Fix config rewrite with an empty "save" parameter. (#8719)

src/config.c

@@ -1381,14 +1381,19 @@ void rewriteConfigSaveOption(struct rewriteConfigState *state) {
         return;
     }
 
-    /* Note that if there are no save parameters at all, all the current
-     * config line with "save" will be detected as orphaned and deleted,
-     * resulting into no RDB persistence as expected. */
-    for (j = 0; j < server.saveparamslen; j++) {
-        line = sdscatprintf(sdsempty(),"save %ld %d",
-            (long) server.saveparams[j].seconds, server.saveparams[j].changes);
-        rewriteConfigRewriteLine(state,"save",line,1);
+    /* Rewrite save parameters, or an empty 'save ""' line to avoid the
+     * defaults from being used.
+     */
+    if (!server.saveparamslen) {
+        rewriteConfigRewriteLine(state,"save",sdsnew("save \"\""),0);
+    } else {
+        for (j = 0; j < server.saveparamslen; j++) {
+            line = sdscatprintf(sdsempty(),"save %ld %d",
+                (long) server.saveparams[j].seconds, server.saveparams[j].changes);
+            rewriteConfigRewriteLine(state,"save",line,1);
+        }
     }
+
     /* Mark "save" as processed in case server.saveparamslen is zero. */
     rewriteConfigMarkAsProcessed(state,"save");
 }

tests/unit/introspection.tcl

@@ -180,6 +180,18 @@ start_server {tags {"introspection"}} {
         }
     }
 
+    test {CONFIG REWRITE handles save properly} {
+        r config set save "3600 1 300 100 60 10000"
+        r config rewrite
+        restart_server 0 true false
+        assert_equal [r config get save] {save {3600 1 300 100 60 10000}}
+
+        r config set save ""
+        r config rewrite
+        restart_server 0 true false
+        assert_equal [r config get save] {save {}}
+    }
+
     # Config file at this point is at a wierd state, and includes all
     # known keywords. Might be a good idea to avoid adding tests here.
 }