Bug#966280: dpkg-source should ignore CRLF vs. LF differences

Hi!

On Sat, 2020-07-25 at 22:42:02 +0200, Martin Quinson wrote:
> Package: dpkg
> Version: 1.19.7
> Severity: normal

> when trying to build the new upstream version of Widelands with git-
> buildpackage, I had an error message saying that some files were modified out
> of the debian/ directory. It turns out that the difference is only about the
> line endings: some files of the upstream tarball are encoded with CRLF while
> most of them are LF only.
> 
> When importing the files in the upstream branch of my git, the CRLF are
> automatically converted to LF by git, but when dpkg-source compares the content
> of the current dir (ie, the checkout) with the content of the tarball, it fails
> with a rather uninformative error message:
> 
>   dpkg-source: info: local changes detected, the modified files are:
>    widelands-21/cmake/Modules/FindSDL2_image.cmake
>    widelands-21/cmake/Modules/FindSDL2_mixer.cmake
>    widelands-21/cmake/Modules/FindSDL2_ttf.cmake
>    widelands-21/data/maps/Twin_Lagoons_v2.wmf/elemental
>    widelands-21/src/third_party/eris/README.eris
>   dpkg-source: error: aborting due to unexpected upstream changes, see
> /tmp/widelands_21-1.diff.YyKJqP
> 
> My first glance at the diff was not enough to understand the pb, stupid me.
> Instead it took me several hours to understand the issue. I repacked and
> reimported my upstream tarball quite a few times before that. Then, I had to
> manually repack the upstream archive after dos2unix'ing the relevant files to
> fix it.
> 
> I think that it'd be really better if dpkg-source would ignore those difference
> in the first place. I'm not completely sure, but I think that this is what the
> --strip-trailing-cr option of diff is meant for.

I don't think using --strip-trailing-cr is safe, because (AFAICT)
patch(1) would reject applying patches on different line endings, so
this could accept diffs that then could not be applied.

I guess we could add a message hint mentioning the potential issue of
CRLF vs LF, but I'm not sure if that's too niche for such message to
be shown always? Otherwise I think I'd close this.

Thanks,
Guillem