Remove dart:mirror usage from package:http

[mkustermann]

A change to the dart2js compiler introduced a warning on mirror usage in dart code -- see Emit warning on import of dart:mirrors.. According to the warning, users will be forced to pass an additional flag to the dart2js compiler when their code is using dart:mirrors. This affects all users of package:http.

When compiling the following example

import 'package:http/http.dart';
main()=> print("hello");

dart2js will print out the following warning:

Warning: 
****************************************************************
* WARNING: dart:mirrors support in dart2js is experimental,
*          and not recommended.
*          This implementation of mirrors is incomplete,
*          and often greatly increases the size of the generated
*          JavaScript code.
*
* Your app imports dart:mirrors via:
*   x.dart => package:http => dart:mirrors
*
* Starting with Dart 1.9, you must use the
* --enable-experimental-mirrors command-line flag to opt-in.
* You can begin using this flag now if mirrors support is critical.
*
* To learn what to do next, please visit:
*    http://dartlang.org/dart2js-reflection
****************************************************************

That flag does not seem to be enforced as of SDK version 1.9.0-dev.1.0+google3-trunk, but that seems to be only a matter of time.

[nex3]

This is blocked on having a viable alternative (issue 6943). I believe the end result of the discussion about this warning was that it also shouldn't be introduced until a viable alternative to mirrors exists.

[skybrian]

I'm told this warning is spurious and dart2js should be fixed to only print it when code size is actually affected.

[skybrian]

Here's the bug for fixing dart2js:
https://code.google.com/p/dart/issues/detail?id=23293

[anders-sandholm]

Just wondering, how can we get package http to not use mirrors, such that it can be used "out of the box" by Flutter?

See also this discussion flutter/flutter#5831 (comment)

Given that cross-platform package support is not there, what is the best viable way to solve this in the short term?

[anders-sandholm]

Having talked to @floitschG it seems we might be able to rewrite things in a way that uses config-specific imports instead of mirrors.

Config-specific imports are tracked here dart-lang/sdk#24581.
DDC is currently still missing (dart-archive/dev_compiler#595).

[matanlurey]

Nice!

[nex3]

I'm definitely planning on rewriting this with config-specific imports—I
even have a local branch that suits it. But the the feature needs to no
longer be behind a flag, and to be supported by DDC, for that branch to be
releasable.

On Sep 13, 2016 4:47 PM, "Matan Lurey" notifications@github.com wrote:

Nice!

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[chinmaygarde]

Flutter would be extremely excited to finally use the package directly. If you are willing to publish the local branch separately, we can even test it out for you by specifying the package as a Git dependency.

Thanks.

[sethladd]

Thanks @nex3 ! We'd love to DEP in your branch so we can use http again.