filenames in dart2js sourcemaps shouldn't expose the location of the Dart SDK

[DartBot]

This issue was originally filed by bslesinsk...@gmail.com

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The filenames in sourcemaps use a relative path to the Dart SDK. This exposes the location of the Dart SDK on the local machine where the Dart app was built. For example:

"sources": ["../../../software/dart/dart-sdk/lib/_internal/lib/interceptors.dart","../../../software/dart/dart-sdk/lib/_internal/lib/js_array.dart","../../../software/dart/dart-sdk/lib/internal/iterable.dart","../../../software/dart/dart-sdk/lib/collection/list.dart",

It would be better hide the location by going through a symlink, as is already done for packages:

ln -s ../../../software/dart-sdk .

"sources": ["dart-sdk/lib/_internal/lib/interceptors.dart","dart-sdk/lib/_internal/lib/js_array.dart","dart-sdk/lib/internal/iterable.dart","dart-sdk/lib/collection/list.dart",

Then we can deploy the sourcemap by copying the dart.js.map file and all the source files it references to the website. This would allow the entire Dart app to be debuggable just by opening Chrome Dev Tools, even without the Dart SDK installed locally.

It would also make the output of the dart2js compiler more deterministic. Currently the sourcemap file will be different depending where the developer happens to install the SDK.

Followup to:
https://code.google.com/p/dart/issues/detail?id=7903

[iposva-google]

Added Area-Dart2JS, Triaged labels.

[sigmundch]

The scenario that had the biggest need for this was pub-serve. Pub has a solution for this already: they serves the sdk and provide the location to dart2js when they invoke it as a transformer, so the source-map points to the right files.

We've found that in many contexts the right solution is to override the output of dart2js to specify a new base-path for the sdk sources. Some ideas here:

• instead of providing the real path to the sdk sources, we could provide a suffix or a special URI scheme (e.g. "sdk:path/to/sdk/file"), so that tools can easily detect these urls and fix them afterwards.
• provide an argument to dart2js so it can set the prefix the user would like to have.

At this time, there is no pressing need for implementing this, so I'm marking this as low priority.

[nex3]

DDC just lists sources as dart:path/to/sdk/file.dart, as in dart:core/string.dart. Matching that behavior would be nice.