Fix CAST_NEVER_SUCCEEDS when casting Nothing to some type

compiler/frontend/src/org/jetbrains/kotlin/types/CastDiagnosticsUtil.kt

@@ -44,6 +44,7 @@ object CastDiagnosticsUtil {
     ): Boolean {
         val rhsNullable = TypeUtils.isNullableType(rhsType)
         val lhsNullable = TypeUtils.isNullableType(lhsType)
+        if (KotlinBuiltIns.isNothing(lhsType)) return true
         if (KotlinBuiltIns.isNullableNothing(lhsType) && !rhsNullable) return false
         if (KotlinBuiltIns.isNothing(rhsType)) return false
         if (KotlinBuiltIns.isNullableNothing(rhsType)) return lhsNullable

compiler/testData/diagnostics/tests/cast/nothingAs.kt

@@ -0,0 +1,31 @@
+// !DIAGNOSTICS: -UNREACHABLE_CODE
+
+fun TODO(): Nothing = throw java.lang.IllegalStateException()
+
+open class OpenClass
+class FinalClass : OpenClass()
+abstract class AbstractClass
+interface Interface
+
+fun test() {
+    TODO() <!USELESS_CAST!>as Any<!>
+    TODO() <!USELESS_CAST!>as Any?<!>
+    TODO() <!USELESS_CAST!>as OpenClass<!>
+    TODO() <!USELESS_CAST!>as FinalClass<!>
+    TODO() <!USELESS_CAST!>as AbstractClass<!>
+    TODO() <!USELESS_CAST!>as Interface<!>
+
+    val a = TODO() as Any
+    val b = TODO() as Any?
+    val c = TODO() as OpenClass
+    val d = TODO() as FinalClass
+    val e = TODO() as AbstractClass
+    val f = TODO() as Interface
+}
+
+fun a() = TODO() <!USELESS_CAST!>as Any<!>
+fun b() = TODO() <!USELESS_CAST!>as Any?<!>
+fun c() = TODO() <!USELESS_CAST!>as OpenClass<!>
+fun d() = TODO() <!USELESS_CAST!>as FinalClass<!>
+fun e() = TODO() <!USELESS_CAST!>as AbstractClass<!>
+fun f() = TODO() <!USELESS_CAST!>as Interface<!>

compiler/testData/diagnostics/tests/cast/nothingAs.txt

@@ -0,0 +1,37 @@
+package
+
+public fun TODO(): kotlin.Nothing
+public fun a(): kotlin.Any
+public fun b(): kotlin.Any?
+public fun c(): OpenClass
+public fun d(): FinalClass
+public fun e(): AbstractClass
+public fun f(): Interface
+public fun test(): kotlin.Unit
+
+public abstract class AbstractClass {
+    public constructor AbstractClass()
+    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
+}
+
+public final class FinalClass : OpenClass {
+    public constructor FinalClass()
+    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
+}
+
+public interface Interface {
+    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
+}
+
+public open class OpenClass {
+    public constructor OpenClass()
+    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

@@ -3058,6 +3058,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("nothingAs.kt")
+            public void testNothingAs() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/cast/nothingAs.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("NullableToNullable.kt")
             public void testNullableToNullable() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/cast/NullableToNullable.kt");

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

@@ -3058,6 +3058,12 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                 doTest(fileName);
             }
 
+            @TestMetadata("nothingAs.kt")
+            public void testNothingAs() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/cast/nothingAs.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("NullableToNullable.kt")
             public void testNullableToNullable() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/cast/NullableToNullable.kt");