vt: tag cells that were form-feed:ed, to allow correct text reflow

To handle text reflow correctly when a line has a printable character
in the last column, but was still line breaked, we need to track the
fact that the slave inserted a line break here.

Otherwise, when the window width is increased, we'll end up pulling up
the next line, when we really should have inserted a line break.

render.c

@@ -1055,7 +1055,10 @@ reflow(struct terminal *term, struct row **new_grid, int new_cols, int new_rows,
          * *entire* old line was empty.
          */
 
-        if (empty_count < old_cols && old_row->cells[old_cols - 1].wc == 0) {
+        if (empty_count < old_cols &&
+            (old_row->cells[old_cols - 1].wc == 0 ||
+             old_row->cells[old_cols - 1].attrs.linefeed))
+        {
             new_col_idx = 0;
             new_row_idx = (new_row_idx + 1) & (new_rows - 1);
 

terminal.c

@@ -1494,6 +1494,14 @@ term_scroll_reverse(struct terminal *term, int rows)
     term_scroll_reverse_partial(term, term->scroll_region, rows);
 }
 
+void
+term_formfeed(struct terminal *term)
+{
+    if (term->cursor.point.col > 0)
+        term->grid->cur_row->cells[term->cursor.point.col - 1].attrs.linefeed = 1;
+    term_cursor_left(term, term->cursor.point.col);
+}
+
 void
 term_linefeed(struct terminal *term)
 {

terminal.h

@@ -42,7 +42,8 @@ struct attributes {
     uint32_t have_fg:1;
     uint32_t have_bg:1;
     uint32_t selected:2;
-    uint32_t reserved:3;
+    uint32_t linefeed:1;
+    uint32_t reserved:2;
     uint32_t bg:24;
 };
 static_assert(sizeof(struct attributes) == 8, "bad size");
@@ -403,6 +404,7 @@ void term_scroll_partial(
 void term_scroll_reverse_partial(
     struct terminal *term, struct scroll_region region, int rows);
 
+void term_formfeed(struct terminal *term);
 void term_linefeed(struct terminal *term);
 void term_reverse_index(struct terminal *term);
 

vt.c

@@ -128,7 +128,7 @@ action_execute(struct terminal *term, uint8_t c)
 
     case '\r':
         /* FF - form feed */
-        term_cursor_left(term, term->cursor.point.col);
+        term_formfeed(term);
         break;
 
     case '\b':
@@ -361,8 +361,8 @@ action_esc_dispatch(struct terminal *term, uint8_t final)
             break;
 
         case 'E':
+            term_formfeed(term);
             term_linefeed(term);
-            term_cursor_left(term, term->cursor.point.col);
             break;
 
         case 'H':