Consider outer interface visibility

Update `SpringMethodVisibilityCheck` to consider interface definitions
when checking method visibility.

Closes gh-140

Author: philwebb

spring-javaformat/spring-javaformat-checkstyle/src/main/java/io/spring/javaformat/checkstyle/check/SpringMethodVisibilityCheck.java

@@ -53,6 +53,14 @@ private void visitPublicMethod(DetailAST modifiers, DetailAST method) {
 				|| classModifiers.findFirstToken(TokenTypes.LITERAL_PROTECTED) != null) {
 			return;
 		}
+		DetailAST interfaceDef = getInterfaceDef(classDef.getParent());
+		if (interfaceDef != null) {
+			DetailAST interfaceModifiers = interfaceDef.findFirstToken(TokenTypes.MODIFIERS);
+			if (interfaceModifiers.findFirstToken(TokenTypes.LITERAL_PUBLIC) != null
+					|| interfaceModifiers.findFirstToken(TokenTypes.LITERAL_PROTECTED) != null) {
+				return;
+			}
+		}
 		DetailAST ident = method.findFirstToken(TokenTypes.IDENT);
 		log(ident.getLineNo(), ident.getColumnNo(), "methodvisibility.publicMethod", ident.getText());
 	}
@@ -73,8 +81,16 @@ private boolean hasOverrideAnnotation(DetailAST modifiers) {
 	}
 
 	private DetailAST getClassDef(DetailAST ast) {
+		return findParent(ast, TokenTypes.CLASS_DEF);
+	}
+
+	private DetailAST getInterfaceDef(DetailAST ast) {
+		return findParent(ast, TokenTypes.INTERFACE_DEF);
+	}
+
+	private DetailAST findParent(DetailAST ast, int classDef) {
 		while (ast != null) {
-			if (ast.getType() == TokenTypes.CLASS_DEF) {
+			if (ast.getType() == classDef) {
 				return ast;
 			}
 			ast = ast.getParent();

spring-javaformat/spring-javaformat-checkstyle/src/test/resources/check/NestedInterfaceItems.txt

@@ -0,0 +1 @@
++0 errors

spring-javaformat/spring-javaformat-checkstyle/src/test/resources/source/NestedInterfaceItems.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2017-2019 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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 io.spring.javaformat.checkstyle;
+
+/**
+ * Interface with implicit public elements.
+ *
+ * @author Phillip Webb
+ */
+public interface NestedInterfaceItems {
+
+	/**
+	 * A nested class class.
+	 */
+	class NestedClass {
+
+		public NestedClass(String arg) {
+			// This is valid because nested class is implicitly public
+		}
+
+		public void thisIsFine() {
+		}
+
+	}
+
+}