patch 8.1.0039: cannot easily delete lines in another buffer

Problem:    Cannot easily delete lines in another buffer.
Solution:   Add deletebufline().

runtime/doc/eval.txt

@@ -2110,6 +2110,8 @@ cursor({lnum}, {col} [, {off}])
 cursor({list})			Number	move cursor to position in {list}
 deepcopy({expr} [, {noref}])	any	make a full copy of {expr}
 delete({fname} [, {flags}])	Number	delete the file or directory {fname}
+deletebufline({expr}, {first}[, {last}])
+				Number	delete lines from buffer {expr}
 did_filetype()			Number	|TRUE| if FileType autocmd event used
 diff_filler({lnum})		Number	diff filler lines about {lnum}
 diff_hlID({lnum}, {col})	Number	diff highlighting at {lnum}/{col}
@@ -3517,8 +3519,19 @@ delete({fname} [, {flags}])					*delete()*
 		successful and -1 when the deletion failed or partly failed.
 
 		Use |remove()| to delete an item from a |List|.
-		To delete a line from the buffer use |:delete|.  Use |:exe|
+		To delete a line from the buffer use |:delete| or
-		when the line number is in a variable.
+		|deletebufline()|.
+
+deletebufline({expr}, {first}[, {last}])		*deletebufline()*
+		Delete lines {first} to {last} (inclusive) from buffer {expr}.
+		If {last} is omitted then delete line {first} only.
+		On success 0 is returned, on failure 1 is returned.
+
+		For the use of {expr}, see |bufname()| above.
+
+		{first} and {last} are used like with |setline()|. Note that
+		when using |line()| this refers to the current buffer. Use "$"
+		to refer to the last line in buffer {expr}.
 
 							*did_filetype()*
 did_filetype()	Returns |TRUE| when autocommands are being executed and the

src/evalfunc.c

@@ -125,6 +125,7 @@ static void f_cscope_connection(typval_T *argvars, typval_T *rettv);
 static void f_cursor(typval_T *argsvars, typval_T *rettv);
 static void f_deepcopy(typval_T *argvars, typval_T *rettv);
 static void f_delete(typval_T *argvars, typval_T *rettv);
+static void f_deletebufline(typval_T *argvars, typval_T *rettv);
 static void f_did_filetype(typval_T *argvars, typval_T *rettv);
 static void f_diff_filler(typval_T *argvars, typval_T *rettv);
 static void f_diff_hlID(typval_T *argvars, typval_T *rettv);
@@ -577,6 +578,7 @@ static struct fst
     {"cursor",		1, 3, f_cursor},
     {"deepcopy",	1, 2, f_deepcopy},
     {"delete",		1, 2, f_delete},
+    {"deletebufline",	2, 3, f_deletebufline},
     {"did_filetype",	0, 0, f_did_filetype},
     {"diff_filler",	1, 1, f_diff_filler},
     {"diff_hlID",	2, 2, f_diff_hlID},
@@ -1209,6 +1211,24 @@ get_tv_lnum_buf(typval_T *argvars, buf_T *buf)
     return (linenr_T)get_tv_number_chk(&argvars[0], NULL);
 }
 
+/*
+ * If there is a window for "curbuf", make it the current window.
+ */
+    static void
+find_win_for_curbuf(void)
+{
+    wininfo_T *wip;
+
+    for (wip = curbuf->b_wininfo; wip != NULL; wip = wip->wi_next)
+    {
+	if (wip->wi_win != NULL)
+	{
+	    curwin = wip->wi_win;
+	    break;
+	}
+    }
+}
+
 /*
  * Set line or list of lines in buffer "buf".
  */
@@ -1241,19 +1261,10 @@ set_buffer_lines(
 
     if (!is_curbuf)
     {
-	wininfo_T *wip;
-
 	curbuf_save = curbuf;
 	curwin_save = curwin;
 	curbuf = buf;
-	for (wip = buf->b_wininfo; wip != NULL; wip = wip->wi_next)
+	find_win_for_curbuf();
-	{
-	    if (wip->wi_win != NULL)
-	    {
-		curwin = wip->wi_win;
-		break;
-	    }
-	}
     }
 
     if (append)
@@ -2807,6 +2818,93 @@ f_delete(typval_T *argvars, typval_T *rettv)
 	EMSG2(_(e_invexpr2), flags);
 }
 
+/*
+ * "deletebufline()" function
+ */
+    static void
+f_deletebufline(argvars, rettv)
+    typval_T	*argvars;
+    typval_T	*rettv;
+{
+    buf_T	*buf;
+    linenr_T	first, last;
+    linenr_T	lnum;
+    long	count;
+    int		is_curbuf;
+    buf_T	*curbuf_save = NULL;
+    win_T	*curwin_save = NULL;
+    tabpage_T	*tp;
+    win_T	*wp;
+
+    buf = get_buf_tv(&argvars[0], FALSE);
+    if (buf == NULL)
+    {
+	rettv->vval.v_number = 1; /* FAIL */
+	return;
+    }
+    is_curbuf = buf == curbuf;
+
+    first = get_tv_lnum_buf(&argvars[1], buf);
+    if (argvars[2].v_type != VAR_UNKNOWN)
+	last = get_tv_lnum_buf(&argvars[2], buf);
+    else
+	last = first;
+
+    if (buf->b_ml.ml_mfp == NULL || first < 1
+			   || first > buf->b_ml.ml_line_count || last < first)
+    {
+	rettv->vval.v_number = 1;	/* FAIL */
+	return;
+    }
+
+    if (!is_curbuf)
+    {
+	curbuf_save = curbuf;
+	curwin_save = curwin;
+	curbuf = buf;
+	find_win_for_curbuf();
+    }
+    if (last > curbuf->b_ml.ml_line_count)
+	last = curbuf->b_ml.ml_line_count;
+    count = last - first + 1;
+
+    // When coming here from Insert mode, sync undo, so that this can be
+    // undone separately from what was previously inserted.
+    if (u_sync_once == 2)
+    {
+	u_sync_once = 1; // notify that u_sync() was called
+	u_sync(TRUE);
+    }
+
+    if (u_save(first - 1, last + 1) == FAIL)
+    {
+	rettv->vval.v_number = 1;	/* FAIL */
+	return;
+    }
+
+    for (lnum = first; lnum <= last; ++lnum)
+	ml_delete(first, TRUE);
+
+    FOR_ALL_TAB_WINDOWS(tp, wp)
+	if (wp->w_buffer == buf)
+	{
+	    if (wp->w_cursor.lnum > last)
+		wp->w_cursor.lnum -= count;
+	    else if (wp->w_cursor.lnum> first)
+		wp->w_cursor.lnum = first;
+	    if (wp->w_cursor.lnum > wp->w_buffer->b_ml.ml_line_count)
+		wp->w_cursor.lnum = wp->w_buffer->b_ml.ml_line_count;
+	}
+    check_cursor_col();
+    deleted_lines_mark(first, count);
+
+    if (!is_curbuf)
+    {
+	curbuf = curbuf_save;
+	curwin = curwin_save;
+    }
+}
+
 /*
  * "did_filetype()" function
  */

src/testdir/test_bufline.vim

@@ -1,4 +1,4 @@
-" Tests for setbufline(), getbufline(), appendbufline()
+" Tests for setbufline(), getbufline(), appendbufline(), deletebufline()
 
 source shared.vim
 
@@ -90,3 +90,25 @@ func Test_appendbufline()
   call assert_equal([], getbufline(b, 6))
   exe "bwipe! " . b
 endfunc
+
+func Test_deletebufline()
+  new
+  let b = bufnr('%')
+  call setline(1, ['aaa', 'bbb', 'ccc'])
+  hide
+  call assert_equal(0, deletebufline(b, 2))
+  call assert_equal(['aaa', 'ccc'], getbufline(b, 1, 2))
+  call assert_equal(0, deletebufline(b, 2, 8))
+  call assert_equal(['aaa'], getbufline(b, 1, 2))
+  exe "bd!" b
+  call assert_equal(1, deletebufline(b, 1))
+
+  split Xtest
+  call setline(1, ['a', 'b', 'c'])
+  let b = bufnr('%')
+  wincmd w
+  call assert_equal(1, deletebufline(b, 4))
+  call assert_equal(0, deletebufline(b, 1))
+  call assert_equal(['b', 'c'], getbufline(b, 1, 2))
+  exe "bwipe! " . b
+endfunc

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    39,
 /**/
     38,
 /**/