matplotlib · ksunden · Jan 27, 2023 · Jul 15, 2022 · Jul 15, 2022 · Jul 19, 2022
diff --git a/lib/matplotlib/backends/backend_pgf.py b/lib/matplotlib/backends/backend_pgf.py
@@ -38,9 +38,9 @@
 @_api.caching_module_getattr
 class __getattr__:
     NO_ESCAPE = _api.deprecated("3.6", obj_type="")(
-        property(lambda self: _NO_ESCAPE))
+        property(lambda self: r"(?<!\\)(?:\\\\)*"))
     re_mathsep = _api.deprecated("3.6", obj_type="")(
-        property(lambda self: _split_math.__self__))
+        property(lambda self: r"(?<!\\)(?:\\\\)*\$"))
 
 
 @_api.deprecated("3.6")
@@ -58,7 +58,15 @@ def get_preamble():
 
 def _get_preamble():
     """Prepare a LaTeX preamble based on the rcParams configuration."""
-    preamble = [mpl.rcParams["pgf.preamble"]]
+    preamble = [
+        # Remove Matplotlib's custom command \mathdefault.  (Not using
+        # \mathnormal instead since this looks odd with Computer Modern.)
+        r"\def\mathdefault#1{#1}",
+        # Use displaystyle for all math.
+        r"\everymath=\expandafter{\the\everymath\displaystyle}",
+        # Allow pgf.preamble to override the above definitions.
+        mpl.rcParams["pgf.preamble"],
+    ]
     if mpl.rcParams["pgf.texsystem"] != "pdflatex":
         preamble.append("\\usepackage{fontspec}")
         if mpl.rcParams["pgf.rcfonts"]:
@@ -83,16 +91,6 @@ def _get_preamble():
 mpl_in_to_pt = 1. / mpl_pt_to_in
 
 
-_NO_ESCAPE = r"(?<!\\)(?:\\\\)*"
-_split_math = re.compile(_NO_ESCAPE + r"\$").split
-_replace_escapetext = functools.partial(
-    # When the next character is an unescaped % or ^, insert a backslash.
-    re.compile(_NO_ESCAPE + "(?=[%^])").sub, "\\\\")
-_replace_mathdefault = functools.partial(
-    # Replace \mathdefault (when not preceded by an escape) by empty string.
-    re.compile(_NO_ESCAPE + r"(\\mathdefault)").sub, "")
-
-
 @_api.deprecated("3.6")
 def common_texification(text):
     return _tex_escape(text)
@@ -102,28 +100,8 @@ def _tex_escape(text):
     r"""
     Do some necessary and/or useful substitutions for texts to be included in
     LaTeX documents.
-
-    This distinguishes text-mode and math-mode by replacing the math separator
-    ``$`` with ``\(\displaystyle %s\)``. Escaped math separators (``\$``)
-    are ignored.
-
-    The following characters are escaped in text segments: ``^%``
     """
-    # Sometimes, matplotlib adds the unknown command \mathdefault.
-    # Not using \mathnormal instead since this looks odd for the latex cm font.
-    text = _replace_mathdefault(text)
-    text = text.replace("\N{MINUS SIGN}", r"\ensuremath{-}")
-    # split text into normaltext and inline math parts
-    parts = _split_math(text)
-    for i, s in enumerate(parts):
-        if not i % 2:
-            # textmode replacements
-            s = _replace_escapetext(s)
-        else:
-            # mathmode replacements
-            s = r"\(\displaystyle %s\)" % s
-        parts[i] = s
-    return "".join(parts)
+    return text.replace("\N{MINUS SIGN}", r"\ensuremath{-}")
 
 
 @_api.deprecated("3.6")
@@ -168,7 +146,17 @@ def _escape_and_apply_props(s, prop):
         commands.append(r"\bfseries")
 
     commands.append(r"\selectfont")
-    return "".join(commands) + " " + _tex_escape(s)
+    return (
+        "{"
+        + "".join(commands)
+        + r"\catcode`\^=\active\def^{\ifmmode\sp\else\^{}\fi}"
+        # It should normally be enough to set the catcode of % to 12 ("normal
+        # character"); this works on TeXLive 2021 but not on 2018, so we just
+        # make it active too.
+        + r"\catcode`\%=\active\def%{\%}"
+        + _tex_escape(s)
+        + "}"
+    )
 
 
 def _metadata_to_str(key, value):
@@ -357,7 +345,11 @@ def _get_box_metrics(self, tex):
         """
         # This method gets wrapped in __init__ for per-instance caching.
         self._stdin_writeln(  # Send textbox to TeX & request metrics typeout.
-            r"\sbox0{%s}\typeout{\the\wd0,\the\ht0,\the\dp0}" % tex)
+            # \sbox doesn't handle catcode assignments inside its argument,
+            # so repeat the assignment of the catcode of "^" and "%" outside.
+            r"{\catcode`\^=\active\catcode`\%%=\active\sbox0{%s}"
+            r"\typeout{\the\wd0,\the\ht0,\the\dp0}}"
+            % tex)
         try:
             answer = self._expect_prompt()
         except LatexError as err:

diff --git a/lib/matplotlib/tests/test_backend_pgf.py b/lib/matplotlib/tests/test_backend_pgf.py
@@ -11,7 +11,7 @@
 import matplotlib.pyplot as plt
 from matplotlib.testing import _has_tex_package, _check_for_pgf
 from matplotlib.testing.compare import compare_images, ImageComparisonFailure
-from matplotlib.backends.backend_pgf import PdfPages, _tex_escape
+from matplotlib.backends.backend_pgf import PdfPages
 from matplotlib.testing.decorators import (
     _image_directories, check_figures_equal, image_comparison)
 from matplotlib.testing._markers import (
@@ -33,21 +33,17 @@ def compare_figure(fname, savefig_kwargs={}, tol=0):
         raise ImageComparisonFailure(err)
 
 
-@pytest.mark.parametrize('plain_text, escaped_text', [
-    (r'quad_sum: $\sum x_i^2$', r'quad_sum: \(\displaystyle \sum x_i^2\)'),
-    ('% not a comment', r'\% not a comment'),
-    ('^not', r'\^not'),
-])
-def test_tex_escape(plain_text, escaped_text):
-    assert _tex_escape(plain_text) == escaped_text
-
-
 @needs_pgf_xelatex
+@needs_ghostscript
 @pytest.mark.backend('pgf')
 def test_tex_special_chars(tmp_path):
     fig = plt.figure()
-    fig.text(.5, .5, "_^ $a_b^c$")
-    fig.savefig(tmp_path / "test.pdf")  # Should not error.
+    fig.text(.5, .5, "%_^ $a_b^c$")
+    buf = BytesIO()
+    fig.savefig(buf, format="png", backend="pgf")
+    buf.seek(0)
+    t = plt.imread(buf)
+    assert not (t == 1).all()  # The leading "%" didn't eat up everything.
 
 
 def create_figure():
@@ -99,7 +95,7 @@ def test_xelatex():
 @pytest.mark.skipif(not _has_tex_package('ucs'), reason='needs ucs.sty')
 @pytest.mark.backend('pgf')
 @image_comparison(['pgf_pdflatex.pdf'], style='default',
-                  tol=11.7 if _old_gs_version else 0)
+                  tol=11.71 if _old_gs_version else 0)
 def test_pdflatex():
     if os.environ.get('APPVEYOR'):
         pytest.xfail("pdflatex test does not work on appveyor due to missing "