PatternMatchingTypingVisitor:

rewrite type inference for 'when' using special constructs.
This fixes several type inference issues for 'when':
KT-9929, KT-9972, KT-10439, KT-10463
along with some other diagnostics-related issues.

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ControlStructureTypingUtils.java

@@ -65,7 +65,7 @@ public class ControlStructureTypingUtils {
     private static final Logger LOG = Logger.getInstance(ControlStructureTypingUtils.class);
 
     public enum ResolveConstruct {
-        IF("if"), ELVIS("elvis"), EXCL_EXCL("ExclExcl");
+        IF("if"), ELVIS("elvis"), EXCL_EXCL("ExclExcl"), WHEN("when");
 
         private final String name;
 
@@ -188,6 +188,20 @@ public class ControlStructureTypingUtils {
         return createIndependentDataFlowInfoForArgumentsForCall(conditionInfo, dataFlowInfoForArgumentsMap);
     }
 
+    public static MutableDataFlowInfoForArguments createDataFlowInfoForArgumentsOfWhenCall(
+            @NotNull Call callForWhen,
+            @NotNull DataFlowInfo subjectDataFlowInfo,
+            @NotNull List<DataFlowInfo> entryDataFlowInfos
+    ) {
+        Map<ValueArgument, DataFlowInfo> dataFlowInfoForArgumentsMap = Maps.newHashMap();
+        int i = 0;
+        for (ValueArgument argument : callForWhen.getValueArguments()) {
+            DataFlowInfo entryDataFlowInfo = entryDataFlowInfos.get(i++);
+            dataFlowInfoForArgumentsMap.put(argument, entryDataFlowInfo);
+        }
+        return createIndependentDataFlowInfoForArgumentsForCall(subjectDataFlowInfo, dataFlowInfoForArgumentsMap);
+    }
+
     /*package*/ static Call createCallForSpecialConstruction(
             @NotNull final KtExpression expression,
             @NotNull final KtExpression calleeExpression,
@@ -320,6 +334,19 @@ public class ControlStructureTypingUtils {
                 return errorWasReported || checkExpressionType(expression, context);
             }
 
+            @Override
+            public Boolean visitWhenExpression(@NotNull KtWhenExpression whenExpression, CheckTypeContext c) {
+                boolean errorWasReported = false;
+                for (KtWhenEntry whenEntry : whenExpression.getEntries()) {
+                    KtExpression entryExpression = whenEntry.getExpression();
+                    if (entryExpression != null) {
+                        errorWasReported |= checkExpressionTypeRecursively(entryExpression, c);
+                    }
+                }
+                errorWasReported |= checkExpressionType(whenExpression, c);
+                return errorWasReported;
+            }
+
             @Override
             public Boolean visitIfExpression(@NotNull KtIfExpression ifExpression, CheckTypeContext c) {
                 KtExpression thenBranch = ifExpression.getThen();

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/DataFlowAnalyzer.java

@@ -32,7 +32,6 @@ import org.jetbrains.kotlin.resolve.calls.context.ResolutionContext;
 import org.jetbrains.kotlin.resolve.calls.smartcasts.*;
 import org.jetbrains.kotlin.resolve.constants.*;
 import org.jetbrains.kotlin.resolve.constants.evaluate.ConstantExpressionEvaluator;
-import org.jetbrains.kotlin.types.DynamicTypesKt;
 import org.jetbrains.kotlin.types.KotlinType;
 import org.jetbrains.kotlin.types.TypeUtils;
 import org.jetbrains.kotlin.types.checker.KotlinTypeChecker;

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/PatternMatchingTypingVisitor.kt

@@ -16,29 +16,26 @@
 
 package org.jetbrains.kotlin.types.expressions
 
-import com.google.common.collect.Maps
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns.isBoolean
 import org.jetbrains.kotlin.cfg.WhenChecker
+import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.diagnostics.Errors
 import org.jetbrains.kotlin.diagnostics.Errors.*
 import org.jetbrains.kotlin.psi.*
-import org.jetbrains.kotlin.resolve.BindingContext
-import org.jetbrains.kotlin.resolve.DescriptorUtils
-import org.jetbrains.kotlin.resolve.TemporaryBindingTrace
-import org.jetbrains.kotlin.resolve.TypeResolutionContext
+import org.jetbrains.kotlin.resolve.*
 import org.jetbrains.kotlin.resolve.calls.context.ContextDependency.INDEPENDENT
+import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall
 import org.jetbrains.kotlin.resolve.calls.smartcasts.DataFlowInfo
 import org.jetbrains.kotlin.resolve.calls.smartcasts.DataFlowValue
 import org.jetbrains.kotlin.resolve.calls.smartcasts.DataFlowValueFactory
 import org.jetbrains.kotlin.resolve.calls.util.CallMaker
-import org.jetbrains.kotlin.resolve.scopes.LexicalScopeKind
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.types.TypeUtils.NO_EXPECTED_TYPE
 import org.jetbrains.kotlin.types.checker.KotlinTypeChecker
-import org.jetbrains.kotlin.types.expressions.ExpressionTypingUtils.newWritableScopeImpl
+import org.jetbrains.kotlin.types.expressions.ControlStructureTypingUtils.*
 import org.jetbrains.kotlin.types.expressions.typeInfoFactory.createTypeInfo
-import org.jetbrains.kotlin.utils.addIfNotNull
+import java.util.*
 
 class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTypingInternals) : ExpressionTypingVisitor(facade) {
 
@@ -47,9 +44,10 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
         val leftHandSide = expression.leftHandSide
         val typeInfo = facade.safeGetTypeInfo(leftHandSide, context.replaceScope(context.scope))
         val knownType = typeInfo.type
-        if (expression.typeReference != null && knownType != null) {
+        val typeReference = expression.typeReference
+        if (typeReference != null && knownType != null) {
             val dataFlowValue = DataFlowValueFactory.createDataFlowValue(leftHandSide, knownType, context)
-            val conditionInfo = checkTypeForIs(context, knownType, expression.typeReference, dataFlowValue).thenInfo
+            val conditionInfo = checkTypeForIs(context, knownType, typeReference, dataFlowValue).thenInfo
             val newDataFlowInfo = conditionInfo.and(typeInfo.dataFlowInfo)
             context.trace.record(BindingContext.DATAFLOW_INFO_AFTER_CONDITION, expression, newDataFlowInfo)
         }
@@ -59,7 +57,11 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
     override fun visitWhenExpression(expression: KtWhenExpression, context: ExpressionTypingContext) =
             visitWhenExpression(expression, context, false)
 
-    fun visitWhenExpression(expression: KtWhenExpression, contextWithExpectedType: ExpressionTypingContext, isStatement: Boolean): KotlinTypeInfo {
+    fun visitWhenExpression(
+            expression: KtWhenExpression,
+            contextWithExpectedType: ExpressionTypingContext,
+            @Suppress("UNUSED_PARAMETER") isStatement: Boolean
+    ): KotlinTypeInfo {
         WhenChecker.checkDeprecatedWhenSyntax(contextWithExpectedType.trace, expression)
         WhenChecker.checkReservedPrefix(contextWithExpectedType.trace, expression)
 
@@ -69,127 +71,154 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
         // TODO :change scope according to the bound value in the when header
         val subjectExpression = expression.subjectExpression
 
-        val contextAfterSubject: ExpressionTypingContext
-        val subjectType: KotlinType
-        val subjectDataFlowValue: DataFlowValue
-        val jumpOutPossible: Boolean
+        val subjectTypeInfo = subjectExpression?.let { facade.getTypeInfo(it, contextBeforeSubject) }
+        val contextAfterSubject = subjectTypeInfo?.let { contextBeforeSubject.replaceDataFlowInfo(it.dataFlowInfo) } ?: contextBeforeSubject
+        val subjectType = subjectTypeInfo?.type ?: ErrorUtils.createErrorType("Unknown type")
+        val jumpOutPossibleInSubject: Boolean = subjectTypeInfo?.jumpOutPossible ?: false
+        val subjectDataFlowValue = subjectExpression?.let {
+            DataFlowValueFactory.createDataFlowValue(it, subjectType, contextAfterSubject)
+        } ?: DataFlowValue.nullValue(components.builtIns)
 
-        if (subjectExpression == null) {
-            subjectType = ErrorUtils.createErrorType("Unknown type")
-            subjectDataFlowValue = DataFlowValue.nullValue(components.builtIns)
-            contextAfterSubject = contextBeforeSubject
-            jumpOutPossible = false
-        }
-        else {
-            val subjectTypeInfo = facade.safeGetTypeInfo(subjectExpression, contextBeforeSubject)
+        checkSmartCastsInSubjectIfRequired(expression, contextBeforeSubject, subjectType)
 
-            contextAfterSubject = contextBeforeSubject.replaceDataFlowInfo(subjectTypeInfo.dataFlowInfo)
-            subjectType = subjectTypeInfo.type!!
-            subjectDataFlowValue = DataFlowValueFactory.createDataFlowValue(subjectExpression, subjectType, contextAfterSubject)
-            jumpOutPossible = subjectTypeInfo.jumpOutPossible
+        val resolvedCall = resolveSpecialCallForWhen(expression, contextWithExpectedType, contextAfterSubject, subjectDataFlowValue, subjectType)
 
-            if (TypeUtils.isNullableType(subjectType) && !WhenChecker.containsNullCase(expression, contextBeforeSubject.trace.bindingContext)) {
-                val trace = TemporaryBindingTrace.create(contextBeforeSubject.trace, "Temporary trace for when subject nullability")
-                val subjectContext = contextBeforeSubject.replaceExpectedType(TypeUtils.makeNotNullable(subjectType)).replaceBindingTrace(trace)
-                val castResult = DataFlowAnalyzer.checkPossibleCast(
-                        subjectType, KtPsiUtil.safeDeparenthesize(subjectExpression), subjectContext)
-                if (castResult != null && castResult.isCorrect) {
-                    trace.commit()
-                }
-            }
-        }
+        val whenReturnType = resolvedCall.resultingDescriptor.returnType
+        val whenResultValue = whenReturnType?.let { DataFlowValueFactory.createDataFlowValue(expression, it, contextAfterSubject) }
+
+        val (outputDataFlowInfo, jumpOutPossible) =
+                joinWhenExpressionBranches(expression, contextAfterSubject, jumpOutPossibleInSubject, whenResultValue)
 
-        val dataFlowInfoBeforeEntryBodies = collectDataFlowInfoBeforeEntryBodies(expression, contextAfterSubject, subjectType, subjectDataFlowValue)
         val isExhaustive = WhenChecker.isWhenExhaustive(expression, contextAfterSubject.trace)
 
-        return getTypeInfoForIncompleteWhen(expression, isStatement, isExhaustive, contextWithExpectedType,
-                                            contextAfterSubject, jumpOutPossible, dataFlowInfoBeforeEntryBodies)
+        val resultDataFlowInfo = if (expression.elseExpression == null && !isExhaustive) {
+            // Without else expression in non-exhaustive when, we *must* take initial data flow info into account,
+            // because data flow can bypass all when branches in this case
+            outputDataFlowInfo.or(contextAfterSubject.dataFlowInfo)
+        }
+        else {
+            outputDataFlowInfo
+        }
+
+        if (whenReturnType != null && isExhaustive && expression.elseExpression == null && KotlinBuiltIns.isNothing(whenReturnType)) {
+            contextAfterSubject.trace.record(BindingContext.IMPLICIT_EXHAUSTIVE_WHEN, expression)
+        }
+
+        val resultType: KotlinType? = whenReturnType?.let {
+            components.dataFlowAnalyzer.checkType(it, expression, contextWithExpectedType)
+        }
+
+        return createTypeInfo(resultType, resultDataFlowInfo, jumpOutPossible, contextWithExpectedType.dataFlowInfo)
     }
 
-    private fun collectDataFlowInfoBeforeEntryBodies(
+    private fun resolveSpecialCallForWhen(
+            expression: KtWhenExpression,
+            contextWithExpectedType: ExpressionTypingContext,
+            contextAfterSubject: ExpressionTypingContext,
+            subjectDataFlowValue: DataFlowValue,
+            subjectType: KotlinType
+    ): ResolvedCall<FunctionDescriptor> {
+        val wrappedArgumentExpressions = wrapWhenEntryExpressionsAsSpecialCallArguments(expression)
+        val argumentDataFlowInfos = collectInputDataFlowForWhenEntryExpressions(expression, contextAfterSubject, subjectDataFlowValue, subjectType)
+
+        val callForWhen = createCallForSpecialConstruction(expression, expression, wrappedArgumentExpressions)
+        val dataFlowInfoForArguments = createDataFlowInfoForArgumentsOfWhenCall(callForWhen, contextAfterSubject.dataFlowInfo, argumentDataFlowInfos)
+
+        return components.controlStructureTypingUtils.resolveSpecialConstructionAsCall(
+                callForWhen, ResolveConstruct.WHEN,
+                object : AbstractList<String>() {
+                    override fun get(index: Int): String = "entry$index"
+                    override val size: Int get() = wrappedArgumentExpressions.size
+                },
+                Collections.nCopies(wrappedArgumentExpressions.size, false),
+                contextWithExpectedType, dataFlowInfoForArguments)
+    }
+
+    private fun wrapWhenEntryExpressionsAsSpecialCallArguments(expression: KtWhenExpression): List<KtExpression> {
+        val psiFactory = KtPsiFactory(expression)
+        val wrappedArgumentExpressions = expression.entries.mapNotNull { whenEntry ->
+            whenEntry.expression?.let { psiFactory.wrapInABlockWrapper(it) }
+        }
+        return wrappedArgumentExpressions
+    }
+
+    private fun collectInputDataFlowForWhenEntryExpressions(
             expression: KtWhenExpression,
             contextAfterSubject: ExpressionTypingContext,
-            subjectType: KotlinType,
-            subjectDataFlowValue: DataFlowValue
-    ): Map<KtWhenEntry, DataFlowInfo> {
+            subjectDataFlowValue: DataFlowValue,
+            subjectType: KotlinType
+    ): ArrayList<DataFlowInfo> {
         val subjectExpression = expression.subjectExpression
-        val thenInfo = Maps.newHashMapWithExpectedSize<KtWhenEntry, DataFlowInfo>(expression.entries.size)
 
+        val argumentDataFlowInfos = ArrayList<DataFlowInfo>()
         var inputDataFlowInfo = contextAfterSubject.dataFlowInfo
         for (whenEntry in expression.entries) {
             val conditionsInfo = analyzeWhenEntryConditions(whenEntry,
                                                             contextAfterSubject.replaceDataFlowInfo(inputDataFlowInfo),
                                                             subjectExpression, subjectType, subjectDataFlowValue)
-            thenInfo[whenEntry] = conditionsInfo.thenInfo
             inputDataFlowInfo = inputDataFlowInfo.and(conditionsInfo.elseInfo)
-        }
 
-        return thenInfo
+            if (whenEntry.expression != null) {
+                argumentDataFlowInfos.add(conditionsInfo.thenInfo)
+            }
+        }
+        return argumentDataFlowInfos
     }
 
-    private fun getTypeInfoForIncompleteWhen(
+    private fun joinWhenExpressionBranches(
             expression: KtWhenExpression,
-            isStatement: Boolean,
-            isExhaustive: Boolean,
-            contextWithExpectedType: ExpressionTypingContext,
             contextAfterSubject: ExpressionTypingContext,
             jumpOutPossibleInSubject: Boolean,
-            dataFlowBeforeEntryBody: Map<KtWhenEntry, DataFlowInfo>
-    ): KotlinTypeInfo {
-        val coercionStrategy = if (isStatement) CoercionStrategy.COERCION_TO_UNIT else CoercionStrategy.NO_COERCION
+            whenResultValue: DataFlowValue?
+    ): Pair<DataFlowInfo, Boolean> {
+        val bindingContext = contextAfterSubject.trace.bindingContext
 
-        val expressionTypes = hashSetOf<KotlinType>()
-        var commonDataFlowInfo: DataFlowInfo? = null
+        var currentDataFlowInfo: DataFlowInfo? = null
         var jumpOutPossible = jumpOutPossibleInSubject
-        val whenValue = DataFlowValueFactory.createDataFlowValue(expression, components.builtIns.nullableAnyType, contextAfterSubject)
-
         for (whenEntry in expression.entries) {
-            val ifTrueInfo = dataFlowBeforeEntryBody[whenEntry]!!
+            val entryExpression = whenEntry.expression ?: continue
 
-            val bodyExpression = whenEntry.expression
-            if (bodyExpression != null) {
-                val scopeToExtend = newWritableScopeImpl(contextAfterSubject, LexicalScopeKind.WHEN)
-                val contextForEntry = contextWithExpectedType.replaceScope(scopeToExtend).replaceDataFlowInfo(ifTrueInfo).replaceContextDependency(INDEPENDENT)
-                val entryTypeInfo = components.expressionTypingServices.getBlockReturnedTypeWithWritableScope(
-                        scopeToExtend, listOf(bodyExpression), coercionStrategy, contextForEntry)
+            val entryTypeInfo = BindingContextUtils.getRecordedTypeInfo(entryExpression, bindingContext) ?:
+                                throw AssertionError("When entry was not processed")
+            val entryType = entryTypeInfo.type
 
-                jumpOutPossible = jumpOutPossible or entryTypeInfo.jumpOutPossible
+            val entryDataFlowInfo =
+                    if (whenResultValue != null && entryType != null) {
+                        val entryValue = DataFlowValueFactory.createDataFlowValue(entryExpression, entryType, contextAfterSubject)
+                        entryTypeInfo.dataFlowInfo.assign(whenResultValue, entryValue)
+                    }
+                    else {
+                        entryTypeInfo.dataFlowInfo
+                    }
 
-                val entryType = entryTypeInfo.type
+            currentDataFlowInfo =
+                    if (entryType != null && KotlinBuiltIns.isNothing(entryType))
+                        currentDataFlowInfo
+                    else if (currentDataFlowInfo != null)
+                        currentDataFlowInfo.or(entryDataFlowInfo)
+                    else
+                        entryDataFlowInfo
 
-                expressionTypes.addIfNotNull(entryType)
+            jumpOutPossible = jumpOutPossible or entryTypeInfo.jumpOutPossible
+        }
 
-                val entryDataFlowInfo = if (entryType != null) {
-                    val entryValue = DataFlowValueFactory.createDataFlowValue(bodyExpression, entryType, contextAfterSubject)
-                    entryTypeInfo.dataFlowInfo.assign(whenValue, entryValue)
-                }
-                else entryTypeInfo.dataFlowInfo
+        return Pair(currentDataFlowInfo ?: contextAfterSubject.dataFlowInfo, jumpOutPossible)
+    }
 
-                commonDataFlowInfo = commonDataFlowInfo?.or(entryDataFlowInfo) ?: entryDataFlowInfo
+    private fun checkSmartCastsInSubjectIfRequired(expression: KtWhenExpression, contextBeforeSubject: ExpressionTypingContext, subjectType: KotlinType) {
+        val subjectExpression = expression.subjectExpression
+        if (subjectExpression != null &&
+            TypeUtils.isNullableType(subjectType) &&
+            !WhenChecker.containsNullCase(expression, contextBeforeSubject.trace.bindingContext)
+        ) {
+            val trace = TemporaryBindingTrace.create(contextBeforeSubject.trace, "Temporary trace for when subject nullability")
+            val subjectContext = contextBeforeSubject.replaceExpectedType(TypeUtils.makeNotNullable(subjectType)).replaceBindingTrace(trace)
+            val castResult = DataFlowAnalyzer.checkPossibleCast(
+                    subjectType, KtPsiUtil.safeDeparenthesize(subjectExpression), subjectContext)
+            if (castResult != null && castResult.isCorrect) {
+                trace.commit()
             }
         }
-
-        if (commonDataFlowInfo == null) {
-            commonDataFlowInfo = contextAfterSubject.dataFlowInfo
-        }
-        else if (expression.elseExpression == null && !isExhaustive) {
-            // Without else expression in non-exhaustive when, we *must* take initial data flow info into account,
-            // because data flow can bypass all when branches in this case
-            commonDataFlowInfo = commonDataFlowInfo.or(contextAfterSubject.dataFlowInfo)
-        }
-
-        var resultType: KotlinType? = if (expressionTypes.isNotEmpty()) {
-            val commonSupertype = CommonSupertypes.commonSupertype(expressionTypes)
-            val resultValue = DataFlowValueFactory.createDataFlowValue(expression, commonSupertype, contextAfterSubject)
-            commonDataFlowInfo = commonDataFlowInfo.assign(resultValue, whenValue)
-            if (isExhaustive && expression.elseExpression == null && KotlinBuiltIns.isNothing(commonSupertype)) {
-                contextAfterSubject.trace.record(BindingContext.IMPLICIT_EXHAUSTIVE_WHEN, expression)
-            }
-            components.dataFlowAnalyzer.checkType(commonSupertype, expression, contextWithExpectedType)
-        }
-        else null
-
-        return createTypeInfo(resultType, commonDataFlowInfo, jumpOutPossible, contextWithExpectedType.dataFlowInfo)
     }
 
     private fun analyzeWhenEntryConditions(
@@ -232,14 +261,14 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
                 if (subjectExpression == null) {
                     context.trace.report(EXPECTED_CONDITION.on(condition))
                     val dataFlowInfo = facade.getTypeInfo(rangeExpression, context).dataFlowInfo
-                    newDataFlowInfo = ConditionalDataFlowInfo(dataFlowInfo, dataFlowInfo)
+                    newDataFlowInfo = ConditionalDataFlowInfo(dataFlowInfo)
                     return
                 }
                 val argumentForSubject = CallMaker.makeExternalValueArgument(subjectExpression)
                 val typeInfo = facade.checkInExpression(condition, condition.operationReference,
                                                         argumentForSubject, rangeExpression, context)
                 val dataFlowInfo = typeInfo.dataFlowInfo
-                newDataFlowInfo = ConditionalDataFlowInfo(dataFlowInfo, dataFlowInfo)
+                newDataFlowInfo = ConditionalDataFlowInfo(dataFlowInfo)
                 val type = typeInfo.type
                 if (type == null || !isBoolean(type)) {
                     context.trace.report(TYPE_MISMATCH_IN_RANGE.on(condition))
@@ -250,8 +279,9 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
                 if (subjectExpression == null) {
                     context.trace.report(EXPECTED_CONDITION.on(condition))
                 }
-                if (condition.typeReference != null) {
-                    val result = checkTypeForIs(context, subjectType, condition.typeReference, subjectDataFlowValue)
+                val typeReference = condition.typeReference
+                if (typeReference != null) {
+                    val result = checkTypeForIs(context, subjectType, typeReference, subjectDataFlowValue)
                     if (condition.isNegated) {
                         newDataFlowInfo = ConditionalDataFlowInfo(result.elseInfo, result.thenInfo)
                     }
@@ -264,8 +294,8 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
             override fun visitWhenConditionWithExpression(condition: KtWhenConditionWithExpression) {
                 val expression = condition.expression
                 if (expression != null) {
-                    newDataFlowInfo = checkTypeForExpressionCondition(context, expression, subjectType, subjectExpression == null,
-                                                                      subjectDataFlowValue)
+                    newDataFlowInfo = checkTypeForExpressionCondition(
+                            context, expression, subjectType, subjectExpression == null, subjectDataFlowValue)
                 }
             }
 
@@ -280,15 +310,12 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
 
     private fun checkTypeForExpressionCondition(
             context: ExpressionTypingContext,
-            expression: KtExpression?,
+            expression: KtExpression,
             subjectType: KotlinType,
             conditionExpected: Boolean,
             subjectDataFlowValue: DataFlowValue
     ): ConditionalDataFlowInfo {
         var newContext = context
-        if (expression == null) {
-            return noChange(newContext)
-        }
         val typeInfo = facade.getTypeInfo(expression, newContext)
         val type = typeInfo.type ?: return noChange(newContext)
         newContext = newContext.replaceDataFlowInfo(typeInfo.dataFlowInfo)
@@ -306,22 +333,18 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
         }
         checkTypeCompatibility(newContext, type, subjectType, expression)
         val expressionDataFlowValue = DataFlowValueFactory.createDataFlowValue(expression, type, newContext)
-        var result = noChange(newContext)
-        result = ConditionalDataFlowInfo(
+        val result = noChange(newContext)
+        return ConditionalDataFlowInfo(
                 result.thenInfo.equate(subjectDataFlowValue, expressionDataFlowValue),
                 result.elseInfo.disequate(subjectDataFlowValue, expressionDataFlowValue))
-        return result
     }
 
     private fun checkTypeForIs(
             context: ExpressionTypingContext,
             subjectType: KotlinType,
-            typeReferenceAfterIs: KtTypeReference?,
+            typeReferenceAfterIs: KtTypeReference,
             subjectDataFlowValue: DataFlowValue
     ): ConditionalDataFlowInfo {
-        if (typeReferenceAfterIs == null) {
-            return noChange(context)
-        }
         val typeResolutionContext = TypeResolutionContext(context.scope, context.trace, true, /*allowBareTypes=*/ true)
         val possiblyBareTarget = components.typeResolver.resolvePossiblyBareType(typeResolutionContext, typeReferenceAfterIs)
         val targetType = TypeReconstructionUtil.reconstructBareType(typeReferenceAfterIs, possiblyBareTarget, subjectType, context.trace, components.builtIns)
@@ -346,21 +369,18 @@ class PatternMatchingTypingVisitor internal constructor(facade: ExpressionTyping
         return ConditionalDataFlowInfo(context.dataFlowInfo.establishSubtyping(subjectDataFlowValue, targetType), context.dataFlowInfo)
     }
 
-    private fun noChange(context: ExpressionTypingContext) = ConditionalDataFlowInfo(context.dataFlowInfo, context.dataFlowInfo)
+    private fun noChange(context: ExpressionTypingContext) = ConditionalDataFlowInfo(context.dataFlowInfo)
 
     /*
      * (a: SubjectType) is Type
      */
     private fun checkTypeCompatibility(
             context: ExpressionTypingContext,
-            type: KotlinType?,
+            type: KotlinType,
             subjectType: KotlinType,
             reportErrorOn: KtElement
     ) {
         // TODO : Take smart casts into account?
-        if (type == null) {
-            return
-        }
         if (TypeIntersector.isIntersectionEmpty(type, subjectType)) {
             context.trace.report(INCOMPATIBLE_TYPES.on(reportErrorOn, type, subjectType))
             return

compiler/testData/diagnostics/tests/controlStructures/ifWhenWithoutElse.kt

@@ -22,7 +22,7 @@ val wxx1 = <!NO_ELSE_IN_WHEN!>when<!> { true -> 42 }
 val wxx2: Unit = <!NO_ELSE_IN_WHEN!>when<!> { true -> <!CONSTANT_EXPECTED_TYPE_MISMATCH!>42<!> }
 val wxx3 = idAny(<!NO_ELSE_IN_WHEN!>when<!> { true -> 42 })
 val wxx4 = id(<!NO_ELSE_IN_WHEN!>when<!> { true -> 42 })
-val wxx5 = idUnit(<!NO_ELSE_IN_WHEN!>when<!> { true -> 42 })
+val wxx5 = idUnit(<!NO_ELSE_IN_WHEN!>when<!> { true -> <!CONSTANT_EXPECTED_TYPE_MISMATCH!>42<!> })
 val wxx6 = null ?: <!NO_ELSE_IN_WHEN!>when<!> { true -> 42 }
 val wxx7 = "" + <!NO_ELSE_IN_WHEN!>when<!> { true -> 42 }
 

compiler/testData/diagnostics/tests/controlStructures/kt10706.kt

@@ -4,8 +4,8 @@ fun fn(c: Char?): Any? =
         if (c == null) TODO()
         else when (<!DEBUG_INFO_SMARTCAST!>c<!>) {
             'a' -> when (<!DEBUG_INFO_SMARTCAST!>c<!>) {
-                'B' -> <!IMPLICIT_CAST_TO_ANY!>1<!>
-                'C' -> <!IMPLICIT_CAST_TO_ANY!>"sdf"<!>
+                'B' -> 1
+                'C' -> "sdf"
                 else -> TODO()
             }
             else -> TODO()

compiler/testData/diagnostics/tests/smartCasts/elvisExprNotNull.kt

@@ -1,11 +1,10 @@
 fun foo(s: Any?): String {
     val t = when {
         // To resolve: String U Nothing? = String?
-        s is String -> s
+        s is String -> <!DEBUG_INFO_SMARTCAST!>s<!>
         else -> null
     } ?: ""
-    // Ideally we should have smart cast to String here
-    return <!TYPE_MISMATCH!>t<!>
+    return t
 }
 
 fun bar(s: Any?): String {
@@ -24,10 +23,10 @@ fun bar(s: Any?): String {
 
 fun baz(s: String?, r: String?): String {
     val t = r ?: when {
-        s != null -> s
+        s != null -> <!DEBUG_INFO_SMARTCAST!>s<!>
         else -> ""
     }
-    return <!DEBUG_INFO_SMARTCAST!>t<!>
+    return t
 }
 
 fun withNull(s: String?): String {

compiler/testData/diagnostics/tests/smartCasts/ifWhenExprNonNull.kt

@@ -6,8 +6,8 @@ fun baz(s: String?): String {
         val u: String? = null
         when (u) {
             null -> ""
-            else -> u
+            else -> <!DEBUG_INFO_SMARTCAST!>u<!>
         }
     }
-    return <!DEBUG_INFO_SMARTCAST!>t<!>
+    return t
 }

compiler/testData/diagnostics/tests/smartCasts/smartCastOnElvis.kt

@@ -1,15 +1,15 @@
 fun foo(s: String) = s.length
 
 fun baz(s: String?, r: String?): Int {
-    return foo(<!DEBUG_INFO_SMARTCAST!>r ?: when {
-        s != null -> s
+    return foo(r ?: when {
+        s != null -> <!DEBUG_INFO_SMARTCAST!>s<!>
         else -> ""
-    }<!>)
+    })
 }
 
 fun bar(s: String?, r: String?): Int {
-    return <!DEBUG_INFO_SMARTCAST!>(r ?: when {
-        s != null -> s
+    return (r ?: when {
+        s != null -> <!DEBUG_INFO_SMARTCAST!>s<!>
         else -> ""
-    })<!>.length
+    }).length
 }

compiler/testData/diagnostics/tests/smartCasts/smartCastOnWhen.kt

@@ -1,10 +1,10 @@
 // Smart casts on complex expressions
 fun baz(s: String?): Int {
     if (s == null) return 0
-    return <!DEBUG_INFO_SMARTCAST!>when(<!DEBUG_INFO_SMARTCAST!>s<!>) {
-        "abc" -> s
+    return when(<!DEBUG_INFO_SMARTCAST!>s<!>) {
+        "abc" -> <!DEBUG_INFO_SMARTCAST!>s<!>
         else -> "xyz"
-    }<!>.length
+    }.length
 }
 
 var ss: String? = null

compiler/testData/diagnostics/tests/smartCasts/whenExprNonNull.kt

@@ -3,16 +3,16 @@ fun baz(s: String?): String {
     // if explicit type String is given for t, problem disappears
     val t = when(<!DEBUG_INFO_SMARTCAST!>s<!>) {
         // !! is detected as unnecessary here
-        "abc" -> s
+        "abc" -> <!DEBUG_INFO_SMARTCAST!>s<!>
         else -> "xyz"
     }
-    return <!DEBUG_INFO_SMARTCAST!>t<!>
+    return t
 }
 
 fun foo(s: String?): String {
     val t = when {
-        s != null -> s
+        s != null -> <!DEBUG_INFO_SMARTCAST!>s<!>
         else -> ""
     }
-    return <!DEBUG_INFO_SMARTCAST!>t<!>
+    return t
 }

compiler/testData/diagnostics/tests/when/WhenTypeDisjunctions.kt

@@ -1,11 +1,11 @@
 fun foo(s: Any): String {
     val x = when (s) {
-        is String -> s
+        is String -> <!DEBUG_INFO_SMARTCAST!>s<!>
         is Int -> "$s"
         else -> return ""
     }
 
-    val y: String = <!DEBUG_INFO_SMARTCAST!>x<!> // should be Ok
+    val y: String = x // should be Ok
     return y
 }
 

compiler/testData/diagnostics/tests/when/kt10439.kt

@@ -0,0 +1,12 @@
+fun foo(x: Int) = x
+
+fun test0(flag: Boolean) {
+    foo(if (flag) <!CONSTANT_EXPECTED_TYPE_MISMATCH!>true<!> else <!TYPE_MISMATCH!>""<!>)
+}
+
+fun test1(flag: Boolean) {
+    foo(when (flag) {
+        true -> <!CONSTANT_EXPECTED_TYPE_MISMATCH!>true<!>
+        else -> <!TYPE_MISMATCH!>""<!>
+    })
+}

compiler/testData/diagnostics/tests/when/kt10439.txt

@@ -0,0 +1,5 @@
+package
+
+public fun foo(/*0*/ x: kotlin.Int): kotlin.Int
+public fun test0(/*0*/ flag: kotlin.Boolean): kotlin.Unit
+public fun test1(/*0*/ flag: kotlin.Boolean): kotlin.Unit

compiler/testData/diagnostics/tests/when/kt9929.kt

@@ -0,0 +1,9 @@
+val test: Int = if (true) {
+    when (2) {
+        1 -> 1
+        else -> <!NULL_FOR_NONNULL_TYPE!>null<!>
+    }
+}
+else {
+    2
+}

compiler/testData/diagnostics/tests/when/kt9929.txt

@@ -0,0 +1,3 @@
+package
+
+public val test: kotlin.Int

compiler/testData/diagnostics/tests/when/kt9972.kt

@@ -0,0 +1,17 @@
+fun test1(): Int {
+    val x: String = if (true) {
+        when {
+            true -> <!TYPE_MISMATCH!>Any()<!>
+            else -> <!NULL_FOR_NONNULL_TYPE!>null<!>
+        }
+    } else ""
+    return x.hashCode()
+}
+
+fun test2(): Int {
+    val x: String = when {
+                        true -> <!TYPE_MISMATCH!>Any()<!>
+                        else -> null
+                    } ?: return 0
+    return x.hashCode()
+}

compiler/testData/diagnostics/tests/when/kt9972.txt

@@ -0,0 +1,4 @@
+package
+
+public fun test1(): kotlin.Int
+public fun test2(): kotlin.Int

compiler/testData/diagnostics/testsWithStdLib/smartcasts/kt10463.kt

@@ -0,0 +1,6 @@
+val test: Int = listOf<Any>().map {
+    when (it) {
+        is Int -> <!DEBUG_INFO_SMARTCAST!>it<!>
+        else -> throw AssertionError()
+    }
+}.sum()

compiler/testData/diagnostics/testsWithStdLib/smartcasts/kt10463.txt

@@ -0,0 +1,3 @@
+package
+
+public val test: kotlin.Int

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -18525,12 +18525,30 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("kt10439.kt")
+            public void testKt10439() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/kt10439.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("kt4434.kt")
             public void testKt4434() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/kt4434.kt");
                 doTest(fileName);
             }
 
+            @TestMetadata("kt9929.kt")
+            public void testKt9929() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/kt9929.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("kt9972.kt")
+            public void testKt9972() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/kt9972.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("NoElseExpectedUnit.kt")
             public void testNoElseExpectedUnit() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/NoElseExpectedUnit.kt");

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithStdLibGenerated.java

@@ -1102,6 +1102,12 @@ public class DiagnosticsTestWithStdLibGenerated extends AbstractDiagnosticsTestW
             doTest(fileName);
         }
 
+        @TestMetadata("kt10463.kt")
+        public void testKt10463() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithStdLib/smartcasts/kt10463.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("lazyDeclaresAndModifies.kt")
         public void testLazyDeclaresAndModifies() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithStdLib/smartcasts/lazyDeclaresAndModifies.kt");

idea/testData/checker/infos/SmartCastOnWhen.kt

@@ -1,7 +1,7 @@
 fun baz(s: String?): Int {
     if (s == null) return 0
-    return <info descr="Smart cast to kotlin.String">when</info>(<info descr="Smart cast to kotlin.String">s</info>) {
-        "abc" -> s
+    return when(<info descr="Smart cast to kotlin.String">s</info>) {
+        "abc" -> <info descr="Smart cast to kotlin.String">s</info>
         else -> "xyz"
     }.length
 }

idea/testData/checker/infos/smartCastOnElvis.kt

@@ -1,15 +1,15 @@
 fun foo(s: String) = s.length
 
 fun baz(s: String?, r: String?): Int {
-    return foo(r <info descr="Smart cast to kotlin.String">?:</info> when {
-        s != null -> s
+    return foo(r ?: when {
+        s != null -> <info descr="Smart cast to kotlin.String">s</info>
         else -> ""
     })
 }
 
 fun bar(s: String?, r: String?): Int {
-    return (r <info descr="Smart cast to kotlin.String">?:</info> when {
-        s != null -> s
+    return (r ?: when {
+        s != null -> <info descr="Smart cast to kotlin.String">s</info>
         else -> ""
     }).length
 }