Introduce Variable: Support extraction of string template fragments

#KT-2089 Fixed

compiler/frontend/src/org/jetbrains/kotlin/psi/KtPsiFactory.kt

@@ -55,15 +55,25 @@ public class KtPsiFactory(private val project: Project) {
         return (createExpression("a?.b") as KtSafeQualifiedExpression).getOperationTokenNode()
     }
 
-    public fun createExpression(text: String): KtExpression {
+    private fun doCreateExpression(text: String): KtExpression {
         //TODO: '\n' below if important - some strange code indenting problems appear without it
         val expression = createProperty("val x =\n$text").getInitializer() ?: error("Failed to create expression from text: '$text'")
+        return expression
+    }
+
+    public fun createExpression(text: String): KtExpression {
+        val expression = doCreateExpression(text)
         assert(expression.getText() == text) {
             "Failed to create expression from text: '$text', resulting expression's text was: '${expression.getText()}'"
         }
         return expression
     }
 
+    public fun createExpressionIfPossible(text: String): KtExpression? {
+        val expression = doCreateExpression(text)
+        return if (expression.getText() == text) expression else null
+    }
+
     public fun createClassLiteral(className: String): KtClassLiteralExpression =
             createExpression("$className::class") as KtClassLiteralExpression
 
@@ -291,6 +301,8 @@ public class KtPsiFactory(private val project: Project) {
         return stringTemplateExpression.getEntries()[0] as KtStringTemplateEntryWithExpression
     }
 
+    public fun createStringTemplate(content: String) = createExpression("\"$content\"") as KtStringTemplateExpression
+
     public fun createPackageDirective(fqName: FqName): KtPackageDirective {
         return createFile("package ${fqName.asString()}").getPackageDirective()!!
     }

compiler/frontend/src/org/jetbrains/kotlin/psi/psiUtil/psiUtils.kt

@@ -138,6 +138,8 @@ public fun PsiElement.getNextSiblingIgnoringWhitespaceAndComments(): PsiElement?
     return siblings(withItself = false).filter { it !is PsiWhiteSpace && it !is PsiComment }.firstOrNull()
 }
 
+inline public fun <reified T : PsiElement> T.nextSiblingOfSameType() = PsiTreeUtil.getNextSiblingOfType(this, T::class.java)
+
 public fun PsiElement?.isAncestor(element: PsiElement, strict: Boolean = false): Boolean {
     return PsiTreeUtil.isAncestor(this, element, strict)
 }