[gn] Fix precompile_tools=True (attempt 2)

Turns out that dart compile exe --depfile produces
depfile which does not work with ninja because
it uses absolute path to the output file
instead of using relative path.

So we can't use it directly and need to fix
depfile.

TEST=manually

Change-Id: I1aadfd5079cc38d392933f9afe333f63407bb295
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/435680
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Slava Egorov <vegorov@google.com>

build/gn_dart_compile_exe.py

@@ -0,0 +1,112 @@
+#!/usr/bin/env python3
+# Copyright 2014 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.
+"""Helper script for GN to run `dart compile exe` and produce a depfile.
+
+Run with:
+  python3 gn_dart_compile_exe.py             \
+    --dart-binary <path to dart binary>      \
+    --entry-point <path to dart entry point>       \
+    --output <path to resulting executable>  \
+    --sdk-hash <SDK hash>                    \
+    --packages <path to package config file> \
+    --depfile <path to depfile to write>
+
+This is workaround for `dart compile exe` not supporting --depfile option
+in the current version of prebuilt SDK. Once we roll in a new version
+of checked in SDK we can remove this helper.
+"""
+
+import argparse
+import os
+import sys
+import subprocess
+from tempfile import TemporaryDirectory
+
+
+def parse_args(argv):
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--dart-sdk",
+                        required=True,
+                        help="Path to the prebuilt Dart SDK")
+    parser.add_argument("--sdk-hash", required=True, help="SDK hash")
+    parser.add_argument("--entry-point",
+                        required=True,
+                        help="Dart entry point to precompile")
+    parser.add_argument("--output",
+                        required=True,
+                        help="Path to resulting executable   ")
+    parser.add_argument("--packages",
+                        required=True,
+                        help="Path to package config file")
+    parser.add_argument("--depfile",
+                        required=True,
+                        help="Path to depfile to write")
+    return parser.parse_args(argv)
+
+
+# Run a command, swallowing the output unless there is an error.
+def run_command(command):
+    try:
+        subprocess.check_output(command, stderr=subprocess.STDOUT)
+        return True
+    except subprocess.CalledProcessError as e:
+        print("Command failed: " + " ".join(command) + "\n" + "output: " +
+              _decode(e.output))
+        return False
+    except OSError as e:
+        print("Command failed: " + " ".join(command) + "\n" + "output: " +
+              _decode(e.strerror))
+        return False
+
+
+def _decode(bytes):
+    return bytes.decode("utf-8")
+
+
+def main(argv):
+    args = parse_args(argv[1:])
+
+    # Unless the path is absolute, this script is designed to run binaries
+    # produced by the current build, which is the current working directory when
+    # this script is run.
+    prebuilt_sdk = os.path.abspath(args.dart_sdk)
+
+    dart_binary = os.path.join(prebuilt_sdk, "bin", "dart")
+    if not os.path.isfile(dart_binary):
+        print("Binary not found: " + dart_binary)
+        return 1
+
+    # Compile the executable.
+    ok = run_command([
+        dart_binary,
+        "compile",
+        "exe",
+        "--packages",
+        args.packages,
+        f"-Dsdk_hash={args.sdk_hash}",
+        "--depfile",
+        args.depfile,
+        "-o",
+        args.output,
+        args.entry_point,
+    ])
+    if not ok:
+        return 1
+
+    # Fix generated depfile to refer to the relative output file name
+    # instead referring to it using absolute path. ninja does not support
+    # that.
+    with open(args.depfile, "r") as f:
+        content = f.read()
+    deps = content.split(": ", 1)[1]
+    with open(args.depfile, "w") as f:
+        f.write(args.output)
+        f.write(": ")
+        f.write(deps)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))

utils/BUILD.gn

@@ -8,7 +8,7 @@ import("../sdk_args.gni")
 _dart_root = get_path_info("..", "abspath")
 
 template("aot_compile_using_prebuilt_sdk") {
-  prebuilt_dart_action(target_name) {
+  action(target_name) {
     forward_variables_from(invoker,
                            [
                              "deps",
@@ -17,24 +17,31 @@ template("aot_compile_using_prebuilt_sdk") {
                              "visibility",
                            ])
 
+    script = "$_dart_root/build/gn_dart_compile_exe.py"
+
     inputs = [
       invoker.entry_point,
       invoker.package_config,
     ]
+
     outputs = [ invoker.output ]
+
     depfile = invoker.output + ".d"
 
+    # TODO(vegorov): support RBE by using rewrapper script.
     args = [
-      "compile",
-      "exe",
+      "--dart-sdk",
+      rebase_path("$_dart_root/tools/sdks/dart-sdk", root_build_dir),
+      "--sdk-hash",
+      "$sdk_hash",
+      "--entry-point",
+      rebase_path(invoker.entry_point, root_build_dir),
+      "--output",
+      rebase_path(invoker.output, root_build_dir),
       "--packages",
       rebase_path(invoker.package_config, root_build_dir),
-      "-Dsdk_hash=$sdk_hash",
       "--depfile",
       rebase_path(depfile, root_build_dir),
-      "-o",
-      rebase_path(invoker.output, root_build_dir),
-      rebase_path(invoker.entry_point, root_build_dir),
     ]
   }
 }