NI: use the inferred type to check of nullable array for vararg

^KT-40555 Fixed

compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirOldFrontendDiagnosticsTestGenerated.java

@@ -24847,6 +24847,11 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirOldFronte
             runTest("compiler/testData/diagnostics/tests/varargs/assigningSingleElementsInNamedFormFunDeprecation_before.kt");
         }
 
+        @TestMetadata("inferredNullableArrayAsVararg.kt")
+        public void testInferredNullableArrayAsVararg() throws Exception {
+            runTest("compiler/testData/diagnostics/tests/varargs/inferredNullableArrayAsVararg.kt");
+        }
+
         @TestMetadata("kt1781.kt")
         public void testKt1781() throws Exception {
             runTest("compiler/testData/diagnostics/tests/varargs/kt1781.kt");

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/checkers/NullableVarargArgumentCallChecker.kt

@@ -8,12 +8,13 @@ package org.jetbrains.kotlin.resolve.calls.checkers
 import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.resolve.BindingContext.EXPRESSION_TYPE_INFO
 import org.jetbrains.kotlin.resolve.calls.components.stableType
+import org.jetbrains.kotlin.resolve.calls.inference.model.TypeVariableTypeConstructor
 import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall
 import org.jetbrains.kotlin.resolve.calls.model.VariableAsFunctionResolvedCall
-import org.jetbrains.kotlin.resolve.calls.tower.ExpressionKotlinCallArgumentImpl
 import org.jetbrains.kotlin.resolve.calls.tower.NewResolvedCallImpl
-import org.jetbrains.kotlin.resolve.calls.tower.NewVariableAsFunctionResolvedCallImpl
+import org.jetbrains.kotlin.resolve.calls.tower.SimplePSIKotlinCallArgument
 import org.jetbrains.kotlin.resolve.scopes.receivers.ReceiverValueWithSmartCastInfo
 import org.jetbrains.kotlin.types.FlexibleType
 import org.jetbrains.kotlin.types.TypeUtils
@@ -29,11 +30,18 @@ object NullableVarargArgumentCallChecker : CallChecker {
         if (resolvedCall !is NewResolvedCallImpl<*>) return
         for (argument in resolvedCall.argumentMappingByOriginal.values) {
             for (arg in argument.arguments) {
-                if (!arg.isSpread || arg !is ExpressionKotlinCallArgumentImpl) continue
-                val spreadElement = arg.valueArgument.getSpreadElement() ?: continue
+                if (!arg.isSpread || arg !is SimplePSIKotlinCallArgument) continue
 
+                val spreadElement = arg.valueArgument.getSpreadElement() ?: continue
                 val receiver = arg.receiver.safeAs<ReceiverValueWithSmartCastInfo>() ?: continue
-                val type = receiver.stableType
+
+                val type = if (receiver.stableType.constructor is TypeVariableTypeConstructor) {
+                    context.trace.bindingContext[EXPRESSION_TYPE_INFO, arg.valueArgument.getArgumentExpression()]?.type
+                        ?: receiver.stableType
+                } else {
+                    receiver.stableType
+                }
+
                 if (type !is FlexibleType && TypeUtils.isNullableType(type)) {
                     context.trace.report(Errors.SPREAD_OF_NULLABLE.on(spreadElement))
                 }

compiler/testData/diagnostics/tests/varargs/inferredNullableArrayAsVararg.fir.kt

@@ -0,0 +1,15 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+// FILE: Test.java
+public class Test {
+    static public void foo(String ... x) {
+
+    }
+}
+
+// FILE: test.kt
+fun <T> select(vararg x: T) = x[1]
+
+fun main(x: Array<String>?) {
+    Test.foo(*(select(arrayOf(""), null))) // no compilation errors before the fix, NPE
+}

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

@@ -0,0 +1,15 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+// FILE: Test.java
+public class Test {
+    static public void foo(String ... x) {
+
+    }
+}
+
+// FILE: test.kt
+fun <T> select(vararg x: T) = x[1]
+
+fun main(x: Array<String>?) {
+    Test.foo(<!SPREAD_OF_NULLABLE!>*<!>(select(arrayOf(""), null))) // no compilation errors before the fix, NPE
+}

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

@@ -0,0 +1,14 @@
+package
+
+public fun main(/*0*/ x: kotlin.Array<kotlin.String>?): kotlin.Unit
+public fun </*0*/ T> select(/*0*/ vararg x: T /*kotlin.Array<out T>*/): T
+
+public open class Test {
+    public constructor Test()
+    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
+
+    // Static members
+    public open fun foo(/*0*/ vararg x: kotlin.String! /*kotlin.Array<(out) kotlin.String!>!*/): kotlin.Unit
+}

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

@@ -24929,6 +24929,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTestWithFirVali
                 runTest("compiler/testData/diagnostics/tests/varargs/assigningSingleElementsInNamedFormFunDeprecation_before.kt");
             }
 
+            @TestMetadata("inferredNullableArrayAsVararg.kt")
+            public void testInferredNullableArrayAsVararg() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/varargs/inferredNullableArrayAsVararg.kt");
+            }
+
             @TestMetadata("kt1781.kt")
             public void testKt1781() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/varargs/kt1781.kt");

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

@@ -24849,6 +24849,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                 runTest("compiler/testData/diagnostics/tests/varargs/assigningSingleElementsInNamedFormFunDeprecation_before.kt");
             }
 
+            @TestMetadata("inferredNullableArrayAsVararg.kt")
+            public void testInferredNullableArrayAsVararg() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/varargs/inferredNullableArrayAsVararg.kt");
+            }
+
             @TestMetadata("kt1781.kt")
             public void testKt1781() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/varargs/kt1781.kt");