Do not disable 'redundant visibility modifier' inspection completely in Explicit API mode.

Instead, disable it only for effectively public declarations.

Add tests for this IDE inspection.

compiler/testData/diagnostics/testsWithExplicitApi/mustBeEffectivelyPublic.kt

@@ -1,3 +1,20 @@
 private class Foo {
     fun method() {}
+}
+
+public interface I {
+    public fun bar()
+}
+
+public fun f() {
+    val i = object : I {
+        internal var foo = 0
+        override fun bar() {}
+    }
+    i.foo = 1
+
+    class LocalClass {
+        internal var foo = 0
+    }
+    LocalClass().foo = 1
 }

compiler/testData/diagnostics/testsWithExplicitApi/mustBeEffectivelyPublic.txt

@@ -1,5 +1,7 @@
 package
 
+public fun f(): kotlin.Unit
+
 private final class Foo {
     public constructor Foo()
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
@@ -7,3 +9,10 @@ private final class Foo {
     public final fun method(): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
+
+public interface I {
+    public abstract fun bar(): kotlin.Unit
+    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
+}

idea/src/org/jetbrains/kotlin/idea/inspections/RedundantVisibilityModifierInspection.kt

@@ -13,6 +13,8 @@ import org.jetbrains.kotlin.descriptors.PropertyDescriptor
 import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.descriptors.Visibility
 import org.jetbrains.kotlin.config.ExplicitApiMode
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptorWithVisibility
+import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptorIfAny
 import org.jetbrains.kotlin.idea.core.implicitVisibility
 import org.jetbrains.kotlin.idea.project.languageVersionSettings
 import org.jetbrains.kotlin.idea.quickfix.RemoveModifierFix
@@ -25,16 +27,18 @@ import org.jetbrains.kotlin.psi.declarationVisitor
 import org.jetbrains.kotlin.psi.psiUtil.containingClassOrObject
 import org.jetbrains.kotlin.psi.psiUtil.visibilityModifier
 import org.jetbrains.kotlin.utils.addToStdlib.firstNotNullResult
+import org.jetbrains.kotlin.resolve.descriptorUtil.isEffectivelyPublicApi
 
 class RedundantVisibilityModifierInspection : AbstractKotlinInspection(), CleanupLocalInspectionTool {
     override fun buildVisitor(holder: ProblemsHolder, isOnTheFly: Boolean, session: LocalInspectionToolSession): PsiElementVisitor {
         return declarationVisitor(fun(declaration: KtDeclaration) {
             val isInApiMode = declaration.languageVersionSettings.getFlag(AnalysisFlags.explicitApiMode) != ExplicitApiMode.DISABLED
-            if (isInApiMode) return@declarationVisitor
 
             if (declaration is KtPropertyAccessor && declaration.isGetter) return // There is a quick fix for REDUNDANT_MODIFIER_IN_GETTER
             val visibilityModifier = declaration.visibilityModifier() ?: return
             val implicitVisibility = declaration.implicitVisibility()
+            if (isInApiMode && (declaration.resolveToDescriptorIfAny() as? DeclarationDescriptorWithVisibility)?.isEffectivelyPublicApi == true) return@declarationVisitor
+
             val redundantVisibility = when {
                 visibilityModifier.node.elementType == implicitVisibility ->
                     implicitVisibility

idea/testData/inspections/redundantVisibilityModifierWithExplicitApi/inspectionData/expected.xml

@@ -0,0 +1,34 @@
+<problems>
+  <problem>
+    <file>redundantVisibilityModifierWithExplicitApi.kt</file>
+    <line>24</line>
+    <module>light_idea_test_case</module>
+    <entry_point TYPE="file" FQNAME="temp:///src/redundantVisibilityModifierWithExplicitApi.kt" />
+    <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Redundant visibility modifier</problem_class>
+    <description>Redundant visibility modifier</description>
+  </problem>
+  <problem>
+    <file>redundantVisibilityModifierWithExplicitApi.kt</file>
+    <line>29</line>
+    <module>light_idea_test_case</module>
+    <entry_point TYPE="file" FQNAME="temp:///src/redundantVisibilityModifierWithExplicitApi.kt" />
+    <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Redundant visibility modifier</problem_class>
+    <description>Redundant visibility modifier</description>
+  </problem>
+  <problem>
+    <file>redundantVisibilityModifierWithExplicitApi.kt</file>
+    <line>40</line>
+    <module>light_idea_test_case</module>
+    <entry_point TYPE="file" FQNAME="temp:///src/redundantVisibilityModifierWithExplicitApi.kt" />
+    <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Redundant visibility modifier</problem_class>
+    <description>Redundant visibility modifier</description>
+  </problem>
+  <problem>
+    <file>redundantVisibilityModifierWithExplicitApi.kt</file>
+    <line>46</line>
+    <module>light_idea_test_case</module>
+    <entry_point TYPE="file" FQNAME="temp:///src/redundantVisibilityModifierWithExplicitApi.kt" />
+    <problem_class severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">Redundant visibility modifier</problem_class>
+    <description>Redundant visibility modifier</description>
+  </problem>
+</problems>

idea/testData/inspections/redundantVisibilityModifierWithExplicitApi/inspectionData/inspections.test

@@ -0,0 +1,2 @@
+// INSPECTION_CLASS: org.jetbrains.kotlin.idea.inspections.RedundantVisibilityModifierInspection
+// COMPILER_ARGUMENTS: -Xexplicit-api=strict

idea/testData/inspections/redundantVisibilityModifierWithExplicitApi/redundantVisibilityModifierWithExplicitApi.kt

@@ -0,0 +1,49 @@
+public class C {
+    public val foo: Int = 0
+
+    public fun bar() {}
+
+}
+
+open class D {
+    protected open fun willRemainProtected() {
+    }
+
+    protected open fun willBecomePublic() {
+    }
+}
+
+class E : D() {
+    protected override fun willRemainProtected() {
+    }
+
+    public override fun willBecomePublic() {
+    }
+}
+
+enum class F private constructor(val x: Int) {
+    FIRST(42)
+}
+
+sealed class G constructor(val y: Int) {
+    private constructor(): this(42)
+
+    object H : G()
+}
+
+interface I {
+    fun bar()
+}
+
+fun f() {
+    val i = object : I {
+        internal var foo = 0
+        override fun bar() {}
+    }
+    i.foo = 1
+
+    class LocalClass {
+        internal var foo = 0
+    }
+    LocalClass().foo = 1
+}

idea/tests/org/jetbrains/kotlin/idea/codeInsight/InspectionTestGenerated.java

@@ -313,6 +313,11 @@ public class InspectionTestGenerated extends AbstractInspectionTest {
             runTest("idea/testData/inspections/redundantVisibilityModifier/inspectionData/inspections.test");
         }
 
+        @TestMetadata("redundantVisibilityModifierWithExplicitApi/inspectionData/inspections.test")
+        public void testRedundantVisibilityModifierWithExplicitApi_inspectionData_Inspections_test() throws Exception {
+            runTest("idea/testData/inspections/redundantVisibilityModifierWithExplicitApi/inspectionData/inspections.test");
+        }
+
         @TestMetadata("redundantWith/inspectionData/inspections.test")
         public void testRedundantWith_inspectionData_Inspections_test() throws Exception {
             runTest("idea/testData/inspections/redundantWith/inspectionData/inspections.test");