Bug#851588: diffoscope: skip tests if binutils can't handle the object file format

[Daniel Shahaf]

Mattia Rizzolo wrote on Mon, Jan 16, 2017 at 18:06:48 +0100:
> So, I finally managed to look into the tests failures were have been
> seeing in ubuntu's autopkgtest in armhf (and probably also ppc64el and
> s390x, but I didn't test for that).
> As supposed, the reason is that we're trying to disassemble x86-64
> binaries, and the installed multiarch can't deal with them;

Then should we look for 'x86_64-linux-gnu-readelf' rather than bare
'readelf'?  And likewise for 'objdump' and friends.

> Now, I came up with a patch, but my python foo has its limit, and I
> think somebody might improve it quite some (e.g. please tell me how I
> can write a decorated fuction that doesn't take any value as input and
> still returns only pytest.mark.skipif()... what I did is uglyugly), so
> I'm filing it as a bug here instead of committing; see the attachment :)

The expression after the "@" sign is evaluated; that should result in
a callable object, which is called with the decoratee as an argument.
In your case, you should be able to pass no parameters, e.g.,
.
    @skip_if_binutils_do_not_support_x86()
.
and then delete the sole formal argument from the function definition.

Note that the parentheses are still required in this case, since the
thing that is called with 'test_obj_compare_non_existing' as an actual
parameter is not 'skip_if_binutils_do_not_support_x86' but rather the
function it returns.

I'm not sure what's the best way to combine skip_unless_tools_exist and
pytest.mark.skipif().  The way decorators work is that they're invoked
on each other's return values, i.e.,
.
    def skip_if_binutils_do_not_support_x86():
        func1 = skip_unless_tools_exist('objdump')
        func2 = pytest.mark.skipif(...)
        return (lambda func: func2(func1(func)))
.
but whether that's readable is a question of taste.

Cheers,

Daniel


>      return obj1.compare(obj2).details
>  
>  @skip_unless_tools_exist('readelf')
> + at skip_if_binutils_do_not_support_x86(True)
>  def test_obj_compare_non_existing(monkeypatch, obj1):
>      monkeypatch.setattr(Config(), 'new_file', True)
>      difference = obj1.compare(MissingFile('/nonexisting', obj1))

> +def skip_if_binutils_do_not_support_x86(func):
> +    if tools_missing('objdump'):
> +         return skip_unless_tools_exists('objdump')
> +    out = subprocess.check_output(('objdump', '-i')).decode('utf-8').splitlines()
> +    return pytest.mark.skipif(
> +        'elf64-x86-64' not in out,
> +        reason="requires a binutils capable of reading x86-64 binaries"
> +    )
> +
>  def load_fixture(filename):
>      return pytest.fixture(
>          lambda: specialize(FilesystemFile(filename))
> -- 
> 2.11.0
>