Also handle QtWebKit Accept-Language correctly

On QtWebKit, we only set Accept-Language in the request interceptor.

qutebrowser/browser/shared.py

@@ -26,8 +26,15 @@ class CallSuper(Exception):
     """Raised when the caller should call the superclass instead."""
 
 
-def custom_headers(url):
-    """Get the combined custom headers."""
+def custom_headers(
+    url: QUrl, *, fallback_accept_language: bool = True
+) -> list[tuple[bytes, bytes]]:
+    """Get the combined custom headers.
+
+    Arguments:
+        fallback_accept_language: Whether to include the global (rather than
+                                  per-domain override) accept language header as well.
+    """
     headers = {}
 
     dnt_config = config.instance.get('content.headers.do_not_track', url=url)
@@ -41,8 +48,9 @@ def custom_headers(url):
         encoded_value = b"" if value is None else value.encode('ascii')
         headers[encoded_header] = encoded_value
 
+    # note: Once we drop QtWebKit, we could hardcode fallback_accept_language to False.
     accept_language = config.instance.get('content.headers.accept_language',
-                                          url=url, fallback=False)
+                                          url=url, fallback=fallback_accept_language)
     if accept_language is not None and not isinstance(accept_language, usertypes.Unset):
         headers[b'Accept-Language'] = accept_language.encode('ascii')
 

qutebrowser/browser/webengine/interceptor.py

@@ -187,7 +187,9 @@ class RequestInterceptor(QWebEngineUrlRequestInterceptor):
         if request.is_blocked:
             info.block(True)
 
-        for header, value in shared.custom_headers(url=url):
+        for header, value in shared.custom_headers(
+            url=url, fallback_accept_language=not is_xhr
+        ):
             if header.lower() == b'accept' and is_xhr:
                 # https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/setRequestHeader
                 # says: "If no Accept header has been set using this, an Accept header

tests/unit/browser/test_shared.py

@@ -36,14 +36,17 @@ def test_custom_headers(config_stub, dnt, accept_language, custom_headers,
     assert shared.custom_headers(url=None) == expected_items
 
 
-@pytest.mark.parametrize("url, expected", [
-    (None, True),  # url is never None in the wild, mostly sanity check
-    (QUrl("http://example.org"), False),
+@pytest.mark.parametrize("url, fallback, expected", [
+    # url is never None in the wild, mostly sanity check
+    (None, True, True),
+    (None, False, True),
+    (QUrl("http://example.org"), True, True),
+    (QUrl("http://example.org"), False, False),
 ])
-def test_accept_language_no_fallback(config_stub, url ,expected):
+def test_accept_language_no_fallback(config_stub, url, fallback, expected):
     config_stub.val.content.headers.accept_language = "de, en"
-    has_header = b"Accept-Language" in dict(shared.custom_headers(url=url))
-    assert has_header == expected
+    headers = shared.custom_headers(url=url, fallback_accept_language=fallback)
+    assert (b"Accept-Language" in dict(headers)) == expected
 
 
 @pytest.mark.parametrize(