Bug 1812868 - Expose scrollbar-inline-size as a CSS variable to chrome code. r=mstange

For that we need to:

 * Make GetDPIRatioForScrollbarPart thread-safe: This was using the
   widget for bug 1727289, but just looking at the print preview scale
   is enough to fix that.

 * Make nsPresContext::UseOverlayScrollbars() thread-safe: We store the
   RDM pane stuff in the pres context.

The rest is pretty straight-forward.

Differential Revision: https://phabricator.services.mozilla.com/D168148

docshell/base/BrowsingContext.cpp

@@ -2757,21 +2757,7 @@ void BrowsingContext::DidSet(FieldIndex<IDX_InRDMPane>, bool aOldValue) {
   if (GetInRDMPane() == aOldValue) {
     return;
   }
-
-  PreOrderWalk([&](BrowsingContext* aContext) {
-    if (nsIDocShell* shell = aContext->GetDocShell()) {
-      if (nsPresContext* pc = shell->GetPresContext()) {
-        pc->RecomputeTheme();
-
-        // This is a bit of a lie, but this affects the overlay-scrollbars
-        // media query and it's the code-path that gets taken for regular system
-        // metrics changes via ThemeChanged().
-        pc->MediaFeatureValuesChanged(
-            {MediaFeatureChangeReason::SystemMetricsChange},
-            MediaFeatureChangePropagation::JustThisDocument);
-      }
-    }
-  });
+  PresContextAffectingFieldChanged();
 }
 
 bool BrowsingContext::CanSet(FieldIndex<IDX_PageAwakeRequestCount>,

layout/base/nsPresContext.cpp

@@ -278,6 +278,7 @@ nsPresContext::nsPresContext(dom::Document* aDocument, nsPresContextType aType)
       mFontFeatureValuesDirty(true),
       mFontPaletteValuesDirty(true),
       mIsVisual(false),
+      mInRDMPane(false),
       mHasWarnedAboutTooLargeDashedOrDottedRadius(false),
       mQuirkSheetAdded(false),
       mHadNonBlankPaint(false),
@@ -858,6 +859,8 @@ void nsPresContext::AttachPresShell(mozilla::PresShell* aPresShell) {
   // have a presshell, and hence a document.
   GetUserPreferences();
 
+  EnsureTheme();
+
   nsIURI* docURI = doc->GetDocumentURI();
 
   if (IsDynamic() && docURI) {
@@ -933,6 +936,8 @@ void nsPresContext::RecomputeBrowsingContextDependentData() {
     return browsingContext->GetEmbedderColorSchemes().mPreferred;
   }());
 
+  SetInRDMPane(top->GetInRDMPane());
+
   if (doc == mDocument) {
     // Medium doesn't apply to resource documents, etc.
     RefPtr<nsAtom> mediumToEmulate;
@@ -1286,6 +1291,14 @@ void nsPresContext::UpdateEffectiveTextZoom() {
       MediaFeatureChangePropagation::JustThisDocument);
 }
 
+void nsPresContext::SetInRDMPane(bool aInRDMPane) {
+  if (mInRDMPane == aInRDMPane) {
+    return;
+  }
+  mInRDMPane = aInRDMPane;
+  RecomputeTheme();
+}
+
 float nsPresContext::GetDeviceFullZoom() {
   return mDeviceContext->GetFullZoom();
 }
@@ -1629,8 +1642,7 @@ void nsPresContext::RecordInteractionTime(InteractionType aType,
 nsITheme* nsPresContext::EnsureTheme() {
   MOZ_ASSERT(!mTheme);
   if (Document()->ShouldAvoidNativeTheme()) {
-    BrowsingContext* bc = Document()->GetBrowsingContext();
-    if (bc && bc->Top()->InRDMPane()) {
+    if (mInRDMPane) {
       mTheme = do_GetRDMThemeDoNotUseDirectly();
     } else {
       mTheme = do_GetBasicNativeThemeDoNotUseDirectly();
@@ -1651,17 +1663,21 @@ void nsPresContext::RecomputeTheme() {
   if (oldTheme == mTheme) {
     return;
   }
-  // Theme only affects layout information, not style, so we just need to
-  // reframe (as it affects whether we create scrollbar buttons for example).
-  RebuildAllStyleData(nsChangeHint_ReconstructFrame, RestyleHint{0});
+  // Theme affects layout information (as it affects whether we create
+  // scrollbar buttons for example) and also style (affects the
+  // scrollbar-inline-size env var).
+  RebuildAllStyleData(nsChangeHint_ReconstructFrame,
+                      RestyleHint::RecascadeSubtree());
+  // This is a bit of a lie, but this affects the overlay-scrollbars
+  // media query and it's the code-path that gets taken for regular system
+  // metrics changes via ThemeChanged().
+  MediaFeatureValuesChanged({MediaFeatureChangeReason::SystemMetricsChange},
+                            MediaFeatureChangePropagation::JustThisDocument);
 }
 
 bool nsPresContext::UseOverlayScrollbars() const {
-  if (LookAndFeel::GetInt(LookAndFeel::IntID::UseOverlayScrollbars)) {
-    return true;
-  }
-  BrowsingContext* bc = Document()->GetBrowsingContext();
-  return bc && bc->Top()->InRDMPane();
+  return LookAndFeel::GetInt(LookAndFeel::IntID::UseOverlayScrollbars) ||
+         mInRDMPane;
 }
 
 void nsPresContext::ThemeChanged(widget::ThemeChangeKind aKind) {

layout/base/nsPresContext.h

@@ -502,7 +502,9 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
    *
    * XXX Temporary: see http://wiki.mozilla.org/Gecko:PrintPreview
    */
-  float GetPrintPreviewScaleForSequenceFrame() { return mPPScale; }
+  float GetPrintPreviewScaleForSequenceFrameOrScrollbars() const {
+    return mPPScale;
+  }
   void SetPrintPreviewScale(float aScale) { mPPScale = aScale; }
 
   nsDeviceContext* DeviceContext() const { return mDeviceContext; }
@@ -573,6 +575,7 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
   }
   void SetFullZoom(float aZoom);
   void SetOverrideDPPX(float);
+  void SetInRDMPane(bool aInRDMPane);
 
  public:
   float GetFullZoom() { return mFullZoom; }
@@ -824,17 +827,9 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
    */
   uint32_t GetBidi() const;
 
-  /*
-   * Obtain a native theme for rendering our widgets (both form controls and
-   * html)
-   *
-   * Guaranteed to return non-null.
-   */
-  nsITheme* Theme() MOZ_NONNULL_RETURN {
-    if (MOZ_LIKELY(mTheme)) {
-      return mTheme;
-    }
-    return EnsureTheme();
+  nsITheme* Theme() const MOZ_NONNULL_RETURN {
+    MOZ_ASSERT(mTheme);
+    return mTheme;
   }
 
   void RecomputeTheme();
@@ -907,6 +902,8 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
     return mType == eContext_Print || mType == eContext_PrintPreview;
   }
 
+  bool IsPrintPreview() const { return mType == eContext_PrintPreview; }
+
   // Is this presentation in a chrome docshell?
   bool IsChrome() const;
 
@@ -1352,6 +1349,9 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
 
   unsigned mIsVisual : 1;
 
+  // Are we in the RDM pane?
+  unsigned mInRDMPane : 1;
+
   unsigned mHasWarnedAboutTooLargeDashedOrDottedRadius : 1;
 
   // Have we added quirk.css to the style set?

layout/generic/nsPageSequenceFrame.cpp

@@ -146,7 +146,7 @@ NS_QUERYFRAME_TAIL_INHERITING(nsContainerFrame)
 
 float nsPageSequenceFrame::GetPrintPreviewScale() const {
   nsPresContext* pc = PresContext();
-  float scale = pc->GetPrintPreviewScaleForSequenceFrame();
+  float scale = pc->GetPrintPreviewScaleForSequenceFrameOrScrollbars();
 
   WritingMode wm = GetWritingMode();
   if (pc->IsScreen() && MOZ_LIKELY(mScrollportSize.ISize(wm) > 0 &&

layout/style/GeckoBindings.cpp

@@ -305,6 +305,16 @@ bool Gecko_AnimationNameMayBeReferencedFromStyle(
   return aPresContext->AnimationManager()->AnimationMayBeReferenced(aName);
 }
 
+float Gecko_GetScrollbarInlineSize(const nsPresContext* aPc) {
+  MOZ_ASSERT(aPc);
+  AutoWriteLock guard(*sServoFFILock);  // We read some look&feel values.
+  auto overlay = aPc->UseOverlayScrollbars() ? nsITheme::Overlay::Yes
+                                             : nsITheme::Overlay::No;
+  LayoutDeviceIntCoord size =
+      aPc->Theme()->GetScrollbarSize(aPc, StyleScrollbarWidth::Auto, overlay);
+  return aPc->DevPixelsToFloatCSSPixels(size);
+}
+
 PseudoStyleType Gecko_GetImplementedPseudo(const Element* aElement) {
   return aElement->GetPseudoElementType();
 }

layout/style/GeckoBindings.h

@@ -350,6 +350,8 @@ void Gecko_NoteAnimationOnlyDirtyElement(const mozilla::dom::Element*);
 bool Gecko_AnimationNameMayBeReferencedFromStyle(const nsPresContext*,
                                                  nsAtom* name);
 
+float Gecko_GetScrollbarInlineSize(const nsPresContext*);
+
 // Incremental restyle.
 mozilla::PseudoStyleType Gecko_GetImplementedPseudo(
     const mozilla::dom::Element*);

layout/style/test/chrome/chrome.ini

@@ -22,6 +22,7 @@ tags = fullscreen
 [test_display_mode_reflow.html]
 support-files = display_mode_reflow.html
 tags = fullscreen
+[test_scrollbar_inline_size.html]
 [test_hover.html]
 skip-if = true # bug 1346353
 [test_moz_document_rules.html]

layout/style/test/chrome/test_scrollbar_inline_size.html

@@ -0,0 +1,35 @@
+<!DOCTYPE HTML>
+<meta charset="utf-8">
+<title>Test for env(scrollbar-inline-size)</title>
+<script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+<script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"></script>
+<link rel="stylesheet" href="chrome://global/skin"/>
+<link rel="stylesheet" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+<div id="scroller" style="width: 100px; height: 100px; overflow: scroll"></div>
+<div id="ref" style="width: env(scrollbar-inline-size, 1000px)"></div>
+<script>
+  SimpleTest.waitForExplicitFinish();
+  async function runTest() {
+    // We need to disable overlay scrollbars to measure the real scrollbar
+    // size.
+    await SpecialPowers.pushPrefEnv({
+      set: [["ui.useOverlayScrollbars", 0]],
+    });
+    runOnce();
+
+    info("with full zoom");
+    SpecialPowers.setFullZoom(window, 2.0);
+
+    runOnce();
+  }
+
+  function runOnce() {
+    let scroller = document.getElementById("scroller");
+    let ref = document.getElementById("ref");
+    let scrollbarSize = scroller.getBoundingClientRect().width - scroller.clientWidth;
+    ok(scrollbarSize > 0, "Should have a scrollbar");
+    is(ref.getBoundingClientRect().width, scrollbarSize, "env() should match the scrollbar size");
+  }
+
+  runTest().then(SimpleTest.finish);
+</script>

layout/style/test/test_non_content_accessible_env_vars.html

@@ -10,6 +10,7 @@ const NON_CONTENT_ACCESSIBLE_ENV_VARS = [
   "-moz-gtk-csd-maximize-button-position",
   "-moz-gtk-csd-close-button-position",
   "-moz-content-preferred-color-scheme",
+  "scrollbar-inline-size",
 ];
 
 const div = document.querySelector("div");

servo/components/style/custom_properties.rs

@@ -78,6 +78,10 @@ fn get_content_preferred_color_scheme(device: &Device) -> VariableValue {
     })
 }
 
+fn get_scrollbar_inline_size(device: &Device) -> VariableValue {
+    VariableValue::pixels(device.scrollbar_inline_size().px())
+}
+
 static ENVIRONMENT_VARIABLES: [EnvironmentVariable; 4] = [
     make_variable!(atom!("safe-area-inset-top"), get_safearea_inset_top),
     make_variable!(atom!("safe-area-inset-bottom"), get_safearea_inset_bottom),
@@ -104,7 +108,7 @@ macro_rules! lnf_int_variable {
     }};
 }
 
-static CHROME_ENVIRONMENT_VARIABLES: [EnvironmentVariable; 6] = [
+static CHROME_ENVIRONMENT_VARIABLES: [EnvironmentVariable; 7] = [
     lnf_int_variable!(
         atom!("-moz-gtk-csd-titlebar-radius"),
         TitlebarRadius,
@@ -130,6 +134,10 @@ static CHROME_ENVIRONMENT_VARIABLES: [EnvironmentVariable; 6] = [
         atom!("-moz-content-preferred-color-scheme"),
         get_content_preferred_color_scheme
     ),
+    make_variable!(
+        atom!("scrollbar-inline-size"),
+        get_scrollbar_inline_size
+    ),
 ];
 
 impl CssEnvironment {

servo/components/style/gecko/media_queries.rs

@@ -199,6 +199,18 @@ impl Device {
         unsafe { bindings::Gecko_GetBaseSize(self.document(), language.as_ptr(), generic) }
     }
 
+    /// Gets the size of the scrollbar in CSS pixels.
+    pub fn scrollbar_inline_size(&self) -> Length {
+        let pc = match self.pres_context() {
+            Some(pc) => pc,
+            // XXX: we could have a more reasonable default perhaps.
+            None => return Length::new(0.0),
+        };
+        Length::new(unsafe {
+            bindings::Gecko_GetScrollbarInlineSize(pc)
+        })
+    }
+
     /// Queries font metrics
     pub fn query_font_metrics(
         &self,
@@ -541,8 +553,11 @@ impl Device {
     }
 
     /// Return whether the document is a chrome document.
+    ///
+    /// This check is consistent with how we enable chrome rules for chrome:// and resource://
+    /// stylesheets (and thus chrome:// documents).
     #[inline]
     pub fn is_chrome_document(&self) -> bool {
-        self.pref_sheet_prefs().mIsChrome
+        self.document().mDocURISchemeIsChrome()
     }
 }

widget/ScrollbarDrawing.cpp

@@ -24,16 +24,12 @@ using mozilla::RelativeLuminanceUtils;
 /* static */
 auto ScrollbarDrawing::GetDPIRatioForScrollbarPart(const nsPresContext* aPc)
     -> DPIRatio {
-  auto ratio = [&] {
-    if (auto* rootPc = aPc->GetRootPresContext()) {
-      if (nsCOMPtr<nsIWidget> widget = rootPc->GetRootWidget()) {
-        return widget->GetDefaultScale();
-      }
-    }
-    return DPIRatio(
-        float(AppUnitsPerCSSPixel()) /
-        float(aPc->DeviceContext()->AppUnitsPerDevPixelAtUnitFullZoom()));
-  }();
+  DPIRatio ratio(
+      float(AppUnitsPerCSSPixel()) /
+      float(aPc->DeviceContext()->AppUnitsPerDevPixelAtUnitFullZoom()));
+  if (aPc->IsPrintPreview()) {
+    ratio.scale *= aPc->GetPrintPreviewScaleForSequenceFrameOrScrollbars();
+  }
   if (mKind == Kind::Cocoa) {
     return DPIRatio(ratio.scale >= 2.0f ? 2.0f : 1.0f);
   }

xpcom/ds/StaticAtoms.py

@@ -1117,6 +1117,7 @@ STATIC_ATOMS = [
     Atom("scrollbarbutton", "scrollbarbutton"),
     Atom("scrollbarDownBottom", "scrollbar-down-bottom"),
     Atom("scrollbarDownTop", "scrollbar-down-top"),
+    Atom("scrollbarInlineSize", "scrollbar-inline-size"),
     Atom("scrollbarUpBottom", "scrollbar-up-bottom"),
     Atom("scrollbarUpTop", "scrollbar-up-top"),
     Atom("scrollbox", "scrollbox"),