dart2js: Importing unittest disables tree shaking

[rakudrama]

It seems unfortunate and perhaps unintended that simply using unittest disables such an important optimization.

To repro, patch in https://codereview.chromium.org/23653003/
and run
$ tools/test.py -mrelease -cdart2js -rd8 dart2js_extra/tree_woe_test

[peter-ahe-google]

Stephen, why do you think this a dart2js bug?

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Added NeedsInfo label.

[gramster]

unittest uses the stacks package, which uses the path package, which imports dart:mirrors.

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cc @nex3.
cc @munificent.

[nex3]

Why is it a problem that importing unittest disables tree-shaking? No one should be deploying code that imports unittest.

For reference, path is using dart:mirrors as a workaround for issue #6943.

[dgrove]

path should probably be using the MirrorsUsed annotation to control this.

[gramster]

It is.

[gramster]

Nathan, I believe Stephen's concern is that the unittest tests could otherwise be useful for finding tree shaking bugs, but if we never tree shake, then we won't get that benefit.

[kasperl]

Added this to the M7 milestone.

[kasperl]

Removed Priority-Unassigned label.
Added Priority-Medium label.

[kasperl]

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

[devoncarew]

No one should be deploying code that imports unittest.

I have a use case for doing just that. I currently see a 10x increase in code size if I import unittest, which is less then ideal.

[peter-ahe-google]

No one should be deploying code that imports unittest.

I have a use case for doing just that. I currently see a 10x increase in code
size if I import unittest, which is less then ideal.

If unittest is written under the assumption that it can force code to run in a mode that isn't appropriate for production, then you can't use unittest to test production code.

[dgrove]

Uri.base is in, which is half of what's needed to get rid of this dependence on mirrors. I don't believe we have a way of knowing the platform (browser, mac, linux, windows) yet.

[kasperl]

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

[kasperl]

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

[rakudrama]

I think this is no longer true.
Putting a throw at "isTreeShakingDisabled = true;" now fails only html/custom/mirrors_test

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Added CannotReproduce label.