Raise an explicit panic when context_lines is 0. Fixes #37

src/common.rs

@@ -101,6 +101,8 @@ pub fn get_diff_ratio(ops: &[DiffOp], old_len: usize, new_len: usize) -> f32 {
 /// This will leave holes behind in long periods of equal ranges so that
 /// you can build things like unified diffs.
 pub fn group_diff_ops(mut ops: Vec<DiffOp>, n: usize) -> Vec<Vec<DiffOp>> {
+    assert!(n > 0, "n must be 1 or larger");
+
     if ops.is_empty() {
         return vec![];
     }

src/text/mod.rs

@@ -758,3 +758,12 @@ fn test_serde_ops() {
     let json = serde_json::to_string_pretty(&changes).unwrap();
     insta::assert_snapshot!(&json);
 }
+
+#[test]
+#[should_panic = "n must be 1 or larger"]
+fn test_regression_issue_37() {
+    let config = TextDiffConfig::default();
+    let diff = config.diff_lines("", "");
+    let mut output = diff.unified_diff();
+    output.context_radius(0).to_string();
+}

src/udiff.rs

@@ -139,7 +139,8 @@ impl<'diff, 'old, 'new, 'bufs, T: DiffableStr + ?Sized> UnifiedDiff<'diff, 'old,
     /// Changes the context radius.
     ///
     /// The context radius is the number of lines between changes that should
-    /// be emitted.  This defaults to `3`.
+    /// be emitted.  This defaults to `3`.  This value must be one or larger or
+    /// creating the diff will panic.
     pub fn context_radius(&mut self, n: usize) -> &mut Self {
         self.context_radius = n;
         self