From c236046a73533f54fb4c4cc34704125172ca2538 Mon Sep 17 00:00:00 2001
From: Florian Bruhin <git@the-compiler.org>
Date: Thu, 14 May 2015 14:48:29 +0200
Subject: [PATCH] Avoid double-opening LineParser.

Hopefully helps with diagnosing #670.
---
 qutebrowser/misc/lineparser.py | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/qutebrowser/misc/lineparser.py b/qutebrowser/misc/lineparser.py
index 5ae90aa8a..5cd6304f5 100644
--- a/qutebrowser/misc/lineparser.py
+++ b/qutebrowser/misc/lineparser.py
@@ -53,12 +53,14 @@ class BaseLineParser(QObject):
             configdir: Directory to read the config from.
             fname: Filename of the config file.
             binary: Whether to open the file in binary mode.
+            _opened: Whether the underlying file is open
         """
         super().__init__(parent)
         self._configdir = configdir
         self._configfile = os.path.join(self._configdir, fname)
         self._fname = fname
         self._binary = binary
+        self._opened = False
 
     def __repr__(self):
         return utils.get_repr(self, constructor=True,
@@ -71,16 +73,23 @@ class BaseLineParser(QObject):
         if not os.path.exists(self._configdir):
             os.makedirs(self._configdir, 0o755)
 
+    @contextlib.contextmanager
     def _open(self, mode):
         """Open self._configfile for reading.
 
         Args:
             mode: The mode to use ('a'/'r'/'w')
         """
+        if self._opened:
+            raise IOError("Refusing to double-open AppendLineParser.")
+        self._opened = True
         if self._binary:
-            return open(self._configfile, mode + 'b')
+            with open(self._configfile, mode + 'b') as f:
+                yield f
         else:
-            return open(self._configfile, mode, encoding='utf-8')
+            with open(self._configfile, mode, encoding='utf-8') as f:
+                yield f
+        self._opened = False
 
     def _write(self, fp, data):
         """Write the data to a file.
@@ -195,9 +204,13 @@ class LineParser(BaseLineParser):
 
     def save(self):
         """Save the config file."""
+        if self._opened:
+            raise IOError("Refusing to double-open AppendLineParser.")
+        self._opened = True
         self._prepare_save()
         with qtutils.savefile_open(self._configfile, self._binary) as f:
             self._write(f, self.data)
+        self._opened = False
 
 
 class LimitLineParser(LineParser):