IH-553: Sexpr.escape should be a noop when nothing to escape

Optimistically check for the presence of escape characters before escaping.
This avoids rebuilding the string when escapable characters are not present (the common case).

Signed-off-by: Edwin Török <[email protected]>

ocaml/libs/sexpr/sExpr.ml

@@ -27,6 +27,8 @@ let unescape_buf buf s =
   if Astring.String.fold_left aux false s then
     Buffer.add_char buf '\\'
 
+let is_escape_char = function '\\' | '"' | '\'' -> true | _ -> false
+
 (* XXX: This escapes "'c'" and "\'c\'" to "\\'c\\'".
  * They are both unescaped as "'c'". They have been ported
  * to make sure that this corner case is left unchanged.
@@ -36,21 +38,24 @@ let unescape_buf buf s =
  * that have guaranteed invariants and optimised performances *)
 let escape s =
   let open Astring in
-  let escaped = Buffer.create (String.length s + 10) in
-  String.iter
-    (fun c ->
-      match c with
-      | '\\' ->
-          Buffer.add_string escaped "\\\\"
-      | '"' ->
-          Buffer.add_string escaped "\\\""
-      | '\'' ->
-          Buffer.add_string escaped "\\\'"
-      | _ ->
-          Buffer.add_char escaped c
-    )
-    s ;
-  Buffer.contents escaped
+  if String.exists is_escape_char s then (
+    let escaped = Buffer.create (String.length s + 10) in
+    String.iter
+      (fun c ->
+        match c with
+        | '\\' ->
+            Buffer.add_string escaped "\\\\"
+        | '"' ->
+            Buffer.add_string escaped "\\\""
+        | '\'' ->
+            Buffer.add_string escaped "\\\'"
+        | _ ->
+            Buffer.add_char escaped c
+      )
+      s ;
+    Buffer.contents escaped
+  ) else
+    s
 
 let unescape s =
   let buf = Buffer.create (String.length s) in