Note minimum supported version for fontconfig.

anntzer · anntzer · commit c93ab96ac4e2 · 2019-11-07T23:39:33.000+01:00
diff --git a/INSTALL.rst b/INSTALL.rst
@@ -150,7 +150,9 @@ etc., you can install the following:
 * `ImageMagick <https://www.imagemagick.org/script/index.php>`_: for saving
   animated gifs;
 * `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.
 
 FreeType and Qhull
 ------------------
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 []
