Bug 1550422 - P27. Do not set WebRender preferences as code don't expect them to exists. r=cpearce
☠☠ backed out by af54b2de7028 ☠ ☠
authorJean-Yves Avenard <jyavenard@mozilla.com>
Fri, 24 May 2019 11:40:04 +0000
changeset 535185 0b40296717100fa26c8f7bdea8e365eeb523cfbd
parent 535184 a162952960355c80a50bc502aae46912b90fd7b8
child 535186 6dc17248fa2c34195c97123f3d0e3916a94e8883
push id11522
push userffxbld-merge
push dateMon, 01 Jul 2019 09:00:55 +0000
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Bug 1550422 - P27. Do not set WebRender preferences as code don't expect them to exists. r=cpearce Listing the preferences in either all.js or StaticPrefList.h would also make them appear in about:config which is something we don't want. Additionally, rename some pref constants to improve code clarity as we can no longer rely on using the StaticPrefs accessor. Differential Revision: https://phabricator.services.mozilla.com/D32416
--- a/gfx/thebes/gfxPlatform.cpp
+++ b/gfx/thebes/gfxPlatform.cpp
@@ -745,18 +745,20 @@ WebRenderMemoryReporter::CollectReports(
   return NS_OK;
 static const char* const WR_ROLLOUT_PREF = "gfx.webrender.all.qualified";
-static const char* const WR_ROLLOUT_PREF_DEFAULT =
+static const bool WR_ROLLOUT_PREF_DEFAULTVALUE = true;
+static const char* const WR_ROLLOUT_DEFAULT_PREF =
+static const bool WR_ROLLOUT_DEFAULT_PREF_DEFAULTVALUE = false;
 static const char* const WR_ROLLOUT_PREF_OVERRIDE =
 static const char* const WR_ROLLOUT_HW_QUALIFIED_OVERRIDE =
 static const char* const PROFILE_BEFORE_CHANGE_TOPIC = "profile-before-change";
 // If the "gfx.webrender.all.qualified" pref is true we want to enable
 // WebRender for qualified hardware. This pref may be set by the Normandy
@@ -814,17 +816,17 @@ class WrRolloutPrefShutdownSaver : publi
       // 1. the user or the WR SHIELD study has set a user pref value, or
       // 2. we've not had a default pref set by Normandy that needs to be saved
       //    for reading before Normandy has started up.
     bool defaultValue =
         Preferences::GetBool(WR_ROLLOUT_PREF, false, PrefValueKind::Default);
-    Preferences::SetBool(WR_ROLLOUT_PREF_DEFAULT, defaultValue);
+    Preferences::SetBool(WR_ROLLOUT_DEFAULT_PREF, defaultValue);
 static void FrameRatePrefChanged(const char* aPref, void*) {
   int32_t newRate = gfxPlatform::ForceSoftwareVsync()
                         ? gfxPlatform::GetSoftwareVsyncRate()
                         : -1;
   if (newRate != gLastUsedFrameRate) {
@@ -2515,39 +2517,51 @@ static bool WebRenderEnvvarDisabled() {
 // observer to save the default value on shutdown, and read the saved default
 // value here instead, and emulate the behavior of the pref system, with
 // respect to default/user values of the rollout pref.
 static bool CalculateWrQualifiedPrefValue() {
   auto clearPrefOnExit = MakeScopeExit([]() {
     // Clear the mirror of the default value of the rollout pref on scope exit,
     // if we have one. This ensures the user doesn't mess with the pref.
     // If we need it again, we'll re-create it on shutdown.
-    Preferences::ClearUser(WR_ROLLOUT_PREF_DEFAULT);
+    Preferences::ClearUser(WR_ROLLOUT_DEFAULT_PREF);
   if (!Preferences::HasUserValue(WR_ROLLOUT_PREF) &&
-      Preferences::HasUserValue(WR_ROLLOUT_PREF_DEFAULT)) {
+      Preferences::HasUserValue(WR_ROLLOUT_DEFAULT_PREF)) {
     // The user has not set a user pref, and we have a default value set by the
-    // shutdown observer. We should use that instead of the StaticPrefs's
-    // default, as if Normandy had a chance to set it before startup, that is
-    // the value StaticPrefs would return, rather than the default set by
-    // DECL_GFX_PREF.
-    return StaticPrefs::WebRenderAllQualifiedDefault();
+    // shutdown observer. Let's use this as it should be the value Normandy set
+    // before startup. WR_ROLLOUT_DEFAULT_PREF should only be set on shutdown by
+    // the shutdown observer.
+    // Normandy runs *during* startup, but *after* this code here runs (hence
+    // the need for the workaround).
+    // To have a value stored in the WR_ROLLOUT_DEFAULT_PREF pref here, during
+    // the previous run Normandy must have set a default value on the in-memory
+    // pref, and on shutdown we stored the default value in this
+    // WR_ROLLOUT_DEFAULT_PREF user pref. Then once the user restarts, we
+    // observe this pref. Normandy is the only way a default (not user) value
+    // can be set for this pref.
+    return Preferences::GetBool(WR_ROLLOUT_DEFAULT_PREF,
+                                WR_ROLLOUT_DEFAULT_PREF_DEFAULTVALUE);
   // We don't have a user value for the rollout pref, and we don't have the
   // value of the rollout pref at last shutdown stored. So we should fallback
-  // to using whatever default is stored in the gfxPref. *But* if we're running
+  // to using the default. *But* if we're running
   // under the Marionette pref rollout work-around test, we may want to override
   // the default value expressed here, so we can test the "default disabled;
   // rollout pref enabled" case.
+  // Note that those preferences can't be defined in all.js nor
+  // StaticPrefsList.h as they would create the pref, leading SaveRolloutPref()
+  // above to abort early as the pref would have a valid type.
+  //  We also don't want those prefs to appear in about:config.
   if (Preferences::HasUserValue(WR_ROLLOUT_PREF_OVERRIDE)) {
     return Preferences::GetBool(WR_ROLLOUT_PREF_OVERRIDE);
-  return StaticPrefs::WebRenderAllQualified();
 static FeatureState& WebRenderHardwareQualificationStatus(
     const IntSize& aScreenSize, bool aHasBattery, nsCString& aOutFailureId) {
   FeatureState& featureWebRenderQualified =
--- a/modules/libpref/init/StaticPrefList.h
+++ b/modules/libpref/init/StaticPrefList.h
@@ -4604,30 +4604,16 @@ VARCACHE_PREF(
   bool, false
-  Once,
-  "gfx.webrender.all.qualified",
-  WebRenderAllQualified,
-  bool, true
-  Once,
-  "gfx.webrender.all.qualified.default",
-  WebRenderAllQualifiedDefault,
-  bool, false
   RelaxedAtomicBool, true