Add a test for :restart

doc/changelog.asciidoc

@@ -196,6 +196,7 @@ Fixed
 - The `asciidoc2html.py` script now correctly uses the virtualenv-installed
   asciidoc rather than requiring a system-wide installation.
 - "Package would be ignored" deprecation warnings when running `setup.py`.
+- ResourceWarning when using `:restart`.
 - Crash when shutting down before fully initialized.
 - Crash with some notification servers when the server is quitting.
 - Crash when using QtWebKit with PAC and the file has an invalid encoding.

qutebrowser/misc/quitter.py

@@ -13,6 +13,7 @@ import shutil
 import argparse
 import tokenize
 import functools
+import warnings
 import subprocess
 from typing import Iterable, Mapping, MutableSequence, Sequence, cast
 
@@ -179,11 +180,18 @@ class Quitter(QObject):
         # Open a new process and immediately shutdown the existing one
         try:
             args = self._get_restart_args(pages, session, override_args)
-            subprocess.Popen(args)  # pylint: disable=consider-using-with
+            proc = subprocess.Popen(args)  # pylint: disable=consider-using-with
         except OSError:
             log.destroy.exception("Failed to restart")
             return False
         else:
+            log.destroy.debug(f"New process PID: {proc.pid}")
+            # Avoid ResourceWarning about still running subprocess when quitting.
+            warnings.filterwarnings(
+                "ignore",
+                category=ResourceWarning,
+                message=f"subprocess {proc.pid} is still running",
+            )
             return True
 
     def shutdown(self, status: int = 0,

tests/end2end/test_invocations.py

@@ -4,6 +4,8 @@
 
 """Test starting qutebrowser with special arguments/environments."""
 
+import os
+import signal
 import configparser
 import subprocess
 import sys
@@ -916,3 +918,25 @@ def test_logfilter_arg_does_not_crash(request, quteproc_new):
     # Waiting for quit to make sure no other warning is emitted
     quteproc_new.send_cmd(':quit')
     quteproc_new.wait_for_quit()
+
+
+def test_restart(request, quteproc_new):
+    args = _base_args(request.config) + ['--temp-basedir']
+    quteproc_new.start(args)
+    quteproc_new.send_cmd(':restart')
+
+    prefix = "New process PID: "
+    line = quteproc_new.wait_for(message=f"{prefix}*")
+    quteproc_new.wait_for_quit()
+
+    assert line.message.startswith(prefix)
+    pid = int(line.message[len(prefix):])
+    os.kill(pid, signal.SIGTERM)
+
+    try:
+        # If the new process hangs, this will hang too.
+        # Still better than just ignoring it, so we can fix it if something is broken.
+        os.waitpid(pid, 0)  # pid, options... positional-only :(
+    except ChildProcessError:
+        # Already gone
+        pass