Treat NovelLinePart as a change

Previously we'd treat it as unchanged, leading to incorrect text diffs
when words were added on a single side.

Fixes #122

CHANGELOG.md

@@ -28,6 +28,9 @@ Difftastic will now use a text diff for large files, rather than
 trying to use more memory than is available. This threshold is
 configurable with `--node-limit` and `DFT_NODE_LIMIT`.
 
+Fixed a bug in the text diff logic where lines weren't shown if they
+did not have both word additions and word removals.
+
 ### Command Line Interface
 
 Difftastic will now error if either argument does not exist, unless

src/line_parser.rs

@@ -249,6 +249,15 @@ mod tests {
         assert!(!positions[0].kind.is_change());
     }
 
+    #[test]
+    fn test_positions_whitespace_is_change() {
+        // Even though the word exists on both sides, it should still
+        // be treated as a change. We're doing a line-based diff and
+        // the lines are different.
+        let positions = change_positions("foo", " foo");
+        assert!(positions[0].kind.is_change());
+    }
+
     #[test]
     fn test_no_changes_trailing_newlines() {
         let positions = change_positions("foo\n", "foo\n");

src/syntax.rs

@@ -562,7 +562,7 @@ impl MatchKind {
     pub fn is_change(&self) -> bool {
         matches!(
             self,
-            MatchKind::Novel { .. } | MatchKind::NovelWord { .. }
+            MatchKind::Novel { .. } | MatchKind::NovelWord { .. } | MatchKind::NovelLinePart { .. }
         )
     }
 }