Trying out extracting return type and checking for whitespaces.

src/main/scala/org/scalastyle/scalariform/ExplicitReturnTypeFormatChecker.scala

@@ -0,0 +1,49 @@
+// Copyright (C) 2011-2012 the original author or authors.
+// See the LICENCE.txt file distributed with this work for additional
+// information regarding copyright ownership.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package org.scalastyle.scalariform
+
+import _root_.scalariform.parser.{CompilationUnit, FullDefOrDcl, FunDefOrDcl, PatDefOrDcl}
+import org.scalastyle._
+import org.scalastyle.scalariform.VisitorHelper._
+
+class ExplicitReturnTypeFormatChecker extends ScalariformChecker {
+  override protected val errorKey: String = "explicit.return.type.format"
+
+  override def verify(ast: CompilationUnit): List[ScalastyleError] = {
+    localvisit(ast).map {
+      case FullDefOrDclVisit(Left(p), _) => p.typedOpt
+      case FullDefOrDclVisit(Right(f), _) => f.returnTypeOpt
+    }.flatten.map(x => println("<" + x._1.associatedWhitespaceAndComments.text + ">")) // It is not possible to get these whitespaces.
+    List(PositionError(0))
+  }
+
+  case class FullDefOrDclVisit(defOrDcl: Either[PatDefOrDcl, FunDefOrDcl],
+                               subs: List[FullDefOrDclVisit]) extends Clazz[FullDefOrDcl]()
+
+  private def localvisit(ast: Any): List[FullDefOrDclVisit] = ast match {
+    case t: FullDefOrDcl => {
+      t.defOrDcl match {
+        case f: FunDefOrDcl => List(FullDefOrDclVisit(Right(f), localvisit(f)))
+        case p: PatDefOrDcl => List(FullDefOrDclVisit(Left(p), localvisit(p)))
+        case _ => localvisit(t.defOrDcl)
+      }
+    }
+    case t: FunDefOrDcl => localvisit(t.funBodyOpt)
+    case t: Any => visit(t, localvisit)
+  }
+
+}

src/test/scala/org/scalastyle/scalariform/ExplicitReturnTypeFormatCheckerTest.scala

@@ -0,0 +1,43 @@
+// Copyright (C) 2011-2012 the original author or authors.
+// See the LICENCE.txt file distributed with this work for additional
+// information regarding copyright ownership.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package org.scalastyle.scalariform
+
+import org.scalastyle.file.CheckerTest
+import org.scalatest.junit.AssertionsForJUnit
+import org.junit.Test
+
+class ExplicitReturnTypeFormatCheckerTest extends AssertionsForJUnit with CheckerTest {
+  override protected val key: String = "explicit.return.type.format"
+  override protected val classUnderTest = classOf[ExplicitReturnTypeFormatChecker]
+
+  @Test def testKO(): Unit = {
+    val source =
+      """
+        |package foobar
+        |
+        |class Dummy {
+        |  val a: Int = 0
+        |  def b: Int = 1
+        |  var c: Int = 2
+        |}
+        |
+      """.stripMargin
+
+    assertErrors(List(columnError(1, 0)), source)
+  }
+
+}