Fix expression evaluation failure after hot restart

The lifetime of program compilers in JavaScriptBundler is too short,
moving the program compiler cache to FrontendCompiler instead
so the ProgramCompilers created during main compilation could be reused
for expression evaluation until the next compilation.

Closes: #45266
Change-Id: I7d41476c7064f16cab2783f88c49114a08a0c038
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/190301
Commit-Queue: Anna Gringauze <annagrin@google.com>
Reviewed-by: Jonah Williams <jonahwilliams@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Mark Zhou <markzipan@google.com>

pkg/frontend_server/lib/frontend_server.dart

@@ -10,7 +10,11 @@ import 'dart:io' hide FileSystemEntity;
 
 import 'package:args/args.dart';
 import 'package:dev_compiler/dev_compiler.dart'
-    show DevCompilerTarget, ExpressionCompiler, parseModuleFormat;
+    show
+        DevCompilerTarget,
+        ExpressionCompiler,
+        parseModuleFormat,
+        ProgramCompiler;
 
 // front_end/src imports below that require lint `ignore_for_file`
 // are a temporary state of things until frontend team builds better api
@@ -631,14 +635,15 @@ class FrontendCompiler implements CompilerInterface {
     final sourceMapsFileSink = sourceMapsFile.openWrite();
     final metadataFileSink =
         emitDebugMetadata ? metadataFile.openWrite() : null;
-    await _bundler.compile(
+    final kernel2JsCompilers = await _bundler.compile(
         results.classHierarchy,
         results.coreTypes,
         results.loadedLibraries,
         sourceFileSink,
         manifestFileSink,
         sourceMapsFileSink,
         metadataFileSink);
+    cachedProgramCompilers.addAll(kernel2JsCompilers);
     await Future.wait([
       sourceFileSink.close(),
       manifestFileSink.close(),
@@ -806,6 +811,12 @@ class FrontendCompiler implements CompilerInterface {
     }
   }
 
+  /// Program compilers per module.
+  ///
+  /// Produced suring initial compilation of the module to JavaScript,
+  /// cached to be used for expression compilation in [compileExpressionToJs].
+  final Map<String, ProgramCompiler> cachedProgramCompilers = {};
+
   @override
   Future<Null> compileExpressionToJs(
       String libraryUri,
@@ -822,7 +833,7 @@ class FrontendCompiler implements CompilerInterface {
       reportError('JavaScript bundler is null');
       return;
     }
-    if (!_bundler.compilers.containsKey(moduleName)) {
+    if (!cachedProgramCompilers.containsKey(moduleName)) {
       reportError('Cannot find kernel2js compiler for $moduleName.');
       return;
     }
@@ -833,13 +844,13 @@ class FrontendCompiler implements CompilerInterface {
     _processedOptions.ticker
         .logMs('Compiling expression to JavaScript in $moduleName');
 
-    var kernel2jsCompiler = _bundler.compilers[moduleName];
+    final kernel2jsCompiler = cachedProgramCompilers[moduleName];
     Component component = _generator.lastKnownGoodComponent;
     component.computeCanonicalNames();
 
     _processedOptions.ticker.logMs('Computed component');
 
-    var expressionCompiler = new ExpressionCompiler(
+    final expressionCompiler = new ExpressionCompiler(
       _compilerOptions,
       parseModuleFormat(_options['dartdevc-module-format'] as String),
       errors,
@@ -848,10 +859,10 @@ class FrontendCompiler implements CompilerInterface {
       component,
     );
 
-    var procedure = await expressionCompiler.compileExpressionToJs(
+    final procedure = await expressionCompiler.compileExpressionToJs(
         libraryUri, line, column, jsFrameValues, expression);
 
-    var result = errors.length > 0 ? errors[0] : procedure;
+    final result = errors.length > 0 ? errors[0] : procedure;
 
     // TODO(annagrin): kernelBinaryFilename is too specific
     // rename to _outputFileName?

pkg/frontend_server/lib/src/javascript_bundle.dart

@@ -29,8 +29,7 @@ class JavaScriptBundler {
       this.emitDebugMetadata = false,
       this.soundNullSafety = false,
       String moduleFormat})
-      : compilers = <String, ProgramCompiler>{},
-        _moduleFormat = parseModuleFormat(moduleFormat ?? 'amd') {
+      : _moduleFormat = parseModuleFormat(moduleFormat ?? 'amd') {
     _summaries = <Component>[];
     _summaryUris = <Uri>[];
     _moduleImportForSummary = <Uri, String>{};
@@ -64,7 +63,6 @@ class JavaScriptBundler {
   final PackageConfig _packageConfig;
   final bool useDebuggerModuleNames;
   final bool emitDebugMetadata;
-  final Map<String, ProgramCompiler> compilers;
   final ModuleFormat _moduleFormat;
   final bool soundNullSafety;
 
@@ -75,7 +73,7 @@ class JavaScriptBundler {
   Map<Uri, Component> _uriToComponent;
 
   /// Compile each component into a single JavaScript module.
-  Future<void> compile(
+  Future<Map<String, ProgramCompiler>> compile(
       ClassHierarchy classHierarchy,
       CoreTypes coreTypes,
       Set<Library> loadedLibraries,
@@ -88,6 +86,7 @@ class JavaScriptBundler {
     var metadataOffset = 0;
     final manifest = <String, Map<String, List<int>>>{};
     final Set<Uri> visited = <Uri>{};
+    final Map<String, ProgramCompiler> kernel2JsCompilers = {};
 
     final importToSummary = Map<Library, Component>.identity();
     final summaryToModule = Map<Component, String>.identity();
@@ -150,9 +149,8 @@ class JavaScriptBundler {
       // so it can map dart symbols to js symbols
       // [issue 40273](https://github.com/dart-lang/sdk/issues/40273)
 
-      // program compiler is used by ExpressionCompiler to evaluate expressions
-      // on demand
-      compilers[moduleName] = compiler;
+      // Save program compiler to reuse for expression evaluation.
+      kernel2JsCompilers[moduleName] = compiler;
 
       final moduleUrl = urlForComponentUri(moduleUri);
       String sourceMapBase;
@@ -201,6 +199,8 @@ class JavaScriptBundler {
       };
     }
     manifestSink.add(utf8.encode(json.encode(manifest)));
+
+    return kernel2JsCompilers;
   }
 }
 

pkg/frontend_server/test/src/javascript_bundle_test.dart

@@ -106,8 +106,14 @@ void main() {
     final metadataSink = _MemorySink();
     final coreTypes = CoreTypes(testComponent);
 
-    await javaScriptBundler.compile(ClassHierarchy(testComponent, coreTypes),
-        coreTypes, {}, codeSink, manifestSink, sourcemapSink, metadataSink);
+    final compilers = await javaScriptBundler.compile(
+        ClassHierarchy(testComponent, coreTypes),
+        coreTypes,
+        {},
+        codeSink,
+        manifestSink,
+        sourcemapSink,
+        metadataSink);
 
     final Map manifest = json.decode(utf8.decode(manifestSink.buffer));
     final String code = utf8.decode(codeSink.buffer);
@@ -122,6 +128,9 @@ void main() {
 
     // verify source map url is correct.
     expect(code, contains('sourceMappingURL=c.dart.lib.js.map'));
+
+    // verify program compilers are created.
+    expect(compilers.keys, equals([urlForComponentUri(library.importUri)]));
   });
 
   test('converts package: uris into /packages/ uris', () async {