Improve matching when highligting mentions

Simple substring search as we did before highlights messages when e.g.
the nick is "abc" and the message is "abcd".

We now take IRC nick syntax into account and only match when the nick
occurs between invalid IRC nick characters.

Fixes: #430

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+- Improve nick matching to avoid highlighting message incorrectly. (#430)
+
 # 2024/01/01: 0.12.0
 
 Thanks to @nate-sys and @jubalh for contributing to this release.

crates/tiny/src/conn.rs

@@ -191,8 +191,8 @@ fn handle_irc_msg(ui: &UI, client: &dyn Client, msg: wire::Msg) {
             match target {
                 wire::MsgTarget::Chan(chan) => {
                     let ui_msg_target = MsgTarget::Chan { serv, chan: &chan };
-                    // highlight the message if it mentions us
-                    if msg.contains(&client.get_nick()) {
+                    // Highlight the message if it mentions us.
+                    if mentions_user(&msg, &client.get_nick()) {
                         ui.add_privmsg(sender, &msg, ts, &ui_msg_target, true, is_action);
                         ui.set_tab_style(TabStyle::Highlight, &ui_msg_target);
                         let mentions_target = MsgTarget::Server { serv: "mentions" };
@@ -591,3 +591,51 @@ fn handle_irc_msg(ui: &UI, client: &dyn Client, msg: wire::Msg) {
         },
     }
 }
+
+/// Whether `msg` mentions `nick`.
+///
+/// This takes IRC nick syntax into account (following [1]) when checking match boundaries, to
+/// avoid generating highlights incorrectly. For example, if the nick is "abc" and the messsage is
+/// "abcd" we don't consider that a mention, but we consider it a mention in message "abc: hi".
+///
+/// [1]: https://modern.ircdocs.horse/#clients
+fn mentions_user(msg: &str, nick: &str) -> bool {
+    for (match_idx, _) in msg.match_indices(nick) {
+        if check_nick_left_boundary(msg, match_idx)
+            && check_nick_right_boundary(msg, match_idx + nick.len())
+        {
+            return true;
+        }
+    }
+
+    false
+}
+
+fn check_nick_left_boundary(msg: &str, idx: usize) -> bool {
+    if idx == 0 {
+        return true;
+    }
+
+    matches!(
+        msg.as_bytes()[idx - 1],
+        b' ' | b',' | b'*' | b'?' | b'!' | b'@' | b'.' | b'&' | b':' | b'#' | b'+' | b'~'
+    )
+}
+
+fn check_nick_right_boundary(msg: &str, idx: usize) -> bool {
+    matches!(
+        msg.as_bytes().get(idx),
+        None | Some(b' ' | b',' | b'*' | b'?' | b'!' | b'@' | b'.' | b':')
+    )
+}
+
+#[test]
+fn mention_check() {
+    assert!(!mentions_user("", "abc"));
+    assert!(mentions_user("abc", "abc"));
+    assert!(mentions_user("abc: hi", "abc"));
+    assert!(mentions_user(" abc", "abc"));
+    assert!(mentions_user(" abc,", "abc"));
+    assert!(!mentions_user(" aaaa ", "aa"));
+    assert!(mentions_user(" aa,aa ", "aa"));
+}