GeezerVison

     for i, ch in enumerate(raw_body[match_start:], match_start):
         if ch == "{":
             brace_depth += 1
             if block_start is None:
                 block_start = i + 1
         elif ch == "}":
             brace_depth -= 1
             if brace_depth == 0:
                 block_end = i
                 break
 
+    if block_start is None or block_end is None:
+        raise ValueError("Could not isolate deopt match block")
+
     match_body = raw_body[block_start:block_end]

Verify each finding against the current code and only fix it if needed.

In `@scripts/generate_opcode_metadata.py` around lines 94 - 109, The current
brace-scan can leave block_start or block_end as None and then silently slice
raw_body[block_start:block_end]; update the scan logic (using variables
brace_depth, block_start, block_end, match_start) to validate after the loop
that both block_start and block_end were found and raise/throw a clear parsing
error (including context like match_start or a snippet of raw_body) if either is
None so the script fails fast instead of producing incomplete
match_body/_specializations.

Learnt from: ShaharNaveh
Repo: RustPython/RustPython PR: 7573
File: scripts/generate_opcode_metadata.py:69-85
Timestamp: 2026-04-15T08:58:35.342Z
Learning: In `scripts/generate_opcode_metadata.py` (RustPython repo), `extract_enum_body` intentionally returns `None` when the enum is not found or the closing brace is missing. The author wants the caller to crash with a `TypeError` in that case, rather than raising an explicit exception. Do not suggest converting `return None` to `raise ValueError(...)` in this function.