fix(cache-manager): match key_prefix literally in clear_pattern

[allen0099]

Summary

CacheManager.clear_pattern(pattern) passed key_prefix + pattern to backend.clear_pattern() as a single glob, so glob characters in the manager's own prefix were live:

• CacheManager(key_prefix="cache[1]:").clear_pattern("*") missed its own keys.
• key_prefix="a?:" also cleared the keys of a manager with prefix ab:.

This PR implements the hybrid option the maintainer chose:

• Fast path, unchanged. A key_prefix without *, ?, [, ] or \ still calls backend.clear_pattern(key_prefix + pattern), e.g. Redis SCAN MATCH. The argument is the same as before.

• Slow path. Any other prefix:

  • get_all_keys() lists every key;
  • it keeps keys that start with key_prefix literally and whose remainder matches pattern under fnmatch.fnmatchcase;
  • delete_many() deletes them;
  • the return value is the number deleted.

  On this path pattern is fnmatch syntax, not Redis glob: case-sensitive, no backslash escapes, [!a] for negation. This is documented in the docstring and the docs.

• UserWarning at construction when key_prefix contains a glob metacharacter. The message says clear_pattern() will list and filter in Python, which is slower on Redis, and suggests a prefix without *?[]\. stacklevel=2 points it at the caller's line. The only internal constructor is get_app_cache(), which uses the default cache: prefix, so the warning never fires from library code.

• Memcached. Both paths return 0 with exactly one RuntimeWarning. On the slow path it comes from get_all_keys(), and delete_many() of nothing is silent.

• Scope. The metacharacter set mirrors _GLOB_SPECIAL in backends/redis.py as a private constant, so no backend API is added. The manager.py change is confined to __init__, clear_pattern and a small private helper.

Behaviour changes

• A prefix with glob characters now clears exactly its own namespace. This can delete more keys (cache[1]:) or fewer keys (a?:) than before.
• Such a prefix now warns at construction.
• Plain prefixes behave exactly as before.

Tests

New file tests/test_cache_manager_clear_pattern.py, run on memory and live Redis where applicable:

• the constructor warning appears for each metacharacter and points at the caller's file; a plain prefix produces no warning;
• the fast path calls backend.clear_pattern("cache:user:*") and never enumerates keys;
• cache[1]: clears its own keys but not cache1:a; a?: leaves the ab: manager's keys alone;
• ?, * and [!u] in the pattern part still work as a glob on the slow path, case-sensitively;
• the prefix is matched only at the start of the key;
• Memcached returns 0 with a single RuntimeWarning on both paths.

Full suite incl. live Redis/Memcached tests: 1204 passed, 1 skipped, coverage 99% (manager.py 100%). ruff, ruff format and mypy --strict are clean.

Changelog

changelog.d/140.fixed.md

Closes #140