From 3a938ae1d3a0923a483ece68aecbed2a8052865a Mon Sep 17 00:00:00 2001
From: Armin Ronacher <armin.ronacher@active-4.com>
Date: Thu, 28 Jul 2022 15:14:54 +0200
Subject: [PATCH] Raise an explicit panic when context_lines is 0. Fixes #37

---
 src/common.rs   | 2 ++
 src/text/mod.rs | 9 +++++++++
 src/udiff.rs    | 3 ++-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/common.rs b/src/common.rs
index 40d1ae7..7adfa11 100644
--- a/src/common.rs
+++ b/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![];
     }
diff --git a/src/text/mod.rs b/src/text/mod.rs
index dbad62b..bdc75a0 100644
--- a/src/text/mod.rs
+++ b/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();
+}
diff --git a/src/udiff.rs b/src/udiff.rs
index 80a30cf..d975068 100644
--- a/src/udiff.rs
+++ b/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