Requests for comment/Reimplement info action

This is a request for comment regarding reimplementing the info action.

Background
The info action has existed in MediaWiki since 4242. Since 4247, the action has been disabled by default behind the  global variable due to performance issues.

Currently, to obtain the information that this proposed action would provide, a user needs to manually query the wiki database, query the MediaWiki API, or hunt down the appropriate MediaWiki Special page (e.g., Special:WhatLinksHere). Many of the proposed additions to the info action are currently completely unexposed in the MediaWiki interface, but these additions provide demonstrable value to readers, editors, and power editors.

Due to the info action being disabled by default in MediaWiki core, it has received very little attention since its introduction in 2004. The current output is below, using the English Wikipedia's w:Talk:Barack Obama page as an example.

Information for "Talk:Barack Obama"

Reimplementation
The "info" action should provide human-readable metadata about a particular page title (e.g., "Main Page" or "Barack Obama"). Some of this data is a view into the page_props table; other data is simply interesting to editors and readers.

The data contained in this info dashboard will likely need to be split between expensive and inexpensive queries. For larger wikis, $wgMiserMode can be relied upon to block the expensive queries.

Inexpensive properties

 * DEFAULTSORT value
 * 38532
 * DISPLAYTITLE value
 * 38533
 * (NO)INDEX status
 * 38531
 * LiquidThreads status
 * 38534
 * 38559
 * page protection status
 * 38536
 * first edit timestamp
 * 38526
 * page creator
 * 38526
 * last edit timestamp
 * 38527
 * most recent editor
 * 38527
 * templates transcluded on this page
 * 38528
 * hidden categories on this page
 * 38529
 * magic word usage
 * 38530
 * broken (red) links?
 * file links
 * category links
 * page links
 * etc.
 * number of recent edits/authors
 * 38558
 * page length (in bytes)
 * 38560
 * page ID
 * 38561
 * number of subpages (with link to Special:PrefixIndex)
 * 38563
 * number of redirects to the title (with link to filtered Special:WhatLinksHere)
 * 38564
 * number of watchers
 * already implemented!

Expensive properties

 * number of total edits
 * number of unique contributors (anonymous and logged in)
 * number of views (link to outside service?)

Action interface exposure
Currently the "info" action is not exposed in the user interface, regardless of the value of $wgAllowPageInfo (16362). A tab or a link in the sidebar in the "Toolbox" section should provide easy access to the "info" action.

Action interface

 * external tools or external links section
 * 38537
 * header and footer messages
 * 38556
 * remove talk page info
 * 38562

Mock-up
Information for "Talk:Barack Obama" The following is an overview of the page "Talk:Barack Obama", as of 01:30, 22 July 2012 (UTC):

Basic information

Edit history

Page properties

External tools
 * History search tool (WikiBlame)
 * Contributor breakdown
 * User edits breakdown
 * Number of page watchers
 * Page view data

Plan

 * File tracking bug about reimplementing the info action
 * 38450
 * File bug about killing $wgAllowPageInfo and enabling the "info" action by default
 * 38451
 * File (many) bugs about adding specific data to the action, as detailed above

Change sets

 * 16235
 * 17634
 * 20735
 * 20739
 * 20886
 * 21598