Format spaces around by keyword (#1016)

idea/formatter/src/org/jetbrains/kotlin/idea/formatter/kotlinSpacingRules.kt

@@ -251,6 +251,9 @@ fun createSpacingBuilder(settings: CodeStyleSettings, builderUtil: KotlinSpacing
             betweenInside(TYPE_ARGUMENT_LIST, LAMBDA_ARGUMENT, CALL_EXPRESSION).spaces(1)
 
             between(WHEN_ENTRY, WHEN_ENTRY).lineBreakInCode()
+
+            around(BY_KEYWORD).spaces(1)
+            betweenInside(IDENTIFIER, PROPERTY_DELEGATE, PROPERTY).spaces(1)
         }
         custom {
 

idea/testData/formatter/By.after.kt

@@ -0,0 +1,4 @@
+class Bar(val r: Runnable) : Runnable by r
+class Foo {
+    val bar by lazy { "" }
+}

idea/testData/formatter/By.kt

@@ -0,0 +1,4 @@
+class Bar(val r: Runnable) : Runnable    by  r
+class Foo {
+    val bar   by    lazy { "" }
+}

idea/tests/org/jetbrains/kotlin/formatter/FormatterTestGenerated.java

@@ -98,6 +98,12 @@ public class FormatterTestGenerated extends AbstractFormatterTest {
             doTest(fileName);
         }
 
+        @TestMetadata("By.after.kt")
+        public void testBy() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/formatter/By.after.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("Cast.after.kt")
         public void testCast() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/formatter/Cast.after.kt");