Read an address typed without a scheme as https (#101)

cnn-com was added as 'cnn.com', stored as typed, and every check failed with "relative URL
without a base" before it reached the site to look for its feed. expand_input, which both the
web page and `ipx add` pass the address through, now makes one without a scheme https, and a
protocol-relative //host/path https too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/feed.rs

@@ -219,11 +219,20 @@ pub fn is_patreon_creator(url: &str) -> bool {
 }
 
 /// What was typed into Add feed, as a URL. A bare Patreon token is taken as its creator's
-/// feed, since the token alone says whose it is.
+/// feed, since the token alone says whose it is. An address with no scheme is https: 'cnn.com'
+/// was stored as typed and every check failed with "relative URL without a base" (#101).
 pub fn expand_input(input: &str) -> String {
     let s = input.trim();
     let token = s.len() >= 20 && s.chars().all(|c| c.is_ascii_alphanumeric() || c == '-' || c == '_');
-    if token { format!("https://www.patreon.com/rss?auth={s}") } else { s.to_owned() }
+    if token {
+        format!("https://www.patreon.com/rss?auth={s}")
+    } else if let Some(rest) = s.strip_prefix("//") {
+        format!("https://{rest}")
+    } else if !s.contains("://") {
+        format!("https://{s}")
+    } else {
+        s.to_owned()
+    }
 }
 
 /// Whether two URLs are the same feed. One Patreon show has several spellings -- by the
@@ -1226,6 +1235,10 @@ mod tests {
         let tok = "AbCdEfGhIjKlMnOpQrStUvWxYz012_-9";
         assert_eq!(expand_input(&format!(" {tok} ")), format!("https://www.patreon.com/rss?auth={tok}"));
         assert_eq!(expand_input("https://example.com/rss"), "https://example.com/rss");
+        assert_eq!(expand_input("http://example.com/rss"), "http://example.com/rss");
+        assert_eq!(expand_input(" cnn.com "), "https://cnn.com");
+        assert_eq!(expand_input("example.com/feed.xml"), "https://example.com/feed.xml");
+        assert_eq!(expand_input("//example.com/rss"), "https://example.com/rss");
 
         assert!(is_patreon_creator(&format!("https://www.patreon.com/rss/glasscannon?auth={tok}")));
         assert!(is_patreon_creator(&format!("https://www.patreon.com/rss?auth={tok}")));