Fix StringIndexOutOfBoundsException on line after tab (#52)

This could occur in the following situation (\t is a tab):

    - foo

    \tbar
    # baz

The tab on the bar line is a partially consumed tab, so columnIsInTab
would be true. On the next line, we wouldn't reset columnIsInTab.

By the time that addLine is called, we would try to get a substring
starting from "after the tab", resulting in the
StringIndexOutOfBoundsException.

commonmark/src/main/java/org/commonmark/internal/DocumentParser.java

@@ -33,11 +33,15 @@ public class DocumentParser implements ParserState {
      */
     private int column = 0;
 
+    /**
+     * if the current column is within a tab character (partially consumed tab)
+     */
+    private boolean columnIsInTab;
+
     private int nextNonSpace = 0;
     private int nextNonSpaceColumn = 0;
     private int indent = 0;
     private boolean blank;
-    private boolean columnIsInTab;
 
     private final List<BlockParserFactory> blockParserFactories;
     private final InlineParserImpl inlineParser;
@@ -144,8 +148,7 @@ private void incorporateLine(CharSequence ln) {
         line = Parsing.prepareLine(ln);
         index = 0;
         column = 0;
-        nextNonSpace = 0;
-        nextNonSpaceColumn = 0;
+        columnIsInTab = false;
 
         // For each containing block, try to parse the associated line start.
         // Bail out on failure: container will point to the last matching block.
@@ -286,6 +289,8 @@ private void setNewIndex(int newIndex) {
         while (index < newIndex && index != line.length()) {
             advance();
         }
+        // If we're going to an index as opposed to a column, we're never within a tab
+        columnIsInTab = false;
     }
 
     private void setNewColumn(int newColumn) {

commonmark/src/test/java/org/commonmark/test/SpecialInputTest.java

@@ -77,4 +77,11 @@ public void orderedListMarkerOnly() {
         assertRendering("2.", "<ol start=\"2\">\n<li></li>\n</ol>\n");
     }
 
+    @Test
+    public void columnIsInTabOnPreviousLine() {
+        assertRendering("- foo\n\n\tbar\n\n# baz\n",
+                "<ul>\n<li>\n<p>foo</p>\n<p>bar</p>\n</li>\n</ul>\n<h1>baz</h1>\n");
+        assertRendering("- foo\n\n\tbar\n# baz\n",
+                "<ul>\n<li>\n<p>foo</p>\n<p>bar</p>\n</li>\n</ul>\n<h1>baz</h1>\n");
+    }
 }