[Reproducible-builds] [diffoscope] Support for --ignore-profile flag in diffoscope

[Jérémy Bobbio]

Ximin Luo:
> Concretely I have some suggestions:
> 
> 1. instead of calling this "ignore" we call it "hide". and instead of
> "irrelevant" we say "common"/"minor"/"known"

Great suggestions! :)

> 2. diffoscope --ignore-* (or --hide-*) MUST NOT return 0 or otherwise
> give the impression that two non-identical files are the same, even if
> all differences are "hidden". It should report "n differences hidden".

There's a tradeoff here: you don't really know how many differences are
going to be hidden until you've computed them, and that might be costly.

Use case: Jane is trying to understand if her patch removing __TIME__
from the source code is enough to make the binary reproducible. As she
knows how this affect the binary, she get faster results and avoid
clutter by adding the flag `--hide=debug-symbols` or
`--hide-pattern='*.debug'`.

I'm writing “faster results” because we can avoid unpacking the debug
symbols and comparing them which are costly operations.

If we display “n differences hidden”, then we always have to compare
everything…

-- 
Lunar                                .''`. 
lunar at debian.org                    : :Ⓐ  :  # apt-get install anarchism
                                    `. `'` 
                                      `-   
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