`pub upgrade` "Cannot assign to final variable 'trace='."

[zoechi]

Since update to

Dart VM version: 1.16.0-edge.2bb2a12720db04afcf6162d3e4a7e30ed638ae1e (Mon Apr 18 18:12:06 2016) on "linux_x64"

( from Dart VM version: 1.16.0-edge.bab552edaf1080fdca423029128516e1c81a3279 (Fri Apr 15 13:25:32 2016) on "linux_x64")

Deleting .pub didn't have any effect. Looks like a breaking change outside of pub anyway.

(master) $ pub upgrade --trace
Resolving dependencies... (13.3s) 
  analyzer 0.27.3
  args 0.13.4
  async 1.10.0
  barback 0.15.2+7
  boolean_selector 1.0.1
  browser 0.10.0+2
  charcode 1.1.0
  cli_util 0.0.1+2
  code_transformers 0.4.2+2
  collection 1.5.1
  convert 1.0.1
  crypto 0.9.2+1 (1.1.0 available)
  csslib 0.12.2
  dart_style 0.2.4
  glob 1.1.2
  html 0.12.2+1
  http_multi_server 2.0.1
  http_parser 2.2.1
  initialize 0.6.2+2
  logging 0.11.2
  matcher 0.12.0+2
  mime 0.9.3
  package_config 0.1.3
  path 1.3.9
  plugin 0.1.0
  polymer 1.0.0-rc.15 (1.0.0-rc.16 available)
  polymer_elements 1.0.0-rc.8
  polymer_interop 1.0.0-rc.9
  pool 1.2.3
  pub_semver 1.2.4
  reflectable 0.5.4
  shelf 0.6.5
  shelf_static 0.2.3+3
  shelf_web_socket 0.2.0
  source_map_stack_trace 1.0.4
  source_maps 0.10.1+1
  source_span 1.2.2
  stack_trace 1.6.5
  stream_channel 1.3.1
  string_scanner 0.1.4+1
  test 0.12.13
  typed_data 1.1.2
  utf 0.9.0+3
  watcher 0.9.7
  web_components 0.12.3
  web_socket_channel 1.0.2
  when 0.2.0
  which 0.1.3
  yaml 2.1.8
No dependencies changed.
Precompiling dependencies... 
Loading source assets... 
Loading initialize/build/loader_replacer, initialize, polymer_interop/src/build/minify_transformer, reflectable/src/transform_import, web_components/build/mirrors_remover and web_components traLoading initialize/build/loader_replacer, initialize, polymer_interop/src/build/minify_transformer, reflectable/src/transform_import, web_components/build/mirrors_remover and web_components traLoading initialize/build/loader_replacer, initialize, polymer_interop/src/build/minify_transformer, reflectable/src/transform_import, web_components/build/mirrors_remover and web_components traLoading initialize/build/loader_replacer, initialize, polymer_interop/src/build/minify_transformer, reflectable/src/transform_import, web_components/build/mirrors_remover and web_components transformers...
cannot assign to final variable 'trace='.

NoSuchMethodError: cannot assign to final variable 'trace='
dart:core                                           NoSuchMethodError._throwNew
package:pub/src/barback/barback_server.dart 200     BarbackServer._serveAsset.<async>
===== asynchronous gap ===========================
dart:async                                          _Completer.completeError
package:pub/src/barback/barback_server.dart 207     BarbackServer._serveAsset.<async>
===== asynchronous gap ===========================
dart:async                                          _asyncThenWrapperHelper
package:pub/src/barback/barback_server.dart         BarbackServer._serveAsset
package:pub/src/barback/barback_server.dart 118     BarbackServer.handleRequest.<async>.<fn>
===== asynchronous gap ===========================
dart:async                                          _Future.then
package:pub/src/barback/barback_server.dart 118     BarbackServer.handleRequest.<async>
===== asynchronous gap ===========================
dart:async                                          Future.Future.microtask
package:pub/src/barback/barback_server.dart         BarbackServer.handleRequest
package:shelf/src/middleware.dart 69                createMiddleware.<fn>.<fn>.<fn>.<fn>
dart:async                                          Future.Future.sync
package:shelf/src/middleware.dart 69                createMiddleware.<fn>.<fn>.<fn>
===== asynchronous gap ===========================
dart:async                                          _Future.then
package:shelf/src/middleware.dart 66                createMiddleware.<fn>.<fn>
package:shelf/shelf_io.dart 76                      handleRequest.<async>
===== asynchronous gap ===========================
dart:async                                          Future.Future.microtask
package:shelf/shelf_io.dart                         handleRequest
package:shelf/shelf_io.dart 52                      serveRequests.<fn>.<fn>
===== asynchronous gap ===========================
dart:async                                          StreamView.listen
package:shelf/shelf_io.dart 52                      serveRequests.<fn>
package:shelf/src/util.dart 20                      catchTopLevelErrors
package:shelf/shelf_io.dart 51                      serveRequests
package:pub/src/barback/base_server.dart 43         BaseServer.BaseServer
package:pub/src/barback/barback_server.dart 69      BarbackServer.BarbackServer._
package:pub/src/barback/barback_server.dart 63      BarbackServer.bind.<fn>
dart:async                                          _SyncCompleter.complete
package:pub/src/io.dart 868                         bindServer.<async>
===== asynchronous gap ===========================
dart:async                                          _Future.then
package:pub/src/barback/barback_server.dart 57      BarbackServer.bind
package:pub/src/barback/asset_environment.dart 476  AssetEnvironment._load.<fn>.<async>
===== asynchronous gap ===========================
dart:async                                          Future.Future.microtask
package:pub/src/barback/asset_environment.dart      AssetEnvironment._load.<fn>
package:pub/src/log.dart 407                        progress
package:pub/src/barback/asset_environment.dart 458  AssetEnvironment._load
package:pub/src/barback/asset_environment.dart 82   AssetEnvironment.create.<fn>.<async>
===== asynchronous gap ===========================
dart:async                                          Future.Future.microtask
package:pub/src/barback/asset_environment.dart      AssetEnvironment.create.<fn>
package:pub/src/log.dart 407                        progress
package:pub/src/barback/asset_environment.dart 74   AssetEnvironment.create
package:pub/src/entrypoint.dart 240                 Entrypoint._precompileDependencies.<async>.<fn>.<async>
===== asynchronous gap ===========================
package:pub                                         Entrypoint._precompileDependencies.<async>.<fn>
package:pub/src/log.dart 407                        progress
package:pub/src/entrypoint.dart 234                 Entrypoint._precompileDependencies.<async>
===== asynchronous gap ===========================
dart:async                                          Future.Future.microtask
package:pub/src/entrypoint.dart                     Entrypoint._precompileDependencies
package:pub/src/entrypoint.dart 204                 Entrypoint.acquireDependencies.<async>
dart:async                                          _SyncCompleter.complete
package:pub/src/entrypoint.dart 443                 Entrypoint._get.<async>
dart:async                                          _SyncCompleter.complete
package:pub/src/source/hosted.dart 122              HostedSource.downloadToSystemCache.<async>
===== asynchronous gap ===========================
dart:async                                          _asyncThenWrapperHelper
package:pub/src/entrypoint.dart                     Entrypoint.acquireDependencies
package:pub/src/command/upgrade.dart 34             UpgradeCommand.run.<async>
===== asynchronous gap ===========================
dart:async                                          Future.Future.microtask
package:pub/src/command/upgrade.dart                UpgradeCommand.run
package:args/command_runner.dart 176                CommandRunner.runCommand.<fn>
dart:async                                          Future.Future.sync
package:args/command_runner.dart 129                CommandRunner.runCommand
package:pub/src/command_runner.dart 131             PubCommandRunner.runCommand.<async>.<fn>
dart:async                                          Future.Future.sync
package:pub/src/utils.dart 113                      captureErrors.<fn>
package:stack_trace                                 Chain.capture
package:pub/src/utils.dart 127                      captureErrors
package:pub/src/command_runner.dart 131             PubCommandRunner.runCommand.<async>
dart:async                                          _SyncCompleter.complete
package:pub/src/command_runner.dart 217             PubCommandRunner._validatePlatform.<async>

[whesse]

The error mentioned above, "cannot assign to final variable trace", is expected, and the code is just written wrong. Changing the line to use a new temporary variable should remove this error. There may be another error, which is making us reach this code (which is error-reporting code) for the first time.