Bump minimum required WordPress version from 3.6 to 4.0

[netweb]

Via ​https://wordpress.org/about/stats/, usage stats for old versions look like this (release dates in parentheses):

• 3.6: 1.6% (2013-08-01)
• 3.7: 1.1% (2013-10-13)
• 3.8: 3.5% (2013-12-12)
• 3.9: 4.9% (2014-04-16)
• 4.0: 5.3% (2014-09-04)

Quoting, paraphrasing and revising Boone via ​https://buddypress.trac.wordpress.org/ticket/6258#comment:9:

I think a good guideline for "most recently stable" is that we should maintain support for WordPress versions going back at least 12 months, which would suggest that we should definitely keep support for at least 4.0.x.

• 3.6 was released ~ 29 months ago and is now less than 5%
• 3.7 was released ~ 27 months ago and is now less than 5%
• 3.8 was released ~ 24 months ago and is now less than 5%
• 3.9 was released ~ 20 months ago and is now less than 5%

The 5% rule suggests that we drop official support for 3.6, 3.7, 3.8, and 3.9.

Further to the above stats are some more stats via w.org relating to bbPress 2.5.x and WordPress 3.x/4.x usage:

• 3.3 - August 2015 0.0% - January 2016 0.0%
• 3.4 - August 2015 0.0% - January 2016 0.0%
• 3.5 - August 2015 0.2% - January 2016 0.0%
• 3.6 - August 2015 0.3% - January 2016 x.x%
• 3.7 - August 2015 0.5% - January 2016 x.x%
• 3.8 - August 2015 3.7% - January 2016 x.x%
• 3.9 - August 2015 6.7% - January 2016 x.x%
• 4.0 - August 2015 9.1% - January 2016 x.x%
• 4.1 - August 2015 16.0% - January 2016 x.x%
• 4.2 - August 2015 51.6% - January 2016 x.x%
• 4.3 - August 2015 11.8% - January 2016 x.x%
• 4.4 - August 2015 0.0% (~20 sites) - January 2016 x.x%

Based on the above, I'm going to suggest we bump the minimum official supported version to 4.0. If everyone else is OK with this, I suggest we do the following:

1. Bump the minimum supported version in trunk

2. Open a separate ticket where someone does a quick review of backward compatibility and progressive enhancements in bbPress that become obsolete when we no longer support 3.6, 3.7, 3.8, and 3.9, and make some recommendations for removal (or leaving stuff alone, as appropriate)

3. Post about this on bbpdevel.wordpress.com

4. Formalize these steps for future release cycles

Related:

• BP 3.8 -> 3.9 ​https://buddypress.trac.wordpress.org/ticket/6805 Bump minimum WP version to 3.9
• BP 3.6 -> 3.8 ​https://buddypress.trac.wordpress.org/ticket/6258 Update supported WordPress versions

Note: Updated January 2016 stats will be provided and updated shortly

[thebrandonallen]

+1

[netweb]

In 5991:

Bump minimum WordPress requirement to 4.0.

Fixes #2902.