Fix error generation for missing pgf.texsystem.

anntzer · anntzer · commit bb41673d5903 · 2023-09-04T08:02:59.000+02:00
If pgf.texsystem isn't installed, then self.latex will not be created
*at all* by _setup_latex_process, and we thus cannot access
self.latex.args[0], but must instead read the rc value again.  To make
this clearer, move the error handling into _setup_latex_process, instead
of having it outside.

No test because that'd require setting up a test env where pgf.texsystem
is explicitly *missing* (or go through lots of mocks), which seems not
worth it.
diff --git a/lib/matplotlib/backends/backend_pgf.py b/lib/matplotlib/backends/backend_pgf.py
@@ -241,24 +241,14 @@ def __init__(self):
         self._finalize_tmpdir = weakref.finalize(self, self._tmpdir.cleanup)
 
         # test the LaTeX setup to ensure a clean startup of the subprocess
-        try:
-            self._setup_latex_process(expect_reply=False)
-        except FileNotFoundError as err:
-            raise RuntimeError(
-                f"{self.latex.args[0]!r} not found.  Install it or change "
-                f"rcParams['pgf.texsystem'] to an available TeX "
-                f"implementation.") from err
-        except OSError as err:
-            raise RuntimeError(
-                f"Error starting process {self.latex.args[0]!r}") from err
+        self._setup_latex_process(expect_reply=False)
         stdout, stderr = self.latex.communicate("\n\\makeatletter\\@@end\n")
         if self.latex.returncode != 0:
             raise LatexError(
                 f"LaTeX errored (probably missing font or error in preamble) "
                 f"while processing the following input:\n"
                 f"{self._build_latex_header()}",
                 stdout)
-
         self.latex = None  # Will be set up on first use.
         # Per-instance cache.
         self._get_box_metrics = functools.lru_cache(self._get_box_metrics)
@@ -268,10 +258,19 @@ def _setup_latex_process(self, *, expect_reply=True):
         # Windows, we must ensure that the subprocess has quit before being
         # able to delete the tmpdir in which it runs; in order to do so, we
         # must first `kill()` it, and then `communicate()` with it.
-        self.latex = subprocess.Popen(
-            [mpl.rcParams["pgf.texsystem"], "-halt-on-error"],
-            stdin=subprocess.PIPE, stdout=subprocess.PIPE,
-            encoding="utf-8", cwd=self.tmpdir)
+        try:
+            self.latex = subprocess.Popen(
+                [mpl.rcParams["pgf.texsystem"], "-halt-on-error"],
+                stdin=subprocess.PIPE, stdout=subprocess.PIPE,
+                encoding="utf-8", cwd=self.tmpdir)
+        except FileNotFoundError as err:
+            raise RuntimeError(
+                f"{rcParams['pgf.texsystem']!r} not found; install it or change "
+                f"rcParams['pgf.texsystem'] to an available TeX implementation"
+            ) from err
+        except OSError as err:
+            raise RuntimeError(
+                f"Error starting process {self.latex.args[0]!r}") from err
 
         def finalize_latex(latex):
             latex.kill()
