Revert "Remove the frontend server wrapper" (#46863)

Reverts #46440

For b/305121780

Author: zanderso

build/dart/rules.gni

@@ -10,115 +10,21 @@ import("//flutter/common/config.gni")
 import("//third_party/dart/build/dart/dart_action.gni")
 import("//third_party/dart/sdk_args.gni")
 
-# Generates a Dart kernel snapshot using flutter_frontend_server.
-#
-# Arguments
-#     main_dart (required):
-#       The Dart entrypoint file.
-#
-#     kernel_output (required):
-#       The path to the output kernel snapshot in the out directory.
-#
-#     package_config (optional):
-#       The path to the package_config.json file.
-#
-#     deps (optional):
-#       Additional dependencies. Dependencies on the frontend server and
-#       Flutter's platform.dill are included by default. This rule creates and
-#       uses a depfile, so listing all Dart sources is not necessary.
-#
-#     extra_args (optional):
-#       Additional frontend server command line arguments.
-template("flutter_frontend_server") {
-  assert(defined(invoker.main_dart), "The Dart test file must be specified.")
-  assert(defined(invoker.kernel_output),
-         "The Dart Kernel file location must be specified.")
-
-  kernel_output = invoker.kernel_output
-
-  common_deps = [
-    "//flutter/flutter_frontend_server:frontend_server",
-    "//flutter/lib/snapshot:strong_platform",
-  ]
-  if (defined(invoker.deps)) {
-    common_deps += invoker.deps
-  }
-
-  extra_args = []
-  if (defined(invoker.extra_args)) {
-    extra_args += invoker.extra_args
-  }
-
-  packages_args = []
-  if (defined(invoker.package_config)) {
-    packages_args += [
-      "--packages",
-      rebase_path(invoker.package_config),
-    ]
-  }
-
-  snapshot_depfile = "$kernel_output.d"
-
-  common_vm_args = [ "--disable-dart-dev" ]
-
-  flutter_patched_sdk = rebase_path("$root_out_dir/flutter_patched_sdk")
-
-  common_args = extra_args + packages_args + [
-                  "--sdk-root",
-                  flutter_patched_sdk,
-                  "--target=flutter",
-                  "--depfile",
-                  rebase_path(snapshot_depfile),
-                  "--output-dill",
-                  rebase_path(invoker.kernel_output),
-                  rebase_path(invoker.main_dart),
-                ]
-
-  if (flutter_prebuilt_dart_sdk) {
-    action(target_name) {
-      forward_variables_from(invoker,
-                             [
-                               "visibility",
-                               "testonly",
-                             ],
-                             [ "pool" ])
-      deps = common_deps
-      pool = "//flutter/build/dart:dart_pool"
-      script = "//build/gn_run_binary.py"
-      inputs = [ invoker.main_dart ]
-      outputs = [ invoker.kernel_output ]
-      depfile = snapshot_depfile
-
-      ext = ""
-      if (is_win) {
-        ext = ".exe"
-      }
-      dart = rebase_path("$host_prebuilt_dart_sdk/bin/dart$ext", root_out_dir)
-      frontend_server =
-          rebase_path("$root_gen_dir/frontend_server.dart.snapshot")
-
-      args = [ dart ] + common_vm_args + [ frontend_server ] + common_args
-    }
-  } else {
-    dart_action(target_name) {
-      forward_variables_from(invoker,
-                             [
-                               "visibility",
-                               "testonly",
-                             ],
-                             [ "pool" ])
-      deps = common_deps
-      pool = "//flutter/build/dart:dart_pool"
-      script = "$root_gen_dir/frontend_server.dart.snapshot"
-      packages = rebase_path(invoker.package_config)
-      inputs = [ invoker.main_dart ]
-      outputs = [ invoker.kernel_output ]
-      depfile = snapshot_depfile
-      vm_args = common_vm_args
-      args = common_args
-    }
-  }
-}
+frontend_server_files =
+    exec_script("//third_party/dart/tools/list_dart_files.py",
+                [
+                  "absolute",
+                  rebase_path("//flutter/flutter_frontend_server"),
+                ],
+                "list lines")
+
+frontend_server_files +=
+    exec_script("//third_party/dart/tools/list_dart_files.py",
+                [
+                  "absolute",
+                  rebase_path("//third_party/dart/pkg"),
+                ],
+                "list lines")
 
 # Creates a dart kernel (dill) file suitable for use with gen_snapshot, as well
 # as the app-jit, aot-elf, or aot-assembly snapshot for targeting Flutter on
@@ -142,38 +48,61 @@ template("flutter_snapshot") {
 
   kernel_output = "$target_gen_dir/kernel_blob.bin"
 
-  extra_frontend_server_args = []
-  if (is_aot) {
-    extra_frontend_server_args += [
-      "--aot",
-      "--tfa",
+  prebuilt_dart_action(kernel_target) {
+    script = "//flutter/flutter_frontend_server/bin/starter.dart"
+
+    main_dart = rebase_path(invoker.main_dart)
+    package_config = rebase_path(invoker.package_config)
+    flutter_patched_sdk = rebase_path("$root_out_dir/flutter_patched_sdk")
+
+    deps = [ "//flutter/lib/snapshot:strong_platform" ]
+
+    inputs = [
+               main_dart,
+               package_config,
+             ] + frontend_server_files
+
+    outputs = [ kernel_output ]
+
+    depfile = "$kernel_output.d"
+    abs_depfile = rebase_path(depfile)
+    vm_args = [ "--disable-dart-dev" ]
+
+    args = [
+      "--depfile=$abs_depfile",
+      "--packages=" + rebase_path(package_config),
+      "--target=flutter",
+      "--sdk-root=" + flutter_patched_sdk,
+      "--output-dill=" + rebase_path(kernel_output, root_build_dir),
     ]
-  } else {
-    # --no-link-platform is only valid when --aot isn't specified
-    extra_frontend_server_args += [ "--no-link-platform" ]
-  }
 
-  if (defined(invoker.product) && invoker.product) {
-    # Setting this flag in a non-product release build for AOT (a "profile"
-    # build) causes the vm service isolate code to be tree-shaken from an app.
-    # See the pragma on the entrypoint here:
-    #
-    # https://github.com/dart-lang/sdk/blob/main/sdk/lib/_internal/vm/bin/vmservice_io.dart#L240
-    #
-    # Also, this define excludes debugging and profiling code from Flutter.
-    extra_frontend_server_args += [ "-Ddart.vm.product=true" ]
-  } else {
-    if (flutter_runtime_mode == "profile") {
-      # The following define excludes debugging code from Flutter.
-      extra_frontend_server_args += [ "-Ddart.vm.profile=true" ]
+    if (is_aot) {
+      args += [
+        "--aot",
+        "--tfa",
+      ]
+    } else {
+      # --no-link-platform is only valid when --aot isn't specified
+      args += [ "--no-link-platform" ]
+    }
+
+    if (defined(invoker.product) && invoker.product) {
+      # Setting this flag in a non-product release build for AOT (a "profile"
+      # build) causes the vm service isolate code to be tree-shaken from an app.
+      # See the pragma on the entrypoint here:
+      #
+      # https://github.com/dart-lang/sdk/blob/main/sdk/lib/_internal/vm/bin/vmservice_io.dart#L240
+      #
+      # Also, this define excludes debugging and profiling code from Flutter.
+      args += [ "-Ddart.vm.product=true" ]
+    } else {
+      if (flutter_runtime_mode == "profile") {
+        # The following define excludes debugging code from Flutter.
+        args += [ "-Ddart.vm.profile=true" ]
+      }
     }
-  }
 
-  flutter_frontend_server(kernel_target) {
-    main_dart = invoker.main_dart
-    package_config = invoker.package_config
-    kernel_output = kernel_output
-    extra_args = extra_frontend_server_args
+    args += [ rebase_path(main_dart) ]
   }
 
   compiled_action(snapshot_target) {
@@ -342,7 +271,7 @@ template("application_snapshot") {
   # Ensure the compiled appliation (e.g. frontend-server, ...) will use this
   # Dart SDK hash when consuming/producing kernel.
   #
-  # (Instead of ensuring every user of the "application_snapshot" passes its
+  # (Instead of ensuring every user of the "application_snapshot" passes it's
   # own)
   snapshot_vm_args += [ "-Dsdk_hash=$sdk_hash" ]
 

common/config.gni

@@ -113,27 +113,18 @@ if (flutter_prebuilt_dart_sdk) {
     _host_os_name = "windows"
   }
 
-  # When building 32-bit Android development artifacts for Windows host (like
-  # gen_snapshot), the host_cpu is set to x86. However, the correct prebuilt
-  # Dart SDK to use during this build is still the 64-bit one.
-  _host_cpu = host_cpu
-  if (host_os == "win" && host_cpu == "x86") {
-    _host_cpu = "x64"
-  }
-
   _target_prebuilt_dart_sdk_config = "$_target_os_name-$target_cpu"
-  _host_prebuilt_dart_sdk_config = "$_host_os_name-$_host_cpu"
+  _host_prebuilt_dart_sdk_config = "$_host_os_name-$host_cpu"
 
   target_prebuilt_dart_sdk =
       "//flutter/prebuilts/$_target_prebuilt_dart_sdk_config/dart-sdk"
   host_prebuilt_dart_sdk =
       "//flutter/prebuilts/$_host_prebuilt_dart_sdk_config/dart-sdk"
 
-  # There is no prebuilt Dart SDK targeting Fuchsia, iOS, and Android, but we
-  # also don't need one, so even when the build is targeting one of these
-  # platforms, we use the prebuilt Dart SDK for the host.
-  if (current_toolchain == host_toolchain || target_os == "android" ||
-      target_os == "fuchsia" || target_os == "ios" || target_os == "wasm") {
+  # There is no prebuilt Dart SDK targeting Fuchsia, but we also don't need
+  # one, so even when the build is targeting Fuchsia, use the prebuilt
+  # Dart SDK for the host.
+  if (current_toolchain == host_toolchain || is_fuchsia || is_wasm) {
     prebuilt_dart_sdk = host_prebuilt_dart_sdk
     prebuilt_dart_sdk_config = _host_prebuilt_dart_sdk_config
   } else {

flutter_frontend_server/BUILD.gn

@@ -2,18 +2,19 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//flutter/common/config.gni")
+import("//flutter/build/dart/rules.gni")
 
-copy("frontend_server") {
-  if (flutter_prebuilt_dart_sdk) {
-    snapshot =
-        "$host_prebuilt_dart_sdk/bin/snapshots/frontend_server.dart.snapshot"
-  } else {
-    deps = [ "//flutter/build/dart:dart_sdk" ]
-    snapshot =
-        "$root_out_dir/dart-sdk/bin/snapshots/frontend_server.dart.snapshot"
-  }
+application_snapshot("frontend_server") {
+  main_dart = "bin/starter.dart"
+  deps = [ "//flutter/lib/snapshot:kernel_platform_files" ]
 
-  sources = [ snapshot ]
-  outputs = [ "$root_gen_dir/frontend_server.dart.snapshot" ]
+  package_config = rebase_path(".dart_tool/package_config.json")
+  flutter_patched_sdk = rebase_path("$root_out_dir/flutter_patched_sdk")
+  training_args = [
+    "--train",
+    "--sdk-root=$flutter_patched_sdk",
+    rebase_path(main_dart),
+  ]
+
+  inputs = frontend_server_files
 }

flutter_frontend_server/README.md

@@ -0,0 +1,71 @@
+# Frontend Server
+
+Frontend server is simple wrapper around Dart Frontend. It is a Dart application
+that compiles Dart source into Dart Kernel binary (.dill-file).
+Documentation on Dart Kernel (semantic, binary format, etc) can be found here:
+https://github.com/dart-lang/sdk/wiki/Kernel-Documentation.
+
+Frontend server runs in two modes:
+ - immediate mode, where Dart source file name is provided as command line
+ argument;
+ - interactive mode, where communication is happening over stdin/stdout.
+
+## Interactive mode instructions
+
+### Compile/Recompile
+```
+compile <input.dart>
+```
+ Compiles <input.dart> Dart source file with Dart Frontend. Replies with `result` response.
+
+```
+recompile <boundary-key>
+<path/to/updated/file1.dart>
+<path/to/updated/file2.dart>
+...
+<boundary-key>
+```
+ Incrementally recompiles Dart program previously compiled in current session, taking into account
+ changes in the listed files. Replies with `result` response.
+
+ Relative paths should be relative to current working directory for the shell that launched
+ Frontend Server.
+
+### Accept/Reject
+```
+accept
+```
+ Accepts results of incremental compilation, so that on next recompilation request Dart Frontend
+ will not include these recompiled files.
+```
+reject
+```
+ Rejects results of incremental compilation, so that on next recompilation request Dart Frontend
+ will include compilation results from previously rejected recompilation in addition to what it
+ will recompile based on newly changed files.
+ Small technical detail is that Dart Frontend will not recompile files from previously rejected
+ recompilation attempts (unless they were changed since then), it will just include appropriate
+ kernel binaries it kept around from those previously rejected compilation requests.
+
+ One use of `accept` and `reject` instructions is in the context of Dart VM hot-reload. Dart VM can
+ reject user-provided incremental change to what is currently running. It could happen for variety
+ of Dart VM internal reasons. For example, if incremental update changes some `class` to `enum`,
+ such update can not be hot-reloaded by VM at this point, will be rejected.
+
+### Quit
+```
+quit
+```
+ Stops the server.
+
+## Response from the server
+
+```
+result <boundary-key>
+<compiler output>
+<boundary-key> [<output.dill>]
+```
+Response from the Dart Frontend compiler is bracketed by `<boundary-key>` tags. If the compiler
+was able to produce a Dart Kernel file, the name of this file `<output.dill>` is provided too.
+If the compiler encountered unrecoverable errors, there will be no output file name provided.
+

flutter_frontend_server/bin/starter.dart

@@ -0,0 +1,15 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+
+import 'dart:io';
+
+import 'package:flutter_frontend_server/server.dart';
+
+Future<void> main(List<String> args) async {
+  final int exitCode = await starter(args);
+  if (exitCode != 0) {
+    exit(exitCode);
+  }
+}