Fix content.headers.referer = 'never' with Qt 5.15

The --no-referrers flag was removed in Chromium 79:
https://chromium-review.googlesource.com/c/chromium/src/+/1808144

We now instead use the request interceptor to remove the referrer, which
is possible ever since Qt 5.12.4 and 5.13.1 and something we've wanted
to do anyways, see #4793.

The setting is still marked as "requires a restart" (and it doesn't
support URL patterns) because that's partially true: The `same-domain`
value is still handled via CLI arguments.

Fixes #5892 (together with the last commit for 'same-domain')

3 files changed, 29 insertions, 7 deletions

diff --git a/qutebrowser/browser/webengine/interceptor.py b/qutebrowser/browser/webengine/interceptor.py
index 95e01588b..1e48cd113 100644
--- a/qutebrowser/browser/webengine/interceptor.py
+++ b/qutebrowser/browser/webengine/interceptor.py
@@ -25,7 +25,7 @@ from PyQt5.QtCore import QUrl, QByteArray
 from PyQt5.QtWebEngineCore import (QWebEngineUrlRequestInterceptor,
                                    QWebEngineUrlRequestInfo)
 
-from qutebrowser.config import websettings
+from qutebrowser.config import websettings, config
 from qutebrowser.browser import shared
 from qutebrowser.utils import utils, log, debug, qtutils
 from qutebrowser.extensions import interceptors
@@ -204,5 +204,11 @@ class RequestInterceptor(QWebEngineUrlRequestInterceptor):
         for header, value in shared.custom_headers(url=url):
             info.setHttpHeader(header, value)
 
+        # Note this is ignored before Qt 5.12.4 and 5.13.1 due to
+        # https://bugreports.qt.io/browse/QTBUG-60203 - there, we set the
+        # commandline-flag in qtargs.py instead.
+        if config.val.content.headers.referer == 'never':
+            info.setHttpHeader(b'Referer', b'')
+
         user_agent = websettings.user_agent(url)
         info.setHttpHeader(b'User-Agent', user_agent.encode('ascii'))
diff --git a/qutebrowser/config/qtargs.py b/qutebrowser/config/qtargs.py
index 6786d7973..7b66c6d92 100644
--- a/qutebrowser/config/qtargs.py
+++ b/qutebrowser/config/qtargs.py
@@ -201,7 +201,6 @@ def _qtwebengine_settings_args() -> Iterator[str]:
         },
         'content.headers.referer': {
             'always': None,
-            'never': '--no-referrers',
         }
     }
 
@@ -216,6 +215,13 @@ def _qtwebengine_settings_args() -> Iterator[str]:
     else:
         referrer_setting['same-domain'] = '--reduced-referrer-granularity'
 
+    can_override_referer = (
+        qtutils.version_check('5.12.4', compiled=False) and
+        not qtutils.version_check('5.13.0', compiled=False, exact=True)
+    )
+    # WORKAROUND for https://bugreports.qt.io/browse/QTBUG-60203
+    referrer_setting['never'] = None if can_override_referer else '--no-referrers'
+
     for setting, args in sorted(settings.items()):
         arg = args[config.instance.get(setting)]
         if arg is not None:
diff --git a/tests/unit/config/test_qtargs.py b/tests/unit/config/test_qtargs.py
index a2af26800..051956a00 100644
--- a/tests/unit/config/test_qtargs.py
+++ b/tests/unit/config/test_qtargs.py
@@ -253,11 +253,21 @@ class TestQtArgs:
             assert arg in args
 
     @pytest.mark.parametrize('qt_version, referer, arg', [
-        ('5.15', 'always', None),
-        ('5.15', 'never', '--no-referrers'),
-        ('5.15', 'same-domain', '--enable-features=ReducedReferrerGranularity'),
-        ('5.14', 'same-domain', '--enable-features=ReducedReferrerGranularity'),
-        ('5.13', 'same-domain', '--reduced-referrer-granularity'),
+        # 'always' -> no arguments
+        ('5.15.0', 'always', None),
+
+        # 'never' is handled via interceptor for most Qt versions
+        ('5.12.3', 'never', '--no-referrers'),
+        ('5.12.4', 'never', None),
+        ('5.13.0', 'never', '--no-referrers'),
+        ('5.13.1', 'never', None),
+        ('5.14.0', 'never', None),
+        ('5.15.0', 'never', None),
+
+        # 'same-domain' - arguments depend on Qt versions
+        ('5.13.0', 'same-domain', '--reduced-referrer-granularity'),
+        ('5.14.0', 'same-domain', '--enable-features=ReducedReferrerGranularity'),
+        ('5.15.0', 'same-domain', '--enable-features=ReducedReferrerGranularity'),
     ])
     def test_referer(self, config_stub, monkeypatch, parser, qt_version, referer, arg):
         monkeypatch.setattr(qtargs.objects, 'backend', usertypes.Backend.QtWebEngine)