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backend/app/dataset/rules/python/resource_leak.py

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+"""AST-level resource leak injection for Python."""
+
+import ast
+from typing import Optional
+
+from app.dataset.rules.base import Mutation, MutationRule
+
+
+class ResourceLeakRule(MutationRule):
+    """Convert a `with open(...)` block into an unclosed `open(...).read()`.
+
+    Uses `ast` to locate a with-statement managing a file resource and replaces
+    it with a direct call chain that leaks the file handle.
+    """
+
+    name = "resource_leak"
+    language = "python"
+    defect_type = "resource_not_closed"
+
+    def detect_and_mutate(self, source: str, filename: str = "") -> Optional[Mutation]:
+        try:
+            tree = ast.parse(source)
+        except SyntaxError:
+            return None
+
+        for node in ast.walk(tree):
+            if not isinstance(node, ast.With):
+                continue
+            first_item = node.items[0]
+            ctx = first_item.context_expr
+            if isinstance(ctx, ast.Call) and isinstance(ctx.func, ast.Name) and ctx.func.id == "open":
+                start = node.lineno
+                end = getattr(node, "end_lineno", node.lineno) or node.lineno
+                lines = source.splitlines(keepends=True)
+                # Keep the with header expression but replace 'with open(...)' by 'f = open(...)'
+                header = lines[start - 1]
+                header_expr = header.split("with ", 1)[1].split(" as ", 1)[0].strip().rstrip(":\n")
+                var = header.split(" as ", 1)[1].strip().rstrip(":\n") if " as " in header else "f"
+                body = lines[start:end]
+                dedented = []
+                for line in body[1:]:
+                    if line.startswith("    "):
+                        dedented.append(line[4:])
+                    else:
+                        dedented.append(line)
+                replacement = [f"{var} = {header_expr}\n"] + dedented
+                mutated = "".join(lines[: start - 1] + replacement + lines[end:])
+                return Mutation(
+                    defect_type=self.defect_type,
+                    language=self.language,
+                    line_start=start,
+                    line_end=end,
+                    mutated_source=mutated,
+                    reference_fix="Use `with open(...) as f:` to ensure the file is closed.",
+                    description="Replaced context-managed open() with an unclosed file handle.",
+                )
+        return None