Add --analyze-only flag to dart2js

sdk/lib/_internal/compiler/implementation/compiler.dart

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compiler.dart b/sdk/lib/_internal/compiler/implementation/compiler.dart
index 75a1eaacbc5fbe8e619089f933edfa3dd9f52158..f111d9bab83a8931e15e339b0c380085369b903d 100644
--- a/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -193,6 +193,7 @@ abstract class Compiler implements DiagnosticListener {
    */
   final int maxConcreteTypeSize;
   final bool analyzeAll;
+  final bool analyzeOnly;
   final bool enableNativeLiveTypeAnalysis;
   final bool rejectDeprecatedFeatures;
   final bool checkDeprecationInSdk;
@@ -204,6 +205,8 @@ abstract class Compiler implements DiagnosticListener {
 
   bool disableInlining = false;
 
+  List<Uri> librariesToAnalyzeWhenRun;
+
   final Tracer tracer;
 
   CompilerTask measuredTask;
@@ -324,6 +327,7 @@ abstract class Compiler implements DiagnosticListener {
             bool generateSourceMap: true,
             bool disallowUnsafeEval: false,
             this.analyzeAll: false,
+            this.analyzeOnly: false,
             this.rejectDeprecatedFeatures: false,
             this.checkDeprecationInSdk: false,
             this.preserveComments: false,
@@ -634,33 +638,64 @@ abstract class Compiler implements DiagnosticListener {
   }
 
   void runCompiler(Uri uri) {
-    log('compiling $uri ($BUILD_ID)');
+    assert(uri != null || analyzeOnly);
     scanBuiltinLibraries();
-    mainApp = libraryLoader.loadLibrary(uri, null, uri);
+    if (librariesToAnalyzeWhenRun != null) {
+      for (Uri libraryUri in librariesToAnalyzeWhenRun) {
+        log('analyzing $libraryUri ($BUILD_ID)');
+        libraryLoader.loadLibrary(libraryUri, null, libraryUri);
+      }
+    }
+    if (uri != null) {
+      if (analyzeOnly) {
+        log('analyzing $uri ($BUILD_ID)');
+      } else {
+        log('compiling $uri ($BUILD_ID)');
+      }
+      mainApp = libraryLoader.loadLibrary(uri, null, uri);
+    }
     libraries.forEach((_, library) {
       maybeEnableJSHelper(library);
       maybeEnableIsolateHelper(library);
     });
-    final Element main = mainApp.find(MAIN);
-    if (main == null) {
-      reportFatalError('Could not find $MAIN', mainApp);
-    } else {
-      if (!main.isFunction()) reportFatalError('main is not a function', main);
-      FunctionElement mainMethod = main;
-      FunctionSignature parameters = mainMethod.computeSignature(this);
-      parameters.forEachParameter((Element parameter) {
-        reportFatalError('main cannot have parameters', parameter);
-      });
+    Element main = null;
+    if (mainApp != null) {
+      main = mainApp.find(MAIN);
+      if (main == null) {
+        if (!analyzeOnly) {
+          // Allow analyze only of libraries with no main.
+          reportFatalError('Could not find $MAIN', mainApp);
+        } else if (!analyzeAll) {
+          reportFatalError(
+              "Could not find $MAIN. "
+              "No source will be analyzed. "
+              "Use '--analyze-all' to analyze all code in the library.",
+              mainApp);
+        }
+      } else {
+        if (!main.isFunction()) {
+          reportFatalError('main is not a function', main);
+        }
+        FunctionElement mainMethod = main;
+        FunctionSignature parameters = mainMethod.computeSignature(this);
+        parameters.forEachParameter((Element parameter) {
+          reportFatalError('main cannot have parameters', parameter);
+        });
+      }
     }
 
     log('Resolving...');
     phase = PHASE_RESOLVING;
-    if (analyzeAll) libraries.forEach((_, lib) => fullyEnqueueLibrary(lib));
+    if (analyzeAll) {
+      libraries.forEach((_, lib) => fullyEnqueueLibrary(lib));
+    }
     backend.enqueueHelpers(enqueuer.resolution);
     processQueue(enqueuer.resolution, main);
     enqueuer.resolution.logSummary(log);
 
     if (compilationFailed) return;
+    if (analyzeOnly) return;
+    assert(main != null);
 
     log('Inferring types...');
     typesTask.onResolutionComplete(main);
@@ -707,7 +742,9 @@ abstract class Compiler implements DiagnosticListener {
 
   void processQueue(Enqueuer world, Element main) {
     world.nativeEnqueuer.processNativeClasses(libraries.values);
-    world.addToWorkList(main);
+    if (main != null) {
+      world.addToWorkList(main);
+    }
     progress.reset();
     world.forEach((WorkItem work) {
       withCurrentElement(work.element, () => work.run(this, world));