Backport PR #15626: Note minimum supported version for fontconfig.

QuLogic · MeeseeksDev[bot] · commit 0e5b8d62a662 · 2019-11-08T01:32:17.000Z
diff --git a/INSTALL.rst b/INSTALL.rst
@@ -164,7 +164,9 @@ etc., you can install the following:
 * `Pillow <https://pillow.readthedocs.io/en/latest/>`_ (>= 3.4): for a larger
   selection of image file formats: JPEG, BMP, and TIFF image files;
 * `LaTeX <https://miktex.org/>`_ and `GhostScript (>=9.0)
-  <https://ghostscript.com/download/>`_ : for rendering text with LaTeX.
+  <https://ghostscript.com/download/>`_ : for rendering text with LaTeX;
+* `fontconfig <https://www.fontconfig.org>`_ (>= 2.7): for detection of system
+  fonts on Linux.
 
 .. note::
 
diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
@@ -273,6 +273,10 @@ def _call_fc_list():
         'This may take a moment.'))
     timer.start()
     try:
+        if b'--format' not in subprocess.check_output(['fc-list', '--help']):
+            _log.warning(  # fontconfig 2.7 implemented --format.
+                'Matplotlib needs fontconfig>=2.7 to query system fonts.')
+            return []
         out = subprocess.check_output(['fc-list', '--format=%{file}\\n'])
     except (OSError, subprocess.CalledProcessError):
         return []
