For the sake of case/switch code readability, 'fall through'
comments added.

src/http/ngx_http_parse.c

diff --git a/src/http/ngx_http_parse.c b/src/http/ngx_http_parse.c
index 876a437..ace6cfe 100644
--- a/src/http/ngx_http_parse.c
+++ b/src/http/ngx_http_parse.c
@@ -1153,6 +1153,7 @@
                 break;
             case '+':
                 r->plus_in_uri = 1;
+                /* fall through */
             default:
                 *u++ = ch;
                 break;

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 7e368c1..a5ed15c 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -3312,6 +3312,8 @@
         switch (n) {
         case 0:
             u->cacheable = 0;
+            /* fall through */
+
         case NGX_ERROR:
             return NGX_OK;
 
@@ -4460,6 +4462,8 @@
     case NGX_DECLINED:
         ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                            "invalid address \"%V\"", &value[1]);
+        /* fall through */
+
     default:
         return NGX_CONF_ERROR;
     }