Added this to the M7 milestone.
Removed Priority-Unassigned label.
Added Priority-Medium label.

Added Triaged label.

Do we want to have a warning for this situation? As far as I can see there's nothing in the specification that disallows it, and as long as the part is empty there won't be any errors or warnings. If not, analyzer can provide a hint.

Set owner to @gbracha.

It's reasonable that importing the same file twice would be a warning...at a minimum.

The big problem here: if someone inadvertently imports the same file twice, it's not obvious why the "already defined" error is being reported. A tough user experience.

M7 -> M8

Removed this from the M7 milestone.
Added this to the M8 milestone.

Removed Area-Analyzer label.
Added Area-Language label.

Removed this from the M8 milestone.
Added this to the 1.6 milestone.

Removed this from the 1.6 milestone.
Added Oldschool-Milestone-1.6 label.

Removed Oldschool-Milestone-1.6 label.

Better error messages would resolve the user experience issue. For example, stating what part directive, at what line, caused the duplicate declaration. I'm not convinced that we need more language rules rather than better tooling.

Added Accepted label.

This is now a static error raised by the analyzer:

$ cat 23674.dart 
library my_library;

part '23674-part.dart';
part '23674-part.dart'; // No warning
$ cat 23674-part.dart 
part of my_library;

class ClassInMyPart {}
$ dartanalyzer --version
dartanalyzer version 2.0.0-dev.63.0
$ dartanalyzer 23674.dart 
Analyzing 23674.dart...
  error • The library already contains a part with the uri 'file:///Users/srawlins/code/23674-part.dart' at 23674.dart:4:6 • duplicate_part
1 error found.