[issue30117] test_lib2to3.test_parser.test_all_project_files() fails

[Eric Appelt]

Eric Appelt added the comment:

I added a PR to fix these two (in my opinion) spurious failure conditions in the lib2to3.tests.test_parser.TestParserIdempotency test_parser test with the following changes to the test:

1. Use the same encoding found in the initial file to write a temp file for a diff. This retains the BOM if the encoding was initially utf-8-sig.

2. If the file cannot be parsed using the normal grammar, try again with no print statement which should succeed for valid files using future print_function

For case (1), the driver was correctly handling a BOM in a utf-8 file, but then the test was not writing a comparison file using 'utf-8-sig' to diff against, so the BOM got removed. I don't think that is the fault of the parser, and lib2to3 will retain the BOM.

For case (2), lib2to3 pre-detects the use of from __future__ import print_function or allows the user to force this interpretation with a -p flag, and then selects a different grammar with the print statement removed. That makes the test cases unfair to this test as the driver itself doesn't know which grammar to use. As a minimal fix, the test will try using a grammar with the print statement, and if that fails fall back on a grammar without it. A more thorough handling of the idempotency test would to be to parse all files using both grammars and ignore if one of the two failed but otherwise check both. I didn't think this was necessary but can change.

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nosy: +Eric Appelt

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30117>
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