[base] Add conversion functions for absl::string_view

This change adds conversion functions between base::StringPiece and
absl::string_view. This is to aid the adoption of other Abseil features,
that make use of the otherwise banned absl::string_view in their public
API.

Fixed: 1113880
Change-Id: Ib038a4e71fb0ce6470304e4151474a5d92809d22
Bug: 1113880
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2345306
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796501}

base/BUILD.gn

@@ -523,6 +523,8 @@ component("base") {
     "sequenced_task_runner_helpers.h",
     "single_thread_task_runner.h",
     "stl_util.h",
+    "strings/abseil_string_conversions.cc",
+    "strings/abseil_string_conversions.h",
     "strings/char_traits.h",
     "strings/escape.cc",
     "strings/escape.h",
@@ -1279,6 +1281,7 @@ component("base") {
     ":synchronization_buildflags",
     ":tracing_buildflags",
     "//base/numerics:base_numerics",
+    "//third_party/abseil-cpp:absl",
   ]
 
   # Needed for <atomic> if using newer C++ library than sysroot, except if
@@ -2785,6 +2788,7 @@ test("base_unittests") {
     "sequence_token_unittest.cc",
     "sequenced_task_runner_unittest.cc",
     "stl_util_unittest.cc",
+    "strings/abseil_string_conversions_unittest.cc",
     "strings/char_traits_unittest.cc",
     "strings/escape_unittest.cc",
     "strings/no_trigraphs_unittest.cc",

base/strings/DEPS

+specific_include_rules = {
+  # absl::string_view is generally banned in Chromium. Including it is only
+  # allowed from abseil_string_conversions* to provide appropriate conversion
+  # functions from and to StringPiece at third party API boundaries.
+  "abseil_string_conversions(\.h|\.cc|_unittest.cc)": [
+    "+third_party/abseil-cpp/absl/strings/string_view.h",
+  ],
+}

base/strings/abseil_string_conversions.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/strings/abseil_string_conversions.h"
+
+#include <algorithm>
+#include <vector>
+
+#include "base/containers/span.h"
+#include "base/strings/string_piece.h"
+#include "third_party/abseil-cpp/absl/strings/string_view.h"
+
+namespace base {
+
+std::vector<absl::string_view> StringPiecesToStringViews(
+    span<const StringPiece> pieces) {
+  std::vector<absl::string_view> views(pieces.size());
+  std::transform(pieces.begin(), pieces.end(), views.begin(),
+                 &StringPieceToStringView);
+  return views;
+}
+
+std::vector<StringPiece> StringViewsToStringPieces(
+    span<const absl::string_view> views) {
+  std::vector<StringPiece> pieces(views.size());
+  std::transform(views.begin(), views.end(), pieces.begin(),
+                 &StringViewToStringPiece);
+  return pieces;
+}
+
+}  // namespace base

base/strings/abseil_string_conversions.h

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_STRINGS_ABSEIL_STRING_CONVERSIONS_H_
+#define BASE_STRINGS_ABSEIL_STRING_CONVERSIONS_H_
+
+#include <vector>
+
+#include "base/base_export.h"
+#include "base/containers/span.h"
+#include "base/strings/string_piece.h"
+#include "third_party/abseil-cpp/absl/strings/string_view.h"
+
+namespace base {
+
+// Converts `piece` to a string view, pointing to the same piece of memory.
+constexpr absl::string_view StringPieceToStringView(StringPiece piece) {
+  return {piece.data(), piece.size()};
+}
+
+// Converts `view` to a string piece, pointing to the same piece of memory.
+constexpr StringPiece StringViewToStringPiece(absl::string_view view) {
+  return {view.data(), view.size()};
+}
+
+// Converts `pieces` to string views, pointing to the same piece of memory.
+BASE_EXPORT std::vector<absl::string_view> StringPiecesToStringViews(
+    span<const StringPiece> pieces);
+
+// Converts `views` to string pieces, pointing to the same piece of memory.
+BASE_EXPORT std::vector<StringPiece> StringViewsToStringPieces(
+    span<const absl::string_view> views);
+
+}  // namespace base
+
+#endif  // BASE_STRINGS_ABSEIL_STRING_CONVERSIONS_H_

base/strings/abseil_string_conversions_unittest.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/strings/abseil_string_conversions.h"
+
+#include <vector>
+
+#include "base/containers/span.h"
+#include "base/strings/string_piece.h"
+#include "base/strings/string_piece_forward.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/abseil-cpp/absl/strings/string_view.h"
+
+namespace base {
+
+namespace {
+using string_view = absl::string_view;
+}  // namespace
+
+TEST(AbseilStringConversionsTest, StringPieceToStringView) {
+  static constexpr StringPiece kPiece = "foo";
+  static constexpr string_view kView = StringPieceToStringView(kPiece);
+  static_assert(kPiece.data() == kView.data(), "");
+  static_assert(kPiece.size() == kView.size(), "");
+}
+
+TEST(AbseilStringConversionsTest, StringViewToStringPiece) {
+  static constexpr string_view kView = "bar";
+  static constexpr StringPiece kPiece = StringViewToStringPiece(kView);
+  static_assert(kView.data() == kPiece.data(), "");
+  static_assert(kView.size() == kPiece.size(), "");
+}
+
+TEST(AbseilStringConversionsTest, StringPiecesToStringViews) {
+  static constexpr StringPiece kFoo = "foo";
+  static constexpr StringPiece kBar = "bar";
+  static constexpr StringPiece kBaz = "baz";
+
+  const std::vector<StringPiece> kPieces = {kFoo, kBar, kBaz};
+  const std::vector<string_view> kViews = StringPiecesToStringViews(kPieces);
+
+  ASSERT_EQ(kViews.size(), 3u);
+  EXPECT_EQ(kViews[0].data(), kFoo);
+  EXPECT_EQ(kViews[0].size(), 3u);
+  EXPECT_EQ(kViews[1].data(), kBar);
+  EXPECT_EQ(kViews[1].size(), 3u);
+  EXPECT_EQ(kViews[2].data(), kBaz);
+  EXPECT_EQ(kViews[2].size(), 3u);
+}
+
+TEST(AbseilStringConversionsTest, StringViewsToStringPieces) {
+  static constexpr string_view kFoo = "foo";
+  static constexpr string_view kBar = "bar";
+  static constexpr string_view kBaz = "baz";
+
+  const std::vector<string_view> kViews = {kFoo, kBar, kBaz};
+  const std::vector<StringPiece> kPieces = StringViewsToStringPieces(kViews);
+
+  ASSERT_EQ(kPieces.size(), 3u);
+  EXPECT_EQ(kPieces[0].data(), kFoo);
+  EXPECT_EQ(kPieces[0].size(), 3u);
+  EXPECT_EQ(kPieces[1].data(), kBar);
+  EXPECT_EQ(kPieces[1].size(), 3u);
+  EXPECT_EQ(kPieces[2].data(), kBaz);
+  EXPECT_EQ(kPieces[2].size(), 3u);
+}
+
+}  // namespace base

third_party/abseil-cpp/BUILD.gn

@@ -80,6 +80,17 @@ group("absl_component_deps") {
     "//third_party/abseil-cpp/absl/types:span",
     "//third_party/abseil-cpp/absl/types:variant",
   ]
+
+  # The following dependencies currently don't build with NaCl.
+  # TODO(https://crbug.com/1114625): Fix build errors and remove this section.
+  if (is_nacl) {
+    public_deps -= [
+      "//third_party/abseil-cpp/absl/container:flat_hash_map",
+      "//third_party/abseil-cpp/absl/container:flat_hash_set",
+      "//third_party/abseil-cpp/absl/debugging:failure_signal_handler",
+    ]
+  }
+
   visibility = [ ":absl" ]
 }