Adjust referrer handling for Qt 6

As suspected in a comment, ReducedReferrerGranularity does not exist anymore
with Chromium 90, and neither does an option for getting the full referrer back:

https://chromium-review.googlesource.com/c/chromium/src/+/2545444
https://bugs.chromium.org/p/chromium/issues/detail?id=1150018

qutebrowser/config/configdata.yml

@@ -679,7 +679,8 @@ content.headers.referer:
   type:
     name: String
     valid_values:
-      - always: "Always send the Referer."
+      - always: "Always send the Referer. With QtWebEngine 6.2+, this value is
+          unavailable and will act like `same-domain`."
       - never: "Never send the Referer. This is not recommended, as some sites
           may break."
       - same-domain: "Only send the Referer for the same domain. This will

qutebrowser/config/qtargs.py

@@ -93,6 +93,8 @@ def _qtwebengine_features(
         versions: The WebEngineVersions to get flags for.
         special_flags: Existing flags passed via the commandline.
     """
+    assert versions.chromium_major is not None
+
     enabled_features = []
     disabled_features = []
 
@@ -143,7 +145,8 @@ def _qtwebengine_features(
         if config.val.scrolling.bar == 'overlay':
             enabled_features.append('OverlayScrollbar')
 
-    if config.val.content.headers.referer == 'same-domain':
+    if (config.val.content.headers.referer == 'same-domain' and
+            versions.chromium_major < 89):
         # Handling of reduced-referrer-granularity in Chromium 76+
         # https://chromium-review.googlesource.com/c/chromium/src/+/1572699
         #

tests/end2end/test_invocations.py

@@ -412,7 +412,18 @@ def test_qute_settings_persistence(short_tmpdir, request, quteproc_new):
 
 
 @pytest.mark.parametrize('value, expected', [
-    ('always', 'http://localhost:(port2)/headers-link/(port)'),
+    # https://chromium-review.googlesource.com/c/chromium/src/+/2545444
+    pytest.param(
+        'always',
+        'http://localhost:(port2)/headers-link/(port)',
+        marks=pytest.mark.qt5_only,
+    ),
+    pytest.param(
+        'always',
+        'http://localhost:(port2)/',
+        marks=pytest.mark.qt6_only,
+    ),
+
     ('never', None),
     ('same-domain', 'http://localhost:(port2)/'),  # None with QtWebKit
 ])

tests/unit/config/test_qtargs.py

@@ -283,8 +283,6 @@ class TestWebEngineArgs:
         assert not set(args) & remaining_flags
 
     @pytest.mark.parametrize('qt_version, referer, arg', [
-        # FIXME:qt6 update?
-
         # 'always' -> no arguments
         ('5.15.2', 'always', None),
         ('5.15.3', 'always', None),
@@ -296,6 +294,9 @@ class TestWebEngineArgs:
         # 'same-domain'
         ('5.15.2', 'same-domain', '--enable-features=ReducedReferrerGranularity'),
         ('5.15.3', 'same-domain', '--enable-features=ReducedReferrerGranularity'),
+        # (Not available anymore)
+        ('6.2', 'same-domain', None),
+        ('6.3', 'same-domain', None),
     ])
     def test_referer(self, config_stub, version_patcher, parser,
                      qt_version, referer, arg):