Linux: Fix automatic detection of bold/italic faces for fonts such as IBM Plex Mono and have the regular face with a full name that is the same as the family name

Fixes #2951

docs/changelog.rst

@@ -40,6 +40,10 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - Implement special rendering for various characters from the set of "Symbols
   for Legacy Computing" from the Unicode 13 standard
 
+- Linux: Fix automatic detection of bold/italic faces for fonts such as IBM
+  Plex Mono and have the regular face with a full name that is the same as the
+  family name (:iss:`2951`)
+
 
 0.18.3 [2020-08-11]
 -------------------

kitty/fonts/fontconfig.py

@@ -84,9 +84,14 @@ def find_best_match(family: str, bold: bool = False, italic: bool = False, monos
     # First look for an exact match
     for selector in ('ps_map', 'full_map', 'family_map'):
         candidates = font_map[selector].get(q)
-        if candidates:
-            candidates.sort(key=score)
-            return candidates[0]
+        if not candidates:
+            continue
+        if len(candidates) == 1 and (bold or italic) and candidates[0].get('family') == candidates[0].get('full_name'):
+            # IBM Plex Mono does this, where the full name of the regular font
+            # face is the same as its family name
+            continue
+        candidates.sort(key=score)
+        return candidates[0]
 
     # Use fc-match to see if we can find a monospaced font that matches family
     for spacing in (FC_MONO, FC_DUAL):