Add inspection to highlight unnecessary explicit companion references

So #KT-22971 Fixed

idea/src/META-INF/plugin.xml

@@ -2746,6 +2746,15 @@
                      language="kotlin"
     />
 
+    <localInspection implementationClass="org.jetbrains.kotlin.idea.inspections.RedundantCompanionReferenceInspection"
+                     displayName="Redundant Companion reference"
+                     groupPath="Kotlin"
+                     groupName="Redundant constructs"
+                     enabledByDefault="true"
+                     level="WARNING"
+                     language="kotlin"
+    />
+
     <referenceImporter implementation="org.jetbrains.kotlin.idea.quickfix.KotlinReferenceImporter"/>
 
     <fileType.fileViewProviderFactory filetype="KJSM" implementationClass="com.intellij.psi.ClassFileViewProviderFactory"/>

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

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2000-2018 JetBrains s.r.o. 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.idea.inspections
+
+import com.intellij.codeInspection.LocalQuickFix
+import com.intellij.codeInspection.ProblemDescriptor
+import com.intellij.codeInspection.ProblemHighlightType
+import com.intellij.codeInspection.ProblemsHolder
+import com.intellij.openapi.project.Project
+import com.intellij.psi.PsiElementVisitor
+import org.jetbrains.kotlin.idea.references.mainReference
+import org.jetbrains.kotlin.idea.search.usagesSearch.descriptor
+import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
+import org.jetbrains.kotlin.resolve.DescriptorUtils
+
+class RedundantCompanionReferenceInspection : AbstractKotlinInspection() {
+    override fun buildVisitor(holder: ProblemsHolder, isOnTheFly: Boolean): PsiElementVisitor {
+        return referenceExpressionVisitor(fun(expression) {
+
+            val descriptor = (expression.mainReference.resolve() as? KtObjectDeclaration)?.descriptor ?: return
+            if (!DescriptorUtils.isCompanionObject(descriptor)) return
+
+            val parent = expression.getStrictParentOfType<KtDotQualifiedExpression>() ?: return
+            if (expression == parent.receiverExpression && expression.text == descriptor.containingDeclaration?.name?.asString()) return
+            if (expression == parent.selectorExpression && parent.parent !is KtDotQualifiedExpression) return
+
+            holder.registerProblem(
+                expression,
+                "Redundant Companion reference",
+                ProblemHighlightType.LIKE_UNUSED_SYMBOL,
+                RemoveRedundantCompanionReferenceFix()
+            )
+        })
+    }
+}
+
+private class RemoveRedundantCompanionReferenceFix : LocalQuickFix {
+    override fun getName() = "Remove redundant Companion reference"
+
+    override fun getFamilyName() = name
+
+    override fun applyFix(project: Project, descriptor: ProblemDescriptor) {
+        val expression = descriptor.psiElement as? KtReferenceExpression ?: return
+        val parent = expression.getStrictParentOfType<KtDotQualifiedExpression>() ?: return
+        val selector = parent.selectorExpression ?: return
+        val receiver = parent.receiverExpression
+        if (expression == receiver) parent.replace(selector) else parent.replace(receiver)
+    }
+}