Report warning on @JvmStatic in private companion objects

Deprecation cycle to prohibit in 1.5.
^KT-25114 In Progress

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/checkers/JvmStaticInPrivateCompanionChecker.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.resolve.jvm.checkers
+
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.descriptors.Visibilities
+import org.jetbrains.kotlin.diagnostics.Errors.JVM_STATIC_IN_PRIVATE_COMPANION
+import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.resolve.annotations.JVM_STATIC_ANNOTATION_FQ_NAME
+import org.jetbrains.kotlin.resolve.checkers.DeclarationChecker
+import org.jetbrains.kotlin.resolve.checkers.DeclarationCheckerContext
+import org.jetbrains.kotlin.resolve.source.KotlinSourceElement
+import org.jetbrains.kotlin.utils.addToStdlib.safeAs
+
+class JvmStaticInPrivateCompanionChecker : DeclarationChecker {
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+
+        descriptor.containingDeclaration.safeAs<ClassDescriptor>()?.takeIf {
+            it.isCompanionObject && Visibilities.isPrivate(it.visibility.delegate)
+        } ?: return
+
+        val jvmStaticAnnotation = descriptor.annotations.findAnnotation(JVM_STATIC_ANNOTATION_FQ_NAME) ?: return
+
+        val reportTarget = jvmStaticAnnotation.source.safeAs<KotlinSourceElement>()?.psi ?: declaration
+        context.trace.report(JVM_STATIC_IN_PRIVATE_COMPANION.on(reportTarget))
+    }
+}

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/platform/JvmPlatformConfigurator.kt

@@ -95,6 +95,7 @@ object JvmPlatformConfigurator : PlatformConfiguratorBase(
 ) {
     override fun configureModuleComponents(container: StorageComponentContainer) {
         container.useImpl<JvmStaticChecker>()
+        container.useImpl<JvmStaticInPrivateCompanionChecker>()
         container.useImpl<JvmReflectionAPICallChecker>()
         container.useImpl<JavaSyntheticScopes>()
         container.useImpl<SamConversionResolverImpl>()

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

@@ -285,6 +285,7 @@ public interface Errors {
     DiagnosticFactory1<PsiElement, String> EXPERIMENTAL_UNSIGNED_LITERALS_ERROR = DiagnosticFactory1.create(ERROR);
 
     DiagnosticFactory0<PsiElement> NON_PARENTHESIZED_ANNOTATIONS_ON_FUNCTIONAL_TYPES = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> JVM_STATIC_IN_PRIVATE_COMPANION = DiagnosticFactory0.create(WARNING);
 
     // Const
     DiagnosticFactory0<PsiElement> CONST_VAL_NOT_TOP_LEVEL_OR_OBJECT = DiagnosticFactory0.create(ERROR);

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

@@ -169,6 +169,7 @@ public class DefaultErrorMessages {
         MAP.put(EXPERIMENTAL_UNSIGNED_LITERALS_ERROR, "{0}", STRING);
 
         MAP.put(NON_PARENTHESIZED_ANNOTATIONS_ON_FUNCTIONAL_TYPES, "Non-parenthesized annotations on function types without receiver aren't yet supported (see KT-31734 for details)");
+        MAP.put(JVM_STATIC_IN_PRIVATE_COMPANION, "@JvmStatic is prohibited in private companion objects. This warning will become an error in the next major version");
 
         MAP.put(REDUNDANT_MODIFIER, "Modifier ''{0}'' is redundant because ''{1}'' is present", TO_STRING, TO_STRING);
         MAP.put(REDUNDANT_OPEN_IN_INTERFACE, "Modifier 'open' is redundant for abstract interface members");

compiler/testData/diagnostics/testsWithStdLib/annotations/jvmStatic/privateCompanionObject.fir.kt

@@ -0,0 +1,29 @@
+// Issue: KT-25114
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+class WithPrivateCompanion {
+    private companion object {
+        @JvmStatic
+        val staticVal1: Int = 42
+
+        val staticVal2: Int
+            @JvmStatic get() = 42
+
+        @get:JvmStatic
+        val staticVal3: Int = 42
+
+        @JvmStatic
+        var staticVar1: Int = 42
+
+        var staticVar2: Int
+            @JvmStatic get() = 42
+            @JvmStatic set(value) {}
+
+        @get: JvmStatic
+        @set: JvmStatic
+        var staticVar3: Int = 42
+
+        @JvmStatic
+        fun staticFunction() {}
+    }
+}

compiler/testData/diagnostics/testsWithStdLib/annotations/jvmStatic/privateCompanionObject.kt

@@ -1,30 +1,29 @@
 // Issue: KT-25114
-// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 class WithPrivateCompanion {
     private companion object {
-        @JvmStatic
+        <!JVM_STATIC_IN_PRIVATE_COMPANION!>@JvmStatic<!>
         val staticVal1: Int = 42
 
         val staticVal2: Int
-            @JvmStatic get() = 42
+            <!JVM_STATIC_IN_PRIVATE_COMPANION!>@JvmStatic<!> get() = 42
 
-        @get:JvmStatic
+        <!JVM_STATIC_IN_PRIVATE_COMPANION!>@get:JvmStatic<!>
         val staticVal3: Int = 42
 
-        @JvmStatic
+        <!JVM_STATIC_IN_PRIVATE_COMPANION!>@JvmStatic<!>
         var staticVar1: Int = 42
 
         var staticVar2: Int
-            @JvmStatic get() = 42
-            @JvmStatic set(value) {}
+            <!JVM_STATIC_IN_PRIVATE_COMPANION!>@JvmStatic<!> get() = 42
+            <!JVM_STATIC_IN_PRIVATE_COMPANION!>@JvmStatic<!> set(value) {}
 
-        @get: JvmStatic
-        @set: JvmStatic
+        <!JVM_STATIC_IN_PRIVATE_COMPANION!>@get: JvmStatic<!>
+        <!JVM_STATIC_IN_PRIVATE_COMPANION!>@set: JvmStatic<!>
         var staticVar3: Int = 42
 
-        @JvmStatic
+        <!JVM_STATIC_IN_PRIVATE_COMPANION!>@JvmStatic<!>
         fun staticFunction() {}
     }
 }