Flip DDC to default to sync-async

See #32868

Change-Id: I757321632c9f383edea398741c67fc7c3e3815e5
Reviewed-on: https://dart-review.googlesource.com/52900
Commit-Queue: Vijay Menon <vsm@google.com>
Reviewed-by: Jenny Messerly <jmesserly@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>

CHANGELOG.md

@@ -23,6 +23,12 @@
   * Force splitting an empty block as the then body of an if with an else.
   * Uses the new lowercase Dart 2 constant names.
 
+#### Dart Dev Compiler
+
+* `async` functions now start synchronously by default.  Build tools
+  (e.g., build_runner) may override the default and/or allow
+  developers to configure.
+
 #### Pub
 
 * The `build` and `serve` commands will now fail and point users to

pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_async.dart

@@ -3,10 +3,9 @@
 // BSD-style license that can be found in the LICENSE file.
 
 main() {
-  // This call is no longer on the stack when the error is thrown.
-  /*:main*/ test();
+  /*1:main*/ test();
 }
 
-test() async {
-  /*1:test*/ throw '>ExceptionMarker<';
+test /*ddk.2:test*/ () /*ddc.2:test*/ async {
+  /*3:test*/ throw '>ExceptionMarker<';
 }

pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_awaited_async.dart

@@ -3,14 +3,13 @@
 // BSD-style license that can be found in the LICENSE file.
 
 main() {
-  test1();
+  /*1:main*/ test1();
 }
 
-test1() async {
-  // This call is no longer on the stack when the error is thrown.
-  await /*:test1*/ test2();
+test1 /*ddk.2:test1*/ () /*ddc.2:test1*/ async {
+  await /*3:test1*/ test2();
 }
 
-test2() async {
-  /*1:test2*/ throw '>ExceptionMarker<';
+test2 /*ddk.4:test2*/ () /*ddc.4:test2*/ async {
+  /*5:test2*/ throw '>ExceptionMarker<';
 }

pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_constructor_from_async.dart

@@ -4,17 +4,17 @@
 
 main() {
   // This call is no longer on the stack when the error is thrown.
-  /*:main*/ test();
+  /*1:main*/ test();
 }
 
-test() async {
+test /*ddk.2:test*/ () /*ddc.2:test*/ async {
   // ignore: UNUSED_LOCAL_VARIABLE
-  var c = new /*1:test*/ Class();
+  var c = new /*3:test*/ Class();
 }
 
 class Class {
   Class() {
     // Some comment
-    /*2:Class.new*/ throw '>ExceptionMarker<';
+    /*4:Class.new*/ throw '>ExceptionMarker<';
   }
 }

pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_top_level_method_from_async.dart

@@ -3,13 +3,13 @@
 // BSD-style license that can be found in the LICENSE file.
 
 main() {
-  test1();
+  /*1:main*/ test1();
 }
 
-test1() async {
-  /*1:test1*/ test2();
+test1 /*ddk.2:test1*/ () /*ddc.2:test1*/ async {
+  /*3:test1*/ test2();
 }
 
 test2() {
-  /*2:test2*/ throw '>ExceptionMarker<';
+  /*4:test2*/ throw '>ExceptionMarker<';
 }

pkg/dev_compiler/test/sourcemap/testfiles/hello_async.dart

@@ -5,10 +5,10 @@
 main() {
   /*bl*/
   /*s:1*/ foo();
-/*nbb:0:3*/ /*s:3*/
+  /*s:4*/
 }
 
-foo() async {
-  /*nbb:0:4*/ /*bc:4*/ print("hello from foo");
-/*s:2*/
+foo() /*sl:2*/ async {
+  print("hello from foo");
+/*s:3*/
 }

pkg/dev_compiler/tool/ddc

@@ -60,12 +60,6 @@ if [ "$1" = "-k" ]; then
   shift
 fi
 
-SYNC_ASYNC=false
-if [ "$1" = "--sync-async" ]; then
-  SYNC_ASYNC=true
-  shift
-fi
-
 BASENAME=$( basename "${1%.*}")
 LIBROOT=$(cd $( dirname "${1%.*}") && pwd)
 
@@ -110,7 +104,6 @@ echo "
     let sdk = require(\"dart_sdk\");
     let main = require(\"./$BASENAME\").$BASENAME.main;
     sdk.dart.ignoreWhitelistedErrors(false);
-    if ($SYNC_ASYNC) sdk.dart.setStartAsyncSynchronously();
     try {
       sdk._isolate_helper.startRootIsolate(main, []);
     } catch(e) {

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/generators.dart

@@ -11,8 +11,9 @@
 /// stepping stone for proposed ES7 async/await, and uses ES6 Promises.
 part of dart._runtime;
 
-// TODO(vsm): Remove once this flag is the default.
-bool startAsyncSynchronously = false;
+// TODO(vsm): Remove once this flag we've removed the ability to
+// whitelist / fallback on the old behavior.
+bool startAsyncSynchronously = true;
 void setStartAsyncSynchronously([bool value = true]) {
   startAsyncSynchronously = value;
 }

tools/testing/dart/browser_test.dart

@@ -40,8 +40,7 @@ String dart2jsHtml(String title, String scriptPath) {
 /// The [testName] is the short name of the test without any subdirectory path
 /// or extension, like "math_test". The [testJSDir] is the relative path to the
 /// build directory where the dartdevc-generated JS file is stored.
-String dartdevcHtml(String testName, String testJSDir, String buildDir,
-    {bool syncAsync}) {
+String dartdevcHtml(String testName, String testJSDir, String buildDir) {
   var packagePaths = testPackages
       .map((package) => '    "$package": "/root_dart/$buildDir/gen/utils/'
           'dartdevc/pkg/$package",')
@@ -87,7 +86,6 @@ window.ddcSettings = {
 requirejs(["$testName", "dart_sdk", "async_helper"],
     function($testName, sdk, async_helper) {  
   sdk.dart.ignoreWhitelistedErrors(false);
-  if ($syncAsync) sdk.dart.setStartAsyncSynchronously();
   // TODO(rnystrom): This uses DDC's forked version of async_helper. Unfork
   // these packages when possible.
   async_helper.async_helper.asyncTestInitialize(function() {});

tools/testing/dart/test_suite.dart

@@ -1062,7 +1062,7 @@ class StandardTestSuite extends TestSuite {
         // Always run with synchronous starts of `async` functions.
         // If we want to make this dependent on other parameters or flags,
         // this flag could be become conditional.
-        content = dartdevcHtml(nameNoExt, jsDir, buildDir, syncAsync: true);
+        content = dartdevcHtml(nameNoExt, jsDir, buildDir);
       }
     }