From 6da5efb815e5ff6d3e0ac19bdde45516fccdd0bf Mon Sep 17 00:00:00 2001
From: Consolatis <35009135+Consolatis@users.noreply.github.com>
Date: Sat, 16 Mar 2024 19:03:06 +0100
Subject: [PATCH] treewide: properly clear the buffer

Before this patch, the OSD would repeat the last buffer
content in case the new buffer content would be empty.

This was mostly happening for the `title` OSD field that is intended
to be empty when it matches the app_id / WM_CLASS of the application.
Due to only buffer.len being reset but its internal allocations being
untouched, buffer.buf would still carry the old data.

This patch fixes it by also overwriting the first byte in the buffer
allocation with '\0' via the new `buf_clear()` function.

Do the same for buf_expand_shell_variables() although that one should
have been fine before as it always writes new data to the buffer.
---
 src/common/buf.c | 2 +-
 src/osd.c        | 4 +---
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/common/buf.c b/src/common/buf.c
index f6667418..f6bde97f 100644
--- a/src/common/buf.c
+++ b/src/common/buf.c
@@ -52,7 +52,7 @@ buf_expand_shell_variables(struct buf *s)
 	for (int i = 0 ; i < s->len ; i++) {
 		if (s->buf[i] == '$' && isvalid(s->buf[i+1])) {
 			/* expand environment variable */
-			environment_variable.len = 0;
+			buf_clear(&environment_variable);
 			buf_add(&environment_variable, s->buf + i + 1);
 			char *p = environment_variable.buf;
 			while (isvalid(*p)) {
diff --git a/src/osd.c b/src/osd.c
index d6d6be56..85e9f433 100644
--- a/src/osd.c
+++ b/src/osd.c
@@ -369,7 +369,7 @@ render_osd(struct server *server, cairo_t *cairo, int w, int h,
 		int nr_fields = wl_list_length(&rc.window_switcher.fields);
 		struct window_switcher_field *field;
 		wl_list_for_each(field, &rc.window_switcher.fields, link) {
-			buf.len = 0;
+			buf_clear(&buf);
 			cairo_move_to(cairo, x, y
 				+ theme->osd_window_switcher_item_padding_y
 				+ theme->osd_window_switcher_item_active_border_width);
@@ -399,8 +399,6 @@ render_osd(struct server *server, cairo_t *cairo, int w, int h,
 				if (wl_list_length(&server->outputs) > 1 &&
 						output_is_usable((*view)->output)) {
 					buf_add(&buf, (*view)->output->wlr_output->name);
-				} else {
-					buf_add(&buf, " ");
 				}
 				break;
 			case LAB_FIELD_IDENTIFIER: