Step one towards stable error messages with details:

pkg/polymer/CHANGELOG.md

Index: pkg/polymer/CHANGELOG.md
diff --git a/pkg/polymer/CHANGELOG.md b/pkg/polymer/CHANGELOG.md
index 3aaedd21808629c95dbd30f230b55fe6d33aa54d..dea6687a227893b0138a529ca986b0d72d4dca1c 100644
--- a/pkg/polymer/CHANGELOG.md
+++ b/pkg/polymer/CHANGELOG.md
@@ -1,29 +1,31 @@
-# changelog
-
 This file contains highlights of what changes on each version of the polymer
 package. We will also note important changes to the polyfill packages (observe,
 web_components, and template_binding) if they impact polymer.
 
-#### Pub version 0.13.0+2
+#### 0.13.1-dev
+  * Upgraded error messages to have a unique and stable identifier. This
+    requires a version of `code_transformers` newer than `0.2.2-dev`.
+
+#### 0.13.0+2
   * Update internal transformers to delete .concat.js and .map files when in
     release mode, saving about 1MB of space in the built output.
 
-#### Pub version 0.13.0+1
+#### 0.13.0+1
   * Bug fix for http://dartbug.com/18171. Elements that extend other elements
     but don't have a template will still inherit styles from those elements.
   * Bug fix for http://dartbug.com/20544. Better runtime logging when attributes
     are defined on an element but have no corresponding property on the class.
 
-#### Pub version 0.13.0
+#### 0.13.0
   * Update to match polymer 0.3.5 ([polymer-dev#5d00e4b][5d00e4b]). There was a
     breaking change in the web_components package where selecting non-rendered 
     elements doesn't work, but it shouldn't affect most people. See 
     https://github.com/Polymer/ShadowDOM/issues/495.
 
-#### Pub version 0.12.2+1
+#### 0.12.2+1
   * Small bug fix for `polymer:new_element`
 
-#### Pub version 0.12.2
+#### 0.12.2
   * Fix for [20539](http://dartbug.com/20539). Log widget will now html escape
     messages.
   * Fix for [20538](http://dartbug.com/20538). Log widget will now surface lint
@@ -36,7 +38,7 @@ web_components, and template_binding) if they impact polymer.
     cannot be extended.
   * other bug fixes in `polymer:new_entry`.
 
-#### Pub version 0.12.1
+#### 0.12.1
   * **New**: When running in pub-serve, any warnings and errors detected by the
     polymer transformers will be displayed in the lower-right corner of your
     entrypoint page. You can opt-out by adding this option to your pubspec:
@@ -82,31 +84,31 @@ web_components, and template_binding) if they impact polymer.
     longer throw an error.
 
 
-#### Pub version 0.12.0+7
+#### 0.12.0+7
   * Widen the constraint on `unittest`.
 
-#### Pub version 0.12.0+6
+#### 0.12.0+6
   * Widen the constraint on analyzer.
   * Support for `_src` and similar attributes in polymer transformers.
 
-#### Pub version 0.12.0+5
+#### 0.12.0+5
   * Raise the lower bound on the source_maps constraint to exclude incompatible
     versions.
 
-#### Pub version 0.12.0+4
+#### 0.12.0+4
   * Widen the constraint on source_maps.
 
-#### Pub version 0.12.0+3
+#### 0.12.0+3
   * Fix a final use of `getLocationMessage`.
 
-#### Pub version 0.12.0+2
+#### 0.12.0+2
   * Widen the constraint on barback.
 
-#### Pub version 0.12.0+1
+#### 0.12.0+1
   * Switch from `source_maps`' `Span` class to `source_span`'s `SourceSpan`
     class.
 
-#### Pub version 0.12.0
+#### 0.12.0
  * Updated to match polymer 0.3.4 ([polymer-dev#6ad2d61][6ad2d61]), this
    includes the following changes:
      * added @ComputedProperty
@@ -123,25 +125,25 @@ web_components, and template_binding) if they impact polymer.
  * Fix for [17596](https://code.google.com/p/dart/issues/detail?id=17596)
  * Fix for [19770](https://code.google.com/p/dart/issues/detail?id=19770)
 
-#### Pub version 0.11.0+5
+#### 0.11.0+5
   * fixes web_components version in dependencies
 
-#### Pub version 0.11.0+4
+#### 0.11.0+4
   * workaround for bug
     [19653](https://code.google.com/p/dart/issues/detail?id=19653)
 
-#### Pub version 0.11.0+3
+#### 0.11.0+3
   * update readme
 
-#### Pub version 0.11.0+2
+#### 0.11.0+2
   * bug fix: event listeners were not in the dirty-checking zone
   * bug fix: dispatch event in auto-binding
 
-#### Pub version 0.11.0+1
+#### 0.11.0+1
   * Added a workaround for bug in HTML imports (issue
     [19650](https://code.google.com/p/dart/issues/detail?id=19650)).
 
-#### Pub version 0.11.0
+#### 0.11.0
   * **breaking change**: platform.js and dart_support.js must be specified in
     your entry points at the beginning of `<head>`.
   * **breaking change**: polymer.html is not required in entrypoints, but it is
@@ -154,14 +156,14 @@ web_components, and template_binding) if they impact polymer.
     places like CSS selectors. To make it reflected back to an attribute use
     `@PublishedProperty(reflect: true)`.
 
-#### Pub version 0.10.1
+#### 0.10.1
   * Reduce the analyzer work by mocking a small subset of the core libraries.
 
-#### Pub version 0.10.0+1
+#### 0.10.0+1
   * Better error message on failures in pub-serve/pub-build when pubspec.yaml
     is missing or has a wrong configuration for the polymer transformers.
 
-#### Pub version 0.10.0
+#### 0.10.0
   * Interop with polymer-js elements now works.
   * Polymer polyfills are now consolidated in package:web_components, which is
     identical to platform.js from http://polymer-project.org.
@@ -178,36 +180,36 @@ web_components, and template_binding) if they impact polymer.
   * **breaking change**: @initMethod and @CustomTag are only supported on
     public classes/methods.
 
-#### Pub version 0.9.5
+#### 0.9.5
   * Improvements on how to handle cross-package HTML imports.
 
-#### Pub version 0.9.4
+#### 0.9.4
   * Removes unused dependency on csslib.
 
-#### Pub version 0.9.3+3
+#### 0.9.3+3
   * Removes workaround now that mirrors implement a missing feature. Requires
     SDK >= 1.1.0-dev.5.0.
 
-#### Pub version 0.9.3+2
+#### 0.9.3+2
   * Fix rare canonicalization bug
     [15694](https://code.google.com/p/dart/issues/detail?id=15694)
 
-#### Pub version 0.9.3+1
+#### 0.9.3+1
   * Fix type error in runner.dart
     [15649](https://code.google.com/p/dart/issues/detail?id=15649).
 
-#### Pub version 0.9.3
+#### 0.9.3
   * pub-build now runs the linter automatically
 
-#### Pub version 0.9.2+4
+#### 0.9.2+4
   * fix linter on SVG and MathML tags with XML namespaces
 
-#### Pub version 0.9.2+3
+#### 0.9.2+3
   * fix [15574](https://code.google.com/p/dart/issues/detail?id=15574),
     event bindings in dart2js, by working around issue
     [15573](https://code.google.com/p/dart/issues/detail?id=15573)
 
-#### Pub version 0.9.2+2
+#### 0.9.2+2
   * fix enteredView in dart2js, by using custom_element >= 0.9.1+1
 
 [6ad2d61]:https://github.com/Polymer/polymer-dev/commit/6a3e1b0e2a0bbe546f6896b3f4f064950d7aee8f