improve cow from string

src/string.rs

@@ -1,7 +1,7 @@
 use alloc::{
     borrow::{Cow, ToOwned},
     boxed::Box,
-    string::{String, ToString},
+    string::{String},
     sync::Arc,
 };
 use core::{borrow::Borrow, fmt::Write as _, hash::Hash, str::FromStr};
@@ -319,8 +319,8 @@ impl<LenT: ValidLength> From<FixedString<LenT>> for String {
         match value.0 {
             // SAFETY: Self holds the type invariant that the array is UTF-8.
             FixedStringRepr::Heap(a) => unsafe { String::from_utf8_unchecked(a.into()) },
-            FixedStringRepr::Inline(a) => a.as_str().to_string(),
-            FixedStringRepr::Static(a) => a.as_str().to_string(),
+            FixedStringRepr::Inline(a) => a.as_str().into(),
+            FixedStringRepr::Static(a) => a.as_str().into(),
         }
     }
 }
@@ -333,7 +333,10 @@ impl<'a, LenT: ValidLength> From<&'a FixedString<LenT>> for Cow<'a, str> {
 
 impl<LenT: ValidLength> From<FixedString<LenT>> for Cow<'_, str> {
     fn from(value: FixedString<LenT>) -> Self {
-        Cow::Owned(value.into_string())
+        match value.0 {
+            FixedStringRepr::Static(static_str) => Cow::Borrowed(static_str.as_str()),
+            _ => Cow::Owned(value.into()),
+        }
     }
 }
 
@@ -443,6 +446,23 @@ mod test {
         assert_ne!(STR, str);
     }
 
+    #[test]
+    fn test_from_static_to_cow() {
+        const STR: &str = "static string";
+
+        let string = FixedString::<u8>::from_static_trunc(STR);
+
+        let cow: std::borrow::Cow<'static, _> = string.into();
+
+        assert_eq!(cow, STR);
+
+        let std::borrow::Cow::Borrowed(string) = cow else {
+            panic!("Expected borrowed string");
+        };
+
+        assert_eq!(string, STR);
+    }
+
     #[test]
     fn check_u8_roundtrip() {
         check_u8_roundtrip_generic(|original| {