KT-12846 Forbid vararg of type 'Nothing' and 'Nothing?'

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -500,6 +500,8 @@ public interface Errors {
 
     DiagnosticFactory0<KtParameter> MULTIPLE_VARARG_PARAMETERS = DiagnosticFactory0.create(ERROR, PARAMETER_VARARG_MODIFIER);
 
+    DiagnosticFactory1<KtParameter, KotlinType> FORBIDDEN_VARARG_PARAMETER_TYPE = DiagnosticFactory1.create(ERROR, PARAMETER_VARARG_MODIFIER);
+
     // Named parameters
 
     DiagnosticFactory0<KtParameter> DEFAULT_VALUE_NOT_ALLOWED_IN_OVERRIDE = DiagnosticFactory0.create(ERROR, PARAMETER_DEFAULT_VALUE);

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -267,6 +267,7 @@ public class DefaultErrorMessages {
         MAP.put(ANONYMOUS_FUNCTION_PARAMETER_WITH_DEFAULT_VALUE, "An anonymous function is not allowed to specify default values for its parameters");
         MAP.put(USELESS_VARARG_ON_PARAMETER, "Vararg on this parameter is useless");
         MAP.put(MULTIPLE_VARARG_PARAMETERS, "Multiple vararg-parameters are prohibited");
+        MAP.put(FORBIDDEN_VARARG_PARAMETER_TYPE, "Forbidden vararg parameter type: {0}", RENDER_TYPE);
 
         MAP.put(HEADER_DECLARATION_WITH_BODY, "Header declaration must not have a body");
         MAP.put(HEADER_DECLARATION_WITH_DEFAULT_PARAMETER, "Header declaration cannot have parameters with default values");

compiler/frontend/src/org/jetbrains/kotlin/resolve/DeclarationsChecker.kt

@@ -34,6 +34,7 @@ import org.jetbrains.kotlin.resolve.BindingContext.*
 import org.jetbrains.kotlin.resolve.DescriptorUtils.classCanHaveAbstractMembers
 import org.jetbrains.kotlin.resolve.DescriptorUtils.classCanHaveOpenMembers
 import org.jetbrains.kotlin.resolve.calls.results.TypeSpecificityComparator
+import org.jetbrains.kotlin.resolve.descriptorUtil.builtIns
 import org.jetbrains.kotlin.resolve.source.KotlinSourceElement
 import org.jetbrains.kotlin.types.*
 import org.jetbrains.kotlin.types.checker.KotlinTypeChecker
@@ -891,15 +892,21 @@ class DeclarationsChecker(
     }
 
     private fun checkVarargParameters(trace: BindingTrace, callableDescriptor: CallableDescriptor) {
-        val numberOfVarargParameters = callableDescriptor.valueParameters.count { it.varargElementType != null }
-        if (numberOfVarargParameters > 1) {
-            for (parameter in callableDescriptor.valueParameters) {
-                if (parameter.varargElementType != null) {
-                    val parameterDeclaration = DescriptorToSourceUtils.descriptorToDeclaration(parameter)
-                    if (parameterDeclaration is KtParameter) {
-                        trace.report(MULTIPLE_VARARG_PARAMETERS.on(parameterDeclaration))
-                    }
-                }
+        val varargParameters = callableDescriptor.valueParameters.filter { it.varargElementType != null }
+
+        if (varargParameters.size > 1) {
+            for (parameter in varargParameters) {
+                val parameterDeclaration = DescriptorToSourceUtils.descriptorToDeclaration(parameter) as? KtParameter ?: continue
+                trace.report(MULTIPLE_VARARG_PARAMETERS.on(parameterDeclaration))
+            }
+        }
+
+        val nullableNothing = callableDescriptor.builtIns.nullableNothingType
+        for (parameter in varargParameters) {
+            val varargElementType = parameter.varargElementType!!.upperIfFlexible()
+            if (KotlinTypeChecker.DEFAULT.isSubtypeOf(varargElementType, nullableNothing)) {
+                val parameterDeclaration = DescriptorToSourceUtils.descriptorToDeclaration(parameter) as? KtParameter ?: continue
+                trace.report(FORBIDDEN_VARARG_PARAMETER_TYPE.on(parameterDeclaration, varargElementType))
             }
         }
     }

compiler/testData/diagnostics/tests/varargs/varargOfNothing.kt

@@ -0,0 +1,15 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+fun testVarargOfNothing(<!FORBIDDEN_VARARG_PARAMETER_TYPE!>vararg<!> v: Nothing) {}
+
+fun testVarargOfNNothing(<!FORBIDDEN_VARARG_PARAMETER_TYPE!>vararg<!> v: Nothing?) {}
+
+fun <T : Nothing?> testVarargOfT(<!FORBIDDEN_VARARG_PARAMETER_TYPE!>vararg<!> v: T) {}
+
+fun outer() {
+    fun testVarargOfNothing(<!FORBIDDEN_VARARG_PARAMETER_TYPE!>vararg<!> v: Nothing) {}
+
+    fun testVarargOfNNothing(<!FORBIDDEN_VARARG_PARAMETER_TYPE!>vararg<!> v: Nothing?) {}
+
+    fun <T : Nothing?> testVarargOfT(<!FORBIDDEN_VARARG_PARAMETER_TYPE!>vararg<!> v: T) {}
+}

compiler/testData/diagnostics/tests/varargs/varargOfNothing.txt

@@ -0,0 +1,6 @@
+package
+
+public fun outer(): kotlin.Unit
+public fun testVarargOfNNothing(/*0*/ vararg v: kotlin.Nothing? /*kotlin.Array<out kotlin.Nothing?>*/): kotlin.Unit
+public fun testVarargOfNothing(/*0*/ vararg v: kotlin.Nothing /*kotlin.Array<out kotlin.Nothing>*/): kotlin.Unit
+public fun </*0*/ T : kotlin.Nothing?> testVarargOfT(/*0*/ vararg v: T /*kotlin.Array<out T>*/): kotlin.Unit

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

@@ -22627,6 +22627,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("varargOfNothing.kt")
+            public void testVarargOfNothing() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/varargs/varargOfNothing.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("varargsAndFunctionLiterals.kt")
             public void testVarargsAndFunctionLiterals() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/varargs/varargsAndFunctionLiterals.kt");