Fix completion for back-ticked name (KT-19863, KT-19864)

^KT-19863 Fixed
^KT-19864 Fixed

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/handlers/BaseDeclarationInsertHandler.kt

@@ -26,7 +26,11 @@ open class BaseDeclarationInsertHandler : InsertHandler<LookupElement> {
     override fun handleInsert(context: InsertionContext, item: LookupElement) {
         val name = (item.`object` as? DeclarationLookupObject)?.name
         if (name != null && !name.isSpecial) {
-            context.document.replaceString(context.startOffset, context.tailOffset, name.render())
+            val startOffset = context.startOffset
+            if (startOffset > 0 && context.document.isTextAt(startOffset - 1, "`")) {
+                context.document.deleteString(startOffset - 1, startOffset)
+            }
+            context.document.replaceString(startOffset, context.tailOffset, name.render())
         }
     }
 }

idea/idea-completion/testData/handlers/basic/KT19863.kt

@@ -0,0 +1,9 @@
+package test
+
+fun `backticked`() {}
+
+fun test() {
+    `ba<caret>
+}
+
+// ELEMENT: backticked

idea/idea-completion/testData/handlers/basic/KT19863.kt.after

@@ -0,0 +1,9 @@
+package test
+
+fun `backticked`() {}
+
+fun test() {
+    backticked()<caret>
+}
+
+// ELEMENT: backticked

idea/idea-completion/testData/handlers/basic/KT19864.kt

@@ -0,0 +1,9 @@
+package test
+
+fun `backticked~name`() {}
+
+fun test() {
+    `ba<caret>
+}
+
+// ELEMENT: backticked~name

idea/idea-completion/testData/handlers/basic/KT19864.kt.after

@@ -0,0 +1,9 @@
+package test
+
+fun `backticked~name`() {}
+
+fun test() {
+    `backticked~name`()<caret>
+}
+
+// ELEMENT: backticked~name

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/handlers/BasicCompletionHandlerTestGenerated.java

@@ -114,6 +114,16 @@ public class BasicCompletionHandlerTestGenerated extends AbstractBasicCompletion
         runTest("idea/idea-completion/testData/handlers/basic/KT14130.kt");
     }
 
+    @TestMetadata("KT19863.kt")
+    public void testKT19863() throws Exception {
+        runTest("idea/idea-completion/testData/handlers/basic/KT19863.kt");
+    }
+
+    @TestMetadata("KT19864.kt")
+    public void testKT19864() throws Exception {
+        runTest("idea/idea-completion/testData/handlers/basic/KT19864.kt");
+    }
+
     @TestMetadata("KT23627.kt")
     public void testKT23627() throws Exception {
         runTest("idea/idea-completion/testData/handlers/basic/KT23627.kt");