Restart pgf's latex instance after bad latex inputs.

anntzer · QuLogic · commit 70b32cd7932d · 2020-03-07T20:37:22.000-05:00
... and also move the warning about pgf-to-stream not supporting raster
images to when actually outputting a raster image (otherwise the warning
is spurious, and affects e.g. test_tex_restart_after_error).
diff --git a/lib/matplotlib/backends/backend_pgf.py b/lib/matplotlib/backends/backend_pgf.py
@@ -252,6 +252,8 @@ def _cleanup_remaining_instances():
             latex_manager._cleanup()
 
     def _stdin_writeln(self, s):
+        if self.latex is None:
+            self._setup_latex_process()
         self.latex_stdin_utf8.write(s)
         self.latex_stdin_utf8.write("\n")
         self.latex_stdin_utf8.flush()
@@ -265,6 +267,8 @@ def _expect(self, s):
             if buf[-len(exp):] == exp:
                 break
             if not len(b):
+                self.latex.kill()
+                self.latex = None
                 raise LatexError("LaTeX process halted", buf.decode("utf8"))
         return buf.decode("utf8")
 
@@ -301,6 +305,10 @@ def __init__(self):
             raise LatexError("LaTeX returned an error, probably missing font "
                              "or error in preamble:\n%s" % stdout)
 
+        self.latex = None  # Will be set up on first use.
+        self.str_cache = {}  # cache for strings already processed
+
+    def _setup_latex_process(self):
         # open LaTeX process for real work
         latex = subprocess.Popen([self.texcommand, "-halt-on-error"],
                                  stdin=subprocess.PIPE, stdout=subprocess.PIPE,
@@ -313,9 +321,6 @@ def __init__(self):
         self._expect("*pgf_backend_query_start")
         self._expect_prompt()
 
-        # cache for strings already processed
-        self.str_cache = {}
-
     def _cleanup(self):
         if not self._os_path.isdir(self.tmpdir):
             return
@@ -427,10 +432,10 @@ def __init__(self, figure, fh, dummy=False):
         else:
             # if fh does not belong to a filename, deactivate draw_image
             if not hasattr(fh, 'name') or not os.path.exists(fh.name):
-                cbook._warn_external("streamed pgf-code does not support "
-                                     "raster graphics, consider using the "
-                                     "pgf-to-pdf option", UserWarning)
-                self.__dict__["draw_image"] = lambda *args, **kwargs: None
+                self.__dict__["draw_image"] = \
+                    lambda *args, **kwargs: cbook._warn_external(
+                        "streamed pgf-code does not support raster graphics, "
+                        "consider using the pgf-to-pdf option")
 
     @cbook.deprecated("3.2")
     @property
diff --git a/lib/matplotlib/tests/test_backend_pgf.py b/lib/matplotlib/tests/test_backend_pgf.py
@@ -1,3 +1,4 @@
+from io import BytesIO
 import os
 from pathlib import Path
 import shutil
@@ -269,3 +270,15 @@ def test_pdf_pages_lualatex():
         pdf.savefig(fig)
 
         assert pdf.get_pagecount() == 2
+
+
+@needs_xelatex
+def test_tex_restart_after_error():
+    fig = plt.figure()
+    fig.suptitle(r"\oops")
+    with pytest.raises(ValueError):
+        fig.savefig(BytesIO(), format="pgf")
+
+    fig = plt.figure()  # start from scratch
+    fig.suptitle(r"this is ok")
+    fig.savefig(BytesIO(), format="pgf")
