[Fuchsia] Remove the use of //build/ in fuchsia (#51072)

### Motivation of the change:

Both dart and flutter are using fairly outdated gn-sdk without properly maintained. Currently @hjfreyer is working on version'ed IDK / SDK libs which requires changes in gn-sdk to use the right version of the libs in fuchsia/sdk/obj/{arch}-api-{level} rather than the one in the fuchsia/sdk/arch. But current implementation does not support choosing the right version.

### Blocking issue:

The new gn-sdk (in flutter/tools/fuchsia/gn-sdk) generates multiple BUILD.gn files rather than a large BUILD.gn the previous version created. So most of the build rules need to switch from the old `fidl:{api}` build rule to `fidl/{api}` rule. The same change will happen in the dart/sdk, i.e. http://go/dart-reviews/356924. But since the two repos cannot have one single atomic change, changing either side first will cause flutter to break. E.g. the linkage error caused by duplicated symbols will happen if we change the dart/sdk first, since in flutter, it will still refer to the old build rules in the middle.

### Solutions:

Ideally we can create redirect rules in the current `build/fuchsia` buildroot tree to redirect the old rules into the new one, so we can make the change in the flutter first then dart/sdk. But creating the rules is not trivial and will only be used once.

So an alternative solution is

- pause the dart/sdk -> flutter roll
- submit dart/sdk change (http://go/dart-reviews/356924)
- update this change to manually bring the dart/sdk change, namely the `dart_revision` in the DEPS file and signatures in the ci/licences.
- resume the dart/sdk -> flutter roll.

But it requires this change itself to be reviewed first, and I'd like to know your opinion before moving forward.

See corresponding dart/sdk change at http://go/dart-reviews/356924.

### //build/fuchsia/ from buildroot should be removed after this change.

Bug: [b/40935282](https://issues.chromium.org/issues/40935282?pli=1&authuser=0)

FYI: @hjfreyer 

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: zijiehe-google-com

DEPS

@@ -62,7 +62,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/main/DEPS
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': '70ca2323a702b1326c9c55943186e4e2fc58c3c8',
+  'dart_revision': '406955fe69503eb11fb16a8405534a979f5eef60',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py
@@ -107,6 +107,12 @@ vars = {
   # //flutter/tools/gn.
   'mac_sdk_min': '10.14',
 
+  # Checkout Fuchsia dependencies only on Linux. This is the umbrella flag which
+  # controls the behavior of all fuchsia related flags. I.e. any fuchsia related
+  # logic or condition may not work if this flag is False.
+  # TODO(zijiehe): Make this condition more strict to only download fuchsia
+  # dependencies when necessary: b/40935282
+  'download_fuchsia_deps': 'host_os == "linux"',
   # Downloads the fuchsia SDK as listed in fuchsia_sdk_path var. This variable
   # is currently only used for the Fuchsia LSC process and is not intended for
   # local development.
@@ -261,7 +267,7 @@ vars = {
 
   # The version / instance id of the cipd:chromium/fuchsia/gn-sdk which will be
   # used altogether with fuchsia-sdk to generate gn based build rules.
-  'fuchsia_gn_sdk_version': 'l8zShEOXGGjtLYRulEX5CjT2RemKvUPOT6L-uXy41tMC',
+  'fuchsia_gn_sdk_version': 'RgErspyYHapUO2SpcW-vo2p8yaRUMUrq0eWjRVPfQjoC',
 }
 
 gclient_gn_args_file = 'src/third_party/dart/build/config/gclient_args.gni'
@@ -359,7 +365,7 @@ deps = {
    Var('dart_git') + '/args.git@7dc7fe0430709229ccc87c3eaae729aeffe10c56',
 
   'src/third_party/dart/third_party/pkg/async':
-   Var('dart_git') + '/async.git@1556660ca5159d84bf28239825a25dca58f1fde3',
+   Var('dart_git') + '/async.git@6cdbc41631054870318ae28baea2c62cf2a91945',
 
   'src/third_party/dart/third_party/pkg/bazel_worker':
    Var('dart_git') + '/bazel_worker.git@8619b92baa9959e55b9fc49d2afcd6dda2ec1c10',
@@ -407,7 +413,7 @@ deps = {
    Var('dart_git') + '/html.git@327e37a6a4dd46599737ee982f280d73a8f646f7',
 
   'src/third_party/dart/third_party/pkg/http':
-   Var('dart_git') + '/http.git@8da6e0ea5d67a08f98a14137e0d2bdcb113ae4ba',
+   Var('dart_git') + '/http.git@8d3c64747f9a6d99b29558b6e612dee83db7cdbb',
 
   'src/third_party/dart/third_party/pkg/http_multi_server':
    Var('dart_git') + '/http_multi_server.git@ba9d07f3596b24718ddf45c9e071d40879cca565',
@@ -428,7 +434,7 @@ deps = {
    Var('dart_git') + '/logging.git@7a7bd5e31ddfe23e34d37ded82d6d0cd5706862c',
 
   'src/third_party/dart/third_party/pkg/markdown':
-   Var('dart_git') + '/markdown.git@9c6b1afc3721571af37eaaefe043a6ae7637bd09',
+   Var('dart_git') + '/markdown.git@1ca51664e7b1b7fe789f6be2668c909ce3aea342',
 
   'src/third_party/dart/third_party/pkg/matcher':
    Var('dart_git') + '/matcher.git@d954c8d979579b4b46427b0ea1d9c721117c191e',
@@ -491,7 +497,7 @@ deps = {
    Var('dart_git') + '/term_glyph.git@85a4aa6bf25cd6ecaa5c56a1b259b2d95264a439',
 
   'src/third_party/dart/third_party/pkg/test':
-   Var('dart_git') + '/test.git@ba64bbbaa26f09e139c26f9ad6409995806aac6e',
+   Var('dart_git') + '/test.git@7724aabe8cd40b376573330f5227a6ec0a47f28e',
 
   'src/third_party/dart/third_party/pkg/test_reflective_loader':
    Var('dart_git') + '/test_reflective_loader.git@9862703a3d14848376c8efde271c88022fba91eb',
@@ -1013,7 +1019,7 @@ deps = {
         'version': 'da-siZ7wPDA0Z0wXJOEBxKat7HqQz9B3rXqV8wblgz8C'
        }
      ],
-     'condition': 'host_os == "linux" and not download_fuchsia_sdk',
+     'condition': 'download_fuchsia_deps and not download_fuchsia_sdk',
      'dep_type': 'cipd',
    },
 
@@ -1024,7 +1030,7 @@ deps = {
         'version': Var('fuchsia_test_scripts_version'),
        }
      ],
-     'condition': 'run_fuchsia_emu',
+     'condition': 'download_fuchsia_deps',
      'dep_type': 'cipd',
    },
 
@@ -1035,6 +1041,7 @@ deps = {
         'version': Var('fuchsia_gn_sdk_version'),
        }
      ],
+     'condition': 'download_fuchsia_deps',
      'dep_type': 'cipd',
    },
 
@@ -1128,7 +1135,7 @@ hooks = [
   {
     'name': 'Download Fuchsia SDK',
     'pattern': '.',
-    'condition': 'download_fuchsia_sdk',
+    'condition': 'download_fuchsia_deps and download_fuchsia_sdk',
     'action': [
       'python3',
       'src/flutter/tools/download_fuchsia_sdk.py',
@@ -1239,5 +1246,15 @@ hooks = [
       '--as-gclient-hook',
       Var('mac_sdk_min')
     ]
-  }
+  },
+  {
+    'name': 'Generate Fuchsia GN build rules',
+    'pattern': '.',
+    'condition': 'download_fuchsia_deps',
+    'action': [
+      'python3',
+      'src/flutter/tools/fuchsia/with_envs.py',
+      'src/flutter/tools/fuchsia/test_scripts/gen_build_defs.py',
+    ],
+  },
 ]

build/config/fuchsia/gn_configs.gni

@@ -2,49 +2,40 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# TODO(richkadel): added this import and modified the fuchsia_sdk assignment.
-# See below.
-import("//build/fuchsia/sdk.gni")
-declare_args() {
-  # Path to the fuchsia SDK. This is intended for use in other templates & rules
-  # to reference the contents of the fuchsia SDK.
-  fuchsia_sdk = "$fuchsia_sdk_path"
-
-  # TODO(richkadel): Since flutter needs build rules from the GN SDK, but also
-  # requires the Fuchsia _Core_ SDK (for dart libraries, in the core SDK, but
-  # excluded from the GN SDK), the Fuchsia SDK assumption that the build files
-  # are in the same SDK directory path as the APIs does not hold true. (And
-  # there are a couple of other minor tweaks that appear to be needed, at
-  # this time.) This use case will be discussed with the SDK team, to see if we
-  # can come up with a cleaner solution.
+# This file is copied from
+# https://crsrc.org/c/build/config/fuchsia/gn_configs.gni?q=gn_configs.gni
+# with some local modifications to match the flutter setup.
 
-  # Build ID uniquely identifying the Fuchsia IDK. This is exposed as a property so
-  # it can be used to locate images and packages on GCS and as a marker to indicate the
-  # "version" of the IDK. If it is empty, then it is most likely that something is fatally wrong.
+declare_args() {
+  # Path to the fuchsia SDK. This is intended for use in other templates &
+  # rules to reference the contents of the fuchsia SDK.
+  fuchsia_sdk = "//fuchsia/sdk/$host_os"
+
+  # ID uniquely identifying the Fuchsia IDK build. This is exposed as a
+  # property so it can be used to locate images and packages on GCS and
+  # as a marker to indicate the "version" of the IDK.
+  # Defaults to the id found in the manifest.json file of the SDK.
   fuchsia_sdk_id = ""
 }
 
-declare_args() {
-  # The SDK manifest file. This is useful to include as a dependency
-  # for some targets in order to cause a rebuild when the version of the
-  # SDK is changed.
-  fuchsia_sdk_manifest_file = "$fuchsia_sdk/meta/manifest.json"
+# TODO(zijiehe): Remove the override and move it into declare_args once the one
+# in //build/config/sdk.gni being removed. - b/40935282
 
-  # fuchsia_tool_dir is use to specify the directory in the SDK to locate tools for the
-  # host cpu architecture. If the host_cpu is not recognized, then tool dir
-  # defaults to x64.
-  fuchsia_tool_dir = "$fuchsia_sdk/tools/x64"
-  if (host_cpu == "x64" || host_cpu == "arm64") {
-    fuchsia_tool_dir = "${fuchsia_sdk}/tools/${host_cpu}"
-  }
+# The target API level for this repository. Embedders should override this
+# value to specify the API level the packages produced from this repository
+# should be targeting, e.g. in their top-level //.gn file. A value of -1
+# means that no API level will be passed to the tools that consumes it.
+fuchsia_target_api_level = 16
 
-  # fuchsia_auto_index_symbols when true adds the ids.txt file generated from a `fuchsia_package`
-  # to the Fuchsia symbol index used to symbolize logs and to find source when using zxdb.
-  # The default value is false, in order to be backwards compatibility with existing builds, and
-  # only makes sense to set to true when building as a developer that will need to symbolize logs
-  # or use the debugger with locally build code.
-  fuchsia_auto_index_symbols = false
-}
+# The SDK manifest file. This is useful to include as a dependency
+# for some targets in order to cause a rebuild when the version of the
+# SDK is changed.
+fuchsia_sdk_manifest_file = "${fuchsia_sdk}/meta/manifest.json"
+
+# fuchsia_tool_dir is used to specify the directory in the SDK to locate
+# tools for the host cpu architecture. If the host_cpu is not recognized,
+# then tool dir defaults to x64.
+fuchsia_tool_dir = "${fuchsia_sdk}/tools/${host_cpu}"
 
 if (fuchsia_sdk_id == "") {
   # Note: If we need to expose more than just the id in the future,
@@ -64,3 +55,6 @@ declare_args() {
     fuchsia_sdk_readelf_exec = ""
   }
 }
+
+# third_party/googletest is still using this condition.
+using_fuchsia_sdk = true

build/secondary/flutter/third_party/googletest/BUILD.gn

@@ -3,7 +3,7 @@
 # found in the LICENSE file.
 
 if (is_fuchsia) {
-  import("//build/fuchsia/sdk.gni")
+  import("//flutter/tools/fuchsia/gn-sdk/src/gn_configs.gni")
 }
 
 config("gtest_private_config") {
@@ -34,8 +34,8 @@ static_library("gtest") {
   if (is_fuchsia) {
     if (using_fuchsia_sdk) {
       deps = [
-        "$fuchsia_sdk_root/pkg:fdio",
-        "$fuchsia_sdk_root/pkg:zx",
+        "${fuchsia_sdk}/pkg/fdio",
+        "${fuchsia_sdk}/pkg/zx",
       ]
     } else {
       deps = [

ci/licenses_golden/excluded_files

@@ -330,7 +330,6 @@
 ../../../flutter/shell/platform/fuchsia/dart_runner/.gitignore
 ../../../flutter/shell/platform/fuchsia/dart_runner/README.md
 ../../../flutter/shell/platform/fuchsia/dart_runner/embedder/pubspec.yaml
-../../../flutter/shell/platform/fuchsia/dart_runner/fidl/meta.json
 ../../../flutter/shell/platform/fuchsia/dart_runner/kernel/libraries.json
 ../../../flutter/shell/platform/fuchsia/dart_runner/kernel/libraries.yaml
 ../../../flutter/shell/platform/fuchsia/dart_runner/tests

ci/licenses_golden/licenses_dart

@@ -1,4 +1,4 @@
-Signature: c01d057033e277986624c640f663a410
+Signature: 6dada66d64680541f83bc84b71ddf2bb
 
 ====================================================================================================
 LIBRARY: dart
@@ -4751,7 +4751,7 @@ Exhibit B - "Incompatible With Secondary Licenses" Notice
   This Source Code Form is "Incompatible With Secondary Licenses", as
   defined by the Mozilla Public License, v. 2.0.
 
-You may obtain a copy of this library's Source Code Form from: https://dart.googlesource.com/sdk/+/d006b668dcb252171d743526e2a2f3ba34f0c48e
+You may obtain a copy of this library's Source Code Form from: https://dart.googlesource.com/sdk/+/406955fe69503eb11fb16a8405534a979f5eef60
 /third_party/fallback_root_certificates/
 
 ====================================================================================================

display_list/BUILD.gn

@@ -2,11 +2,14 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//build/fuchsia/sdk.gni")
 import("//flutter/common/config.gni")
 import("//flutter/impeller/tools/impeller.gni")
 import("//flutter/testing/testing.gni")
 
+if (is_fuchsia) {
+  import("//flutter/tools/fuchsia/gn-sdk/src/gn_configs.gni")
+}
+
 config("display_list_config") {
   defines = []
 
@@ -142,8 +145,7 @@ if (enable_unittests) {
     # This is needed for //flutter/third_party/googletest for linking zircon
     # symbols.
     if (is_fuchsia) {
-      libs =
-          [ "${fuchsia_sdk_path}/arch/${target_cpu}/sysroot/lib/libzircon.so" ]
+      libs = [ "${fuchsia_arch_root}/sysroot/lib/libzircon.so" ]
     }
   }
 
@@ -174,8 +176,7 @@ if (enable_unittests) {
     # This is needed for //flutter/third_party/googletest for linking zircon
     # symbols.
     if (is_fuchsia) {
-      libs =
-          [ "${fuchsia_sdk_path}/arch/${target_cpu}/sysroot/lib/libzircon.so" ]
+      libs = [ "${fuchsia_arch_root}/sysroot/lib/libzircon.so" ]
     }
   }
 

flow/BUILD.gn

@@ -2,12 +2,15 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//build/fuchsia/sdk.gni")
 import("//flutter/common/config.gni")
 import("//flutter/impeller/tools/impeller.gni")
 import("//flutter/shell/config.gni")
 import("//flutter/testing/testing.gni")
 
+if (is_fuchsia) {
+  import("//flutter/tools/fuchsia/gn-sdk/src/gn_configs.gni")
+}
+
 source_set("flow") {
   sources = [
     "compositor_context.cc",

fml/BUILD.gn

@@ -2,10 +2,13 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//build/fuchsia/sdk.gni")
 import("//flutter/common/config.gni")
 import("//flutter/testing/testing.gni")
 
+if (is_fuchsia) {
+  import("//flutter/tools/fuchsia/gn-sdk/src/gn_configs.gni")
+}
+
 source_set("fml") {
   sources = [
     "ascii_trie.cc",
@@ -227,16 +230,16 @@ source_set("fml") {
     ]
 
     public_deps += [
-      "$fuchsia_sdk_root/fidl:fuchsia.diagnostics",
-      "$fuchsia_sdk_root/fidl:fuchsia.logger",
-      "$fuchsia_sdk_root/pkg:async-cpp",
-      "$fuchsia_sdk_root/pkg:async-loop-cpp",
-      "$fuchsia_sdk_root/pkg:async-loop-default",
-      "$fuchsia_sdk_root/pkg:component_incoming_cpp",
-      "$fuchsia_sdk_root/pkg:syslog_structured_backend",
-      "$fuchsia_sdk_root/pkg:trace",
-      "$fuchsia_sdk_root/pkg:trace-engine",
-      "$fuchsia_sdk_root/pkg:zx",
+      "${fuchsia_sdk}/fidl/fuchsia.diagnostics:fuchsia.diagnostics_cpp",
+      "${fuchsia_sdk}/fidl/fuchsia.logger:fuchsia.logger_cpp",
+      "${fuchsia_sdk}/pkg/async-cpp",
+      "${fuchsia_sdk}/pkg/async-loop-cpp",
+      "${fuchsia_sdk}/pkg/async-loop-default",
+      "${fuchsia_sdk}/pkg/component_incoming_cpp",
+      "${fuchsia_sdk}/pkg/syslog_structured_backend",
+      "${fuchsia_sdk}/pkg/trace",
+      "${fuchsia_sdk}/pkg/trace-engine",
+      "${fuchsia_sdk}/pkg/zx",
     ]
   }
 
@@ -407,14 +410,13 @@ if (enable_unittests) {
 
     if (is_fuchsia) {
       deps += [
-        "$fuchsia_sdk_root/pkg:async-loop-testing",
-        "$fuchsia_sdk_root/pkg:sys_component_cpp_testing",
+        "${fuchsia_sdk}/pkg/async-loop-testing",
+        "${fuchsia_sdk}/pkg/sys_component_cpp_testing",
       ]
 
       # This is needed for //flutter/third_party/googletest for linking zircon
       # symbols.
-      libs =
-          [ "${fuchsia_sdk_path}/arch/${target_cpu}/sysroot/lib/libzircon.so" ]
+      libs = [ "${fuchsia_arch_root}/sysroot/lib/libzircon.so" ]
     }
   }
 

lib/snapshot/BUILD.gn

@@ -3,13 +3,16 @@
 # found in the LICENSE file.
 
 import("//build/compiled_action.gni")
-import("//build/fuchsia/sdk.gni")
 import("//flutter/build/bin_to_obj.gni")
 import("//flutter/common/config.gni")
 import("//flutter/impeller/tools/impeller.gni")
 import("//flutter/lib/ui/dart_ui.gni")
 import("$dart_src/utils/compile_platform.gni")
 
+if (is_fuchsia) {
+  import("//flutter/tools/fuchsia/gn-sdk/src/gn_configs.gni")
+}
+
 # Generates the Dart/Flutter core platform files and tools.
 #
 # This target generates the platform-specific snapshots and snapshot-related

lib/ui/BUILD.gn

@@ -2,12 +2,15 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//build/fuchsia/sdk.gni")
 import("//flutter/common/config.gni")
 import("//flutter/impeller/tools/impeller.gni")
 import("//flutter/shell/config.gni")
 import("//flutter/testing/testing.gni")
 
+if (is_fuchsia) {
+  import("//flutter/tools/fuchsia/gn-sdk/src/gn_configs.gni")
+}
+
 source_set("ui") {
   cflags = [
     # Dart gives us doubles. Skia and Impeller work in floats.