Make fmt return Cow instead of Result

src/lib.rs

@@ -2,4 +2,4 @@
 
 mod short_name;
 
-pub use short_name::ShortName;
+pub use short_name::{DisplayShortName, ShortName};

src/short_name.rs

@@ -1,3 +1,7 @@
+use std::{borrow::Cow, fmt, str};
+
+const SPECIAL_TYPE_CHARS: [u8; 9] = *b" <>()[],;";
+
 /// Lazily shortens a type name to remove all module paths.
 ///
 /// The short name of a type is its full name as returned by
@@ -46,87 +50,71 @@ impl<'a> From<&'a str> for ShortName<'a> {
     }
 }
 
-impl<'a> core::fmt::Debug for ShortName<'a> {
-    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-        let &ShortName(full_name) = self;
-        // Generics result in nested paths within <..> blocks.
-        // Consider "bevy_render::camera::camera::extract_cameras<bevy_render::camera::bundle::Camera3d>".
-        // To tackle this, we parse the string from left to right, collapsing as we go.
-        let mut index: usize = 0;
-        let end_of_string = full_name.len();
-
-        while index < end_of_string {
-            let rest_of_string = full_name.get(index..end_of_string).unwrap_or_default();
+impl<'a> fmt::Debug for ShortName<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut remaining = f.as_bytes();
+        let mut parsed_name = Vec::new();
+        let mut complex_type = false;
 
+        loop {
             // Collapse everything up to the next special character,
             // then skip over it
-            if let Some(special_character_index) = rest_of_string.find(|c: char| {
-                (c == ' ')
-                    || (c == '<')
-                    || (c == '>')
-                    || (c == '(')
-                    || (c == ')')
-                    || (c == '[')
-                    || (c == ']')
-                    || (c == ',')
-                    || (c == ';')
-            }) {
-                let segment_to_collapse = rest_of_string
-                    .get(0..special_character_index)
-                    .unwrap_or_default();
-
-                f.write_str(collapse_type_name(segment_to_collapse))?;
-
-                // Insert the special character
-                let special_character =
-                    &rest_of_string[special_character_index..=special_character_index];
-
-                f.write_str(special_character)?;
-
-                match special_character {
-                    ">" | ")" | "]"
-                        if rest_of_string[special_character_index + 1..].starts_with("::") =>
-                    {
-                        f.write_str("::")?;
+            let is_special = |c| SPECIAL_TYPE_CHARS.contains(c);
+            if let Some(next_special_index) = remaining.iter().position(is_special) {
+                complex_type = true;
+                if parsed_name.is_empty() {
+                    parsed_name.reserve(remaining.len());
+                }
+                let (pre_special, post_special) = remaining.split_at(next_special_index + 1);
+                parsed_name.extend_from_slice(collapse_type_name(pre_special));
+                match pre_special.last().unwrap() {
+                    b'>' | b')' | b']' if post_special.get(..2) == Some(b"::") => {
+                        parsed_name.extend_from_slice(b"::");
                         // Move the index past the "::"
-                        index += special_character_index + 3;
+                        remaining = &post_special[2..];
                     }
                     // Move the index just past the special character
-                    _ => index += special_character_index + 1,
+                    _ => remaining = post_special,
                 }
+            } else if !complex_type {
+                let collapsed = collapse_type_name(remaining);
+                // SAFETY: We only split on ASCII characters, and the input is valid UTF8, since
+                // it was a &str
+                let str = unsafe { str::from_utf8_unchecked(collapsed) };
+                return Cow::Borrowed(str);
             } else {
                 // If there are no special characters left, we're done!
-                f.write_str(collapse_type_name(rest_of_string))?;
-                index = end_of_string;
+                parsed_name.extend_from_slice(collapse_type_name(remaining));
+                // SAFETY: see above
+                let utf8_name = unsafe { String::from_utf8_unchecked(parsed_name) };
+                return Cow::Owned(utf8_name);
             }
         }
+    }
+}
 
-        Ok(())
+impl<'a> fmt::Display for ShortName<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        <Self as fmt::Debug>::fmt(self, f)
     }
 }
 
-impl<'a> core::fmt::Display for ShortName<'a> {
-    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-        <Self as core::fmt::Debug>::fmt(self, f)
+/// Wrapper around `AsRef<str>` that uses the [`get_short_name`] format when
+/// displayed.
+pub struct DisplayShortName<T: AsRef<str>>(pub T);
+
+impl<T: AsRef<str>> fmt::Display for DisplayShortName<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let as_short_name = ShortName(self.0.as_ref());
+        write!(f, "{as_short_name}")
     }
 }
 
 #[inline(always)]
-fn collapse_type_name(string: &str) -> &str {
-    // Enums types are retained.
-    // As heuristic, we assume the enum type to be uppercase.
-    let mut segments = string.rsplit("::");
-    let (last, second_last): (&str, Option<&str>) = (segments.next().unwrap(), segments.next());
-    let Some(second_last) = second_last else {
-        return last;
-    };
-
-    if second_last.starts_with(char::is_uppercase) {
-        let index = string.len() - last.len() - second_last.len() - 2;
-        &string[index..]
-    } else {
-        last
-    }
+fn collapse_type_name(string: &[u8]) -> &[u8] {
+    let find = |(index, window)| (window == b"::").then_some(index + 2);
+    let split_index = string.windows(2).enumerate().rev().find_map(find);
+    &string[split_index.unwrap_or(0)..]
 }
 
 #[cfg(all(test, feature = "alloc"))]
@@ -187,6 +175,14 @@ mod name_formatting_tests {
         );
     }
 
+    #[test]
+    fn utf8_generics() {
+        assert_eq!(
+            fmt("bévï::camérą::łørđ::_öñîòñ<ķràźÿ::Москва::東京>"),
+            "_öñîòñ<東京>".to_string()
+        );
+    }
+
     #[test]
     fn nested_generics() {
         assert_eq!(