Bug 1764696 - Replace dom.storage.next_gen with a new pref; r=dom-storage-reviewers,jstutte

Differential Revision: https://phabricator.services.mozilla.com/D143688

dom/localstorage/LocalStorageCommon.cpp

@@ -50,7 +50,10 @@ bool NextGenLocalStorageEnabled() {
       // Ideally all this Mutex stuff would be replaced with just using
       // an AtStartup StaticPref, but there are concerns about this causing
       // deadlocks if this access needs to init the AtStartup cache.
-      bool enabled = StaticPrefs::dom_storage_next_gen_DoNotUseDirectly();
+      bool enabled =
+          !StaticPrefs::
+              dom_storage_enable_unsupported_legacy_implementation_DoNotUseDirectly();
+
       gNextGenLocalStorageEnabled = enabled ? 1 : 0;
     }
 

dom/localstorage/test/unit/test_lsng_enabled.js

@@ -0,0 +1,14 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+/**
+ * This test is mainly to verify that LSNG is not accidentally disabled which
+ * can lead to a data loss in a combination with disabled shadow writes.
+ */
+
+// eslint-disable-next-line no-unused-vars
+async function testSteps() {
+  ok(Services.domStorageManager.nextGenLocalStorageEnabled, "LSNG enabled");
+}

dom/localstorage/test/unit/test_old_lsng_pref.js

@@ -0,0 +1,18 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+/**
+ * This test is mainly to verify that the old pref for switching LS
+ * implementations has no effect anymore.
+ */
+
+// eslint-disable-next-line no-unused-vars
+async function testSteps() {
+  info("Setting pref");
+
+  Services.prefs.setBoolPref("dom.storage.next_gen", false);
+
+  ok(Services.domStorageManager.nextGenLocalStorageEnabled, "LSNG enabled");
+}

dom/localstorage/test/unit/xpcshell.ini

@@ -40,7 +40,9 @@ run-sequentially = this test depends on a file produced by test_databaseShadowin
 [test_groupLimit.js]
 [test_groupMismatch.js]
 [test_largeItems.js]
+[test_lsng_enabled.js]
 [test_migration.js]
+[test_old_lsng_pref.js]
 [test_orderingAfterRemoveAdd.js]
 [test_originInit.js]
 [test_preloading.js]

dom/quota/test/xpcshell/test_removeLocalStorage.js

@@ -10,7 +10,10 @@ function* testSteps() {
 
   info("Setting pref");
 
-  SpecialPowers.setBoolPref("dom.storage.next_gen", false);
+  SpecialPowers.setBoolPref(
+    "dom.storage.enable_unsupported_legacy_implementation",
+    true
+  );
 
   // Profile 1
   info("Clearing");

modules/libpref/init/StaticPrefList.yaml

@@ -3577,11 +3577,15 @@
   value: 25 * 1024
   mirror: always
 
-# Whether or not LSNG (Next Generation Local Storage) is enabled.
-# See bug 1599979 for enabling this unconditionally (second attempt).
-- name: dom.storage.next_gen
+# Whether or not the unsupported legacy implemenation should be enabled. Please
+# don't advertise this pref as a way for disabling LSNG. This pref is intended
+# for internal testing only and will be removed in near future. Accidental
+# disabling of LSNG can lead to a data loss in a combination with disabled
+# shadow writes. Disabling of shadow writes is the initial step towards
+# removing legacy implementation and will be done soon.
+- name: dom.storage.enable_unsupported_legacy_implementation
   type: RelaxedAtomicBool
-  value: true
+  value: false
   mirror: always
   do_not_use_directly: true