Re-enable source maps

lib/src/codegen/js_printer.dart

 // Copyright (c) 2015, 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.
 
 library dev_compiler.src.codegen.js_printer;
 
 import 'dart:io' show Directory, File, Platform, Process;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:path/path.dart' as path;
@@ skipping 54 matching lines @@
   Uri uri;
 
   SourceMapPrintingContext(this.printer, this.outputDir);
 
   void emit(String string) {
     printer.add(string);
   }
 
   void enterNode(JS.Node jsNode) {
     AstNode node = jsNode.sourceInformation;
-    if (node is CompilationUnit) {
-      unit = node;
+    if (node == null || node.offset == -1) return;
+    if (node.parent is CompilationUnit) {

[Jennifer Messerly, 2015/11/09 18:38:46]

We'll keep making the URI over and over, right? Since many things have the
CompilationUnit as their parent.

The idea of the old code is we'd visit the compilation unit at some point
(which, oops, should've been an invariant we asserted somewhere).

I think we lost the _visit call on the CompilationUnit. Maybe that's an
alternate way to fix this?

Alternatively, it's probably worth adding a unit != null check here, so we only
go down this path once, and then below, assert that unit must not be null. Also
exitNode needs to be changed to match the new logic here in enterNode ...

[vsm, 2015/11/09 19:15:42]

If there is a natural visit on the CompilationUnit, that seems best - but since
we're mixing parts up, I didn't think there would be.  What do you think?

I'll make the other fixes you suggested.

[vsm, 2015/11/09 19:15:42]

BTW, I tested this with Angular - seems like we have some declarations without a
unit?  The old code had a 

if (unit ==null && ... ) return;

Will dig in further.

+      unit = node.parent;
       uri = _makeRelativeUri(unit.element.source.uri);
-      return;
     }
-    if (unit == null || node == null || node.offset == -1) return;
 
     var loc = _location(node.offset);
     var name = _getIdentifier(node);
     if (name != null) {
       // TODO(jmesserly): mark only uses the beginning of the span, but
       // we're required to pass this as a valid span.
       var end = _location(node.end);
       printer.mark(new SourceMapSpan(loc, end, name, isIdentifier: true));
     } else {
       printer.mark(loc);
@@ skipping 18 matching lines @@
 
     // TODO(jmesserly): in many cases marking the end will be unnecessary.
     printer.mark(_location(node.end));
   }
 
   String _getIdentifier(AstNode node) {
     if (node is SimpleIdentifier) return node.name;
     return null;
   }
 }