Fix a bug caused by too long return expressions

kotlinpoet/src/main/java/com/squareup/kotlinpoet/CodeBlock.kt

@@ -270,7 +270,11 @@ public class CodeBlock private constructor(
         if (format[p] != '%') {
           var nextP = format.nextPotentialPlaceholderPosition(startIndex = p + 1)
           if (nextP == -1) nextP = format.length
-          formatParts += format.substring(p, nextP)
+          var formatPart = format.substring(p, nextP)
+          if (formatPart.startsWith(RETURN_WITH_SPACE)) {
+            formatPart = formatPart.replaceRange(RETURN_WITH_SPACE.indices, RETURN_WITH_NBSP)
+          }
+          formatParts += formatPart
           p = nextP
           continue
         }
@@ -458,6 +462,8 @@ public class CodeBlock private constructor(
     private const val TYPE_NAME = 2
     private val NO_ARG_PLACEHOLDERS = setOf("⇥", "⇤", "«", "»")
     internal val EMPTY = CodeBlock(emptyList(), emptyList())
+    internal const val RETURN_WITH_SPACE = "return "
+    internal const val RETURN_WITH_NBSP = "return·"
 
     @JvmStatic public fun of(format: String, vararg args: Any?): CodeBlock =
       Builder().add(format, *args).build()

kotlinpoet/src/main/java/com/squareup/kotlinpoet/FunSpec.kt

@@ -558,8 +558,8 @@ public class FunSpec private constructor(
     internal val String.isConstructor get() = this == CONSTRUCTOR
     internal val String.isAccessor get() = this.isOneOf(GETTER, SETTER)
 
-    private val RETURN_EXPRESSION_BODY_PREFIX_SPACE = CodeBlock.of("return ")
-    private val RETURN_EXPRESSION_BODY_PREFIX_NBSP = CodeBlock.of("return·")
+    private val RETURN_EXPRESSION_BODY_PREFIX_SPACE = CodeBlock.of(CodeBlock.RETURN_WITH_SPACE)
+    private val RETURN_EXPRESSION_BODY_PREFIX_NBSP = CodeBlock.of(CodeBlock.RETURN_WITH_NBSP)
     private val THROW_EXPRESSION_BODY_PREFIX_SPACE = CodeBlock.of("throw ")
     private val THROW_EXPRESSION_BODY_PREFIX_NBSP = CodeBlock.of("throw·")
 

kotlinpoet/src/test/java/com/squareup/kotlinpoet/FunSpecTest.kt

@@ -206,6 +206,31 @@ class FunSpecTest {
     )
   }
 
+  @Test fun returnLongExpression() {
+    val funSpec = FunSpec.builder("foo")
+      .returns(String::class)
+      .addStatement("val placeholder = 1")
+      .addStatement("return \"Loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong\"")
+      .build()
+    val sb = StringBuilder()
+    CodeWriter(sb).use {
+      funSpec.emit(
+        codeWriter = it,
+        enclosingName = null,
+        implicitModifiers = setOf(KModifier.PUBLIC),
+        includeKdocTags = false
+      )
+    }
+    assertThat(sb.toString()).isEqualTo(
+      """
+      |public fun foo(): kotlin.String {
+      |  val placeholder = 1
+      |  return "Loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong"
+      |}
+      |""".trimMargin()
+    )
+  }
+
   @Test fun functionParamWithKdoc() {
     val funSpec = FunSpec.builder("foo")
       .addParameter(