C++ port: add C++ equivalent of FSTDocumentKey. (firebase#762)

Also move kDocumentKeyPath to the only point of usage - make it a static
member variable of FieldPath.

Author: var-const

Firestore/Example/Firestore.xcodeproj/project.pbxproj

@@ -150,6 +150,7 @@
 		ABE6637A201FA81900ED349A /* database_id_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB71064B201FA60300344F18 /* database_id_test.cc */; };
 		ABF6506C201131F8005F2C74 /* timestamp_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = ABF6506B201131F8005F2C74 /* timestamp_test.cc */; };
 		AFE6114F0D4DAECBA7B7C089 /* Pods_Firestore_IntegrationTests.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = B2FA635DF5D116A67A7441CD /* Pods_Firestore_IntegrationTests.framework */; };
+		B6152AD7202A53CB000E5744 /* document_key_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = B6152AD5202A5385000E5744 /* document_key_test.cc */; };
 		B686F2AF2023DDEE0028D6BE /* field_path_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = B686F2AD2023DDB20028D6BE /* field_path_test.cc */; };
 		B686F2B22025000D0028D6BE /* resource_path_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = B686F2B02024FFD70028D6BE /* resource_path_test.cc */; };
 		C4E749275AD0FBDF9F4716A8 /* Pods_SwiftBuildTest.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 32AD40BF6B0E849B07FFD05E /* Pods_SwiftBuildTest.framework */; };
@@ -352,6 +353,7 @@
 		ABC1D7E22023CDC500BA84F0 /* firebase_credentials_provider_test.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = firebase_credentials_provider_test.mm; sourceTree = "<group>"; };
 		ABF6506B201131F8005F2C74 /* timestamp_test.cc */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = timestamp_test.cc; sourceTree = "<group>"; };
 		B2FA635DF5D116A67A7441CD /* Pods_Firestore_IntegrationTests.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Pods_Firestore_IntegrationTests.framework; sourceTree = BUILT_PRODUCTS_DIR; };
+		B6152AD5202A5385000E5744 /* document_key_test.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = document_key_test.cc; sourceTree = "<group>"; };
 		B686F2AD2023DDB20028D6BE /* field_path_test.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = field_path_test.cc; sourceTree = "<group>"; };
 		B686F2B02024FFD70028D6BE /* resource_path_test.cc */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = resource_path_test.cc; sourceTree = "<group>"; };
 		CE00BABB5A3AAB44A4C209E2 /* Pods-Firestore_Tests.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-Firestore_Tests.debug.xcconfig"; path = "Pods/Target Support Files/Pods-Firestore_Tests/Pods-Firestore_Tests.debug.xcconfig"; sourceTree = "<group>"; };
@@ -582,6 +584,7 @@
 		AB356EF5200E9D1A0089B766 /* model */ = {
 			isa = PBXGroup;
 			children = (
+				B6152AD5202A5385000E5744 /* document_key_test.cc */,
 				B686F2B02024FFD70028D6BE /* resource_path_test.cc */,
 				B686F2AD2023DDB20028D6BE /* field_path_test.cc */,
 				AB71064B201FA60300344F18 /* database_id_test.cc */,
@@ -1320,6 +1323,7 @@
 				5492E0C82021557E00B64F25 /* FSTDatastoreTests.mm in Sources */,
 				5492E065202154B900B64F25 /* FSTViewTests.mm in Sources */,
 				5492E03C2021401F00B64F25 /* XCTestCase+Await.mm in Sources */,
+				B6152AD7202A53CB000E5744 /* document_key_test.cc in Sources */,
 				54764FAF1FAA21B90085E60A /* FSTGoogleTestTests.mm in Sources */,
 				AB380D04201BC6E400D97691 /* ordered_code_test.cc in Sources */,
 				5492E03F2021401F00B64F25 /* FSTHelpers.mm in Sources */,

Firestore/core/src/firebase/firestore/model/CMakeLists.txt

@@ -18,6 +18,8 @@ cc_library(
     base_path.h
     database_id.cc
     database_id.h
+    document_key.cc
+    document_key.h
     field_path.cc
     field_path.h
     field_value.cc

Firestore/core/src/firebase/firestore/model/document_key.cc

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/model/document_key.h"
+
+#include <utility>
+
+#include "Firestore/core/src/firebase/firestore/util/firebase_assert.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+namespace {
+
+void AssertValidPath(const ResourcePath& path) {
+  FIREBASE_ASSERT_MESSAGE(DocumentKey::IsDocumentKey(path),
+                          "invalid document key path: %s",
+                          path.CanonicalString().c_str());
+}
+
+}  // namespace
+
+DocumentKey::DocumentKey(const ResourcePath& path)
+    : path_{std::make_shared<ResourcePath>(path)} {
+  AssertValidPath(*path_);
+}
+
+DocumentKey::DocumentKey(ResourcePath&& path)
+    : path_{std::make_shared<ResourcePath>(std::move(path))} {
+  AssertValidPath(*path_);
+}
+
+const DocumentKey& DocumentKey::Empty() {
+  static const DocumentKey empty;
+  return empty;
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase

Firestore/core/src/firebase/firestore/model/document_key.h

@@ -0,0 +1,101 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DOCUMENT_KEY_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DOCUMENT_KEY_H_
+
+#include <initializer_list>
+#include <memory>
+#include <string>
+
+#include "Firestore/core/src/firebase/firestore/model/resource_path.h"
+#include "absl/strings/string_view.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+/**
+ * DocumentKey represents the location of a document in the Firestore database.
+ */
+class DocumentKey {
+ public:
+  /** Creates a "blank" document key not associated with any document. */
+  DocumentKey() : path_{std::make_shared<ResourcePath>()} {
+  }
+
+  /** Creates a new document key containing a copy of the given path. */
+  explicit DocumentKey(const ResourcePath& path);
+
+  /** Creates a new document key, taking ownership of the given path. */
+  explicit DocumentKey(ResourcePath&& path);
+
+  /**
+   * Creates and returns a new document key using '/' to split the string into
+   * segments.
+   */
+  static DocumentKey FromPathString(const absl::string_view path) {
+    return DocumentKey{ResourcePath::FromString(path)};
+  }
+
+  /** Creates and returns a new document key with the given segments. */
+  static DocumentKey FromSegments(std::initializer_list<std::string> list) {
+    return DocumentKey{ResourcePath{list}};
+  }
+
+  /** Returns a shared instance of an empty document key. */
+  static const DocumentKey& Empty();
+
+  /** Returns true iff the given path is a path to a document. */
+  static bool IsDocumentKey(const ResourcePath& path) {
+    return path.size() % 2 == 0;
+  }
+
+  /** The path to the document. */
+  const ResourcePath& path() const {
+    return path_ ? *path_ : Empty().path();
+  }
+
+ private:
+  // This is an optimization to make passing DocumentKey around cheaper (it's
+  // copied often).
+  std::shared_ptr<const ResourcePath> path_;
+};
+
+inline bool operator==(const DocumentKey& lhs, const DocumentKey& rhs) {
+  return lhs.path() == rhs.path();
+}
+inline bool operator!=(const DocumentKey& lhs, const DocumentKey& rhs) {
+  return lhs.path() != rhs.path();
+}
+inline bool operator<(const DocumentKey& lhs, const DocumentKey& rhs) {
+  return lhs.path() < rhs.path();
+}
+inline bool operator<=(const DocumentKey& lhs, const DocumentKey& rhs) {
+  return lhs.path() <= rhs.path();
+}
+inline bool operator>(const DocumentKey& lhs, const DocumentKey& rhs) {
+  return lhs.path() > rhs.path();
+}
+inline bool operator>=(const DocumentKey& lhs, const DocumentKey& rhs) {
+  return lhs.path() >= rhs.path();
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DOCUMENT_KEY_H_

Firestore/core/src/firebase/firestore/model/field_path.cc

@@ -30,9 +30,6 @@ namespace model {
 
 namespace {
 
-// TODO(varconst): move to C++ equivalent of FSTDocumentKey.{h,cc}
-const char* const kDocumentKeyPath = "__name__";
-
 /**
  * True if the string could be used as a segment in a field path without
  * escaping. Valid identifies follow the regex [a-zA-Z_][a-zA-Z0-9_]*
@@ -146,12 +143,12 @@ const FieldPath& FieldPath::EmptyPath() {
 }
 
 const FieldPath& FieldPath::KeyFieldPath() {
-  static const FieldPath key_field_path{kDocumentKeyPath};
+  static const FieldPath key_field_path{FieldPath::kDocumentKeyPath};
   return key_field_path;
 }
 
 bool FieldPath::IsKeyFieldPath() const {
-  return size() == 1 && first_segment() == kDocumentKeyPath;
+  return size() == 1 && first_segment() == FieldPath::kDocumentKeyPath;
 }
 
 std::string FieldPath::CanonicalString() const {

Firestore/core/src/firebase/firestore/model/field_path.h

@@ -35,6 +35,9 @@ namespace model {
  */
 class FieldPath : public impl::BasePath<FieldPath> {
  public:
+  /** The field path string that represents the document's key. */
+  static constexpr const char* kDocumentKeyPath = "__name__";
+
   // Note: Xcode 8.2 requires explicit specification of the constructor.
   FieldPath() : impl::BasePath<FieldPath>() {
   }

Firestore/core/src/firebase/firestore/model/resource_path.cc

@@ -28,7 +28,7 @@ namespace firebase {
 namespace firestore {
 namespace model {
 
-ResourcePath ResourcePath::Parse(const absl::string_view path) {
+ResourcePath ResourcePath::FromString(const absl::string_view path) {
   // NOTE: The client is ignorant of any path segments containing escape
   // sequences (e.g. __id123__) and just passes them through raw (they exist
   // for legacy reasons and should not be used frequently).

Firestore/core/src/firebase/firestore/model/resource_path.h

@@ -45,7 +45,7 @@ class ResourcePath : public impl::BasePath<ResourcePath> {
    * Creates and returns a new path from the given resource-path string, where
    * the path segments are separated by a slash "/".
    */
-  static ResourcePath Parse(absl::string_view path);
+  static ResourcePath FromString(absl::string_view path);
 
   /** Returns a standardized string representation of this path. */
   std::string CanonicalString() const;

Firestore/core/test/firebase/firestore/model/CMakeLists.txt

@@ -16,6 +16,7 @@ cc_test(
   firebase_firestore_model_test
   SOURCES
     database_id_test.cc
+    document_key_test.cc
     field_path_test.cc
     field_value_test.cc
     snapshot_version_test.cc