult() throws Exception {
+            runTest("compiler/testData/codegen/box/inference/mapCollectChainWithNullResult.kt");
+        }
+
         @TestMetadata("noCoercionToUniForNullableLambdaReturnType.kt")
         public void testNoCoercionToUniForNullableLambdaReturnType() throws Exception {
             runTest("compiler/testData/codegen/box/inference/noCoercionToUniForNullableLambdaReturnType.kt");