String.truncate calls Vec.truncate, in turn, and that states

"is greater or equal to". Beside common sense.

Author: deep-outcome

library/alloc/src/string.rs

@@ -1382,7 +1382,7 @@ impl String {
 
     /// Shortens this `String` to the specified length.
     ///
-    /// If `new_len` is greater than the string's current length, this has no
+    /// If `new_len` is greater  than or equal to the string's current length, this has no
     /// effect.
     ///
     /// Note that this method has no effect on the allocated capacity