Fix snippet reader tab and indent handling

doxia-core/src/main/java/org/apache/maven/doxia/macro/snippet/SnippetReader.java

@@ -73,7 +73,9 @@ public StringBuffer readSnippet(String snippetId) throws IOException {
         int minIndent = minIndent(lines);
         StringBuffer result = new StringBuffer();
         for (String line : lines) {
-            result.append(line.substring(minIndent));
+            if (line.length() > minIndent) {
+                result.append(line.substring(minIndent));
+            }
             result.append(EOL);
         }
         return result;
@@ -88,6 +90,9 @@ public StringBuffer readSnippet(String snippetId) throws IOException {
     int minIndent(List<String> lines) {
         int minIndent = Integer.MAX_VALUE;
         for (String line : lines) {
+            if (StringUtils.isBlank(line)) {
+                continue;
+            }
             minIndent = Math.min(minIndent, indent(line));
         }
         return minIndent;
@@ -103,7 +108,7 @@ int indent(String line) {
         char[] chars = line.toCharArray();
         int indent = 0;
         for (; indent < chars.length; indent++) {
-            if (chars[indent] != ' ') {
+            if (chars[indent] != ' ' && chars[indent] != '\t') {
                 break;
             }
         }

doxia-core/src/test/java/org/apache/maven/doxia/macro/snippet/SnippetMacroTest.java

@@ -151,6 +151,40 @@ public void testIgnoreDownloadError() throws Exception {
         assertThat(snippet, CoreMatchers.containsString("Error during retrieving content"));
     }
 
+    @Test
+    public void testIndentHandling() throws MacroExecutionException {
+        Map<String, Object> macroParameters = new HashMap<>();
+        macroParameters.put("file", "src/test/resources/macro/snippet/testSnippet-indent.txt");
+        macroParameters.put("encoding", "UTF-8");
+        macroParameters.put("id", "firstId");
+        macroParameters.put("verbatim", "false");
+
+        // 1. Ensure leading tabs are trimmed
+        SinkEventTestingSink sink = executeSnippetMacro(macroParameters);
+        String snippet = (String) sink.getEventList().get(0).getArgs()[0];
+        assertEquals(1, sink.getEventList().size(), "There should only be one event");
+        assertEquals("first snippet\n", snippet);
+
+        // 2. Ensure leading spaces are trimmed
+        macroParameters.put("id", "secondId");
+        sink = executeSnippetMacro(macroParameters);
+        snippet = (String) sink.getEventList().get(0).getArgs()[0];
+        assertEquals("second snippet\n", snippet);
+
+        // 3. Ensure empty lines don't break the minIndent calculation
+        macroParameters.put("id", "thirdId");
+        sink = executeSnippetMacro(macroParameters);
+        snippet = (String) sink.getEventList().get(0).getArgs()[0];
+        String[] lines = snippet.split(System.getProperty("line.separator"));
+        assertEquals("Line1", lines[0], "There should not be any leading indentation since the minIndent is two");
+        assertEquals("	Line2", lines[1]);
+        assertEquals("", lines[2]);
+        assertEquals("", lines[3]);
+        assertEquals("", lines[4]);
+        assertEquals("	", lines[5], "The tab should be preserved");
+        assertEquals("		Line6", lines[6]);
+    }
+
     private SinkEventTestingSink executeSnippetMacro(Map<String, Object> macroParameters)
             throws MacroExecutionException {
         File basedir = new File(getBasedir());

doxia-core/src/test/resources/macro/snippet/testSnippet-indent.txt

@@ -0,0 +1,40 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+
+preamble
+
+SNIPPET START firstId
+		first snippet
+SNIPPET END   firstId
+
+interlude
+
+another snippet to start: secondId
+    second snippet
+another snippet to end:   secondId
+
+snippet start thirdId
+		Line1
+			Line2
+
+
+
+
+				Line6
+snippet end thirdId
+
+conclusion