Do not discard error message if _imagingft fails to import

[nulano]

Helps #7040

Changes:

• use _util.DeferredError if _imagingft fails to import instead of a custom helper from before the fork (similarly to ImageCms, added in Readthedocs #600),
• if a module fails to import but is present (i.e. triggers ImportError but not ModuleNotFoundError), raise a warning in PIL.features,
• remove no longer needed backwards compatibility code:
  • FT_LOAD_COLOR was added in FreeType 2.5, Pillow currently requires FreeType>=2.8 (Remove support for FreeType 2.7 and older #5777)
  • FT_LOAD_TARGET_MONO version added is undocumented, but has been around since FreeType 2.1.3,
  • remove #define KEEP_PY_UNICODE, was only used in file py3.h which was removed in Drop support for EOL Python 2.7 #4109

I've tested these changes by compiling Pillow in a Fedora 26 Docker container (with FreeType 2.7.1 and no other optional dependencies) with an intentional error in _imagingft:

# python3.7 -c "import PIL.ImageFont
> PIL.ImageFont.core.test"
Traceback (most recent call last):
  File "<string>", line 2, in <module>
  File "/usr/lib64/python3.7/site-packages/PIL/_util.py", line 19, in __getattr__
    raise self.ex
  File "/usr/lib64/python3.7/site-packages/PIL/ImageFont.py", line 58, in <module>
    from . import _imagingft as core
ImportError: /usr/lib64/python3.7/site-packages/PIL/_imagingft.cpython-37m-x86_64-linux-gnu.so: undefined symbol: FT_Done_MM_Var

# python3.7 -m PIL
--------------------------------------------------------------------
Pillow 9.5.0.dev0
Python 3.7.0b4 (default, May 16 2018, 15:51:23)
       [GCC 7.3.1 20180130 (Red Hat 7.3.1-2)]
--------------------------------------------------------------------
Python modules loaded from /usr/lib64/python3.7/site-packages/PIL
Binary modules loaded from /usr/lib64/python3.7/site-packages/PIL
--------------------------------------------------------------------
--- PIL CORE support ok, compiled for 9.5.0.dev0
--- TKINTER support ok, loaded 8.6
/usr/lib64/python3.7/site-packages/PIL/features.py:39: UserWarning: /usr/lib64/python3.7/site-packages/PIL/_imagingft.cpython-37m-x86_64-linux-gnu.so: undefined symbol: FT_Done_MM_Var
  warnings.warn(str(ex))
*** FREETYPE2 support not installed
*** LITTLECMS2 support not installed
*** WEBP support not installed
*** WEBP Transparency support not installed
*** WEBPMUX support not installed
*** WEBP Animation support not installed
--- JPEG support ok, compiled for libjpeg-turbo 1.5.3
*** OPENJPEG (JPEG2000) support not installed
--- ZLIB (PNG/ZIP) support ok, loaded 1.2.11
*** LIBTIFF support not installed
/usr/lib64/python3.7/site-packages/PIL/features.py:154: UserWarning: /usr/lib64/python3.7/site-packages/PIL/_imagingft.cpython-37m-x86_64-linux-gnu.so: undefined symbol: FT_Done_MM_Var
  warnings.warn(str(ex))
*** RAQM (Bidirectional Text) support not installed
*** LIBIMAGEQUANT (Quantization method) support not installed
*** XCB (X protocol) support not installed
--------------------------------------------------------------------
...

[radarhere]

Would you mind sharing more specific details about how to replicate the intentional error you tested with?

[nulano]

I commented out the following lines:

Pillow/src/_imagingft.c

Lines 1068 to 1069 in 93afedf

	#if FREETYPE_MAJOR > 2 || (FREETYPE_MAJOR == 2 && FREETYPE_MINOR > 9) || \
	(FREETYPE_MAJOR == 2 && FREETYPE_MINOR == 9 && FREETYPE_PATCH == 1)

Pillow/src/_imagingft.c

Line 1249 in 93afedf

#endif

Pillow/src/_imagingft.c

Lines 1266 to 1267 in 93afedf

	#if FREETYPE_MAJOR > 2 || (FREETYPE_MAJOR == 2 && FREETYPE_MINOR > 9) || \
	(FREETYPE_MAJOR == 2 && FREETYPE_MINOR == 9 && FREETYPE_PATCH == 1)

Pillow/src/_imagingft.c

Line 1272 in 93afedf

#endif

Then installed Pillow from source with pip as usual in a Fedora 26 Docker container which has FreeType 2.7.1.

[radarhere]

I'm trying, but for reasons I don't understand, Pillow still thinks it has access to FreeType 2.12.1.

[nulano]

It looks like it downloaded the wheel: https://github.com/radarhere/docker-images/actions/runs/4575672322/jobs/8078793400#step:6:10950

For my tests I cloned my branch in ~/pillow, made the changes to src/_imagingft.c from my previous comment, then ran the following commands:

$ docker run -it --rm -v ~/pillow:/pillow fedora:26 bash
...
# cat /root/.bash_history
dnf install -y python37 gcc freetype-devel zlib-devel libjpeg-devel
cd /pillow/
python3.7 -m ensurepip
python3.7 -m pip install -U pip setuptools
python3.7 -m pip install . --no-cache-dir --ignore-installed
python3.7 -c "import PIL.ImageFont; PIL.ImageFont.core.test"
python3.7 -m PIL
history -a

[radarhere]

You're right, I realised that shortly after posting. Thanks for the more in-depth instructions.

If anyone else is interested, here is the ImageFont import before and after, features.check_module before and after and features.check_feature before and after.