Re-land "Search for main in the exported names of the main library, not in the library itself."

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 067ee8832462ed521dcf011f14cf57bf43853467..e0de9ffee27b0c102d411996203d5534b3ced5d3 100644
--- a/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -416,7 +416,9 @@ abstract class Compiler implements DiagnosticListener {
   LibraryElement jsHelperLibrary;
   LibraryElement interceptorsLibrary;
   LibraryElement foreignLibrary;
+
   LibraryElement mainApp;
+  FunctionElement mainFunction;
 
   /// Initialized when dart:mirrors is loaded.
   LibraryElement mirrorsLibrary;
@@ -1025,7 +1027,7 @@ abstract class Compiler implements DiagnosticListener {
   void compileLoadedLibraries() {
     Element main = null;
     if (mainApp != null) {
-      main = mainApp.find(MAIN);
+      main = mainApp.findExported(MAIN);
       if (main == null) {
         if (!analyzeOnly) {
           // Allow analyze only of libraries with no main.
@@ -1042,14 +1044,19 @@ abstract class Compiler implements DiagnosticListener {
               "Use '--analyze-all' to analyze all code in the library."});
         }
       } else {
-        if (!main.isFunction()) {
+        if (main.isErroneous()) {
+          reportFatalError(
+              main,
+              MessageKind.GENERIC,
+              {'text': "Error: Cannot determine which '$MAIN' to use."});
+        } else if (!main.isFunction()) {
           reportFatalError(
               main,
               MessageKind.GENERIC,
               {'text': "Error: '$MAIN' is not a function."});
         }
-        FunctionElement mainMethod = main;
-        FunctionSignature parameters = mainMethod.computeSignature(this);
+        mainFunction = main;
+        FunctionSignature parameters = mainFunction.computeSignature(this);
         if (parameters.parameterCount > 2) {
           int index = 0;
           parameters.forEachParameter((Element parameter) {
@@ -1110,7 +1117,7 @@ abstract class Compiler implements DiagnosticListener {
     if (hasIsolateSupport()) {
       enqueuer.codegen.addToWorkList(
           isolateHelperLibrary.find(Compiler.START_ROOT_ISOLATE));
-      enqueuer.codegen.registerGetOfStaticFunction(mainApp.find(MAIN));
+      enqueuer.codegen.registerGetOfStaticFunction(main);
     }
     if (enabledNoSuchMethod) {
       backend.enableNoSuchMethod(enqueuer.codegen);