Improve info logged by tex subsystem.

- Call kpsewhich in text mode (with the correct encoding).
- Suppress empty stdout/stderr from logged outputs.

Together this changes the entries logged by dviread from
```
DEBUG:matplotlib.dviread:kpsewhich cmss10.tfm
DEBUG:matplotlib.dviread:stdout:
b'/usr/local/texlive/2019/texmf-dist/fonts/tfm/public/cm/cmss10.tfm\n'
DEBUG:matplotlib.dviread:stderr:
b''
```
to
```
DEBUG:matplotlib.dviread:kpsewhich cmss10.tfm
DEBUG:matplotlib.dviread:stdout:
/usr/local/texlive/2019/texmf-dist/fonts/tfm/public/cm/cmss10.tfm

```

- Fix logged info about loading of tex fonts (it's the font that
  matters, not the font family).

Author: anntzer

lib/matplotlib/cbook/__init__.py

@@ -2133,15 +2133,23 @@ def _check_and_log_subprocess(command, logger, **kwargs):
     proc = subprocess.run(
         command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, **kwargs)
     if proc.returncode:
+        stdout = proc.stdout
+        if isinstance(stdout, bytes):
+            stdout = stdout.decode()
+        stderr = proc.stderr
+        if isinstance(stderr, bytes):
+            stderr = stderr.decode()
         raise RuntimeError(
             f"The command\n"
             f"    {_pformat_subprocess(command)}\n"
             f"failed and generated the following output:\n"
-            f"{proc.stdout.decode('utf-8')}\n"
+            f"{stdout}\n"
             f"and the following error:\n"
-            f"{proc.stderr.decode('utf-8')}")
-    logger.debug("stdout:\n%s", proc.stdout)
-    logger.debug("stderr:\n%s", proc.stderr)
+            f"{stderr}")
+    if proc.stdout:
+        logger.debug("stdout:\n%s", proc.stdout)
+    if proc.stderr:
+        logger.debug("stderr:\n%s", proc.stderr)
     return proc.stdout
 
 

lib/matplotlib/dviread.py

@@ -25,6 +25,7 @@
 from pathlib import Path
 import re
 import struct
+import sys
 import textwrap
 
 import numpy as np
@@ -1067,9 +1068,11 @@ def find_tex_file(filename, format=None):
         # On Windows only, kpathsea can use utf-8 for cmd args and output.
         # The `command_line_encoding` environment variable is set to force it
         # to always use utf-8 encoding.  See Matplotlib issue #11848.
-        kwargs = dict(env=dict(os.environ, command_line_encoding='utf-8'))
-    else:
-        kwargs = {}
+        kwargs = {'env': {**os.environ, 'command_line_encoding': 'utf-8'},
+                  'encoding': 'utf-8'}
+    else:  # On POSIX, run through the equivalent of os.fsdecode().
+        kwargs = {'encoding': sys.getfilesystemencoding(),
+                  'errors': 'surrogatescape'}
 
     cmd = ['kpsewhich']
     if format is not None:
@@ -1079,10 +1082,7 @@ def find_tex_file(filename, format=None):
         result = cbook._check_and_log_subprocess(cmd, _log, **kwargs)
     except RuntimeError:
         return ''
-    if os.name == 'nt':
-        return result.decode('utf-8').rstrip('\r\n')
-    else:
-        return os.fsdecode(result).rstrip('\n')
+    return result.rstrip('\n')
 
 
 @lru_cache()

lib/matplotlib/texmanager.py

@@ -131,8 +131,7 @@ def get_font_config(self):
                                font_family, font, self.font_info[font.lower()])
                     break
                 else:
-                    _log.debug('%s font is not compatible with usetex.',
-                               font_family)
+                    _log.debug('%s font is not compatible with usetex.', font)
             else:
                 _log.info('No LaTeX-compatible font found for the %s font '
                           'family in rcParams. Using default.', font_family)