bibfetch: a title Open Library will not find as written is asked again

Open Library's title search, given an author as well, finds nothing for
The Ladder of Divine Ascent and four editions of Ladder of Divine Ascent.
When the title as given finds nothing, the title without a leading The, A
or An is asked, then the title and author as one free-text query, each
only when the one before found nothing. Google Books, whose anonymous
quota runs out, is asked only after all three.

crates/bibfetch/src/search.rs

@@ -40,7 +40,13 @@ const GOOGLE_BOOKS: &str = "https://www.googleapis.com/books/v1/volumes";
 /// named.
 ///
 /// Open Library's index first, and Google Books only when that answered with
-/// nothing. Once Google Books has been asked, its failure is the answer:
+/// nothing. Open Library's title search is strict: given an author too, it
+/// finds nothing for "The Ladder of Divine Ascent" that it finds for "Ladder
+/// of Divine Ascent". So when the title as given finds nothing, the title
+/// without a leading article is asked, and then the title and author as one
+/// free-text query, before Google Books is. Each later question is asked only
+/// when the one before it found nothing, and a looser one can return books
+/// that only share words with the title, which the caller judges. Once Google Books has been asked, its failure is the answer:
 /// [`Error::Limited`] when it refused for its quota, [`Error::Unreachable`]
 /// when it could not be reached, since saying no register has the title
 /// would be a claim no register made. Asks nothing when `limit` is zero; a
@@ -79,8 +85,14 @@ fn search_with(
         None => Err(Error::Unreachable(format!("{url}: answered 404"))),
     };
 
-    let open_library =
-        fetch(open_library_url(title, author, limit)).and_then(|body| open_library(&body, limit));
+    let mut from_open_library = Ok(Vec::new());
+    for url in open_library_urls(title, author, limit) {
+        from_open_library = fetch(url).and_then(|body| open_library(&body, limit));
+        if !from_open_library.as_ref().is_ok_and(Vec::is_empty) {
+            break;
+        }
+    }
+    let open_library = from_open_library;
     if open_library.as_ref().is_ok_and(|found| !found.is_empty()) {
         return open_library;
     }
@@ -141,7 +153,36 @@ fn refused(url: &str, status: u16) -> Option<Error> {
     })
 }
 
-/// Where to ask Open Library.
+/// Every question to put to Open Library, strictest first.
+fn open_library_urls(title: &str, author: Option<&str>, limit: usize) -> Vec<String> {
+    let mut urls = vec![open_library_url(title, author, limit)];
+    if let Some(rest) = without_article(title) {
+        urls.push(open_library_url(rest, author, limit));
+    }
+    let words = match author {
+        Some(author) => format!("{title} {author}"),
+        None => title.to_string(),
+    };
+    urls.push(format!(
+        "https://openlibrary.org/search.json?q={}&fields={OPEN_LIBRARY_FIELDS}&limit={limit}",
+        source::encode(&words),
+    ));
+    urls
+}
+
+/// A title without its leading English article, when it has one and
+/// something follows it.
+fn without_article(title: &str) -> Option<&str> {
+    let (first, rest) = title.split_once(char::is_whitespace)?;
+    let rest = rest.trim_start();
+    (["the", "a", "an"]
+        .iter()
+        .any(|article| first.eq_ignore_ascii_case(article))
+        && !rest.is_empty())
+    .then_some(rest)
+}
+
+/// Where to ask Open Library by title and author.
 fn open_library_url(title: &str, author: Option<&str>, limit: usize) -> String {
     let author = author
         .map(|author| format!("&author={}", source::encode(author)))
@@ -630,8 +671,19 @@ mod tests {
             recorded(&mut asked, &bodies),
         )
         .expect("candidates");
-        assert_eq!(asked.len(), 2);
-        assert!(asked[1].starts_with("https://www.googleapis.com/books/v1/volumes?q="));
+        // The title as given, without its article, as free text, then Google.
+        assert_eq!(asked.len(), 4, "{asked:?}");
+        assert!(
+            asked[1].contains("?title=Google%20Story&author=Vise&"),
+            "{}",
+            asked[1]
+        );
+        assert!(
+            asked[2].contains("?q=The%20Google%20Story%20Vise&"),
+            "{}",
+            asked[2]
+        );
+        assert!(asked[3].starts_with("https://www.googleapis.com/books/v1/volumes?q="));
 
         assert_eq!(found.len(), 2);
         let first = &found[0];
@@ -686,7 +738,8 @@ mod tests {
         ];
         let failed = search_with("Nothing", None, 5, recorded(&mut asked, &bodies));
         assert!(matches!(failed, Err(Error::Unreachable(_))), "{failed:?}");
-        assert_eq!(asked.len(), 2);
+        // By title, as free text, then Google.
+        assert_eq!(asked.len(), 3, "{asked:?}");
     }
 
     #[test]
@@ -765,8 +818,50 @@ mod tests {
         ];
         search_with("Anathem", Some("  "), 5, recorded(&mut asked, &bodies)).expect("ok");
         assert!(!asked[0].contains("author="), "{}", asked[0]);
-        assert!(!asked[1].contains("inauthor"), "{}", asked[1]);
-        assert!(asked[1].contains("q=intitle%3AAnathem&"), "{}", asked[1]);
+        assert!(asked[1].contains("?q=Anathem&"), "{}", asked[1]);
+        assert!(!asked[2].contains("inauthor"), "{}", asked[2]);
+        assert!(asked[2].contains("q=intitle%3AAnathem&"), "{}", asked[2]);
+    }
+
+    #[test]
+    fn a_leading_article_is_dropped_when_the_title_as_given_finds_nothing() {
+        let mut asked = Vec::new();
+        let mut answered = 0;
+        let found = search_with(
+            "The Ladder of Divine Ascent",
+            Some("John Climacus"),
+            5,
+            |url: &str| {
+                asked.push(url.to_string());
+                answered += 1;
+                Ok(Some(
+                    if answered == 2 { TOLSTOY } else { NOTHING }.to_string(),
+                ))
+            },
+        )
+        .expect("candidates");
+        assert!(!found.is_empty());
+        assert_eq!(
+            asked.len(),
+            2,
+            "nothing is asked after a question finds something"
+        );
+        assert!(
+            asked[1].contains("?title=Ladder%20of%20Divine%20Ascent&author=John%20Climacus&"),
+            "{}",
+            asked[1]
+        );
+    }
+
+    #[test]
+    fn only_a_leading_article_with_words_after_it_is_dropped() {
+        assert_eq!(without_article("The Republic"), Some("Republic"));
+        assert_eq!(without_article("an  Essay"), Some("Essay"));
+        assert_eq!(without_article("A"), None);
+        assert_eq!(without_article("The "), None);
+        assert_eq!(without_article("Theology"), None);
+        assert_eq!(without_article("Anathem"), None);
+        assert_eq!(open_library_urls("Anathem", None, 5).len(), 2);
     }
 
     #[test]
@@ -838,7 +933,9 @@ intitle:y intitle:z inauthor:O'Brien inauthor:Sons";
         let found = search_with("?!", Some("Someone"), 5, recorded(&mut asked, &bodies))
             .expect("an answer");
         assert!(found.is_empty());
-        assert_eq!(asked.len(), 1);
+        // By title and as free text; never Google.
+        assert_eq!(asked.len(), 2, "{asked:?}");
+        assert!(asked.iter().all(|url| url.contains("openlibrary.org")));
     }
 
     #[test]
@@ -859,13 +956,25 @@ intitle:y intitle:z inauthor:O'Brien inauthor:Sons";
         let found =
             search_with("The Google Story", None, 1, recorded(&mut asked, &bodies)).expect("ok");
         assert_eq!(found.len(), 1);
-        assert!(asked[0].ends_with("&limit=1"), "{}", asked[0]);
-        assert!(asked[1].ends_with("&maxResults=1"), "{}", asked[1]);
+        let google = asked.last().expect("Google was asked");
+        assert!(
+            asked[..asked.len() - 1]
+                .iter()
+                .all(|url| url.ends_with("&limit=1")),
+            "{asked:?}"
+        );
+        assert!(google.ends_with("&maxResults=1"), "{google}");
 
         let mut asked = Vec::new();
         search_with("The Google Story", None, 500, recorded(&mut asked, &bodies)).expect("ok");
-        assert!(asked[0].ends_with("&limit=40"), "{}", asked[0]);
-        assert!(asked[1].ends_with("&maxResults=40"), "{}", asked[1]);
+        let google = asked.last().expect("Google was asked");
+        assert!(
+            asked[..asked.len() - 1]
+                .iter()
+                .all(|url| url.ends_with("&limit=40")),
+            "{asked:?}"
+        );
+        assert!(google.ends_with("&maxResults=40"), "{google}");
 
         let mut asked = Vec::new();
         let found =