Flag tabs if possible in the grid cell so they can be preserved on

copying and capture-pane. From Alexander Arch in GitHub issue 4201.

grid-reader.c

@@ -345,6 +345,8 @@ grid_reader_cell_equals_data(const struct grid_cell *gc,
 {
 	if (gc->flags & GRID_FLAG_PADDING)
 		return (0);
+	if (gc->flags & GRID_FLAG_TAB && ud->size == 1 && *ud->data == '\t')
+		return (1);
 	if (gc->data.size != ud->size)
 		return (0);
 	return (memcmp(gc->data.data, ud->data, gc->data.size) == 0);

grid.c

@@ -92,6 +92,8 @@ grid_need_extended_cell(const struct grid_cell_entry *gce,
 		return (1);
 	if (gc->link != 0)
 		return (1);
+	if (gc->flags & GRID_FLAG_TAB)
+		return (1);
 	return (0);
 }
 
@@ -124,7 +126,10 @@ grid_extended_cell(struct grid_line *gl, struct grid_cell_entry *gce,
 		fatalx("offset too big");
 	gl->flags |= GRID_LINE_EXTENDED;
 
-	utf8_from_data(&gc->data, &uc);
+	if (gc->flags & GRID_FLAG_TAB)
+		uc = gc->data.width;
+	else
+		utf8_from_data(&gc->data, &uc);
 
 	gee = &gl->extddata[gce->offset];
 	gee->data = uc;
@@ -252,6 +257,16 @@ grid_cells_equal(const struct grid_cell *gc1, const struct grid_cell *gc2)
 	return (memcmp(gc1->data.data, gc2->data.data, gc1->data.size) == 0);
 }
 
+/* Set grid cell to a tab. */
+void
+grid_set_tab(struct grid_cell *gc, u_int width)
+{
+	memset(&gc->data, 0, sizeof gc->data);
+	gc->flags |= GRID_FLAG_TAB;
+	gc->data.width = gc->data.size = gc->data.have = width;
+	memset(&gc->data, ' ', gc->data.size);
+}
+
 /* Free one line. */
 static void
 grid_free_line(struct grid *gd, u_int py)
@@ -515,7 +530,11 @@ grid_get_cell1(struct grid_line *gl, u_int px, struct grid_cell *gc)
 			gc->bg = gee->bg;
 			gc->us = gee->us;
 			gc->link = gee->link;
-			utf8_to_data(gee->data, &gc->data);
+
+			if (gc->flags & GRID_FLAG_TAB)
+				grid_set_tab(gc, gee->data);
+			else
+				utf8_to_data(gee->data, &gc->data);
 		}
 		return;
 	}
@@ -1077,13 +1096,18 @@ grid_string_cells(struct grid *gd, u_int px, u_int py, u_int nx,
 		} else
 			codelen = 0;
 
-		data = gc.data.data;
+		if (gc.flags & GRID_FLAG_TAB) {
-		size = gc.data.size;
+			data = "\t";
-		if ((flags & GRID_STRING_ESCAPE_SEQUENCES) &&
+			size = 1;
-		    size == 1 &&
+		} else {
-		    *data == '\\') {
+			data = gc.data.data;
-			data = "\\\\";
+			size = gc.data.size;
-			size = 2;
+			if ((flags & GRID_STRING_ESCAPE_SEQUENCES) &&
+			    size == 1 &&
+			    *data == '\\') {
+				data = "\\\\";
+				size = 2;
+			}
 		}
 
 		while (len < off + size + codelen + 1) {

input.c

@@ -1213,6 +1213,10 @@ input_c0_dispatch(struct input_ctx *ictx)
 	struct screen_write_ctx	*sctx = &ictx->ctx;
 	struct window_pane	*wp = ictx->wp;
 	struct screen		*s = sctx->s;
+	struct grid_cell	 gc, first_gc;
+	u_int			 cx = s->cx, line = s->cy + s->grid->hsize;
+	u_int			 width;
+	int			 has_content = 0;
 
 	ictx->utf8started = 0; /* can't be valid UTF-8 */
 
@@ -1234,11 +1238,28 @@ input_c0_dispatch(struct input_ctx *ictx)
 			break;
 
 		/* Find the next tab point, or use the last column if none. */
+		grid_get_cell(s->grid, s->cx, line, &first_gc);
 		do {
-			s->cx++;
+			if (!has_content) {
-			if (bit_test(s->tabs, s->cx))
+				grid_get_cell(s->grid, cx, line, &gc);
+				if (gc.data.size != 1 ||
+				    *gc.data.data != ' ' ||
+				    !grid_cells_look_equal(&gc, &first_gc))
+					has_content = 1;
+			}
+			cx++;
+			if (bit_test(s->tabs, cx))
 				break;
-		} while (s->cx < screen_size_x(s) - 1);
+		} while (cx < screen_size_x(s) - 1);
+
+		width = cx - s->cx;
+		if (has_content || width > sizeof gc.data.data)
+			s->cx = cx;
+		else {
+			grid_get_cell(s->grid, s->cx, line, &gc);
+			grid_set_tab(&gc, width);
+			screen_write_collect_add(sctx, &gc);
+		}
 		break;
 	case '\012':	/* LF */
 	case '\013':	/* VT */

screen-write.c

@@ -1814,6 +1814,8 @@ screen_write_collect_add(struct screen_write_ctx *ctx,
 	collect = 1;
 	if (gc->data.width != 1 || gc->data.size != 1 || *gc->data.data >= 0x7f)
 		collect = 0;
+	else if (gc->flags & GRID_FLAG_TAB)
+		collect = 0;
 	else if (gc->attr & GRID_ATTR_CHARSET)
 		collect = 0;
 	else if (~s->mode & MODE_WRAP)

tmux.h

@@ -709,6 +709,7 @@ struct colour_palette {
 #define GRID_FLAG_SELECTED 0x10
 #define GRID_FLAG_NOPALETTE 0x20
 #define GRID_FLAG_CLEARED 0x40
+#define GRID_FLAG_TAB 0x80
 
 /* Grid line flags. */
 #define GRID_LINE_WRAPPED 0x1
@@ -2861,6 +2862,7 @@ int	 attributes_fromstring(const char *);
 /* grid.c */
 extern const struct grid_cell grid_default_cell;
 void	 grid_empty_line(struct grid *, u_int, u_int);
+void	 grid_set_tab(struct grid_cell *, u_int);
 int	 grid_cells_equal(const struct grid_cell *, const struct grid_cell *);
 int	 grid_cells_look_equal(const struct grid_cell *,
 	     const struct grid_cell *);

window-copy.c

@@ -3301,6 +3301,11 @@ window_copy_cellstring(const struct grid_line *gl, u_int px, size_t *size,
 		*allocated = 0;
 		return (&gce->data.data);
 	}
+	if (gce->flags & GRID_FLAG_TAB) {
+		*size = 1;
+		*allocated = 0;
+		return ("\t");
+	}
 
 	utf8_to_data(gl->extddata[gce->offset].data, &ud);
 	if (ud.size == 0) {
@@ -4083,9 +4088,15 @@ window_copy_match_at_cursor(struct window_copy_mode_data *data)
 		px = at - (py * sx);
 
 		grid_get_cell(gd, px, gd->hsize + py - data->oy, &gc);
-		buf = xrealloc(buf, len + gc.data.size + 1);
+		if (gc.flags & GRID_FLAG_TAB) {
-		memcpy(buf + len, gc.data.data, gc.data.size);
+			buf = xrealloc(buf, len + 2);
-		len += gc.data.size;
+			buf[len] = '\t';
+			len++;
+		} else {
+			buf = xrealloc(buf, len + gc.data.size + 1);
+			memcpy(buf + len, gc.data.data, gc.data.size);
+			len += gc.data.size;
+		}
 	}
 	if (len != 0)
 		buf[len] = '\0';
@@ -4812,7 +4823,13 @@ window_copy_copy_line(struct window_mode_entry *wme, char **buf, size_t *off,
 			grid_get_cell(gd, i, sy, &gc);
 			if (gc.flags & GRID_FLAG_PADDING)
 				continue;
-			utf8_copy(&ud, &gc.data);
+			if (gc.flags & GRID_FLAG_TAB) {
+				memset(ud.data, 0, sizeof ud.data);
+				*ud.data = '\t';
+				ud.have = ud.size = 1;
+				ud.width = gc.data.width;
+			} else
+				utf8_copy(&ud, &gc.data);
 			if (ud.size == 1 && (gc.attr & GRID_ATTR_CHARSET)) {
 				s = tty_acs_get(NULL, ud.data[0]);
 				if (s != NULL && strlen(s) <= sizeof ud.data) {