Allow ENCODE_FILE and DECODE_FILE to use no-copy conversion

They already did return their argument under some circumstances;
this change broadens it to further reduce allocation in common cases
(bug#40407).

* src/coding.c (convert_string_nocopy): New function.
(decode_file_name, encode_file_name): Use convert_string_nocopy.
* src/coding.h (ENCODE_FILE, DECODE_FILE): Note the nocopy semantics.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/coding.h b/src/coding.h
index 91856c5702b..c2a7b2a00ff 100644
--- a/src/coding.h
+++ b/src/coding.h
@@ -642,11 +642,11 @@ struct coding_system
   } while (false)
 
 /* Encode the file name NAME using the specified coding system
-   for file names, if any.  */
+   for file names, if any.  May return NAME itself.  */
 #define ENCODE_FILE(NAME)  encode_file_name (NAME)
 
 /* Decode the file name NAME using the specified coding system
-   for file names, if any.  */
+   for file names, if any.  May return NAME itself.  */
 #define DECODE_FILE(NAME)  decode_file_name (NAME)
 
 /* Encode the string STR using the specified coding system