Use hunter for line tracing.

qutebrowser/app.py

@@ -36,6 +36,10 @@ from PyQt5.QtWidgets import QApplication, QDialog, QMessageBox
 from PyQt5.QtGui import QDesktopServices, QPixmap, QIcon
 from PyQt5.QtCore import (pyqtSlot, qInstallMessageHandler, QTimer, QUrl,
                           QObject, Qt, QSocketNotifier)
+try:
+    import hunter
+except ImportError:
+    hunter = None
 
 import qutebrowser
 import qutebrowser.resources  # pylint: disable=unused-import
@@ -50,7 +54,7 @@ from qutebrowser.misc import (crashdialog, readline, ipc, earlyinit,
 from qutebrowser.misc import utilcmds  # pylint: disable=unused-import
 from qutebrowser.keyinput import modeman
 from qutebrowser.utils import (log, version, message, utils, qtutils, urlutils,
-                               debug, objreg, usertypes, standarddir)
+                               objreg, usertypes, standarddir)
 # We import utilcmds to run the cmdutils.register decorators.
 
 
@@ -924,6 +928,10 @@ class Application(QApplication):
         """Extend QApplication::exit to log the event."""
         log.destroy.debug("Now calling QApplication::exit.")
         if self._args.debug_exit:
-            print("Now logging late shutdown.", file=sys.stderr)
+            if hunter is None:
-            debug.trace_lines(True)
+                print("Not logging late shutdown because hunter could not be "
+                      "imported!", file=sys.stderr)
+            else:
+                print("Now logging late shutdown.", file=sys.stderr)
+                hunter.trace()
         super().exit(status)

qutebrowser/misc/earlyinit.py

@@ -20,6 +20,13 @@
 At this point we can be sure we have all python 3.4 features available.
 """
 
+try:
+    # Importing hunter to register its atexit handler early so it gets called
+    # late.
+    import hunter  # pylint: disable=import-error,unused-import
+except ImportError:
+    hunter = None
+
 import os
 import sys
 import faulthandler

qutebrowser/misc/utilcmds.py

@@ -24,6 +24,10 @@ import functools
 import types
 
 from PyQt5.QtCore import QCoreApplication
+try:
+    import hunter
+except ImportError:
+    hunter = None
 
 from qutebrowser.utils import log, objreg, usertypes
 from qutebrowser.commands import cmdutils, runners, cmdexc
@@ -119,6 +123,22 @@ def debug_console():
     con_widget.show()
 
 
+@cmdutils.register(debug=True, maxsplit=0)
+def debug_trace(expr=""):
+    """Trace executed code via hunter.
+
+    Args:
+        expr: What to trace, passed to hunter.
+    """
+    if hunter is None:
+        raise cmdexc.CommandError("You need to install 'hunter' to use this "
+                                  "command!")
+    try:
+        eval('hunter.trace({})'.format(expr))
+    except Exception as e:
+        raise cmdexc.CommandError("{}: {}".format(e.__class__.__name__, e))
+
+
 @cmdutils.register(hide=True)
 def fooled():
     """Turn off april's fools."""

qutebrowser/utils/debug.py

@@ -20,7 +20,6 @@
 """Utilities used for debugging."""
 
 import re
-import sys
 import inspect
 import functools
 import datetime
@@ -87,36 +86,6 @@ def log_signals(obj):
         connect_log_slot(obj)
 
 
-def trace_lines(do_trace):
-    """Turn on/off printing each executed line.
-
-    Args:
-        do_trace: Whether to start tracing (True) or stop it (False).
-    """
-    def trace(frame, event, arg):
-        """Trace function passed to sys.settrace.
-
-        Return:
-            Itself, so tracing continues.
-        """
-        if sys is not None:
-            loc = '{}:{}'.format(frame.f_code.co_filename, frame.f_lineno)
-            if arg is not None:
-                arg = utils.compact_text(str(arg), 200)
-            else:
-                arg = ''
-            print("{:11} {:80} {}".format(event, loc, arg), file=sys.stderr)
-            return trace
-        else:
-            # When tracing while shutting down, it seems sys can be None
-            # sometimes... if that's the case, we stop tracing.
-            return None
-    if do_trace:
-        sys.settrace(trace)
-    else:
-        sys.settrace(None)
-
-
 def qenum_key(base, value, add_base=False, klass=None):
     """Convert a Qt Enum value to its key as a string.