880733 - Make it easy to add JS features that are pref'd-off-by-default in beta, on in nightly and aurora

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, defect)

Description

[Jason Orendorff [:jorendorff]]

We have to be able to work on features that aren't completely specified yet, or that have general consensus in TC39, but not consensus on every detail.

So how about we add some infrastructure so that it's easy to make a new feature subject to a pref (with a specific pref per new feature), and those can be off-by-default in beta and release, on-by-default in nightly and aurora.

Once a new feature is ready to ship in release, we can just remove the pref for that feature entirely, so it's always on.

Comment 1

[Steve Fink [:sfink] [:s:]]

Since I misread this initially:

please note this this is for a *preference*. Compile-time setting is already available:

#ifdef NIGHTLY_BUILD  => nightly
#ifndef RELEASE_BUILD => nightly | aurora
#ifdef RELEASE_BUILD  => beta | release

Variables with the same names are available to Makefile.in. Both variables are set based on js/src/config/milestone.txt.

Most uses of the pref requested in this bug would require a restart, since it tends to influence what gets added to global objects. It would be best if this capability were available in all binaries, including the browser, xpcshell, and the JS shell, at least. (Obviously, it would need to be controlled by a different mechanism in the browser vs the JS shell.)

Comment 2

[Matthew Gaudet (he/him) [:mgaudet]]

Not as nice as I would like, but this totally works today.