Better error when force-compile fails

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

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:io';
 import 'package:analyzer/src/command_line/arguments.dart'
     show
         defineAnalysisArguments,
         filterUnknownArguments,
         ignoreUnrecognizedFlagsFlag;
@@ skipping 168 matching lines @@
     moduleRoot = path.dirname(firstOutPath);
     modulePath = path.basenameWithoutExtension(firstOutPath);
   }
 
   var unit = new BuildUnit(modulePath, libraryRoot, argResults.rest,
       (source) => _moduleForLibrary(moduleRoot, source, compilerOpts));
 
   var module = compiler.compile(unit, compilerOpts);
   module.errors.forEach(printFn);
 
-  if (!module.isValid) throw new CompileErrorException();
+  if (!module.isValid) {
+    throw compilerOpts.unsafeForceCompile
+        ? new ForceCompileErrorException()
+        : new CompileErrorException();
+  }
 
   // Write JS file, as well as source map and summary (if requested).
   for (var i = 0; i < outPaths.length; i++) {
     module.writeCodeSync(moduleFormats[i], outPaths[i],
         singleOutFile: singleOutFile);
   }
   if (module.summaryBytes != null) {
     var summaryPaths = compilerOpts.summaryOutPath != null
         ? [compilerOpts.summaryOutPath]
         : outPaths.map((p) =>
@@ skipping 55 matching lines @@
 }
 
 void _usageException(String message) {
   throw new UsageException(message, _usageMessage);
 }
 
 /// Thrown when the input source code has errors.
 class CompileErrorException implements Exception {
   toString() => '\nPlease fix all errors before compiling (warnings are okay).';
 }
+
+/// Thrown when force compilation failed (probably due to static errors).
+class ForceCompileErrorException extends CompileErrorException {
+  toString() =>
+      '\nForce-compilation not successful. Please check static errors.';
+}