Final tweaks for "Abseil is allowed in first-party code":

* Improve comments
* Make DEPS block "third_party/abseil-cpp" and "absl" both
* Update formal "allowed on" date to date this lands
* Remove visibility restrictions

Bug: 1096380
Change-Id: I10f615cfd02c397a988f73e4548cdf2309b44b81
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2327638
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793629}

DEPS

@@ -4097,8 +4097,11 @@ include_rules = [
   '+third_party/icu/source/i18n/unicode',
   '+url',
 
-  # Chromium cannot directly depend on Abseil.
+  # Abseil features must be allowlisted explicitly for now. See
+  # //styleguide/c++/c++11.html. Allowed features' headers will be listed
+  # explicitly here.
   '-absl',
+  '-third_party/abseil-cpp',
 ]
 
 

build_overrides/build.gni

@@ -27,8 +27,7 @@ declare_args() {
   # TODO(crbug/1006769): Switch to perfetto's client library.
   use_perfetto_client_library = false
 
-  # If true, it assumes that //third_party/abseil-cpp is an available
-  # dependency for googletest.
+  # Allows googletest to pretty-print various absl types.
   gtest_enable_absl_printers = false
 }
 

styleguide/c++/c++11.html

@@ -51,7 +51,7 @@ The current status of existing standards and Abseil features is:
 <li><b>C++14:</b> <i>Default allowed; see banned features below</i></li>
 <li><b>C++17:</b> <i>Not yet supported in Chromium, unlikely before mid-2021; <a href="http://crbug.com/752720">tracking bug</a></i></li>
 <li><b>C++20:</b> <i>Not yet standardized</i></li>
-<li><b>Abseil:</b> Initially supported July 27, 2020; see allowed/banned/TBD features below</li>
+<li><b>Abseil:</b> Initially supported July 31, 2020; see allowed/banned/TBD features below</li>
 </ul></p>
 
 

third_party/abseil-cpp/BUILD.gn

@@ -53,14 +53,6 @@ component("absl") {
       }
     }
   }
-
-  # Usage of Abseil in Chromium is guarded by an explicit opt-in list, before
-  # adding projects to this list please reach out to cxx@chromium.org and CC:
-  # - https://cs.chromium.org/chromium/src/third_party/abseil-cpp/OWNERS
-  #
-  # More information can be found at:
-  # https://docs.google.com/document/d/1DgS1-A3rzboTLjpf4m1sqkJgWjnY_Ru2dokk1X1vBDU
-  visibility = absl_visibility
 }
 
 group("absl_component_deps") {
@@ -69,8 +61,8 @@ group("absl_component_deps") {
     "//third_party/abseil-cpp/absl/base",
     "//third_party/abseil-cpp/absl/base:config",
     "//third_party/abseil-cpp/absl/base:core_headers",
-    "//third_party/abseil-cpp/absl/container:flat_hash_map",
     "//third_party/abseil-cpp/absl/container:fixed_array",
+    "//third_party/abseil-cpp/absl/container:flat_hash_map",
     "//third_party/abseil-cpp/absl/container:flat_hash_set",
     "//third_party/abseil-cpp/absl/container:inlined_vector",
     "//third_party/abseil-cpp/absl/debugging:failure_signal_handler",

third_party/abseil-cpp/README.chromium

@@ -9,8 +9,10 @@ Security Critical: yes
 
 Description:
 This directory contains the source code of Abseil for C++. This can be used by
-Chromium's dependencies, but shouldn't be used by Chromium itself.
-See: https://goo.gl/TgnJb8.
+Chromium, subject to the guidance at https://chromium-cpp.appspot.com/; it can
+be used without restriction by Chromium's dependencies, except that objects
+compiled into Chromium itself cannot use anything relying on
+absl::base_internal::FastTypeId (see https://crbug.com/1096380).
 
 How to update Abseil:
 

third_party/abseil-cpp/absl.gni

@@ -7,9 +7,6 @@
 # This template will correctly set "configs" and "public_configs" in order
 # to correctly compile abseil in Chromium.
 #
-# Targets that set visibility should set it to something more restrictive than
-# `absl_visibility` (defined below).
-#
 # Usage:
 # Most of the times its usage will be similar to the example below but all
 # the arguments avilable in source_set are also available for absl_source_set.
@@ -22,35 +19,6 @@
 
 import("//build_overrides/build.gni")
 
-# Usage of Abseil in Chromium is guarded by an explicit opt-in list, before
-# adding projects to this list please reach out to cxx@chromium.org and CC:
-# - https://cs.chromium.org/chromium/src/third_party/abseil-cpp/OWNERS
-#
-# More information can be found at:
-# https://docs.google.com/document/d/1DgS1-A3rzboTLjpf4m1sqkJgWjnY_Ru2dokk1X1vBDU
-declare_args() {
-  # Additional targets that can depend on absl.
-  additional_absl_clients = []
-}
-
-_chromium_absl_clients = [
-  "//chrome/services/sharing/nearby/platform_v2/*",
-  "//third_party/blink/renderer/modules/peerconnection",
-  "//third_party/blink/renderer/platform",
-  "//third_party/googletest:gtest",
-  "//third_party/openscreen/src/third_party/abseil/*",
-  "//third_party/private_membership/*",
-  "//third_party/shell-encryption/*",
-  "//third_party/webrtc/*",
-  "//third_party/nearby/*",
-]
-
-# When adding a new package to `absl_visibility`, please check that all the
-# Abseil dependencies that are required are listed in the dependencies of
-# //third_party/abseil-cpp:absl. If not, please add them and run:
-# //third_party/abseil-cpp/generate_def_file.py.
-absl_visibility = _chromium_absl_clients + additional_absl_clients
-
 template("absl_source_set") {
   source_set(target_name) {
     forward_variables_from(invoker, "*")
@@ -75,8 +43,14 @@ template("absl_source_set") {
     public_configs += [ "//third_party/abseil-cpp:absl_include_config" ]
 
     if (!defined(visibility)) {
+      # Within Chromium builds, restrict direct visibility of Abseil sources, so
+      # users must depend on //third_party/abseil-cpp:absl. This prevents use of
+      # banned targets like absl/types:any. A few targets require exceptions.
+      # TODO(crbug.com/1096380): Consider replacing build_with_chromium with
+      # is_component_build for a narrower, more accurate condition.
       if (build_with_chromium) {
         visibility = [
+          # Abseil itself.
           "//third_party/abseil-cpp/*",
 
           # WebRTC binary to run PSNR and SSIM video quality analysis. It
@@ -85,7 +59,7 @@ template("absl_source_set") {
           # component because it uses absl/flags.
           "//third_party/webrtc/rtc_tools:frame_analyzer",
 
-          # WebRTC binaries used by //:chromium_builder_asan, they both
+          # WebRTC binaries used by //:chromium_builder_asan. They both
           # statically link absl (because they depend on absl/flags) and are
           # used by Chromium only when is_component_build=false.
           "//third_party/webrtc/rtc_tools:rtp_generator",