Allow ddc in kernel mode to output used inputs

This change basically consists of these steps:
* Enable the incremental compiler to trace used inputs.
* Translate used libraries into used dill inputs.
* Output the list of used dills.

Bug: #37788
Change-Id: Icbc3942226f50ba733196586fac8715e21d6ed34
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/112385
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Vijay Menon <vsm@google.com>
Reviewed-by: Mark Zhou <markzipan@google.com>

pkg/dev_compiler/lib/src/kernel/command.dart

@@ -101,7 +101,9 @@ Future<CompilerResult> _compile(List<String> args,
     ..addFlag('compile-sdk',
         help: 'Build an SDK module.', defaultsTo: false, hide: true)
     ..addOption('libraries-file',
-        help: 'The path to the libraries.json file for the sdk.');
+        help: 'The path to the libraries.json file for the sdk.')
+    ..addOption('used-inputs-file',
+        help: 'If set, the file to record inputs used.', hide: true);
   SharedCompilerOptions.addArguments(argParser);
 
   var declaredVariables = parseAndRemoveDeclaredVariables(args);
@@ -237,6 +239,7 @@ Future<CompilerResult> _compile(List<String> args,
   List<Component> doneInputSummaries;
   fe.IncrementalCompiler incrementalCompiler;
   fe.WorkerInputComponent cachedSdkInput;
+  bool recordUsedInputs = argResults['used-inputs-file'] != null;
   if (useAnalyzer || !useIncrementalCompiler) {
     compilerState = await fe.initializeCompiler(
         oldCompilerState,
@@ -267,7 +270,8 @@ Future<CompilerResult> _compile(List<String> args,
             TargetFlags(trackWidgetCreation: trackWidgetCreation)),
         fileSystem: fileSystem,
         experiments: experiments,
-        environmentDefines: declaredVariables);
+        environmentDefines: declaredVariables,
+        trackNeededDillLibraries: recordUsedInputs);
     incrementalCompiler = compilerState.incrementalCompiler;
     cachedSdkInput =
         compilerState.workerInputCache[sourcePathToUri(sdkSummaryPath)];
@@ -386,6 +390,31 @@ Future<CompilerResult> _compile(List<String> args,
     }
   }
 
+  if (recordUsedInputs) {
+    Set<Uri> usedOutlines = Set<Uri>();
+    if (!useAnalyzer && useIncrementalCompiler) {
+      compilerState.incrementalCompiler
+          .updateNeededDillLibrariesWithHierarchy(result.classHierarchy, null);
+      for (Library lib
+          in compilerState.incrementalCompiler.neededDillLibraries) {
+        if (lib.importUri.scheme == "dart") continue;
+        Uri uri = compilerState.libraryToInputDill[lib.importUri];
+        if (uri == null) {
+          throw StateError("Library ${lib.importUri} was recorded as used, "
+              "but was not in the list of known libraries.");
+        }
+        usedOutlines.add(uri);
+      }
+    } else {
+      // Used inputs wasn't recorded: Say we used everything.
+      usedOutlines.addAll(summaryModules.keys);
+    }
+
+    var outputUsedFile = File(argResults['used-inputs-file'] as String);
+    outputUsedFile.createSync(recursive: true);
+    outputUsedFile.writeAsStringSync(usedOutlines.join("\n"));
+  }
+
   await Future.wait(outFiles);
   return CompilerResult(0, kernelState: compilerState);
 }

pkg/front_end/lib/src/api_unstable/ddc.dart

@@ -142,7 +142,8 @@ Future<InitializedCompilerState> initializeIncrementalCompiler(
     Target target,
     {FileSystem fileSystem,
     Map<ExperimentalFlag, bool> experiments,
-    Map<String, String> environmentDefines}) async {
+    Map<String, String> environmentDefines,
+    bool trackNeededDillLibraries: false}) async {
   inputSummaries.sort((a, b) => a.toString().compareTo(b.toString()));
 
   IncrementalCompiler incrementalCompiler;
@@ -189,6 +190,7 @@ Future<InitializedCompilerState> initializeIncrementalCompiler(
     workerInputCache[sdkSummary] = cachedSdkInput;
     incrementalCompiler = new IncrementalCompiler.fromComponent(
         new CompilerContext(processedOpts), cachedSdkInput.component);
+    incrementalCompiler.trackNeededDillLibraries = trackNeededDillLibraries;
   } else {
     options = oldState.options;
     options.inputSummaries = inputSummaries;
@@ -205,6 +207,7 @@ Future<InitializedCompilerState> initializeIncrementalCompiler(
     // Reuse the incremental compiler, but reset as needed.
     incrementalCompiler = oldState.incrementalCompiler;
     incrementalCompiler.invalidateAllSources();
+    incrementalCompiler.trackNeededDillLibraries = trackNeededDillLibraries;
     options.packagesFileUri = packagesFile;
     options.fileSystem = fileSystem;
     processedOpts.clearFileSystemCache();
@@ -215,6 +218,10 @@ Future<InitializedCompilerState> initializeIncrementalCompiler(
       incrementalCompiler: incrementalCompiler);
 
   CanonicalName nameRoot = cachedSdkInput.component.root;
+  Map<Uri, Uri> libraryToInputDill;
+  if (trackNeededDillLibraries) {
+    libraryToInputDill = new Map<Uri, Uri>();
+  }
   List<int> loadFromDillIndexes = new List<int>();
 
   // Notice that the ordering of the input summaries matter, so we need to
@@ -238,6 +245,9 @@ Future<InitializedCompilerState> initializeIncrementalCompiler(
       var component = cachedInput.component;
       for (var lib in component.libraries) {
         lib.isExternal = cachedInput.externalLibs.contains(lib.importUri);
+        if (trackNeededDillLibraries) {
+          libraryToInputDill[lib.importUri] = inputSummary;
+        }
       }
       component.computeCanonicalNames();
       doneInputSummaries[i] = component;
@@ -258,13 +268,19 @@ Future<InitializedCompilerState> initializeIncrementalCompiler(
             .loadComponent(bytes, nameRoot, alwaysCreateNewNamedNodes: true));
     workerInputCache[summary] = cachedInput;
     doneInputSummaries[index] = cachedInput.component;
+    if (trackNeededDillLibraries) {
+      for (var lib in cachedInput.component.libraries) {
+        libraryToInputDill[lib.importUri] = summary;
+      }
+    }
   }
 
   incrementalCompiler.setModulesToLoadOnNextComputeDelta(doneInputSummaries);
 
   return new InitializedCompilerState(options, processedOpts,
       workerInputCache: workerInputCache,
-      incrementalCompiler: incrementalCompiler);
+      incrementalCompiler: incrementalCompiler,
+      libraryToInputDill: libraryToInputDill);
 }
 
 Future<DdcResult> compile(InitializedCompilerState compilerState,