paths.set_temp_cache and paths.set_temp_config don't reset value if exception occurs in creation

Description

The context managers paths.set_temp_cache and paths.set_temp_config are supposed to let users temporarily reset the locations of the astropy cache and config file. These are used in the test suite but are also user-visible. Unfortunately, as context managers, if an exception occurs in their __enter__ methods, their __exit__ methods are never called; these exit methods are what is supposed to reset the values to their original state, so if an exception is produced, say because something is badly wrong with the requested cache setup, the bogus cache setup is left behind.

This appears as bug #9634 and PR #9703 revealed and should fix the problem; there should be an example in the code for it.

Reveal bug astropy#9704

Fix astropy#9704

https://github.com/astropy/astropy/pull/9703/files#diff-a084bf6259662e3a035cd3aeca0323fbR1373 is where the problem is detected - the download dir is not returned to its original value.

https://github.com/astropy/astropy/pull/9703/files#diff-6e8757768603143a75fb8363ec462764R77 is a better example/regression test:

def test_set_temp_cache_resets_on_exception(tmpdir):
    """Test for regression of  bug #9704"""
    t = paths.get_cache_dir()
    a = tmpdir / 'a'
    with open(a, 'wt') as f:
        f.write("not a good cache\n")
    with pytest.raises(OSError):
        with paths.set_temp_cache(a):
            pass
    assert t == paths.get_cache_dir()

Closed by #9703

Re-enable cache warnings, reveal and fix bug astropy#9704

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paths.set_temp_cache and paths.set_temp_config don't reset value if exception occurs in creation #9704

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paths.set_temp_cache and paths.set_temp_config don't reset value if exception occurs in creation #9704

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aarchiba commented on Nov 29, 2019

aarchiba commented on Nov 29, 2019

aarchiba commented on Nov 30, 2019

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