Explicit this inspection: fix false negative with local variable

#KT-30136 Fixed

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

@@ -22,13 +22,18 @@ import com.intellij.codeInspection.ProblemHighlightType.LIKE_UNUSED_SYMBOL
 import com.intellij.codeInspection.ProblemsHolder
 import com.intellij.openapi.project.Project
 import org.jetbrains.kotlin.config.LanguageFeature.CallableReferencesToClassMembersWithEmptyLHS
+import org.jetbrains.kotlin.descriptors.FunctionDescriptor
+import org.jetbrains.kotlin.descriptors.VariableDescriptor
+import org.jetbrains.kotlin.descriptors.impl.LocalVariableDescriptor
 import org.jetbrains.kotlin.idea.caches.resolve.analyze
 import org.jetbrains.kotlin.idea.intentions.getCallableDescriptor
 import org.jetbrains.kotlin.idea.project.languageVersionSettings
+import org.jetbrains.kotlin.idea.references.mainReference
 import org.jetbrains.kotlin.idea.util.*
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.getChildOfType
 import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.lazy.descriptors.LazyClassDescriptor
 import org.jetbrains.kotlin.synthetic.SyntheticJavaPropertyDescriptor
 import org.jetbrains.kotlin.types.typeUtil.isSubtypeOf
 
@@ -60,7 +65,14 @@ class ExplicitThisInspection : AbstractKotlinInspection() {
 
             //we avoid overload-related problems by enforcing that there is only one candidate
             val name = referenceExpression.getReferencedNameAsName()
-            val candidates = scope.getAllAccessibleVariables(name) + scope.getAllAccessibleFunctions(name)
+            val candidates = if (reference is KtCallExpression
+                || (expression is KtCallableReferenceExpression && reference.mainReference.resolve() is KtFunction)
+            ) {
+                scope.getAllAccessibleFunctions(name) +
+                        scope.getAllAccessibleVariables(name).filter { it is LocalVariableDescriptor && it.canInvoke() }
+            } else {
+                scope.getAllAccessibleVariables(name)
+            }
             if (referenceExpression.getCallableDescriptor() is SyntheticJavaPropertyDescriptor) {
                 if (candidates.map { it.containingDeclaration }.distinct().size != 1) return
             } else {
@@ -76,6 +88,11 @@ class ExplicitThisInspection : AbstractKotlinInspection() {
 
             holder.registerProblem(thisExpression, "Redundant explicit this", LIKE_UNUSED_SYMBOL, Fix(thisExpression.text))
         }
+        
+        private fun VariableDescriptor.canInvoke(): Boolean {
+            val declarationDescriptor = this.type.constructor.declarationDescriptor as? LazyClassDescriptor ?: return false
+            return declarationDescriptor.declaredCallableMembers.any { (it as? FunctionDescriptor)?.isOperator == true }
+        }
 
         private fun ReceiverExpressionFactory.matchesLabel(label: String): Boolean {
             val implicitLabel = expressionText.substringAfter("@", "")

idea/testData/inspectionsLocal/explicitThis/functionWithSameNameInvocableVariable.kt

@@ -0,0 +1,14 @@
+// PROBLEM: none
+class Some {
+    operator fun invoke() {}
+}
+
+class Other {
+    fun foo() {
+        val a = Some()
+        <caret>this.a()
+        a()
+    }
+
+    fun a() {}
+}

idea/testData/inspectionsLocal/explicitThis/functionWithSameNameVariable.kt

@@ -0,0 +1,9 @@
+class Foo {
+    fun foo() {
+        val a = 1
+        <caret>this.a()
+    }
+
+    fun a() {
+    }
+}

idea/testData/inspectionsLocal/explicitThis/functionWithSameNameVariable.kt.after

@@ -0,0 +1,9 @@
+class Foo {
+    fun foo() {
+        val a = 1
+        <caret>a()
+    }
+
+    fun a() {
+    }
+}

idea/testData/inspectionsLocal/explicitThis/variableWithSameNameFunction.kt

@@ -0,0 +1,9 @@
+class Foo {
+    fun foo() {
+        fun a() {
+        }
+        <caret>this.a
+    }
+
+    val a = 1
+}

idea/testData/inspectionsLocal/explicitThis/variableWithSameNameFunction.kt.after

@@ -0,0 +1,9 @@
+class Foo {
+    fun foo() {
+        fun a() {
+        }
+        <caret>a
+    }
+
+    val a = 1
+}

idea/tests/org/jetbrains/kotlin/idea/inspections/LocalInspectionTestGenerated.java

@@ -4196,6 +4196,16 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
             runTest("idea/testData/inspectionsLocal/explicitThis/functionReference.kt");
         }
 
+        @TestMetadata("functionWithSameNameInvocableVariable.kt")
+        public void testFunctionWithSameNameInvocableVariable() throws Exception {
+            runTest("idea/testData/inspectionsLocal/explicitThis/functionWithSameNameInvocableVariable.kt");
+        }
+
+        @TestMetadata("functionWithSameNameVariable.kt")
+        public void testFunctionWithSameNameVariable() throws Exception {
+            runTest("idea/testData/inspectionsLocal/explicitThis/functionWithSameNameVariable.kt");
+        }
+
         @TestMetadata("multipleReceivers.kt")
         public void testMultipleReceivers() throws Exception {
             runTest("idea/testData/inspectionsLocal/explicitThis/multipleReceivers.kt");
@@ -4265,6 +4275,11 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
         public void testVariableWithSameName() throws Exception {
             runTest("idea/testData/inspectionsLocal/explicitThis/variableWithSameName.kt");
         }
+
+        @TestMetadata("variableWithSameNameFunction.kt")
+        public void testVariableWithSameNameFunction() throws Exception {
+            runTest("idea/testData/inspectionsLocal/explicitThis/variableWithSameNameFunction.kt");
+        }
     }
 
     @TestMetadata("idea/testData/inspectionsLocal/foldInitializerAndIfToElvis")