In order to run GeneratedFile scripts under python3, we need a way to select which scripts will run under py3 instead of py2. Since the end result will be all scripts running in python3, that should be the default. All existing scripts can be annotated to run under py2, and the converted individually.

GENERATED_FILES now defaults to python3 unless py2=True is specified as
an argument. All existing GENERATED_FILES scripts and GeneratedFile
templates have the py2=True attribute added, so this patch should
effectively be a no-op.

Going forward, individual scripts can be converted to python3 and their
corresponding py2=True attribute can be deleted. In effect, this patch
will be backed out in pieces until all scripts run in python3, at which
point the py2 attribute itself can be removed.

Backed out changeset 7fefed11f117 (Bug 1611326) for build bustages at update-1.xpi.stub.
https://hg.mozilla.org/integration/autoland/rev/80b5de57706c4bde8bb6d1a97881b33e400fd99c

Push with failures:
https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=pending%2Crunning%2Csuccess%2Ctestfailed%2Cbusted%2Cexception&revision=7fefed11f1176375055cc846a2c906013a6b72e0&selectedJob=288812460

Failure log:
https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=288812460&repo=autoland&lineNumber=1657

Bug 1599581 landed after I wrote the patch, which added a new GENERATED_FILES script that needs to run in python2 for now. After I rebased and double-checked the patch with try -p all this morning, the 'Android 4.0 API16+ GeckoView multi-arch fat AAR opt' build did not run but is apparently a tier-1 build platform.

https://hg.mozilla.org/mozilla-central/rev/77e54e76848a

Comment 6 or Bug 1613263 https://hg.mozilla.org/mozilla-central/rev/36ba18ac3a68 caused these l10n bustages so we decided to backout both of them: https://treeherder.mozilla.org/#/jobs?repo=mozilla-central&group_state=expanded&resultStatus=testfailed%2Cbusted%2Cexception&revision=ccbbd26e4bec0cda9a2d4e4b73de319092569c28&searchStr=l10n&selectedJob=288917169

Failure log: https://treeherder.mozilla.org/logviewer.html#?job_id=288917169&repo=mozilla-central

Backout link: https://hg.mozilla.org/mozilla-central/rev/ca97340e64722330f45043b3fa8a819ad7c59835

Pushed by mkmelin@iki.fi:
https://hg.mozilla.org/comm-central/rev/6a58c483b49d
set charsetalias to use py2. rs=bustage-fix for Thunderbird

FYI, bug 1615589 landed ar to the locales to run on try and autoland, and should catch the unicode problems on locale metadata early now.

It looks like the issue was actually caused by bug 1613263, so I'll try to re-land. Feel free to ping me if something looks off again.

https://hg.mozilla.org/mozilla-central/rev/5804c68ea337