chat: fix emoji completions when word consists of emojis (#9107)

https://github.com/zed-industries/zed/assets/53836821/f4b31c47-d306-43f5-b971-0969f64a48f9

Fix for #9096 @JosephTLyons 

Release Notes:
- Fixed emoji completion not showing up when word contains only emojis
(#9096)

crates/util/Cargo.toml

@@ -28,6 +28,7 @@ lazy_static.workspace = true
 log.workspace = true
 parking_lot.workspace = true
 rand.workspace = true
+regex.workspace = true
 rust-embed.workspace = true
 serde.workspace = true
 serde_json.workspace = true

crates/util/src/util.rs

@@ -524,6 +524,22 @@ impl<'a> PartialOrd for NumericPrefixWithSuffix<'a> {
         Some(self.cmp(other))
     }
 }
+lazy_static! {
+    static ref EMOJI_REGEX: regex::Regex = regex::Regex::new("(\\p{Emoji}|\u{200D})").unwrap();
+}
+
+/// Returns true if the given string consists of emojis only.
+/// E.g. "👨‍👩‍👧‍👧👋" will return true, but "👋!" will return false.
+pub fn word_consists_of_emojis(s: &str) -> bool {
+    let mut prev_end = 0;
+    for capture in EMOJI_REGEX.find_iter(s) {
+        if capture.start() != prev_end {
+            return false;
+        }
+        prev_end = capture.end();
+    }
+    prev_end == s.len()
+}
 
 #[cfg(test)]
 mod tests {
@@ -583,4 +599,21 @@ mod tests {
             )
         }
     }
+
+    #[test]
+    fn test_word_consists_of_emojis() {
+        let words_to_test = vec![
+            ("👨‍👩‍👧‍👧👋🥒", true),
+            ("👋", true),
+            ("!👋", false),
+            ("👋!", false),
+            ("👋 ", false),
+            (" 👋", false),
+            ("Test", false),
+        ];
+
+        for (text, expected_result) in words_to_test {
+            assert_eq!(word_consists_of_emojis(text), expected_result);
+        }
+    }
 }