Version solver should skip versions with unparseable pubspecs

[kevmoo]

From @stephan-gruen on December 1, 2016 11:2

sdk 1.21.0-dev.11.0
Windows 7 / WebStorm 2016.3.1
All works well with the stable sdk version 1.20.1, but I'm not able to use the latest dev sdk version (I tryed 9 and 11) anymore, because pub throws "Duplicate mapping key" if polymer_elements are used.

Not really sure if this is a sdk or a pub error or what to do or update to solve it.

Pub:

Working dir: C:\Users\Stephan\dart\Angular2\test
D:\dart\dartium-1.21.0-dev.11.0\dart-sdk\bin\pub.bat get
Resolving dependencies...
Error on line 198, column 1 of ..\..\..\AppData\Roaming\Pub\Cache\hosted\pub.dartlang.org\polymer_elements-1.0.0-rc.9\pubspec.yaml: Duplicate mapping key.
environment:
^^^^^^^^^^^
Process finished with exit code 65

yaml:

name: test
description: A Dart app that uses Angular 2
version: 0.0.1
environment:
  sdk: '>=1.19.0 <2.0.0'
dependencies:
  angular2: ^2.1.1
  angular2_components: ^0.2.0
  browser: ^0.10.0
  polymer: ^1.0.0-rc.18
  polymer_elements: ^1.0.0-rc.9
  web_components: ^0.12.0
dev_dependencies:
  dart_to_js_script_rewriter: ^1.0.1
transformers:
- polymer:
    entry_points: web/index.html
- angular2:
    platform_directives:
    - 'package:angular2/common.dart#COMMON_DIRECTIVES'
    platform_pipes:
    - 'package:angular2/common.dart#COMMON_PIPES'
    entry_points: web/main.dart
- dart_to_js_script_rewriter
- $dart2js:
    $include: '**/*.bootstrap.initialize.dart'
    minify: true
    commandLineOptions:
    - --trust-type-annotations
    - --trust-primitives

If you do not specify a version for polymer_elements pub will simply get the first version:

Working dir: C:\Users\Stephan\dart\Angular2\test
D:\dart\dartium-1.21.0-dev.11.0\dart-sdk\bin\pub.bat get
Resolving dependencies...
+ polymer_elements 0.0.2 (0.3.0 available)
Changed 1 dependency!
Process finished with exit code 0

Copied from original issue: dart-lang/sdk#27956

[nex3]

This all seems like the expected behavior to me. If you look at the polymer_elements 1.0.0-rc.9 pubspec, it does in fact have two environment: keys in the root mapping. This is invalid. Pub is telling you it's invalid. What's the issue?

[kevmoo]

@nex3 I believe the issue is that the user did nothing but updated Dart and now things are broken. The publisher of polymer_elements had no idea that the uploaded package would break at a future date.

[nex3]

Hmm, I suppose pub should probably skip versions with unparseable pubspecs rather than crashing.

[nex3]

Looking at this more, I don't think it's something we can do efficiently on the client side. We don't consume pubspecs directly while version solving, we consume JSON from pub.dartlang.org that's derived from the pubspecs. We'll need the server to mark these packages as invalid somehow.

[nex3]

I've filed dart-lang/pub-dev#62 to track the necessary change to pub.dartlang.org. I'm going to leave this open for now because we should at least be resilient to busted pubspecs in the local pub cache, especially when running with --offline.