charset: Fix transchar() with multibyte characters

It appears that transchar() was working under assumption that 
`transchar_nonprint()` may be used for multibyte characters while its 
documentation stated exact opposite. It was not actually untrue though, except 
that longer buffer would be needed then the one stated in documentation. But it 
is false now with assert().

1 files changed, 11 insertions, 7 deletions

diff --git a/src/nvim/charset.c b/src/nvim/charset.c
index d8d080ee8a..aecde29ce2 100644
--- a/src/nvim/charset.c
+++ b/src/nvim/charset.c
@@ -517,14 +517,16 @@ char_u* str_foldcase(char_u *str, int orglen, char_u *buf, int buflen)
 // Does NOT work for multi-byte characters, c must be <= 255.
 // Also doesn't work for the first byte of a multi-byte, "c" must be a
 // character!
-static char_u transchar_buf[7];
+static char_u transchar_buf[11];
 
-/// Translates a character
+/// Translate a character into a printable one, leaving printable ASCII intact
 ///
-/// @param c
+/// All unicode characters are considered non-printable in this function.
+///
+/// @param[in]  c  Character to translate.
 ///
-/// @return translated character.
-char_u* transchar(int c)
+/// @return translated character into a static buffer.
+char_u *transchar(int c)
 {
   int i = 0;
   if (IS_SPECIAL(c)) {
@@ -537,12 +539,14 @@ char_u* transchar(int c)
 
   if ((!chartab_initialized && (((c >= ' ') && (c <= '~'))
                                 || (p_altkeymap && F_ischar(c))))
-      || ((c < 256) && vim_isprintc_strict(c))) {
+      || ((c <= 0xFF) && vim_isprintc_strict(c))) {
     // printable character
     transchar_buf[i] = (char_u)c;
     transchar_buf[i + 1] = NUL;
-  } else {
+  } else if (c <= 0xFF){
     transchar_nonprint(transchar_buf + i, c);
+  } else {
+    transchar_hex((char *)transchar_buf + i, c);
   }
   return transchar_buf;
 }