1 files changed, 161 insertions, 0 deletions
diff --git a/layout/style/StyleContextSource.h b/layout/style/StyleContextSource.h
new file mode 100644
index 000000000..7c6a00730
--- /dev/null
+++ b/layout/style/StyleContextSource.h
@@ -0,0 +1,161 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StyleContextSource_h
+#define mozilla_StyleContextSource_h
+
+#include "mozilla/ServoBindingTypes.h"
+#include "nsRuleNode.h"
+
+namespace mozilla {
+
+// Tagged union between Gecko Rule Nodes and Servo Computed Values.
+//
+// The rule node is the node in the lexicographic tree of rule nodes
+// (the "rule tree") that indicates which style rules are used to
+// compute the style data, and in what cascading order.  The least
+// specific rule matched is the one whose rule node is a child of the
+// root of the rule tree, and the most specific rule matched is the
+// |mRule| member of the rule node.
+//
+// In the Servo case, we hold an atomically-refcounted handle to a
+// Servo ComputedValues struct, which is more or less the Servo equivalent
+// of an nsStyleContext.
+
+// Underlying pointer without any strong ownership semantics.
+struct NonOwningStyleContextSource
+{
+  MOZ_IMPLICIT NonOwningStyleContextSource(nsRuleNode* aRuleNode)
+    : mBits(reinterpret_cast<uintptr_t>(aRuleNode)) {}
+  explicit NonOwningStyleContextSource(const ServoComputedValues* aComputedValues)
+    : mBits(reinterpret_cast<uintptr_t>(aComputedValues) | 1) {}
+
+  bool operator==(const NonOwningStyleContextSource& aOther) const {
+    MOZ_ASSERT(IsServoComputedValues() == aOther.IsServoComputedValues(),
+               "Comparing Servo to Gecko - probably a bug");
+    return mBits == aOther.mBits;
+  }
+  bool operator!=(const NonOwningStyleContextSource& aOther) const {
+    return !(*this == aOther);
+  }
+
+  // We intentionally avoid exposing IsGeckoRuleNode() here, because that would
+  // encourage callers to do:
+  //
+  // if (source.IsGeckoRuleNode()) {
+  //   // Code that we would run unconditionally if it weren't for Servo.
+  // }
+  //
+  // We want these branches to compile away when MOZ_STYLO is disabled, but that
+  // won't happen if there's an implicit null-check.
+  bool IsNull() const { return !mBits; }
+  bool IsGeckoRuleNodeOrNull() const { return !IsServoComputedValues(); }
+  bool IsServoComputedValues() const {
+#ifdef MOZ_STYLO
+    return mBits & 1;
+#else
+    return false;
+#endif
+  }
+
+  nsRuleNode* AsGeckoRuleNode() const {
+    MOZ_ASSERT(IsGeckoRuleNodeOrNull() && !IsNull());
+    return reinterpret_cast<nsRuleNode*>(mBits);
+  }
+
+  const ServoComputedValues* AsServoComputedValues() const {
+    MOZ_ASSERT(IsServoComputedValues());
+    return reinterpret_cast<ServoComputedValues*>(mBits & ~1);
+  }
+
+  bool MatchesNoRules() const {
+    if (IsGeckoRuleNodeOrNull()) {
+      return AsGeckoRuleNode()->IsRoot();
+    }
+
+    // Just assume a Servo-backed StyleContextSource always matches some rules.
+    //
+    // MatchesNoRules is used to ensure style contexts that match no rules
+    // go into a separate mEmptyChild list on their parent.  This is only used
+    // as an optimization so that calling FindChildWithRules for style context
+    // sharing is faster for text nodes (which match no rules, and are common).
+    // Since Servo will handle sharing for us, there's no need to split children
+    // into two lists.
+    return false;
+  }
+
+private:
+  uintptr_t mBits;
+};
+
+// Higher-level struct that owns a strong reference to the source. The source
+// is never null.
+struct OwningStyleContextSource
+{
+  explicit OwningStyleContextSource(already_AddRefed<nsRuleNode> aRuleNode)
+    : mRaw(aRuleNode.take())
+  {
+    MOZ_COUNT_CTOR(OwningStyleContextSource);
+    MOZ_ASSERT(!mRaw.IsNull());
+  };
+
+  explicit OwningStyleContextSource(already_AddRefed<ServoComputedValues> aComputedValues)
+    : mRaw(aComputedValues.take())
+  {
+    MOZ_COUNT_CTOR(OwningStyleContextSource);
+    MOZ_ASSERT(!mRaw.IsNull());
+  }
+
+  OwningStyleContextSource(OwningStyleContextSource&& aOther)
+    : mRaw(aOther.mRaw)
+  {
+    MOZ_COUNT_CTOR(OwningStyleContextSource);
+    aOther.mRaw = nullptr;
+  }
+
+  OwningStyleContextSource& operator=(OwningStyleContextSource&) = delete;
+  OwningStyleContextSource(OwningStyleContextSource&) = delete;
+
+  ~OwningStyleContextSource() {
+    MOZ_COUNT_DTOR(OwningStyleContextSource);
+    if (mRaw.IsNull()) {
+      // We must have invoked the move constructor.
+    } else if (IsGeckoRuleNode()) {
+      RefPtr<nsRuleNode> releaseme = dont_AddRef(AsGeckoRuleNode());
+    } else {
+      MOZ_ASSERT(IsServoComputedValues());
+      RefPtr<ServoComputedValues> releaseme =
+        dont_AddRef(AsServoComputedValues());
+    }
+  }
+
+  bool operator==(const OwningStyleContextSource& aOther) const {
+    return mRaw == aOther.mRaw;
+  }
+  bool operator!=(const OwningStyleContextSource& aOther) const {
+    return !(*this == aOther);
+  }
+  bool IsNull() const { return mRaw.IsNull(); }
+  bool IsGeckoRuleNode() const {
+    MOZ_ASSERT(!mRaw.IsNull());
+    return mRaw.IsGeckoRuleNodeOrNull();
+  }
+  bool IsServoComputedValues() const { return mRaw.IsServoComputedValues(); }
+
+  NonOwningStyleContextSource AsRaw() const { return mRaw; }
+  nsRuleNode* AsGeckoRuleNode() const { return mRaw.AsGeckoRuleNode(); }
+  ServoComputedValues* AsServoComputedValues() const {
+    return const_cast<ServoComputedValues*>(mRaw.AsServoComputedValues());
+  }
+
+  bool MatchesNoRules() const { return mRaw.MatchesNoRules(); }
+
+private:
+  NonOwningStyleContextSource mRaw;
+};
+
+} // namespace mozilla
+
+#endif // mozilla_StyleContextSource_h