From 7f1eb421c90424203a67a805ff5223be4c76d9e9 Mon Sep 17 00:00:00 2001
From: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
Date: Tue, 3 Dec 2019 06:11:21 +0100
Subject: [PATCH] Backport PR #15601: Fix FontProperties conversion to/from
 strings

---
 lib/matplotlib/fontconfig_pattern.py          | 33 ++++++---
 .../tests/test_fontconfig_pattern.py          | 70 +++++++++++++++++++
 2 files changed, 95 insertions(+), 8 deletions(-)
 create mode 100644 lib/matplotlib/tests/test_fontconfig_pattern.py

diff --git a/lib/matplotlib/fontconfig_pattern.py b/lib/matplotlib/fontconfig_pattern.py
index d15b937b249a..1f4df32c0fcd 100644
--- a/lib/matplotlib/fontconfig_pattern.py
+++ b/lib/matplotlib/fontconfig_pattern.py
@@ -14,7 +14,7 @@
 
 from functools import lru_cache
 import re
-
+import numpy as np
 from pyparsing import (Literal, ZeroOrMore, Optional, Regex, StringEnd,
                        ParseException, Suppress)
 
@@ -177,19 +177,36 @@ def _property(self, s, loc, tokens):
 parse_fontconfig_pattern = lru_cache()(FontconfigPatternParser().parse)
 
 
+def _escape_val(val, escape_func):
+    """
+    Given a string value or a list of string values, run each value through
+    the input escape function to make the values into legal font config
+    strings.  The result is returned as a string.
+    """
+    if not np.iterable(val) or isinstance(val, str):
+        val = [val]
+
+    return ','.join(escape_func(r'\\\1', str(x)) for x in val
+                    if x is not None)
+
+
 def generate_fontconfig_pattern(d):
     """
     Given a dictionary of key/value pairs, generates a fontconfig
     pattern string.
     """
     props = []
-    for key in 'family style variant weight stretch file size'.split():
+
+    # Family is added first w/o a keyword
+    family = d.get_family()
+    if family is not None and family != []:
+        props.append(_escape_val(family, family_escape))
+
+    # The other keys are added as key=value
+    for key in ['style', 'variant', 'weight', 'stretch', 'file', 'size']:
         val = getattr(d, 'get_' + key)()
+        # Don't use 'if not val' because 0 is a valid input.
         if val is not None and val != []:
-            if type(val) == list:
-                val = [value_escape(r'\\\1', str(x)) for x in val
-                       if x is not None]
-                if val != []:
-                    val = ','.join(val)
-            props.append(":%s=%s" % (key, val))
+            props.append(":%s=%s" % (key, _escape_val(val, value_escape)))
+
     return ''.join(props)
diff --git a/lib/matplotlib/tests/test_fontconfig_pattern.py b/lib/matplotlib/tests/test_fontconfig_pattern.py
new file mode 100644
index 000000000000..521a3e882d70
--- /dev/null
+++ b/lib/matplotlib/tests/test_fontconfig_pattern.py
@@ -0,0 +1,70 @@
+from matplotlib.font_manager import FontProperties
+
+
+# Attributes on FontProperties object to check for consistency
+keys = [
+    "get_family",
+    "get_style",
+    "get_variant",
+    "get_weight",
+    "get_size",
+    ]
+
+
+def test_fontconfig_pattern():
+    "Test converting a FontProperties to string then back."
+
+    # Defaults
+    test = "defaults "
+    f1 = FontProperties()
+    s = str(f1)
+
+    f2 = FontProperties(s)
+    for k in keys:
+        assert getattr(f1, k)() == getattr(f2, k)(), test + k
+
+    # Basic inputs
+    test = "basic "
+    f1 = FontProperties(family="serif", size=20, style="italic")
+    s = str(f1)
+
+    f2 = FontProperties(s)
+    for k in keys:
+        assert getattr(f1, k)() == getattr(f2, k)(), test + k
+
+    # Full set of inputs.
+    test = "full "
+    f1 = FontProperties(family="sans-serif", size=24, weight="bold",
+                        style="oblique", variant="small-caps",
+                        stretch="expanded")
+    s = str(f1)
+
+    f2 = FontProperties(s)
+    for k in keys:
+        assert getattr(f1, k)() == getattr(f2, k)(), test + k
+
+
+def test_fontconfig_str():
+    "Test FontProperties string conversions for correctness"
+
+    # Known good strings taken from actual font config specs on a linux box
+    # and modified for MPL defaults.
+
+    # Default values found by inspection.
+    test = "defaults "
+    s = ("sans\\-serif:style=normal:variant=normal:weight=normal"
+         ":stretch=normal:size=12.0")
+    font = FontProperties(s)
+    right = FontProperties()
+    for k in keys:
+        assert getattr(font, k)() == getattr(right, k)(), test + k
+
+    test = "full "
+    s = ("serif:size=24:style=oblique:variant=small-caps:weight=bold"
+         ":stretch=expanded")
+    font = FontProperties(s)
+    right = FontProperties(family="serif", size=24, weight="bold",
+                           style="oblique", variant="small-caps",
+                           stretch="expanded")
+    for k in keys:
+        assert getattr(font, k)() == getattr(right, k)(), test + k