1 files changed, 143 insertions, 0 deletions
diff --git a/layout/style/ShadowParts.cpp b/layout/style/ShadowParts.cpp
new file mode 100644
index 0000000000..43a1a54d8c
--- /dev/null
+++ b/layout/style/ShadowParts.cpp
@@ -0,0 +1,143 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#include "ShadowParts.h"
+#include "nsContentUtils.h"
+#include "nsString.h"
+
+namespace mozilla {
+
+static bool IsSpace(char16_t aChar) {
+  return nsContentUtils::IsHTMLWhitespace(aChar);
+};
+
+using SingleMapping = std::pair<RefPtr<nsAtom>, RefPtr<nsAtom>>;
+
+// https://drafts.csswg.org/css-shadow-parts/#parsing-mapping
+//
+// Returns null on both tokens to signal an error.
+static SingleMapping ParseSingleMapping(const nsAString& aString) {
+  const char16_t* c = aString.BeginReading();
+  const char16_t* end = aString.EndReading();
+
+  const auto CollectASequenceOfSpaces = [&c, end]() {
+    while (c != end && IsSpace(*c)) {
+      ++c;
+    }
+  };
+
+  const auto CollectToken = [&c, end]() -> RefPtr<nsAtom> {
+    const char16_t* t = c;
+    while (c != end && !IsSpace(*c) && *c != ':') {
+      ++c;
+    }
+    if (c == t) {
+      return nullptr;
+    }
+    return NS_AtomizeMainThread(Substring(t, c));
+  };
+
+  // Steps 1 and 2 are variable declarations.
+  //
+  // 3. Collect a sequence of code points that are space characters.
+  CollectASequenceOfSpaces();
+
+  // 4. Collect a sequence of code points that are not space characters or
+  // U+003A COLON characters, and call the result first token.
+  RefPtr<nsAtom> firstToken = CollectToken();
+
+  // 5. If first token is empty then return error.
+  if (!firstToken) {
+    return {nullptr, nullptr};
+  }
+
+  // 6. Collect a sequence of code points that are space characters.
+  CollectASequenceOfSpaces();
+
+  // 7. If the end of the input has been reached, return the pair first
+  // token/first token.
+  if (c == end) {
+    return {firstToken, firstToken};
+  }
+
+  // 8. If character at position is not a U+003A COLON character, return error.
+  if (*c != ':') {
+    return {nullptr, nullptr};
+  }
+
+  // 9. Consume the U+003A COLON character.
+  ++c;
+
+  // 10. Collect a sequence of code points that are space characters.
+  CollectASequenceOfSpaces();
+
+  // 11. Collect a sequence of code points that are not space characters or
+  // U+003A COLON characters. and let second token be the result.
+  RefPtr<nsAtom> secondToken = CollectToken();
+
+  // 12. If second token is empty then return error.
+  if (!secondToken) {
+    return {nullptr, nullptr};
+  }
+
+  // 13. Collect a sequence of code points that are space characters.
+  CollectASequenceOfSpaces();
+
+  // 14. If position is not past the end of input then return error.
+  if (c != end) {
+    return {nullptr, nullptr};
+  }
+
+  // 15. Return the pair first token/second token.
+  return {std::move(firstToken), std::move(secondToken)};
+}
+
+// https://drafts.csswg.org/css-shadow-parts/#parsing-mapping-list
+ShadowParts ShadowParts::Parse(const nsAString& aString) {
+  ShadowParts parts;
+
+  for (const auto& substring : aString.Split(',')) {
+    auto mapping = ParseSingleMapping(substring);
+    if (!mapping.first) {
+      MOZ_ASSERT(!mapping.second);
+      continue;
+    }
+    nsAtom* second = mapping.second.get();
+    parts.mMappings.LookupForAdd(mapping.first)
+        .OrInsert([] { return new PartList(); })
+        ->AppendElement(std::move(mapping.second));
+    parts.mReverseMappings.GetOrInsert(second) = std::move(mapping.first);
+  }
+
+  return parts;
+}
+
+#ifdef DEBUG
+void ShadowParts::Dump() const {
+  if (mMappings.IsEmpty()) {
+    printf("  (empty)\n");
+    return;
+  }
+  for (auto& entry : mMappings) {
+    nsAutoCString key;
+    entry.GetKey()->ToUTF8String(key);
+    printf("  %s: ", key.get());
+
+    bool first = true;
+    for (nsAtom* part : *entry.GetData()) {
+      if (!first) {
+        printf(", ");
+      }
+      first = false;
+      nsAutoCString value;
+      part->ToUTF8String(value);
+      printf("%s", value.get());
+    }
+    printf("\n");
+  }
+}
+#endif
+}  // namespace mozilla