[Matplotlib-devel] On testing with other FreeType versions

[Antony Lee]

Hi,

1. Sticking to testing with the old FreeType.

Injecting an older FreeType version is "relatively" easy to do (the
question is whether you want to do it...).  Naively, one could just set
LD_PRELOAD to /path/to/libfreetype.so, but that will also affect
subprocesses such as imagemagick, which (IIRC) don't like that, so instead
the correct way is to ensure that the Python process calls
`dlopen('/path/to/libfreetype.so', RTLD_GLOBAL)` which forces symbol
resolution *in this process* to first check the given path, but does not
affect subprocess (alternatively, one could remove LD_PRELOAD from the
environment before calling the subprocess but that seems messier).
Fortunately, dlopen is "effectively" available under the name of
`ctypes.CDLL` in Python.

I have a proof of principle somewhere that patches the testing framework to
1) ensure that an old freetype is built (basically moving the
local_freetype implemenation from setupext to the main lib), and 2) loads
it as above.

Another relevant issue is the manylinux wheels, which must somehow embed a
libfreetype.  Currently I believe this is done via static linking.  This is
not so great if you also want to load freetype for other reasons; for
example mplcairo (which loads freetype via cairo) currently cannot work
with local_freetype builds due to symbol conflicts.  I believe that
switching to the standard manylinux approach (which is to include the
shared object in a hidden folder and set RPATH appropriately) would work
better (and allow us to strip out the static linking code).

2. Switching to newer FreeTypes.

I don't think committing all test images to the main repo is really a
viable option: FreeType is also making new releases every once in a while
and different Linuxes have different versions (
https://pkgs.org/download/freetype gives 2.8.1 (Arch, Debian Sid), 2.8
(Fedora 27, Ubuntu 17.10), 2.6.3 (Debian 9, OpenSUSE 42.3), 2.6.1 (Ubuntu
16.04 LTS) and that's only a few).

I do believe that adding tooling that generates the test images to a side
repo for each tag + FreeType version (say, using the FT versions of the
major distros at the time of the tag) may be reasonable.

3. Side note.

If #9763 (or #5414) gets accepted (new FT wrappers), they will also require
a new generation of the test images: ft2font currently generates "wiggly
baselines" in certain cases (see example in #5414), and try as I might
(i.e. not so much) I could not reproduce them in the new wrapper :-)

Antony

2017-12-10 21:44 GMT-08:00 Elliott Sales de Andrade <
quantum.analyst at gmail.com>:

> Hi all,
>
> Downstream in Fedora (and maybe Debian), they are running into issues with
> testing and text. Fedora 26 has FreeType 2.7.1 and Fedora 27 & Rawhide has
> FreeType 2.8. Fedora 25 uses 2.6.5, but it will be EOL in the next week.
> Many other distros are also transitioning to these newer FreeType as well
> [1] and I think anaconda recently added 2.8 too.
>
> With 2.7.1, a few tests fail (rms < 1) and it is straightforward to patch
> that [2]. With 2.8 though, over 800 tests fail [3] ranging up to ~80 rms
> [4]. This is a bit harder to paper over.
>
> I see a few ways to mitigate the problem, with varying
> advantages/disadvantages:
>
> 1. Bundle the older version in the Matplotlib package like we do with
> tests. I don't really believe this to be a viable option for downstream,
> but I'm just mentioning it to be thorough. There are already a few (minor)
> security issues in the one we test against.
> 2. Inject older FreeType just to run tests on the package. Again I don't
> like this idea. The point of running tests is to be sure that the version
> in a distro works *in that distro*. Testing with something a user could
> never install seems useless.
> 3. Re-create all our current and future test images with 2.8. While this
> is most future-proof, adding over 800 images is going to bloat the repo
> quite a bit.
> 4. Create some sort of side repo with test images for other FreeType
> releases. This would reduce bloat in the main repo but be somewhat more
> work. Thus I'd only suggest doing so for tags.
>
> I dislike the first two options as they would be repetitive across distros
> (unless they just stopped testing altogether), but the last two are not
> without work for us.
>
> Opinions? Alternative ideas?
>
> [1] https://repology.org/metapackage/freetype/versions
> [2] https://github.com/QuLogic/matplotlib/commit/cfdc8359234
> 07810bd087f60332cdc8cdcb23f05
> [3] https://kojipkgs.fedoraproject.org//work/tasks/3137/23623137/build.log
> [4] https://gist.github.com/QuLogic/477055a847a44cd444a0932432acffd1
>
> --
> Elliott
>
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>
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