Avoid self-link suggestions for redirect targets

test_web_view.py

@@ -55,6 +55,61 @@ class ArticlePageSkipTests(unittest.TestCase):
         )
         self.assertIn("Useful candidate", body)
 
+    def test_redirect_target_is_left_out_of_candidates(self) -> None:
+        hits = [
+            hit("Documentary film"),
+            hit("Useful candidate"),
+        ]
+
+        with (
+            patch("web_view.api.get_wiki_info", return_value="Documentary film"),
+            patch("web_view.search_count", return_value=2),
+            patch("web_view.search_count_with_link", return_value=0),
+            patch("web_view.search_no_link", return_value=(2, hits)),
+        ):
+            response = self.client.get("/link/DVD_documentary")
+
+        body = response.get_data(as_text=True)
+        self.assertEqual(response.status_code, 200)
+        self.assertNotIn('data-title="Documentary film"', body)
+        self.assertIn("Useful candidate", body)
+
+    def test_redirect_target_case_variant_is_left_out_of_candidates(self) -> None:
+        hits = [hit("documentary film")]
+
+        with (
+            patch("web_view.api.get_wiki_info", return_value="Documentary film"),
+            patch("web_view.search_count", return_value=1),
+            patch("web_view.search_count_with_link", return_value=0),
+            patch("web_view.search_no_link", return_value=(1, hits)),
+        ):
+            response = self.client.get("/link/DVD_documentary")
+
+        body = response.get_data(as_text=True)
+        self.assertEqual(response.status_code, 200)
+        self.assertIn("No more candidates found for this article.", body)
+
+
+class ValidHitTests(unittest.TestCase):
+    def setUp(self) -> None:
+        web_view.app.config["TESTING"] = True
+        self.client = web_view.app.test_client()
+
+    def test_redirect_target_is_not_valid_hit(self) -> None:
+        with patch("web_view.get_diff") as get_diff:
+            response = self.client.get(
+                "/api/1/valid_hit",
+                query_string={
+                    "link_to": "DVD documentary",
+                    "link_from": "Documentary film",
+                    "redirect_to": "Documentary film",
+                },
+            )
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.get_json(), {"valid": False})
+        get_diff.assert_not_called()
+
 
 class ProtectedCandidateTests(unittest.TestCase):
     def test_edit_protected_hits_are_filtered_out(self) -> None:

web_view.py

@@ -104,6 +104,28 @@ def article_url(title: str) -> str:
     return flask.url_for("article_page", url_title=title.replace(" ", "_"))
 
 
+def canonical_title_key(title: str) -> str:
+    """Normalize a Wikipedia article title for same-page comparisons."""
+    title = title.replace("_", " ").strip()
+    return title[:1].casefold() + title[1:]
+
+
+def same_article_title(a: str | None, b: str | None) -> bool:
+    """Compare titles using Wikipedia's first-letter case-insensitive rule."""
+    if not a or not b:
+        return False
+    return canonical_title_key(a) == canonical_title_key(b)
+
+
+def is_self_link_candidate(
+    hit_title: str, from_title: str, redirect_to: str | None = None
+) -> bool:
+    """Return true when a candidate is the source article or its redirect target."""
+    return same_article_title(hit_title, from_title) or same_article_title(
+        hit_title, redirect_to
+    )
+
+
 def get_hit_count(q: str) -> int:
     """Search Wikipedia and return hit count."""
     return typing.cast(int, run_search(q, limit=0)["searchinfo"]["totalhits"])
@@ -391,6 +413,8 @@ def handle_post(url_title: str) -> Response:
     except mediawiki_oauth.LoginNeeded:
         next_url = flask.url_for("article_page", url_title=url_title, title=hit_title)
         return flask.redirect(flask.url_for("start_oauth", next=next_url))
+    except NoMatch:
+        return flask.make_response(render_error("No valid unlinked mention found."), 400)
     except (mediawiki_api.APIError, api.MediawikiError) as e:
         return flask.make_response(
             render_mediawiki_error(e, prefix="Save failed"), 502
@@ -437,8 +461,12 @@ def article_page(url_title: str) -> str | Response:
         hits = [h for h in hits if h["title"] == title_param] + \
                [h for h in hits if h["title"] != title_param]
 
-    hits = [h for h in hits if h["title"] not in session_skipped
+    hits = [
-            and h["title"] != from_title and h["title"] != case_flip_first(from_title)]
+        h
+        for h in hits
+        if h["title"] not in session_skipped
+        and not is_self_link_candidate(h["title"], from_title, redirect_to)
+    ]
 
     if not hits:
         return flask.render_template("all_done.html")
@@ -460,13 +488,16 @@ def article_page(url_title: str) -> str | Response:
 
 def do_save(title: str, hit_title: str) -> str:
     """Update page on Wikipedia."""
-    token = mediawiki_oauth.get_token()
-
     try:
         redirect_to = api.get_wiki_info(title)
     except (api.MissingPage, api.MultipleRedirects, api.MediawikiError):
         redirect_to = None
 
+    if is_self_link_candidate(hit_title, title, redirect_to):
+        raise NoMatch
+
+    token = mediawiki_oauth.get_token()
+
     found = get_match(title, hit_title, redirect_to)
 
     summary = (
@@ -510,6 +541,10 @@ def api_valid_hit() -> werkzeug.wrappers.response.Response:
     link_from = flask.request.args["link_from"]
     redirect_to = flask.request.args.get("redirect_to") or None
 
+    if is_self_link_candidate(link_from, link_to, redirect_to):
+        _record_skip(link_to, link_from)
+        return flask.jsonify(valid=False)
+
     try:
         found = get_diff(link_to, link_from, redirect_to)
     except NoMatch: