[dart2js] Don't emit deferred loading logs in part files when flag is disabled.

Change-Id: I70a3a3a3c7bd56d8fd994e766f0ab2ab8c1f9ec4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/432820
Reviewed-by: Mayank Patke <[email protected]>
Commit-Queue: Nate Biggs <[email protected]>

Author: natebiggs

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart

@@ -416,16 +416,24 @@ class ModelEmitter {
     js.LiteralString partFileName, {
     js.Expression? code,
   }) {
-    return js.js.statement(
-      '((s,d,e) => {s[d] = s[d] || {}; s[d][e] = s[d][e] || [];'
-      's[d][e].push({p:#part,e:"beginPart"});})'
-      '(self,#deferredInitializers, #eventLog)',
-      {
-        'deferredInitializers': js.string(deferredInitializersGlobal),
-        'eventLog': js.string(INITIALIZATION_EVENT_LOG),
-        'part': partFileName,
-      },
-    );
+    if (_options.enableDeferredLoadingEventLog) {
+      return js.js.statement(
+        '((s,d,e) => {s[d] = s[d] || {}; s[d][e] = s[d][e] || [];'
+        's[d][e].push({p:#part,e:"beginPart"});})'
+        '(self,#deferredInitializers, #eventLog)',
+        {
+          'deferredInitializers': js.string(deferredInitializersGlobal),
+          'eventLog': js.string(INITIALIZATION_EVENT_LOG),
+          'part': partFileName,
+        },
+      );
+    } else {
+      return js.js.statement(
+        '((s,d) => {s[d] = s[d] || {};})'
+        '(self,#deferredInitializers)',
+        {'deferredInitializers': js.string(deferredInitializersGlobal)},
+      );
+    }
   }
 
   js.Statement buildStartupMetrics() {
@@ -684,17 +692,28 @@ var $startupMetricsGlobal =
     String hash = hasher.getHash();
 
     // Now we copy the deferredInitializer.current into its correct hash.
-    final epilogue = js.js.statement(
-      '((d,h)=>{d[h]=d.current; '
-      'd.#eventLog.push({p:#part,e:"endPart",h:h})})'
-      '(#deferredInitializers,#hash)',
-      {
-        'deferredInitializers': deferredInitializersGlobal,
-        'hash': js.string(hash),
-        'eventLog': js.string(INITIALIZATION_EVENT_LOG),
-        'part': outputFileJsString,
-      },
-    );
+    js.Statement epilogue;
+    if (_options.enableDeferredLoadingEventLog) {
+      epilogue = js.js.statement(
+        '((d,h)=>{d[h]=d.current; '
+        'd.#eventLog.push({p:#part,e:"endPart",h:h})})'
+        '(#deferredInitializers,#hash)',
+        {
+          'deferredInitializers': deferredInitializersGlobal,
+          'hash': js.string(hash),
+          'eventLog': js.string(INITIALIZATION_EVENT_LOG),
+          'part': outputFileJsString,
+        },
+      );
+    } else {
+      epilogue = js.js.statement(
+        '((d)=>{d[#hash]=d.current;})(#deferredInitializers)',
+        {
+          'deferredInitializers': deferredInitializersGlobal,
+          'hash': js.string(hash),
+        },
+      );
+    }
     output.add('\n');
     output.add(
       js

pkg/compiler/test/dump_info/data/deferred/main.dart

@@ -105,7 +105,7 @@
   "id": "outputUnit/1",
   "kind": "outputUnit",
   "name": "1",
-  "size": 1184,
+  "size": 1035,
   "filename": "out_1.part.js",
   "imports": [
     "lib"

pkg/compiler/test/dump_info/data/deferred_future/main.dart

@@ -113,7 +113,7 @@
   "id": "outputUnit/1",
   "kind": "outputUnit",
   "name": "1",
-  "size": 908,
+  "size": 759,
   "filename": "out_1.part.js",
   "imports": [
     "lib1"

pkg/compiler/test/end_to_end/bundle_parts_test.dart

@@ -15,6 +15,17 @@ const String verifyParts = '''
 if (!\$__dart_deferred_initializers__) {
   throw 'Did not intialize \$__dart_deferred_initializers__';
 }
+// Expect 'current', and 2 hashes for part files.
+if (Object.keys(\$__dart_deferred_initializers__).length != 3) {
+  var data =  JSON.stringify(\$__dart_deferred_initializers__);
+  throw '\$__dart_deferred_initializers__ has unexpected format: ' + data;
+}
+''';
+
+const String verifyPartsWithEventLog = '''
+if (!\$__dart_deferred_initializers__) {
+  throw 'Did not intialize \$__dart_deferred_initializers__';
+}
 // Expect 'eventLog', 'current', and 2 hashes for part files.
 if (Object.keys(\$__dart_deferred_initializers__).length != 4) {
   var data =  JSON.stringify(\$__dart_deferred_initializers__);
@@ -26,7 +37,10 @@ Future<Directory> createTempDir() {
   return Directory.systemTemp.createTemp('dart2js_bundle_parts_test-');
 }
 
-Future<void> runTestWithOptions(List<String> options) async {
+Future<void> runTestWithOptions(
+  List<String> options,
+  String verificationString,
+) async {
   print('Running with flags: $options');
   final tmpDir = await createTempDir();
   Uri inUri = Platform.script.resolve('deferred_data/deferred_main.dart');
@@ -41,7 +55,10 @@ Future<void> runTestWithOptions(List<String> options) async {
     await part2.readAsBytes(),
     mode: FileMode.append,
   );
-  await bundledParts.writeAsString('\n$verifyParts', mode: FileMode.append);
+  await bundledParts.writeAsString(
+    '\n$verificationString',
+    mode: FileMode.append,
+  );
   final result = executeJsWithD8([bundledPartsUri]);
   if (result.exitCode != 0) {
     Expect.fail(
@@ -53,6 +70,10 @@ Future<void> runTestWithOptions(List<String> options) async {
 }
 
 void main() async {
-  await runTestWithOptions([]);
-  await runTestWithOptions(['--minify']);
+  await runTestWithOptions([], verifyParts);
+  await runTestWithOptions(['--minify'], verifyParts);
+  await runTestWithOptions([
+    '--minify',
+    '--log-deferred-loading-events',
+  ], verifyPartsWithEventLog);
 }

sdk/lib/_internal/js_runtime/lib/js_helper.dart

@@ -3244,8 +3244,10 @@ void _addEvent({
 ///
 /// The events are printed in reverse chronological order in case the tail gets
 /// truncated, the newest events are retained.
-String _getEventLog() {
+String? _getEventLog() {
   var initializationEventLog = JS_EMBEDDED_GLOBAL('', INITIALIZATION_EVENT_LOG);
+  if (initializationEventLog == null) return null;
+
   final o = JS('', 'Array.from(#).reverse()', initializationEventLog);
   JS(
     '',