Translate package URIs to resource URIs for diagnostics.

pkg/compiler/lib/src/apiimpl.dart

Index: pkg/compiler/lib/src/apiimpl.dart
diff --git a/pkg/compiler/lib/src/apiimpl.dart b/pkg/compiler/lib/src/apiimpl.dart
index a36ee9ab9ba9beb8328e606bbd9292d64c67769c..a7c937abe1c5f12ef7f7beecca6da79710ceb754 100644
--- a/pkg/compiler/lib/src/apiimpl.dart
+++ b/pkg/compiler/lib/src/apiimpl.dart
@@ -423,7 +423,13 @@ class Compiler extends leg.Compiler {
     if (span == null || span.uri == null) {
       callUserHandler(null, null, null, '$message', kind);
     } else {
-      callUserHandler(span.uri, span.begin, span.end, '$message', kind);
+      // Translate uri into a resource uri if possible.
+      Uri uri = translateUri(null, span.uri);

[ahe, 2015/06/26 07:56:05]

If I understand this correctly, this may invoke a user-provided plugin for
resolving packages.

This code assumes that plugin is idempotent. However, it might be
extraordinarily complicated to implement a plugin such that it is idempotent,
for example, let's say you provide a plugin which reads an external resource
(for example searches directories, or reads a file). 

Also, what happens if the user-provided plugin throws an exception?

There is one source of truth, and that was established when calling the input
provider. If that URI is preserved and used here, no assumptions about
idempotency are needed.

[Johnni Winther, 2015/06/26 10:15:06]

Good point. Will cache the resource URIs.

[Johnni Winther, 2015/06/26 17:06:54]

No need for extra caching; it was already in Script.resourceUri.

+      if (uri == null) {
+        // Use readable uri as fallback.
+        uri = span.uri;
+      }
+      callUserHandler(uri, span.begin, span.end, '$message', kind);
     }
   }