https://github.com/jrfonseca/xdot.py/issues/92
https://bugs.gentoo.org/873490

From 2ace1a12d78423d9e7af20fdb0bca34827010408 Mon Sep 17 00:00:00 2001
From: Jose Fonseca <jose.r.fonseca@gmail.com>
Date: Tue, 28 Sep 2021 13:19:49 +0100
Subject: [PATCH] Handle xdot backslashes correctly.

Irrespectively of graphviz version.

Fixes https://github.com/jrfonseca/xdot.py/issues/92
---
 tests/issue_92_a.dot |  3 +++
 tests/issue_92_b.dot |  3 +++
 xdot/dot/parser.py   | 26 +++++++++++++++++++++-----
 xdot/ui/window.py    | 11 ++++++++++-
 4 files changed, 37 insertions(+), 6 deletions(-)
 create mode 100644 tests/issue_92_a.dot
 create mode 100644 tests/issue_92_b.dot

diff --git a/tests/issue_92_a.dot b/tests/issue_92_a.dot
new file mode 100644
index 0000000..ea486b0
--- /dev/null
+++ b/tests/issue_92_a.dot
@@ -0,0 +1,3 @@
+digraph {
+   1 [label="a\\00"]
+}
diff --git a/tests/issue_92_b.dot b/tests/issue_92_b.dot
new file mode 100644
index 0000000..ba90566
--- /dev/null
+++ b/tests/issue_92_b.dot
@@ -0,0 +1,3 @@
+digraph {
+   1 [label="a\\b"]
+}
diff --git a/xdot/dot/parser.py b/xdot/dot/parser.py
index 4244e03..6578c23 100644
--- a/xdot/dot/parser.py
+++ b/xdot/dot/parser.py
@@ -14,8 +14,11 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 import colorsys
+import re
 import sys
 
+from distutils.version import LooseVersion
+
 from .lexer import ParseError, DotLexer
 
 from ..ui.colors import lookup_color
@@ -85,7 +88,14 @@ class XDotAttrParser:
     - http://www.graphviz.org/doc/info/output.html#d:xdot
     """
 
-    def __init__(self, parser, buf):
+    def __init__(self, parser, buf, broken_backslashes):
+
+        # `\` should be escaped as `\\`, but older versions of graphviz xdot
+        # output failed to properly escape it.  See also
+        # https://github.com/jrfonseca/xdot.py/issues/92
+        if not broken_backslashes:
+            buf = re.sub(br'\\(.)', br'\1', buf)
+
         self.parser = parser
         self.buf = buf
         self.pos = 0
@@ -427,10 +437,16 @@ class XDotParser(DotParser):
 
     XDOTVERSION = '1.7'
 
-    def __init__(self, xdotcode):
+    def __init__(self, xdotcode, graphviz_version=None):
         lexer = DotLexer(buf=xdotcode)
         DotParser.__init__(self, lexer)
 
+        # https://github.com/jrfonseca/xdot.py/issues/92
+        self.broken_backslashes = False
+        if graphviz_version is not None and \
+                LooseVersion(graphviz_version) < LooseVersion("2.46.0"):
+            self.broken_backslashes = True
+
         self.nodes = []
         self.edges = []
         self.shapes = []
@@ -480,7 +496,7 @@ def handle_graph(self, attrs):
 
         for attr in ("_draw_", "_ldraw_", "_hdraw_", "_tdraw_", "_hldraw_", "_tldraw_"):
             if attr in attrs:
-                parser = XDotAttrParser(self, attrs[attr])
+                parser = XDotAttrParser(self, attrs[attr], self.broken_backslashes)
                 self.shapes.extend(parser.parse())
 
     def handle_node(self, id, attrs):
@@ -502,7 +518,7 @@ def handle_node(self, id, attrs):
         shapes = []
         for attr in ("_draw_", "_ldraw_"):
             if attr in attrs:
-                parser = XDotAttrParser(self, attrs[attr])
+                parser = XDotAttrParser(self, attrs[attr], self.broken_backslashes)
                 shapes.extend(parser.parse())
         try:
             url = attrs['URL']
@@ -525,7 +541,7 @@ def handle_edge(self, src_id, dst_id, attrs):
         shapes = []
         for attr in ("_draw_", "_ldraw_", "_hdraw_", "_tdraw_", "_hldraw_", "_tldraw_"):
             if attr in attrs:
-                parser = XDotAttrParser(self, attrs[attr])
+                parser = XDotAttrParser(self, attrs[attr], self.broken_backslashes)
                 shapes.extend(parser.parse())
         if shapes:
             src = self.node_by_name[src_id]
diff --git a/xdot/ui/window.py b/xdot/ui/window.py
index 893bd1d..e27f000 100644
--- a/xdot/ui/window.py
+++ b/xdot/ui/window.py
@@ -56,6 +56,7 @@ class DotWidget(Gtk.DrawingArea):
     }
 
     filter = 'dot'
+    graphviz_version = None
 
     def __init__(self):
         Gtk.DrawingArea.__init__(self)
@@ -100,6 +101,7 @@ def error_dialog(self, message):
 
     def set_filter(self, filter):
         self.filter = filter
+        self.graphviz_version = None
 
     def run_filter(self, dotcode):
         if not self.filter:
@@ -153,7 +155,14 @@ def set_dotcode(self, dotcode, filename=None, center=True):
 
     def set_xdotcode(self, xdotcode, center=True):
         assert isinstance(xdotcode, bytes)
-        parser = XDotParser(xdotcode)
+        if self.graphviz_version is None:
+            stdout = subprocess.check_output([self.filter, '-V'], stderr=subprocess.STDOUT)
+            stdout = stdout.rstrip()
+            mo = re.match(br'^.* - .* version (?P<version>.*) \(.*\)$', stdout)
+            assert mo
+            self.graphviz_version = mo.group('version').decode('ascii')
+
+        parser = XDotParser(xdotcode, graphviz_version=self.graphviz_version)
         self.graph = parser.parse()
         self.zoom_image(self.zoom_ratio, center=center)