commit 77dd24f44c127286214d10f3059827f1453f0783
from: Omar Polo <op@omarpolo.com>
date: Mon Jul 05 17:27:20 2021 UTC

fix top_line/current_line wrt L_HIDDEN

this fixes some infinite loops that may happen if the first line is
hidden, or things happens.

The idea is to move the line forward/backward until a non-hidden one
is found.

commit - 60e8771930c10a9d8820102108342f0a53eda424
commit + 77dd24f44c127286214d10f3059827f1453f0783
blob - ccedaa8e62420b77214b4475aff8f6ef22da0464
blob + e8aa4f0a5a8bb9205f2f9116ec2fb1d8059df8f6
--- ui.c
+++ ui.c
@@ -782,7 +782,38 @@ redraw_tabline(void)
 		mvwprintw(tabline, 0, COLS-1, ">");
 	wattr_off(tabline, tab_face.background, NULL);
 }
+
+/*
+ * Compute the first visible line around vl.  Try to search forward
+ * until the end of the buffer; if a visible line is not found, search
+ * backward.  Return NULL if no viable line was found.
+ */
+static inline struct vline *
+adjust_line(struct vline *vl, struct buffer *buffer)
+{
+	struct vline *t;
 
+	if (!(vl->parent->flags & L_HIDDEN))
+		return vl;
+
+	/* search forward */
+	for (t = vl;
+	     t != NULL && t->parent->flags & L_HIDDEN;
+	     t = TAILQ_NEXT(t, vlines))
+		;		/* nop */
+
+	if (t != NULL)
+		return t;
+
+	/* search backward */
+	for (t = vl;
+	     t != NULL && t->parent->flags & L_HIDDEN;
+	     t = TAILQ_PREV(t, vhead, vlines))
+		;		/* nop */
+
+	return t;
+}
+
 static void
 redraw_window(WINDOW *win, int height, int width, struct buffer *buffer)
 {
@@ -804,8 +835,14 @@ again:
 	buffer->curs_y = 0;
 
 	if (TAILQ_EMPTY(&buffer->head))
+		goto end;
+
+	buffer->top_line = adjust_line(buffer->top_line, buffer);
+	if (buffer->top_line == NULL)
 		goto end;
 
+	buffer->current_line = adjust_line(buffer->current_line, buffer);
+
 	l = 0;
 	onscreen = 0;
 	for (vl = buffer->top_line; vl != NULL; vl = TAILQ_NEXT(vl, vlines)) {