Fix the bytecode incompatibility due to the change to 'narrow-to-region'.

* src/editfns.c (narrow_to_region_internal): New function, which
contains the body previously in 'Fnarrow_to_region' but accepts
a third argument.
(Fnarrow_to_region): Use the new function. Update the docstring.
(Fwiden): Update the docstring.

* src/lisp.h: Prototype of the new function.

* src/xdisp.c (handle_fontified_prop): Use the new function instead
of 'Fnarrow_to_region'.

* src/process.c (Finternal_default_process_filter):
* src/lread.c (readevalloop): Remove the third argument to
'Fnarrow_to_region'.

* src/bytecode.c (exec_byte_code):
* lisp/emacs-lisp/comp.el (comp-limplify-lap-inst):
* lisp/emacs-lisp/bytecomp.el: Restore the statu quo ante.

* etc/NEWS: Remove the entry about the new optional argument.

* doc/lispref/positions.texi (Narrowing): Update the documentation.

6 files changed, 37 insertions, 27 deletions

diff --git a/src/bytecode.c b/src/bytecode.c
index 2b1eccdc518..d75767bb0c5 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -1480,8 +1480,8 @@ exec_byte_code (Lisp_Object fun, ptrdiff_t args_template,
 
         CASE (Bnarrow_to_region):
           {
-            Lisp_Object v2 = POP, v1 = POP;
-            TOP = Fnarrow_to_region (TOP, v1, v2);
+            Lisp_Object v1 = POP;
+            TOP = Fnarrow_to_region (TOP, v1);
             NEXT;
           }
 
diff --git a/src/editfns.c b/src/editfns.c
index 79af27d24da..35b2415e8b1 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -2660,9 +2660,10 @@ DEFUN ("widen", Fwiden, Swiden, 0, 0, "",
        doc: /* Remove restrictions (narrowing) from current buffer.
 This allows the buffer's full text to be seen and edited.
 
-When called from Lisp inside a body form in which `narrow-to-region'
-was called with an optional argument LOCK non-nil, this function does
-not produce any effect.  */)
+Note that, when the current buffer contains one or more lines whose
+length is above `long-line-threshold', Emacs may decide to leave, for
+performance reasons, the accessible portion of the buffer unchanged
+after this function is called.  */)
   (void)
 {
   if (! NILP (Vrestrictions_locked))
@@ -2689,22 +2690,11 @@ unwind_locked_zv (Lisp_Object point_max)
   SET_BUF_ZV (current_buffer, XFIXNUM (point_max));
 }
 
-DEFUN ("narrow-to-region", Fnarrow_to_region, Snarrow_to_region, 2, 3, "r",
-       doc: /* Restrict editing in this buffer to the current region.
-The rest of the text becomes temporarily invisible and untouchable
-but is not deleted; if you save the buffer in a file, the invisible
-text is included in the file.  \\[widen] makes all visible again.
-See also `save-restriction'.
-
-When calling from Lisp, pass two arguments START and END:
-positions (integers or markers) bounding the text that should
-remain visible.
-
-When called from Lisp with the optional argument LOCK non-nil,
-calls to `widen', or to `narrow-to-region' with an optional
-argument LOCK nil, do not produce any effect until the end of
-the current body form.  */)
-  (Lisp_Object start, Lisp_Object end, Lisp_Object lock)
+/* Internal function for Fnarrow_to_region, meant to be used with a
+   third argument 'true', in which case it should be followed by "specbind
+   (Qrestrictions_locked, Qt)".  */
+Lisp_Object
+narrow_to_region_internal (Lisp_Object start, Lisp_Object end, bool lock)
 {
   EMACS_INT s = fix_position (start), e = fix_position (end);
 
@@ -2713,7 +2703,7 @@ the current body form.  */)
       EMACS_INT tem = s; s = e; e = tem;
     }
 
-  if (! NILP (lock))
+  if (lock)
     {
       if (!(BEGV <= s && s <= e && e <= ZV))
         args_out_of_range (start, end);
@@ -2727,8 +2717,6 @@ the current body form.  */)
 
       SET_BUF_BEGV (current_buffer, s);
       SET_BUF_ZV (current_buffer, e);
-
-      specbind (Qrestrictions_locked, Qt);
     }
   else
     {
@@ -2754,6 +2742,26 @@ the current body form.  */)
   return Qnil;
 }
 
+DEFUN ("narrow-to-region", Fnarrow_to_region, Snarrow_to_region, 2, 2, "r",
+       doc: /* Restrict editing in this buffer to the current region.
+The rest of the text becomes temporarily invisible and untouchable
+but is not deleted; if you save the buffer in a file, the invisible
+text is included in the file.  \\[widen] makes all visible again.
+See also `save-restriction'.
+
+When calling from Lisp, pass two arguments START and END:
+positions (integers or markers) bounding the text that should
+remain visible.
+
+Note that, when the current buffer contains one or more lines whose
+length is above `long-line-threshold', Emacs may decide to leave, for
+performance reasons, the accessible portion of the buffer unchanged
+after this function is called.  */)
+  (Lisp_Object start, Lisp_Object end)
+{
+  return narrow_to_region_internal (start, end, false);
+}
+
 Lisp_Object
 save_restriction_save (void)
 {
diff --git a/src/lisp.h b/src/lisp.h
index 807fcb0e5ba..c8ad0bc56f5 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4679,6 +4679,7 @@ extern void save_restriction_restore (Lisp_Object);
 extern Lisp_Object make_buffer_string (ptrdiff_t, ptrdiff_t, bool);
 extern Lisp_Object make_buffer_string_both (ptrdiff_t, ptrdiff_t, ptrdiff_t,
                                             ptrdiff_t, bool);
+extern Lisp_Object narrow_to_region_internal (Lisp_Object, Lisp_Object, bool);
 extern void init_editfns (void);
 extern void syms_of_editfns (void);
 
diff --git a/src/lread.c b/src/lread.c
index 0720774db2b..0b46a2e4ee5 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -2261,7 +2261,7 @@ readevalloop (Lisp_Object readcharfun,
           /* Set point and ZV around stuff to be read.  */
           Fgoto_char (start);
           if (!NILP (end))
-            Fnarrow_to_region (make_fixnum (BEGV), end, Qnil);
+            Fnarrow_to_region (make_fixnum (BEGV), end);
 
           /* Just for cleanliness, convert END to a marker
              if it is an integer.  */
diff --git a/src/process.c b/src/process.c
index a15efa39bd1..1ac5a509e56 100644
--- a/src/process.c
+++ b/src/process.c
@@ -6339,7 +6339,7 @@ Otherwise it discards the output.  */)
 
       /* If the restriction isn't what it should be, set it.  */
       if (old_begv != BEGV || old_zv != ZV)
-        Fnarrow_to_region (make_fixnum (old_begv), make_fixnum (old_zv), Qnil);
+        Fnarrow_to_region (make_fixnum (old_begv), make_fixnum (old_zv));
 
       bset_read_only (current_buffer, old_read_only);
       SET_PT_BOTH (opoint, opoint_byte);
diff --git a/src/xdisp.c b/src/xdisp.c
index 88a489e290f..65d9221a159 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -4406,7 +4406,8 @@ handle_fontified_prop (struct it *it)
               if (!begv) begv = BEGV;
               zv = get_narrowed_zv (it->w, charpos);
             }
-          Fnarrow_to_region (make_fixnum (begv), make_fixnum (zv), Qt);
+          narrow_to_region_internal (make_fixnum (begv), make_fixnum (zv), true);
+          specbind (Qrestrictions_locked, Qt);
         }
 
       /* Don't allow Lisp that runs from 'fontification-functions'