Fix compiler crash when we declare several (global) variables, but only define some of them.

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 9e17d7a9a503202de4c087bd2b3aba3d73dcb598..0e357afa7bcc693f00c3c52e6ee0db1a0c1f2718 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -747,10 +747,20 @@ class SsaBuilder extends ast.Visitor
     visit(initializer);
     HInstruction value = pop();
     value = potentiallyCheckOrTrustType(value, variable.type);
-    ast.SendSet sendSet = node.definitions.nodes.head;
-    closeAndGotoExit(new HReturn(value,
-        sourceInformationBuilder.buildReturn(sendSet.assignmentOperator)));
-    return closeFunction();
+    // In the case of multiple declarations (and some definitions) on the same
+    // line, the source pointer needs to point to the right initialized
+    // variable. So find the specific initialized variable we are referring to.
+    ast.Node sourceInfoNode = initializer;
+    for (var definition in node.definitions) {
+      if (definition is ast.SendSet &&
+          definition.selector.toString() == variable.name) {

[Siggi Cherem (dart-lang), 2016/11/02 18:17:20]

toString is mainly something we use for debugging (for complex nodes it can
recreate a string representation of the ast). In this case I think it's safe to
assume that the selctor is an identifier and do:

  definition.selector.asIdentifier().source == variable.name

[Emily Fortuna, 2016/11/02 18:24:58]

Done.

+        sourceInfoNode = definition.assignmentOperator;

[Siggi Cherem (dart-lang), 2016/11/02 18:17:20]

let's add a break here as well (it doesn't change things, but we'd stop
iterating the rest of the definitions if there are more.

[Emily Fortuna, 2016/11/02 18:24:58]

Done.

+      }
+    }
+
+    closeAndGotoExit(new HReturn(value, sourceInformationBuilder.buildReturn(
+            sourceInfoNode)));
+    return closeFunction(); // token or source

[Siggi Cherem (dart-lang), 2016/11/02 18:17:20]

remove trailing comment?

[Emily Fortuna, 2016/11/02 18:24:58]

whoops thanks.

   }
 
   /**