[NI] Eliminate special intersection type from result type

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/inference/model/NewConstraintSystemImpl.kt

@@ -25,10 +25,14 @@ import org.jetbrains.kotlin.resolve.calls.inference.components.NewTypeSubstituto
 import org.jetbrains.kotlin.resolve.calls.inference.components.ResultTypeResolver
 import org.jetbrains.kotlin.resolve.calls.model.KotlinCallDiagnostic
 import org.jetbrains.kotlin.resolve.calls.tower.isSuccess
+import org.jetbrains.kotlin.types.IntersectionTypeConstructor
 import org.jetbrains.kotlin.types.TypeConstructor
 import org.jetbrains.kotlin.types.UnwrappedType
+import org.jetbrains.kotlin.types.typeUtil.builtIns
 import org.jetbrains.kotlin.types.typeUtil.contains
+import org.jetbrains.kotlin.types.typeUtil.isTypeParameter
 import org.jetbrains.kotlin.utils.SmartList
+import org.jetbrains.kotlin.utils.addToStdlib.safeAs
 
 class NewConstraintSystemImpl(
         private val constraintInjector: ConstraintInjector,
@@ -201,7 +205,8 @@ class NewConstraintSystemImpl(
     override fun fixVariable(variable: NewTypeVariable, resultType: UnwrappedType) {
         checkState(State.BUILDING, State.COMPLETION)
 
-        constraintInjector.addInitialEqualityConstraint(this, variable.defaultType, resultType, FixVariableConstraintPosition(variable))
+        val actualResultType = eliminateSpecialIntersectionType(resultType) ?: resultType
+        constraintInjector.addInitialEqualityConstraint(this, variable.defaultType, actualResultType, FixVariableConstraintPosition(variable))
         notFixedTypeVariables.remove(variable.freshTypeConstructor)
 
         for (variableWithConstraint in notFixedTypeVariables.values) {
@@ -210,7 +215,16 @@ class NewConstraintSystemImpl(
             }
         }
 
-        storage.fixedTypeVariables[variable.freshTypeConstructor] = resultType
+        storage.fixedTypeVariables[variable.freshTypeConstructor] = actualResultType
+    }
+
+    private fun eliminateSpecialIntersectionType(type: UnwrappedType): UnwrappedType? {
+        val constructor = type.constructor.safeAs<IntersectionTypeConstructor>() ?: return null
+
+        if (constructor.supertypes.size != 2) return null
+        val actualType = constructor.supertypes.singleOrNull { it != type.builtIns.anyType }
+
+        return actualType?.unwrap()
     }
 
     // KotlinConstraintSystemCompleter.Context, PostponedArgumentsAnalyzer.Context

compiler/testData/codegen/box/regressions/approximateIntersectionType.kt

@@ -0,0 +1,30 @@
+// WITH_RUNTIME
+// IGNORE_BACKEND: JS, NATIVE
+
+// FILE: First.java
+
+import java.util.List;
+import java.util.Iterator;
+
+public class First {
+    public static <A> List<A> from(List<A> var0) {
+        return null;
+    }
+}
+
+// FILE: second.kt
+
+fun <T> List<T>.listFromJava() = First.from(this)
+fun <T> List<T>.listFromKotlin() = fromKotlin(this)
+
+fun <T> fromKotlin(var0: List<T?>): List<T?> = var0
+
+fun test(a: List<Int>) {
+    val b: List<Int>? = a.listFromJava()
+    val c: List<Int?> = a.listFromKotlin()
+}
+
+fun box(): String {
+    test(listOf(1))
+    return "OK"
+}

compiler/testData/codegen/box/regressions/intersectionAsLastLambda.kt

@@ -0,0 +1,23 @@
+// IGNORE_BACKEND: JS, NATIVE
+
+// FILE: First.java
+
+public class First<T> {
+    public static <K> First<K> first(K key) {
+        return null;
+    }
+}
+
+// FILE: second.kt
+
+class Inv<T>(val key: T)
+
+fun <T, R> lastLambda(x: T, block: (T) -> R): R = block(x)
+
+fun <S> myTest(m: Inv<S>) {
+    lastLambda(m) { First.first(it.key) }
+}
+
+fun box(): String {
+    return "OK"
+}

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

@@ -16580,6 +16580,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/regressions"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
         }
 
+        @TestMetadata("approximateIntersectionType.kt")
+        public void testApproximateIntersectionType() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/approximateIntersectionType.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("arrayLengthNPE.kt")
         public void testArrayLengthNPE() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/arrayLengthNPE.kt");
@@ -16652,6 +16658,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             doTest(fileName);
         }
 
+        @TestMetadata("intersectionAsLastLambda.kt")
+        public void testIntersectionAsLastLambda() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/intersectionAsLastLambda.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("intersectionOfEqualTypes.kt")
         public void testIntersectionOfEqualTypes() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/intersectionOfEqualTypes.kt");

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

@@ -16580,6 +16580,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/regressions"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
         }
 
+        @TestMetadata("approximateIntersectionType.kt")
+        public void testApproximateIntersectionType() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/approximateIntersectionType.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("arrayLengthNPE.kt")
         public void testArrayLengthNPE() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/arrayLengthNPE.kt");
@@ -16652,6 +16658,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
+        @TestMetadata("intersectionAsLastLambda.kt")
+        public void testIntersectionAsLastLambda() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/intersectionAsLastLambda.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("intersectionOfEqualTypes.kt")
         public void testIntersectionOfEqualTypes() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/intersectionOfEqualTypes.kt");

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

@@ -16580,6 +16580,12 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/regressions"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
         }
 
+        @TestMetadata("approximateIntersectionType.kt")
+        public void testApproximateIntersectionType() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/approximateIntersectionType.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("arrayLengthNPE.kt")
         public void testArrayLengthNPE() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/arrayLengthNPE.kt");
@@ -16652,6 +16658,12 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             doTest(fileName);
         }
 
+        @TestMetadata("intersectionAsLastLambda.kt")
+        public void testIntersectionAsLastLambda() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/intersectionAsLastLambda.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("intersectionOfEqualTypes.kt")
         public void testIntersectionOfEqualTypes() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/intersectionOfEqualTypes.kt");

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

@@ -20222,6 +20222,18 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/regressions"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JS, true);
         }
 
+        @TestMetadata("approximateIntersectionType.kt")
+        public void testApproximateIntersectionType() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/approximateIntersectionType.kt");
+            try {
+                doTest(fileName);
+            }
+            catch (Throwable ignore) {
+                return;
+            }
+            throw new AssertionError("Looks like this test can be unmuted. Remove IGNORE_BACKEND directive for that.");
+        }
+
         @TestMetadata("arrayLengthNPE.kt")
         public void testArrayLengthNPE() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/arrayLengthNPE.kt");
@@ -20306,6 +20318,18 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             doTest(fileName);
         }
 
+        @TestMetadata("intersectionAsLastLambda.kt")
+        public void testIntersectionAsLastLambda() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/intersectionAsLastLambda.kt");
+            try {
+                doTest(fileName);
+            }
+            catch (Throwable ignore) {
+                return;
+            }
+            throw new AssertionError("Looks like this test can be unmuted. Remove IGNORE_BACKEND directive for that.");
+        }
+
         @TestMetadata("intersectionOfEqualTypes.kt")
         public void testIntersectionOfEqualTypes() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/regressions/intersectionOfEqualTypes.kt");