fix!: Panic if Patch span is beyond the end of buffer

Author: Muscraft

src/renderer/source_map.rs

@@ -379,6 +379,19 @@ impl<'a> SourceMap<'a> {
             }
             line_count
         }
+
+        let source_len = self.source.len();
+        if let Some(bigger) = patches.iter().find_map(|x| {
+            // Allow patching one past the last character in the source.
+            if source_len + 1 < x.span.end {
+                Some(&x.span)
+            } else {
+                None
+            }
+        }) {
+            panic!("Patch span `{bigger:?}` is beyond the end of buffer `{source_len}`")
+        }
+
         // Assumption: all spans are in the same file, and all spans
         // are disjoint. Sort in ascending order.
         patches.sort_by_key(|p| p.span.start);

tests/formatter.rs

@@ -2706,6 +2706,7 @@ help: or use `IntoIterator::into_iter(..)` instead of `.into_iter()` to explicit
 }
 
 #[test]
+#[should_panic = "Patch span `47..47` is beyond the end of buffer `45`"]
 fn suggestion_span_bigger_than_source() {
     let snippet_source = r#"#![allow(unused)]
 fn main() {