From 35a279ecb9af41a6f95ddbc6a0f1beaa2472d165 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Micha=C5=82=20G=C3=B3rny?= Date: Sun, 26 Feb 2023 01:04:34 +0100 Subject: [PATCH] _build_tables: Invalidate cache before importing generated modules (#494) Make sure to invalidate finder caches before trying to import generated modules. This is necessary according to the Python documentation: https://docs.python.org/3/library/importlib.html#importlib.invalidate_caches This fixes a hard-to-reproduce bug that Python would be unable to find just-generated `lextab.py` if mtime of the current directory did not change from the moment the script was started. This could e.g. be the case if one has second-precision timestamps and removes the generated file just before starting the build, e.g.: $ rm pycparser/lextab.py; python -m build -nw It could also be reproduced easier by doing something like: $ cd pycparser $ touch .; python -B _build_tables.py Traceback (most recent call last): File "/var/tmp/pycparser/pycparser/_build_tables.py", line 38, in import lextab ModuleNotFoundError: No module named 'lextab' This is because the first command (`rm` or `touch`) updates the mtime of the directory to the current time. If the script is run fast enough, it manages to scan the directory and then write the new `lextab.py` within the same second. As a result, mtime of the directory after writing the new file is the same as when the script was started, finder does not invalidate the cache and assumes that `lextab.py` does not exist since it did not exist when the directory was scanned earlier. This potentially fixes #493. It was originally reported on https://bugs.gentoo.org/701878. Thanks to Gary E. Miller for patience in reproducing the problem and proxy-debugging it for me, as well as testing the final patch before submission. --- pycparser/_build_tables.py | 3 +++ 1 file changed, 3 insertions(+) diff --git a/pycparser/_build_tables.py b/pycparser/_build_tables.py index 958381ad..4f371079 100644 --- a/pycparser/_build_tables.py +++ b/pycparser/_build_tables.py @@ -13,6 +13,7 @@ # Insert '.' and '..' as first entries to the search path for modules. # Restricted environments like embeddable python do not include the # current working directory on startup. +import importlib import sys sys.path[0:0] = ['.', '..'] @@ -32,6 +33,8 @@ # Load to compile into .pyc # +importlib.invalidate_caches() + import lextab import yacctab import c_ast