Fix AssertionError on completing after template in string literal

#KT-16402 Fixed

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/KotlinCompletionContributor.kt

@@ -333,9 +333,7 @@ class KotlinCompletionContributor : CompletionContributor() {
                 val psiDocumentManager = PsiDocumentManager.getInstance(context.project)
                 psiDocumentManager.commitAllDocuments()
 
-                assert(startOffset > 1 && document.charsSequence[startOffset - 1] == '.')
-                val token = context.file.findElementAt(startOffset - 2)!!
-                assert(token.node.elementType == KtTokens.IDENTIFIER || token.node.elementType == KtTokens.THIS_KEYWORD)
+                val token = getToken(context.file, document.charsSequence, startOffset)
                 val nameRef = token.parent as KtNameReferenceExpression
 
                 document.insertString(nameRef.startOffset, "{")
@@ -346,6 +344,15 @@ class KotlinCompletionContributor : CompletionContributor() {
 
                 super.handleInsert(context)
             }
+
+            private fun getToken(file: PsiFile, charsSequence: CharSequence, startOffset: Int): PsiElement {
+                assert(startOffset > 1 && charsSequence[startOffset - 1] == '.')
+                val token = file.findElementAt(startOffset - 2)!!
+                return if (token.node.elementType == KtTokens.IDENTIFIER || token.node.elementType == KtTokens.THIS_KEYWORD)
+                    token
+                else
+                    getToken(file, charsSequence, token.startOffset + 1)
+            }
         }
     }
 

idea/idea-completion/testData/basic/common/inStringLiterals/StringTemplateDot2.kt

@@ -0,0 +1,8 @@
+class Foo(val bar: Bar)
+class Bar(val baz: String)
+
+fun foo(foo: Foo) {
+    val s = "$foo.bar.<caret>"
+}
+
+// EXIST: baz

idea/idea-completion/testData/handlers/basic/stringTemplate/AfterDot4.kt

@@ -0,0 +1,8 @@
+class Foo(val bar: Bar)
+class Bar(val baz: String)
+
+fun foo(foo: Foo) {
+    val s = "$foo.bar.<caret>"
+}
+
+// ELEMENT: baz

idea/idea-completion/testData/handlers/basic/stringTemplate/AfterDot4.kt.after

@@ -0,0 +1,8 @@
+class Foo(val bar: Bar)
+class Bar(val baz: String)
+
+fun foo(foo: Foo) {
+    val s = "${foo.bar.baz}"
+}
+
+// ELEMENT: baz

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/JSBasicCompletionTestGenerated.java

@@ -1825,6 +1825,12 @@ public class JSBasicCompletionTestGenerated extends AbstractJSBasicCompletionTes
                 doTest(fileName);
             }
 
+            @TestMetadata("StringTemplateDot2.kt")
+            public void testStringTemplateDot2() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/inStringLiterals/StringTemplateDot2.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("StringTemplateDotSomething.kt")
             public void testStringTemplateDotSomething() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/inStringLiterals/StringTemplateDotSomething.kt");

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/JvmBasicCompletionTestGenerated.java

@@ -1825,6 +1825,12 @@ public class JvmBasicCompletionTestGenerated extends AbstractJvmBasicCompletionT
                 doTest(fileName);
             }
 
+            @TestMetadata("StringTemplateDot2.kt")
+            public void testStringTemplateDot2() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/inStringLiterals/StringTemplateDot2.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("StringTemplateDotSomething.kt")
             public void testStringTemplateDotSomething() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/basic/common/inStringLiterals/StringTemplateDotSomething.kt");

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

@@ -835,6 +835,12 @@ public class BasicCompletionHandlerTestGenerated extends AbstractBasicCompletion
             doTest(fileName);
         }
 
+        @TestMetadata("AfterDot4.kt")
+        public void testAfterDot4() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/handlers/basic/stringTemplate/AfterDot4.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("AfterThisDot.kt")
         public void testAfterThisDot() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/idea-completion/testData/handlers/basic/stringTemplate/AfterThisDot.kt");