Issue checkstyle#4735: make RegexpHeaderCheck detect and enforce rege…

…x having '\n\n'

src/main/java/com/puppycrawl/tools/checkstyle/checks/header/AbstractHeaderCheck.java

@@ -170,10 +170,13 @@ private void loadHeader(final Reader headerReader) throws IOException {
         final LineNumberReader lnr = new LineNumberReader(headerReader);
         try {
             while (true) {
-                final String line = lnr.readLine();
+                String line = lnr.readLine();
                 if (line == null) {
                     break;
                 }
+                if (line.isEmpty()) {
+                    line = "^$";
+                }
                 readerLines.add(line);
             }
             postProcessHeaderLines();

src/test/java/com/puppycrawl/tools/checkstyle/checks/header/RegexpHeaderCheckTest.java

@@ -211,6 +211,29 @@ public void testFailureForMultilineRegexp() throws Exception {
         }
     }
 
+    @Test
+    public void testInlineRegexpHeaderConsecutiveNewlines() throws Exception {
+        final DefaultConfiguration checkConfig =
+                createCheckConfig(RegexpHeaderCheck.class);
+        checkConfig.addAttribute("header", "^/*$\\n// .*\\n\\n// Created: 2017\\n^//.*");
+        final String[] expected = {
+            "3: " + getCheckMessage(MSG_HEADER_MISMATCH, "^$"),
+        };
+        verify(checkConfig, getPath("InputRegexpHeaderConsecutiveNewLines.java"), expected);
+    }
+
+    @Test
+    public void testInlineRegexpHeaderConsecutiveNewlinesThroughConfigFile() throws Exception {
+        final DefaultConfiguration checkConfig =
+                createCheckConfig(RegexpHeaderCheck.class);
+        final URI uri = new File(getPath("InputRegexpHeaderNewLines.header")).toURI();
+        checkConfig.addAttribute("headerFile", uri.toString());
+        final String[] expected = {
+            "3: " + getCheckMessage(MSG_HEADER_MISMATCH, "^$"),
+        };
+        verify(checkConfig, getPath("InputRegexpHeaderConsecutiveNewLines.java"), expected);
+    }
+
     @Test
     public void testRegexpHeaderIgnore() throws Exception {
         final DefaultConfiguration checkConfig =

src/test/resources/com/puppycrawl/tools/checkstyle/checks/header/regexpheader/InputRegexpHeaderConsecutiveNewLines.java

@@ -0,0 +1,13 @@
+////////////////////////////////////////////////////////////////////////////////
+// Test case file for checkstyle.
+/* */
+// Created: 2017
+////////////////////////////////////////////////////////////////////////////////
+package com.puppycrawl.tools.checkstyle.checks.header.regexpheader;
+
+/**
+ * @author Vivek Rao
+ */
+public class InputRegexpHeaderConsecutiveNewLines
+{
+}

src/test/resources/com/puppycrawl/tools/checkstyle/checks/header/regexpheader/InputRegexpHeaderNewLines.header

@@ -0,0 +1,5 @@
+^/*$
+// .*
+
+// Created: 2017
+^.*$

src/xdocs/config_header.xml

@@ -225,7 +225,8 @@ line 14: ^ \*/
           four digit year. Line 5 is an example how to enforce revision
           control keywords in a file header. Lines 12-14 is a template for
           javadoc (line 13 is so complicated to remove conflict with and of
-          javadoc comment).
+          javadoc comment). Lines 7, 9 and 11 will be treated as '^$' and
+          will forcefully expect the line to be empty.
         </p>
 
         <p>