Allow 'make-string' callers force creation of multibyte strings

* src/alloc.c (Fmake_string): Accept additional argument
MULTIBYTE, and produce a multibyte string if it is non-nil.
(make_event_array):
* src/lread.c (read0):
* src/editfns.c (Ftranslate_region_internal):
* src/coding.c (Fdefine_coding_system_internal):
* src/cmds.c (internal_self_insert):
* src/xdisp.c (build_desired_tool_bar_string)
(store_mode_line_string): All C callers changed.

* doc/lispref/strings.texi (Creating Strings): Document the new
optional argument.

* etc/NEWS: Mention the new optional argument.

* lisp/ruler-mode.el (ruler-mode-ruler): Call make-string with the
3rd argument non-nil.

9 files changed, 41 insertions, 27 deletions

diff --git a/doc/lispref/strings.texi b/doc/lispref/strings.texi
index 09c3bdf71f6..31734c5ecf6 100644
--- a/doc/lispref/strings.texi
+++ b/doc/lispref/strings.texi
@@ -121,7 +121,7 @@ character (i.e., an integer), @code{nil} otherwise.
   The following functions create strings, either from scratch, or by
 putting strings together, or by taking them apart.
 
-@defun make-string count character
+@defun make-string count character &optional multibyte
 This function returns a string made up of @var{count} repetitions of
 @var{character}.  If @var{count} is negative, an error is signaled.
 
@@ -132,6 +132,13 @@ This function returns a string made up of @var{count} repetitions of
      @result{} ""
 @end example
 
+  Normally, if @var{character} is an @acronym{ASCII} character, the
+result is a unibyte string.  But if the optional argument
+@var{multibyte} is non-@code{nil}, the function will produce a
+multibyte string instead.  This is useful when you later need to
+concatenate the result with non-@acronym{ASCII} strings or replace
+some of its characters with non-@acronym{ASCII} characters.
+
   Other functions to compare with this one include @code{make-vector}
 (@pxref{Vectors}) and @code{make-list} (@pxref{Building Lists}).
 @end defun
diff --git a/etc/NEWS b/etc/NEWS
index f9481405e4e..0dd6e36c70a 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -131,6 +131,11 @@ bug on OS X 10.8 and later (Bug#28639).
 ** The function 'get-free-disk-space' returns now a non-nil value for
 remote systems, which support this check.
 
++++
+** The function 'make-string' accepts an additional optional argument.
+If the optional third argument is non-nil, 'make-string' will produce
+a multibyte string even if its second argument is an ASCII character.
+
 
 * Changes in Emacs 27.1 on Non-Free Operating Systems
 
diff --git a/lisp/ruler-mode.el b/lisp/ruler-mode.el
index 3d27858d0fe..cac91e421e0 100644
--- a/lisp/ruler-mode.el
+++ b/lisp/ruler-mode.el
@@ -709,20 +709,18 @@ Optional argument PROPS specifies other text properties to apply."
          ;; Create an "clean" ruler.
          (ruler
           (propertize
-           ;; FIXME: `make-string' returns a unibyte string if it's ASCII-only,
-           ;; which prevents further `aset' from inserting non-ASCII chars,
-           ;; hence the need for `string-to-multibyte'.
-           ;; https://lists.gnu.org/archive/html/emacs-devel/2017-05/msg00841.html
-           (string-to-multibyte
-            ;; Make the part of header-line corresponding to the
-            ;; line-number display be blank, not filled with
-            ;; ruler-mode-basic-graduation-char.
-            (if display-line-numbers
-                (let* ((lndw (round (line-number-display-width 'columns)))
-                       (s (make-string lndw ?\s)))
-                  (concat s (make-string (- w lndw)
-                                         ruler-mode-basic-graduation-char)))
-              (make-string w ruler-mode-basic-graduation-char)))
+           ;; Make the part of header-line corresponding to the
+           ;; line-number display be blank, not filled with
+           ;; ruler-mode-basic-graduation-char.
+           (if display-line-numbers
+               (let* ((lndw (round (line-number-display-width 'columns)))
+                      ;; We need a multibyte string here so we could
+                      ;; later use aset to insert multibyte characters
+                      ;; into that string.
+                      (s (make-string lndw ?\s t)))
+                 (concat s (make-string (- w lndw)
+                                        ruler-mode-basic-graduation-char t)))
+             (make-string w ruler-mode-basic-graduation-char t))
            'face 'ruler-mode-default
            'local-map ruler-mode-map
            'help-echo (cond
diff --git a/src/alloc.c b/src/alloc.c
index 0fc79fe68ac..f479226845a 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -2298,11 +2298,13 @@ string_overflow (void)
   error ("Maximum string size exceeded");
 }
 
-DEFUN ("make-string", Fmake_string, Smake_string, 2, 2, 0,
+DEFUN ("make-string", Fmake_string, Smake_string, 2, 3, 0,
        doc: /* Return a newly created string of length LENGTH, with INIT in each element.
 LENGTH must be an integer.
-INIT must be an integer that represents a character.  */)
-  (Lisp_Object length, Lisp_Object init)
+INIT must be an integer that represents a character.
+If optional argument MULTIBYTE is non-nil, the result will be
+a multibyte string even if INIT is an ASCII character.  */)
+  (Lisp_Object length, Lisp_Object init, Lisp_Object multibyte)
 {
   register Lisp_Object val;
   int c;
@@ -2312,7 +2314,7 @@ INIT must be an integer that represents a character.  */)
   CHECK_CHARACTER (init);
 
   c = XFASTINT (init);
-  if (ASCII_CHAR_P (c))
+  if (ASCII_CHAR_P (c) && NILP (multibyte))
     {
       nbytes = XINT (length);
       val = make_uninit_string (nbytes);
@@ -3930,7 +3932,7 @@ make_event_array (ptrdiff_t nargs, Lisp_Object *args)
   {
     Lisp_Object result;
 
-    result = Fmake_string (make_number (nargs), make_number (0));
+    result = Fmake_string (make_number (nargs), make_number (0), Qnil);
     for (i = 0; i < nargs; i++)
       {
 	SSET (result, i, XINT (args[i]));
diff --git a/src/cmds.c b/src/cmds.c
index e4c0c866916..f76fe873720 100644
--- a/src/cmds.c
+++ b/src/cmds.c
@@ -439,12 +439,13 @@ internal_self_insert (int c, EMACS_INT n)
       int mc = ((NILP (BVAR (current_buffer, enable_multibyte_characters))
 		 && SINGLE_BYTE_CHAR_P (c))
 		? UNIBYTE_TO_CHAR (c) : c);
-      Lisp_Object string = Fmake_string (make_number (n), make_number (mc));
+      Lisp_Object string = Fmake_string (make_number (n), make_number (mc),
+					 Qnil);
 
       if (spaces_to_insert)
 	{
 	  tem = Fmake_string (make_number (spaces_to_insert),
-			      make_number (' '));
+			      make_number (' '), Qnil);
 	  string = concat2 (string, tem);
 	}
 
diff --git a/src/coding.c b/src/coding.c
index d790ad08ea9..1705838ffad 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -10236,7 +10236,7 @@ usage: (define-coding-system-internal ...)  */)
       ASET (attrs, coding_attr_ccl_encoder, val);
 
       val = args[coding_arg_ccl_valids];
-      valids = Fmake_string (make_number (256), make_number (0));
+      valids = Fmake_string (make_number (256), make_number (0), Qnil);
       for (tail = val; CONSP (tail); tail = XCDR (tail))
 	{
 	  int from, to;
diff --git a/src/editfns.c b/src/editfns.c
index e250c91ecbc..84cfbb2c877 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3718,7 +3718,7 @@ It returns the number of characters changed.  */)
 		}
 	      else
 		{
-		  string = Fmake_string (make_number (1), val);
+		  string = Fmake_string (make_number (1), val, Qnil);
 		}
 	      replace_range (pos, pos + len, string, 1, 0, 1, 0);
 	      pos_byte += SBYTES (string);
diff --git a/src/lread.c b/src/lread.c
index 33da8667228..19ed07220cd 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -2269,7 +2269,7 @@ read0 (Lisp_Object readcharfun)
     return val;
 
   xsignal1 (Qinvalid_read_syntax,
-	    Fmake_string (make_number (1), make_number (c)));
+	    Fmake_string (make_number (1), make_number (c), Qnil));
 }
 
 /* Grow a read buffer BUF that contains OFFSET useful bytes of data,
diff --git a/src/xdisp.c b/src/xdisp.c
index dc23959aadb..900a8dc1637 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -12320,7 +12320,7 @@ build_desired_tool_bar_string (struct frame *f)
   /* Reuse f->desired_tool_bar_string, if possible.  */
   if (size < size_needed || NILP (f->desired_tool_bar_string))
     fset_desired_tool_bar_string
-      (f, Fmake_string (make_number (size_needed), make_number (' ')));
+      (f, Fmake_string (make_number (size_needed), make_number (' '), Qnil));
   else
     {
       AUTO_LIST4 (props, Qdisplay, Qnil, Qmenu_item, Qnil);
@@ -23837,7 +23837,8 @@ store_mode_line_string (const char *string, Lisp_Object lisp_string,
   if (field_width > len)
     {
       field_width -= len;
-      lisp_string = Fmake_string (make_number (field_width), make_number (' '));
+      lisp_string = Fmake_string (make_number (field_width), make_number (' '),
+				  Qnil);
       if (!NILP (props))
 	Fadd_text_properties (make_number (0), make_number (field_width),
 			      props, lisp_string);