Implement buffer-widen-limits functionalityscratch/widen-limits

 `widen` now respects restrictions imposed by new variable
 `hard-widen-limits`

3 files changed, 48 insertions, 3 deletions

diff --git a/src/buffer.c b/src/buffer.c
index f06d7e08e49..1b62d3a4d51 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -329,6 +329,11 @@ bset_scroll_up_aggressively (struct buffer *b, Lisp_Object val)
   b->scroll_up_aggressively_ = val;
 }
 static void
+bset_widen_limits (struct buffer *b, Lisp_Object val)
+{
+  b->widen_limits_ = val;
+}
+static void
 bset_selective_display (struct buffer *b, Lisp_Object val)
 {
   b->selective_display_ = val;
@@ -847,6 +852,7 @@ CLONE nil means the indirect buffer's state is reset to default values.  */)
       bset_display_count (b, make_number (0));
       bset_backed_up (b, Qnil);
       bset_auto_save_file_name (b, Qnil);
+      bset_widen_limits (b, b->base_buffer->widen_limits_);
       set_buffer_internal_1 (b);
       Fset (intern ("buffer-save-without-query"), Qnil);
       Fset (intern ("buffer-file-number"), Qnil);
@@ -961,6 +967,7 @@ reset_buffer_local_variables (struct buffer *b, bool permanent_too)
      things that depend on the major mode.
      default-major-mode is handled at a higher level.
      We ignore it here.  */
+  bset_widen_limits(b, Qnil);
   bset_major_mode (b, Qfundamental_mode);
   bset_keymap (b, Qnil);
   bset_mode_name (b, QSFundamental);
@@ -2167,7 +2174,7 @@ so the buffer is truly empty after this.  */)
 {
   Fwiden ();
 
-  del_range (BEG, Z);
+  del_range (BEGWL, ZWL);
 
   current_buffer->last_window_start = 1;
   /* Prevent warnings, or suspension of auto saving, that would happen
@@ -5037,6 +5044,7 @@ init_buffer_once (void)
   bset_display_count (&buffer_local_flags, make_number (-1));
   bset_display_time (&buffer_local_flags, make_number (-1));
   bset_enable_multibyte_characters (&buffer_local_flags, make_number (-1));
+  bset_widen_limits (&buffer_local_flags, make_number (-1));
 
   /* These used to be stuck at 0 by default, but now that the all-zero value
      means Qnil, we have to initialize them explicitly.  */
@@ -5160,6 +5168,7 @@ init_buffer_once (void)
   bset_cursor_type (&buffer_defaults, Qt);
   bset_extra_line_spacing (&buffer_defaults, Qnil);
   bset_cursor_in_non_selected_windows (&buffer_defaults, Qt);
+  bset_widen_limits (&buffer_defaults, Qnil);
 
   bset_enable_multibyte_characters (&buffer_defaults, Qt);
   bset_buffer_file_coding_system (&buffer_defaults, Qnil);
@@ -5367,7 +5376,6 @@ defvar_per_buffer (struct Lisp_Buffer_Objfwd *bo_fwd, const char *namestring,
     emacs_abort ();
 }
 
-
 /* Initialize the buffer routines.  */
 void
 syms_of_buffer (void)
@@ -5796,6 +5804,13 @@ If you set this to -2, that means don't turn off auto-saving in this buffer
 if its text size shrinks.   If you use `buffer-swap-text' on a buffer,
 you probably should set this to -2 in that buffer.  */);
 
+  DEFVAR_PER_BUFFER ("buffer-widen-limits", &BVAR (current_buffer, widen_limits),
+                     Qnil,
+                     doc: /* When non-nil `widen` will widen to these limits.
+Must be a cons of the form (MIN . MAX) where MIN and MAX are integers
+of hard widen limits in this buffer. This is an experimental variable
+intended primarily for multi-mode engines.  */);
+
   DEFVAR_PER_BUFFER ("selective-display", &BVAR (current_buffer, selective_display),
                      Qnil,
                      doc: /* Non-nil enables selective display.
diff --git a/src/buffer.h b/src/buffer.h
index 87b7cee4413..4075bbf555c 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -59,6 +59,10 @@ INLINE_HEADER_BEGIN
 #define Z (current_buffer->text->z)
 #define Z_BYTE (current_buffer->text->z_byte)
 
+/* Positions that take into account widen limits.  */
+#define BEGWL (BUF_BEGWL (current_buffer))
+#define ZWL (BUF_ZWL(current_buffer))
+
 /* Macros for the addresses of places in the buffer.  */
 
 /* Address of beginning of buffer.  */
@@ -128,6 +132,15 @@ INLINE_HEADER_BEGIN
     : NILP (BVAR (buf, begv_marker)) ? buf->begv_byte   \
     : marker_byte_position (BVAR (buf, begv_marker)))
 
+/* Hard positions in buffer. */
+#define BUF_BEGWL(buf)                                          \
+  ((NILP (BVAR (buf, widen_limits))) ?  BUF_BEG (buf)    \
+   : XINT( XCAR (BVAR (buf, widen_limits))))
+
+#define BUF_ZWL(buf)                                    \
+  ((NILP (BVAR (buf, widen_limits))) ?  BUF_Z (buf)      \
+   : XINT( XCDR (BVAR (buf, widen_limits))))
+
 /* Position of point in buffer.  */
 #define BUF_PT(buf)                                     \
    (buf == current_buffer ? PT                          \
@@ -150,6 +163,7 @@ INLINE_HEADER_BEGIN
     : NILP (BVAR (buf, zv_marker)) ? buf->zv_byte       \
     : marker_byte_position (BVAR (buf, zv_marker)))
 
+
 /* Position of gap in buffer.  */
 #define BUF_GPT(buf) ((buf)->text->gpt)
 #define BUF_GPT_BYTE(buf) ((buf)->text->gpt_byte)
@@ -748,6 +762,9 @@ struct buffer
      See `cursor-type' for other values.  */
   Lisp_Object cursor_in_non_selected_windows_;
 
+  /* Cons of hard widen limits */
+  Lisp_Object widen_limits_;
+
   /* No more Lisp_Object beyond this point.  Except undo_list,
      which is handled specially in Fgarbage_collect.  */
 
diff --git a/src/editfns.c b/src/editfns.c
index 2ac0537eddb..e5ab637aba1 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3480,12 +3480,25 @@ DEFUN ("delete-and-extract-region", Fdelete_and_extract_region,
     return empty_unibyte_string;
   return del_range_1 (XINT (start), XINT (end), 1, 1);
 }
+
 
 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.  */)
+This allows the buffer's full text to be seen and edited.
+If `buffer-widen-limits` is non-nil, widen only to those limits.  */)
   (void)
 {
+
+  if (!NILP (BVAR(current_buffer, widen_limits)))
+    {
+      Lisp_Object hl = BVAR(current_buffer,  widen_limits);
+      CHECK_CONS(hl);
+      CHECK_NUMBER(XCAR(hl));
+      CHECK_NUMBER(XCDR(hl));
+      Fnarrow_to_region(XCAR(hl), XCDR(hl));
+      return Qnil;
+    }
+
   if (BEG != BEGV || Z != ZV)
     current_buffer->clip_changed = 1;
   BEGV = BEG;