avoid underflow when inserting route without leading slash

Author: ibraheemdev

src/tree.rs

@@ -393,8 +393,10 @@ impl<T> Node<T> {
                 }
 
                 // Similarly, if we are inserting a longer prefix, and there is a route that leads to this
-                // parameter that includes a suffix, we have a prefix-suffix conflicts.
-                if common_remaining[common_prefix - 1] != b'/'
+                // parameter that includes a suffix, we have a prefix-suffix conflict.
+                if common_prefix
+                    .checked_sub(1)
+                    .is_some_and(|i| common_remaining[i] != b'/')
                     && node.suffix_wild_child_in_segment()
                 {
                     return Err(InsertError::conflict(&route, remaining, node));

tests/insert.rs

@@ -16,10 +16,18 @@ fn conflict(with: &'static str) -> InsertError {
     InsertError::Conflict { with: with.into() }
 }
 
-// https://github.com/ibraheemdev/matchit/issues/84
+// Regression test for https://github.com/ibraheemdev/matchit/issues/84.
 #[test]
-fn root_prefix_issue() {
-    InsertTest(vec![("{foo}", Ok(())), ("{foo}suffix", Ok(()))]).run()
+fn missing_leading_slash_suffix() {
+    InsertTest(vec![("/{foo}", Ok(())), ("/{foo}suffix", Ok(()))]).run();
+    InsertTest(vec![("{foo}", Ok(())), ("{foo}suffix", Ok(()))]).run();
+}
+
+// Regression test for https://github.com/ibraheemdev/matchit/issues/82.
+#[test]
+fn missing_leading_slash_conflict() {
+    InsertTest(vec![("{foo}/", Ok(())), ("foo/", Ok(()))]).run();
+    InsertTest(vec![("foo/", Ok(())), ("{foo}/", Ok(()))]).run();
 }
 
 #[test]