fix: prevent duplicate fragments for decorated definitions in tree-sitter

Author: nikolay-e

src/treemapper/diffctx/fragments.py

@@ -358,10 +358,13 @@ def _extract_definitions(
         fragments: list[Fragment],
         covered: set[tuple[int, int]],
     ) -> None:
-        if node.type in definition_types:
-            start = node.start_point[0] + 1
-            end = node.end_point[0] + 1
+        start = node.start_point[0] + 1
+        end = node.end_point[0] + 1
+
+        if self._is_covered(start, end, covered):
+            return
 
+        if node.type in definition_types:
             if end - start + 1 >= _MIN_FRAGMENT_LINES:
                 snippet = code_bytes[node.start_byte : node.end_byte].decode("utf-8", errors="replace")
                 if not snippet.endswith("\n"):
@@ -377,10 +380,17 @@ def _extract_definitions(
                     )
                 )
                 covered.add((start, end))
+                return
 
         for child in node.children:
             self._extract_definitions(child, code_bytes, path, lines, definition_types, fragments, covered)
 
+    def _is_covered(self, start: int, end: int, covered: set[tuple[int, int]]) -> bool:
+        for cov_start, cov_end in covered:
+            if cov_start <= start and end <= cov_end:
+                return True
+        return False
+
     def _node_type_to_kind(self, node_type: str) -> str:
         if "function" in node_type or "method" in node_type:
             return "function"