Bug 1920357 - Ignore viewport meta tag when we're in RDM and we also force desktop viewport. r=devtools-reviewers,jdescottes

Currently DevTools doesn't do it, but it feels like the right API and is
already there. This allows fixing this on the devtools side however you
want :)

Differential Revision: https://phabricator.services.mozilla.com/D223627

docshell/base/BrowsingContext.cpp

@@ -2759,6 +2759,20 @@ void BrowsingContext::DidSet(FieldIndex<IDX_InRDMPane>, bool aOldValue) {
   PresContextAffectingFieldChanged();
 }
 
+void BrowsingContext::DidSet(FieldIndex<IDX_ForceDesktopViewport>,
+                             bool aOldValue) {
+  MOZ_ASSERT(IsTop(), "Should only set in the top-level browsing context");
+  if (ForceDesktopViewport() == aOldValue) {
+    return;
+  }
+  PresContextAffectingFieldChanged();
+  if (nsIDocShell* shell = GetDocShell()) {
+    if (RefPtr ps = shell->GetPresShell()) {
+      ps->MaybeRecreateMobileViewportManager(/* aAfterInitialization= */ true);
+    }
+  }
+}
+
 bool BrowsingContext::CanSet(FieldIndex<IDX_PageAwakeRequestCount>,
                              uint32_t aNewValue, ContentParent* aSource) {
   return IsTop() && XRE_IsParentProcess() && !aSource;

docshell/base/BrowsingContext.h

@@ -1111,6 +1111,8 @@ class BrowsingContext : public nsILoadContext, public nsWrapperCache {
   }
 
   void DidSet(FieldIndex<IDX_InRDMPane>, bool aOldValue);
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY void DidSet(FieldIndex<IDX_ForceDesktopViewport>,
+                                          bool aOldValue);
 
   void DidSet(FieldIndex<IDX_EmbedderColorSchemes>,
               EmbedderColorSchemes&& aOldValue);

dom/base/Document.cpp

@@ -10767,11 +10767,36 @@ nsViewportInfo Document::GetViewportInfo(const ScreenIntSize& aDisplaySize) {
   CSSToScreenScale defaultScale =
       layoutDeviceScale * LayoutDeviceToScreenScale(1.0);
 
-  // Special behaviour for desktop mode, provided we are not on an about: page,
-  // or fullscreen.
-  const bool fullscreen = Fullscreen();
   auto* bc = GetBrowsingContext();
-  if (bc && bc->ForceDesktopViewport() && !IsAboutPage() && !fullscreen) {
+  const bool inRDM = bc && bc->InRDMPane();
+  const bool ignoreMetaTag = [&] {
+    if (!nsLayoutUtils::ShouldHandleMetaViewport(this)) {
+      return true;
+    }
+    if (Fullscreen()) {
+      // We ignore viewport meta tag etc when in fullscreen, see bug 1696717.
+      return true;
+    }
+    if (inRDM && bc->ForceDesktopViewport()) {
+      // We ignore meta viewport when devtools tells us to force desktop
+      // viewport on RDM.
+      return true;
+    }
+    return false;
+  }();
+
+  if (ignoreMetaTag) {
+    return nsViewportInfo(aDisplaySize, defaultScale,
+                          nsLayoutUtils::AllowZoomingForDocument(this)
+                              ? nsViewportInfo::ZoomFlag::AllowZoom
+                              : nsViewportInfo::ZoomFlag::DisallowZoom,
+                          StaticPrefs::apz_allow_zooming_out()
+                              ? nsViewportInfo::ZoomBehaviour::Mobile
+                              : nsViewportInfo::ZoomBehaviour::Desktop);
+  }
+
+  // Special behaviour for desktop mode, provided we are not on an about: page.
+  if (bc && bc->ForceDesktopViewport() && !IsAboutPage()) {
     CSSCoord viewportWidth =
         StaticPrefs::browser_viewport_desktopWidth() / fullZoom;
     CSSToScreenScale scaleToFit(aDisplaySize.width / viewportWidth);
@@ -10784,17 +10809,6 @@ nsViewportInfo Document::GetViewportInfo(const ScreenIntSize& aDisplaySize) {
                           nsViewportInfo::AutoScaleFlag::AutoScale);
   }
 
-  // We ignore viewport meta tage etc when in fullscreen, see bug 1696717.
-  if (fullscreen || !nsLayoutUtils::ShouldHandleMetaViewport(this)) {
-    return nsViewportInfo(aDisplaySize, defaultScale,
-                          nsLayoutUtils::AllowZoomingForDocument(this)
-                              ? nsViewportInfo::ZoomFlag::AllowZoom
-                              : nsViewportInfo::ZoomFlag::DisallowZoom,
-                          StaticPrefs::apz_allow_zooming_out()
-                              ? nsViewportInfo::ZoomBehaviour::Mobile
-                              : nsViewportInfo::ZoomBehaviour::Desktop);
-  }
-
   // In cases where the width of the CSS viewport is less than or equal to the
   // width of the display (i.e. width <= device-width) then we disable
   // double-tap-to-zoom behaviour. See bug 941995 for details.
@@ -10929,15 +10943,13 @@ nsViewportInfo Document::GetViewportInfo(const ScreenIntSize& aDisplaySize) {
       // default size has a complicated calculation, we fixup the maxWidth
       // value after setting it, above.
       if (maxWidth == nsViewportInfo::kAuto && !mValidScaleFloat) {
-        if (bc && bc->TouchEventsOverride() == TouchEventsOverride::Enabled &&
+        maxWidth = StaticPrefs::browser_viewport_desktopWidth();
-            bc->InRDMPane()) {
+        if (inRDM &&
+            bc->TouchEventsOverride() == TouchEventsOverride::Enabled) {
           // If RDM and touch simulation are active, then use the simulated
           // screen width to accommodate for cases where the screen width is
           // larger than the desktop viewport default.
-          maxWidth = nsViewportInfo::Max(
+          maxWidth = nsViewportInfo::Max(displaySize.width, maxWidth);
-              displaySize.width, StaticPrefs::browser_viewport_desktopWidth());
-        } else {
-          maxWidth = StaticPrefs::browser_viewport_desktopWidth();
         }
         // Divide by fullZoom to stretch CSS pixel size of viewport in order
         // to keep device pixel size unchanged after full zoom applied.