Introduce Variable: Remove braces from replaced string template entries when possible

#KT-5310 Fixed

idea/src/org/jetbrains/jet/plugin/intentions/RemoveCurlyBracesFromTemplateIntention.kt

@@ -21,11 +21,13 @@ import org.jetbrains.jet.lang.psi.JetBlockStringTemplateEntry
 import org.jetbrains.jet.lang.psi.JetSimpleNameExpression
 import org.jetbrains.jet.lang.psi.JetPsiFactory
 import java.util.regex.*
+import org.jetbrains.jet.lang.psi.JetStringTemplateEntryWithExpression
 
 public class RemoveCurlyBracesFromTemplateIntention : JetSelfTargetingIntention<JetBlockStringTemplateEntry>(
         "remove.unnecessary.curly.brackets.from.string.template", javaClass()) {
 
     class object {
+        val INSTANCE = RemoveCurlyBracesFromTemplateIntention()
         val pattern = Pattern.compile("[a-zA-Z0-9_].*")
     }
 
@@ -35,10 +37,15 @@ public class RemoveCurlyBracesFromTemplateIntention : JetSelfTargetingIntention<
         return element.getExpression() is JetSimpleNameExpression
     }
 
-    override fun applyTo(element: JetBlockStringTemplateEntry, editor: Editor) {
-        if (!isApplicableTo(element)) return
+    fun convertIfApplicable(element: JetBlockStringTemplateEntry): JetStringTemplateEntryWithExpression {
+        if (!isApplicableTo(element)) return element
 
         val name = (element.getExpression() as JetSimpleNameExpression).getReferencedName()
-        element.replace(JetPsiFactory(element).createSimpleNameStringTemplateEntry(name))
+        val newEntry = JetPsiFactory(element).createSimpleNameStringTemplateEntry(name)
+        return element.replace(newEntry) as JetStringTemplateEntryWithExpression
+    }
+
+    override fun applyTo(element: JetBlockStringTemplateEntry, editor: Editor) {
+        convertIfApplicable(element)
     }
 }

idea/src/org/jetbrains/jet/plugin/refactoring/introduce/introduceVariable/KotlinIntroduceVariableHandler.java

@@ -53,6 +53,7 @@ import org.jetbrains.jet.plugin.caches.resolve.ResolvePackage;
 import org.jetbrains.jet.plugin.codeInsight.CodeInsightUtils;
 import org.jetbrains.jet.plugin.codeInsight.ShortenReferences;
 import org.jetbrains.jet.plugin.intentions.ConvertToBlockBodyAction;
+import org.jetbrains.jet.plugin.intentions.RemoveCurlyBracesFromTemplateIntention;
 import org.jetbrains.jet.plugin.refactoring.JetNameSuggester;
 import org.jetbrains.jet.plugin.refactoring.JetNameValidatorImpl;
 import org.jetbrains.jet.plugin.refactoring.JetRefactoringBundle;
@@ -445,6 +446,14 @@ public class KotlinIntroduceVariableHandler extends KotlinIntroduceHandlerBase {
                 else {
                     result = (JetExpression)replace.replace(replacement);
                 }
+
+                PsiElement parent = result != null ? result.getParent() : null;
+                if (parent instanceof JetBlockStringTemplateEntry) {
+                    JetStringTemplateEntryWithExpression newEntry =
+                            RemoveCurlyBracesFromTemplateIntention.INSTANCE.convertIfApplicable((JetBlockStringTemplateEntry) parent);
+                    result = newEntry.getExpression();
+                }
+
                 references.add(result);
                 if (isActualExpression) reference.set(result);
 

idea/testData/refactoring/introduceVariable/OccurrencesInStringTemplate.kt.after

@@ -1,5 +1,5 @@
 fun a(x: Int) {
     val i = x + 1
     val a = i
-    "it's a number ${i}"
+    "it's a number $i"
 }

idea/testData/refactoring/introduceVariable/StringInjection.kt.after

@@ -1,4 +1,4 @@
 fun a() {
     val i = 1
-    "it's a number ${i}"
+    "it's a number $i"
 }