WPCOM MERGE Infinite Scroll (Automattic#6246)

* VIP: Query errors generated for HoopsHype are caused by the infinite scroll functionality. This filter will allow to use rewrite rules so that the infinity functions can be called by rewrite rules that will be cached by batcache.

Merges r120201-wpcom.

* Infinite Scroll: only disable in the Customizer when previewing a non-active theme.

Fixes Automattic#7507
See [115743] Automattic#6795

Merges r122634-wpcom.

* Infinite Scroll: allow `get_settings` to be filtered at later points than just `__construct`. See Automattic#7539.

Merges r123819-wpcom.

* Infinite Scroll: add translation function to credit line.

Merges Automattic#2537
Fixes Automattic#2528

https://[private link]

Merges r132540-wpcom.

* Infinite Scroll: fix IS when content includes Curly Quotes (and other non-UTF8 chars)

Using wp_json_encode instead of json_encode allowing us to replace invalid chars with HTML entities.

Merges Automattic#1447
Fixes Automattic#1446
props jtsternberg

https://[private link]

Merges r132541-wpcom.

* Infinite Scroll: add check on ob_end_clean for cases where output_buffering is disabled

Merges Automattic#2545
Props drrobotnik

https://[private link]

Merges r132542-wpcom.

* Infinite Scroll: check that search terms exist before matching against post title.

Merges Automattic#2128
Fixes Automattic#2075
Props cainm

https://[private link]

Merges r132543-wpcom.

* Infinite Scroll: Fatal error when calling protected method from WP_Query

Since we already have wp_query() we can use its query_vars['search_terms'] property instead of calling parse_search_terms().
It gets populated on https://github.com/WordPress/WordPress/blob/4.3.1/wp-includes/query.php#L2075 with the same data.

Merges Automattic#2827
Fixes Automattic#2255
Props osiux

https://[private link]

Merges r132544-wpcom.

* Infinite Scroll: Hide infinite-scroll class if the option is disabled

The Jetpack support page says that the infinite-scroll class should be used in a theme to hide the navigation links.
However, even when disabled in the Reading page, the class is still visible and the CSS is applied just as if the scroll is enabled.

This commit adds an option check before filtering the body_class classes.

Merges Automattic#1208
Props mpeshev

https://[private link]

Merges r132546-wpcom.

* Infinite Scroll: Don't clobber the posts_per_page option if provided

Infinite Scroll currently clobbers any passed-in value for posts_per_page if the type is set to click.
This commit changes the behavior to match the documentation:
https://jetpack.me/support/infinite-scroll/

Merges Automattic#2808
Props codebykat

https://[private link]

Merges r132547-wpcom.

* Infinite Scroll: document all filter and action hooks

Merges Automattic#2852

https://[private link]

Merges r132551-wpcom.

* Infinite Scroll: favor user set settings over theme settings

If user changed their posts_per_page option, use that in Infinite Scroll instead of the value set in theme's IS support declaration.
Only true when IS is set to click.

Related: r132547
Discussion: https://[private link]#comment-31306

Merges r132764-wpcom.

* Infinite Scroll: Merge changes from Jetpack into wpcom

Just removing some whitespace so the 2 files are exactly similar and do not trigger the build script anymore.

Merges r132787-wpcom.

* Infinite Scroll: Make sure the body class gets updated once we are done with IS even when we just click

Merges r134572-wpcom.

* Remove `target="_blank"` from internal link.

Accidentally added by Automattic#3600, which was intended to add only to external links.

modules/infinite-scroll/infinity.js

@@ -339,6 +339,8 @@ Scroller.prototype.refresh = function() {
 					if ( response.lastbatch ) {
 						if ( self.click_handle ) {
 							$( '#infinite-handle' ).remove();
+							// Update body classes
+							self.body.addClass( 'infinity-end' ).removeClass( 'infinity-success' );
 						} else {
 							self.body.trigger( 'infinite-scroll-posts-end' );
 						}

modules/infinite-scroll/infinity.php

@@ -1466,7 +1466,7 @@ function_exists( 'wp_get_theme' ) ? wp_get_theme()->Name : get_current_theme()
 		<div id="infinite-footer">
 			<div class="container">
 				<div class="blog-info">
-					<a id="infinity-blog-title" href="<?php echo home_url( '/' ); ?>" target="_blank" rel="home">
+					<a id="infinity-blog-title" href="<?php echo home_url( '/' ); ?>" rel="home">
 						<?php bloginfo( 'name' ); ?>
 					</a>
 				</div>