Silence unexpected Octave:mixed-string-concat warning in num2str.m (bug #66647)

* pt-mat.cc (maybe_warn_string_concat): Clarify that cause of warning message
is concatenation of single and double quoted strings.

* num2str.m: Disable "Octave:mixed-string-concat" warning locally.

* warning_ids.m: Clarify that cause of Octave:mixed-string-concat warning
message is concatenation of single and double quoted strings.

Author: Rik

libinterp/parse-tree/pt-mat.cc

@@ -135,7 +135,7 @@ maybe_warn_string_concat (bool all_dq_strings_p, bool all_sq_strings_p)
 {
   if (! (all_dq_strings_p || all_sq_strings_p))
     warning_with_id ("Octave:mixed-string-concat",
-                     "concatenation of different character string types may have unintended consequences");
+                     "concatenation of single and double quoted string objects creates a single quoted string object");
 }
 
 tree_expression *

scripts/general/num2str.m

@@ -134,6 +134,8 @@
         fmt = "%3d";
       endif
     endif
+    ## FIXME: Remove when Matlab strings are implemented in Octave.
+    warning ('off', 'Octave:mixed-string-concat', 'local');
     fmt = do_string_escapes (fmt);  # required now that '\n' is interpreted.
     nd = ndims (x);
     nc = columns (x) * (nd - 1);    # ND-arrays are expanded in columns

scripts/help/warning_ids.m

@@ -300,7 +300,7 @@
 ##
 ## @item Octave:mixed-string-concat
 ## If the @code{Octave:mixed-string-concat} warning is enabled, print a
-## warning when concatenating a mixture of double and single quoted strings.
+## warning when concatenating a mixture of single and double quoted strings.
 ## By default, the @code{Octave:mixed-string-concat} warning is disabled.
 ##
 ## @item  Octave:nearly-singular-matrix