Bring back PyQt (but not Qt) 5.7.0 support with QtWebEngine

This was originally removed in a86170f45, however Debian testing (Stretch) comes
with Qt 5.7.1, but PyQt 5.7.

CHANGELOG.asciidoc

@@ -37,7 +37,7 @@ Added
 Changed
 ~~~~~~~
 
-- PyQt/Qt 5.7.1 is now required for the QtWebEngine backend
+- PyQt 5.7/Qt 5.7.1 is now required for the QtWebEngine backend
 - Scrolling with the scrollwheel while holding shift now scrolls sideways
 - New way of clicking hints with which solves various small issues
 - When yanking a mailto: link via hints, the mailto: prefix is now stripped

qutebrowser/browser/webengine/webview.py

@@ -244,16 +244,20 @@ class WebEnginePage(QWebEnginePage):
         except shared.CallSuper:
             return super().javaScriptConfirm(url, js_msg)
 
-    def javaScriptPrompt(self, url, js_msg, default):
-        """Override javaScriptPrompt to use qutebrowser prompts."""
-        if self._is_shutting_down:
-            return (False, "")
-        try:
-            return shared.javascript_prompt(url, js_msg, default,
-                                            abort_on=[self.loadStarted,
-                                                      self.shutting_down])
-        except shared.CallSuper:
-            return super().javaScriptPrompt(url, js_msg, default)
+    if PYQT_VERSION > 0x050700:
+        # WORKAROUND
+        # Can't override javaScriptPrompt with older PyQt versions
+        # https://www.riverbankcomputing.com/pipermail/pyqt/2016-November/038293.html
+        def javaScriptPrompt(self, url, js_msg, default):
+            """Override javaScriptPrompt to use qutebrowser prompts."""
+            if self._is_shutting_down:
+                return (False, "")
+            try:
+                return shared.javascript_prompt(url, js_msg, default,
+                                                abort_on=[self.loadStarted,
+                                                          self.shutting_down])
+            except shared.CallSuper:
+                return super().javaScriptPrompt(url, js_msg, default)
 
     def javaScriptAlert(self, url, js_msg):
         """Override javaScriptAlert to use qutebrowser prompts."""

qutebrowser/misc/earlyinit.py

@@ -271,8 +271,8 @@ def check_qt_version(backend):
         _die(text)
     elif (backend == 'webengine' and (
             qtutils.version_check('5.7.0', operator.lt) or
-            PYQT_VERSION < 0x050701)):
-        text = ("Fatal error: Qt and PyQt >= 5.7.1 are required for "
+            PYQT_VERSION < 0x050700)):
+        text = ("Fatal error: Qt >= 5.7.1 and PyQt >= 5.7 are required for "
                 "QtWebEngine support, but Qt {} / PyQt {} is installed."
                 .format(qVersion(), PYQT_VERSION_STR))
         _die(text)

tests/conftest.py

@@ -120,9 +120,13 @@ def pytest_collection_modifyitems(config, items):
         _apply_platform_markers(item)
         if item.get_marker('xfail_norun'):
             item.add_marker(pytest.mark.xfail(run=False))
-        if item.get_marker('js_prompt') and not config.webengine:
+        if item.get_marker('js_prompt'):
+            if config.webengine:
+                js_prompt_pyqt_version = 0x050700
+            else:
+                js_prompt_pyqt_version = 0x050300
             item.add_marker(pytest.mark.skipif(
-                PYQT_VERSION <= 0x050300,
+                PYQT_VERSION <= js_prompt_pyqt_version,
                 reason='JS prompts are not supported with this PyQt version'))
 
         if deselected: