Avoid false positives for classes defined in methods

If a class has the `EnclosingMethod` attribute, we know it was defined
in the body of a method (or a val/var initializer), and is not part of
the API of a class.

Fixes lightbend-labs#147

core/src/main/scala/com/typesafe/tools/mima/core/ClassInfo.scala

@@ -59,6 +59,9 @@ abstract class ClassInfo(val owner: PackageInfo) extends HasDeclarationName with
   var _innerClasses: Seq[String] = Seq.empty
   def innerClasses = { ensureLoaded(); _innerClasses }
 
+  var _isLocalClass = false
+  def isLocalClass = { ensureLoaded(); _isLocalClass}
+
   var _isTopLevel = true
   def isTopLevel = { ensureLoaded(); _isTopLevel }
 

core/src/main/scala/com/typesafe/tools/mima/core/ClassfileParser.scala

@@ -278,6 +278,8 @@ abstract class ClassfileParser(definitions: Definitions) {
              if (pool.getClassName(outerIndex) == c.bytecodeName) n else ""
            } else ""
          }.filterNot(_.isEmpty)
+       } else if (attrName == "EnclosingMethod") {
+         c._isLocalClass = true
        } else if (attrName == "Scala" || attrName == "ScalaSig") {
          this.parsedClass.isScala = true
        }

core/src/main/scala/com/typesafe/tools/mima/core/PackageInfo.scala

@@ -79,7 +79,7 @@ abstract class PackageInfo(val owner: PackageInfo) {
         else if (prefix.isEmpty) clazz.isTopLevel && !clazz.bytecodeName.contains("$$")
         else prefix.exists(_.innerClasses contains clazz.bytecodeName)
       }
-      clazz.isPublic && isReachable
+      clazz.isPublic && !clazz.isLocalClass && isReachable
     }
 
     accessibleClassesUnder(Set.empty, Set.empty)

reporter/functional-tests/src/test/class-added-local-class-ok/v1/A.scala

@@ -0,0 +1 @@
+class A { def f() = { class Local } }

reporter/functional-tests/src/test/class-added-local-class-ok/v2/A.scala

@@ -0,0 +1 @@
+class A { def f() = { } }

reporter/functional-tests/src/test/class-changed-local-class-ok/v1/A.scala

@@ -0,0 +1 @@
+class A { def f() = { class Local { def v1 = "v1"} } }

reporter/functional-tests/src/test/class-changed-local-class-ok/v2/A.scala

@@ -0,0 +1 @@
+class A { def f() = { class Local } }

reporter/functional-tests/src/test/class-removed-local-class-ok/v1/A.scala

@@ -0,0 +1 @@
+class A { def f() = { } }

reporter/functional-tests/src/test/class-removed-local-class-ok/v2/A.scala

@@ -0,0 +1 @@
+class A { def f() = { class Local } }