[NI] Fix coercion to Unit for lambdas with empty labeled return

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/tower/KotlinResolutionCallbacksImpl.kt

@@ -178,10 +178,10 @@ class KotlinResolutionCallbacksImpl(
         }
 
         val lastExpressionArgument = getLastDeparentesizedExpression(psiCallArgument)?.let { lastExpression ->
-            if (expectedReturnType?.isUnit() == true) return@let null // coercion to Unit
+            if (expectedReturnType?.isUnit() == true || hasReturnWithoutExpression) return@let null // coercion to Unit
 
             // todo lastExpression can be if without else
-            val lastExpressionType = if (hasReturnWithoutExpression) null else trace.getType(lastExpression)
+            val lastExpressionType = trace.getType(lastExpression)
             val contextInfo = lambdaInfo.lastExpressionInfo
             val lastExpressionTypeInfo = KotlinTypeInfo(lastExpressionType, contextInfo.dataFlowInfoAfter ?: functionTypeInfo.dataFlowInfo)
             createCallArgument(lastExpression, lastExpressionTypeInfo, contextInfo.lexicalScope, contextInfo.trace)

compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionToUnitForIfAsLastExpressionInLambda.kt

@@ -0,0 +1,42 @@
+// !LANGUAGE: +NewInference
+
+class Obj
+
+fun foo(): String? {
+    run {
+        if (true) return@run
+
+        if (true) Obj()
+    }
+
+    run {
+        if (true) return@run
+
+        if (true) return <!TYPE_MISMATCH, TYPE_MISMATCH!>Obj()<!> // correct error, type check against return type of function "foo"
+    }
+
+    run {
+        if (true)
+            return@run
+        else
+            if (true) <!UNUSED_EXPRESSION!>42<!>
+    }
+
+    run {
+        if (true)
+            42
+        else
+            <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42
+    }
+
+    run {
+        if (true) return@run
+
+        if (true) {
+            Obj()
+        } else
+            if (true) return null
+    }
+
+    return ""
+}

compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionToUnitForIfAsLastExpressionInLambda.txt

@@ -0,0 +1,10 @@
+package
+
+public fun foo(): kotlin.String?
+
+public final class Obj {
+    public constructor Obj()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/inference/coercionToUnit/nonPropagationOfCoercionToUnitInsideNestedLambda.kt

@@ -0,0 +1,52 @@
+// !LANGUAGE: +NewInference
+
+class Obj
+
+fun foo(): String? {
+    run {
+        if (true) return@run
+
+        run {
+            if (true) {
+                Obj()
+            } else
+                <!INVALID_IF_AS_EXPRESSION!>if<!> (true) return null // Error, coercion to Unit doesn't propagate inside nested lambdas
+        }
+
+        if (true) {
+            Obj()
+        } else
+            if (true) return null // OK, no error
+    }
+
+    run {
+        if (true) return@run
+
+        run {
+            if (true) {
+                Obj()
+            } else
+            <!INVALID_IF_AS_EXPRESSION!>if<!> (true) return null // Error, coercion to Unit doesn't propagate inside nested lambdas
+        }
+    }
+
+    run {
+        if (true) return@run
+
+        run nestedRun@{
+            if (true) return@nestedRun
+
+            if (true) {
+                Obj()
+            } else
+                if (true) return null // OK, additional empty labeled return helps
+        }
+
+        if (true) {
+            Obj()
+        } else
+            if (true) return null // OK, no error
+    }
+
+    return ""
+}

compiler/testData/diagnostics/tests/inference/coercionToUnit/nonPropagationOfCoercionToUnitInsideNestedLambda.txt

@@ -0,0 +1,10 @@
+package
+
+public fun foo(): kotlin.String?
+
+public final class Obj {
+    public constructor Obj()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

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

@@ -9710,6 +9710,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/diagnostics/tests/inference/coercionToUnit"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.ANY, true);
                 }
 
+                @TestMetadata("coercionToUnitForIfAsLastExpressionInLambda.kt")
+                public void testCoercionToUnitForIfAsLastExpressionInLambda() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionToUnitForIfAsLastExpressionInLambda.kt");
+                }
+
                 @TestMetadata("coercionWithExpectedType.kt")
                 public void testCoercionWithExpectedType() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionWithExpectedType.kt");
@@ -9739,6 +9744,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 public void testNoCoercion() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/coercionToUnit/noCoercion.kt");
                 }
+
+                @TestMetadata("nonPropagationOfCoercionToUnitInsideNestedLambda.kt")
+                public void testNonPropagationOfCoercionToUnitInsideNestedLambda() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/coercionToUnit/nonPropagationOfCoercionToUnitInsideNestedLambda.kt");
+                }
             }
 
             @TestMetadata("compiler/testData/diagnostics/tests/inference/commonSystem")

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java

@@ -9710,6 +9710,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/diagnostics/tests/inference/coercionToUnit"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.ANY, true);
                 }
 
+                @TestMetadata("coercionToUnitForIfAsLastExpressionInLambda.kt")
+                public void testCoercionToUnitForIfAsLastExpressionInLambda() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionToUnitForIfAsLastExpressionInLambda.kt");
+                }
+
                 @TestMetadata("coercionWithExpectedType.kt")
                 public void testCoercionWithExpectedType() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionWithExpectedType.kt");
@@ -9739,6 +9744,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                 public void testNoCoercion() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/inference/coercionToUnit/noCoercion.kt");
                 }
+
+                @TestMetadata("nonPropagationOfCoercionToUnitInsideNestedLambda.kt")
+                public void testNonPropagationOfCoercionToUnitInsideNestedLambda() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/coercionToUnit/nonPropagationOfCoercionToUnitInsideNestedLambda.kt");
+                }
             }
 
             @TestMetadata("compiler/testData/diagnostics/tests/inference/commonSystem")