Introduce amp_get_slug() to replace AMP_QUERY_VAR

amp.php

@@ -55,7 +55,7 @@ function amp_deactivate() {
 	// We need to manually remove the amp endpoint
 	global $wp_rewrite;
 	foreach ( $wp_rewrite->endpoints as $index => $endpoint ) {
-		if ( AMP_QUERY_VAR === $endpoint[1] ) {
+		if ( amp_get_slug() === $endpoint[1] ) {
 			unset( $wp_rewrite->endpoints[ $index ] );
 			break;
 		}
@@ -73,24 +73,12 @@ function amp_deactivate() {
  * @since 0.6
  */
 function amp_after_setup_theme() {
+	amp_get_slug(); // Ensure AMP_QUERY_VAR is set.
+
 	if ( false === apply_filters( 'amp_is_enabled', true ) ) {
-		// Set a fallback value to avoid constant not defined warnings
-		if ( ! defined( 'AMP_QUERY_VAR' ) ) {
-			define( 'AMP_QUERY_VAR', false );
-		}
 		return;
 	}
 
-	if ( ! defined( 'AMP_QUERY_VAR' ) ) {
-		/**
-		 * Filter the AMP query variable.
-		 *
-		 * @since 0.3.2
-		 * @param string $query_var The AMP query variable.
-		 */
-		define( 'AMP_QUERY_VAR', apply_filters( 'amp_query_var', 'amp' ) );
-	}
-
 	add_action( 'init', 'amp_init', 0 ); // Must be 0 because widgets_init happens at init priority 1.
 }
 add_action( 'after_setup_theme', 'amp_after_setup_theme', 5 );
@@ -111,7 +99,7 @@ function amp_init() {
 
 	load_plugin_textdomain( 'amp', false, plugin_basename( AMP__DIR__ ) . '/languages' );
 
-	add_rewrite_endpoint( AMP_QUERY_VAR, EP_PERMALINK );
+	add_rewrite_endpoint( amp_get_slug(), EP_PERMALINK );
 
 	AMP_Validation_Utils::init();
 	AMP_Theme_Support::init();
@@ -136,8 +124,8 @@ function amp_init() {
 // Make sure the `amp` query var has an explicit value.
 // Avoids issues when filtering the deprecated `query_string` hook.
 function amp_force_query_var_value( $query_vars ) {
-	if ( isset( $query_vars[ AMP_QUERY_VAR ] ) && '' === $query_vars[ AMP_QUERY_VAR ] ) {
-		$query_vars[ AMP_QUERY_VAR ] = 1;
+	if ( isset( $query_vars[ amp_get_slug() ] ) && '' === $query_vars[ amp_get_slug() ] ) {
+		$query_vars[ amp_get_slug() ] = 1;
 	}
 	return $query_vars;
 }
@@ -206,7 +194,7 @@ function amp_correct_query_when_is_front_page( WP_Query $query ) {
 		$query->is_home()
 		&&
 		// Is AMP endpoint.
-		false !== $query->get( AMP_QUERY_VAR, false )
+		false !== $query->get( amp_get_slug(), false )
 		&&
 		// Is query not yet fixed uo up to be front page.
 		! $query->is_front_page()
@@ -218,7 +206,7 @@ function amp_correct_query_when_is_front_page( WP_Query $query ) {
 		get_option( 'page_on_front' )
 		&&
 		// See line in WP_Query::parse_query() at <https://github.com/WordPress/wordpress-develop/blob/0baa8ae/src/wp-includes/class-wp-query.php#L961>.
-		0 === count( array_diff( array_keys( wp_parse_args( $query->query ) ), array( AMP_QUERY_VAR, 'preview', 'page', 'paged', 'cpage' ) ) )
+		0 === count( array_diff( array_keys( wp_parse_args( $query->query ) ), array( amp_get_slug(), 'preview', 'page', 'paged', 'cpage' ) ) )
 	);
 	if ( $is_front_page_query ) {
 		$query->is_home     = false;
@@ -308,9 +296,9 @@ function amp_render_post( $post ) {
 	 * which is not ideal for any code that expects to run in an AMP context.
 	 * Let's force the value to be true while we render AMP.
 	 */
-	$was_set = isset( $wp_query->query_vars[ AMP_QUERY_VAR ] );
+	$was_set = isset( $wp_query->query_vars[ amp_get_slug() ] );
 	if ( ! $was_set ) {
-		$wp_query->query_vars[ AMP_QUERY_VAR ] = true;
+		$wp_query->query_vars[ amp_get_slug() ] = true;
 	}
 
 	// Prevent New Relic from causing invalid AMP responses due the NREUM script it injects after the meta charset.
@@ -332,7 +320,7 @@ function amp_render_post( $post ) {
 	$template->load();
 
 	if ( ! $was_set ) {
-		unset( $wp_query->query_vars[ AMP_QUERY_VAR ] );
+		unset( $wp_query->query_vars[ amp_get_slug() ] );
 	}
 }
 
@@ -363,7 +351,7 @@ function _amp_bootstrap_customizer() {
 function amp_redirect_old_slug_to_new_url( $link ) {
 
 	if ( is_amp_endpoint() ) {
-		$link = trailingslashit( trailingslashit( $link ) . AMP_QUERY_VAR );
+		$link = trailingslashit( trailingslashit( $link ) . amp_get_slug() );
 	}
 
 	return $link;

includes/admin/class-amp-customizer.php

@@ -134,7 +134,7 @@ public function add_customizer_scripts() {
 
 		wp_add_inline_script( 'amp-customize-controls', sprintf( 'ampCustomizeControls.boot( %s );',
 			wp_json_encode( array(
-				'queryVar' => AMP_QUERY_VAR,
+				'queryVar' => amp_get_slug(),
 				'panelId'  => self::PANEL_ID,
 				'ampUrl'   => amp_admin_get_preview_permalink(),
 				'l10n'     => array(

includes/admin/class-amp-post-meta-box.php

@@ -145,7 +145,7 @@ public function enqueue_admin_assets() {
 		);
 		wp_add_inline_script( self::ASSETS_HANDLE, sprintf( 'ampPostMetaBox.boot( %s );',
 			wp_json_encode( array(
-				'previewLink'     => esc_url_raw( add_query_arg( AMP_QUERY_VAR, '', get_preview_post_link( $post ) ) ),
+				'previewLink'     => esc_url_raw( add_query_arg( amp_get_slug(), '', get_preview_post_link( $post ) ) ),
 				'canonical'       => amp_is_canonical(),
 				'enabled'         => post_supports_amp( $post ),
 				'canSupport'      => count( AMP_Post_Type_Support::get_support_errors( $post ) ) === 0,
@@ -237,7 +237,7 @@ public function preview_post_link( $link ) {
 		);
 
 		if ( $is_amp ) {
-			$link = add_query_arg( AMP_QUERY_VAR, true, $link );
+			$link = add_query_arg( amp_get_slug(), true, $link );
 		}
 
 		return $link;

includes/admin/functions.php

@@ -48,7 +48,7 @@ function amp_admin_get_preview_permalink() {
 	 */
 	$post_type = (string) apply_filters( 'amp_customizer_post_type', 'post' );
 
-	if ( ! post_type_supports( $post_type, AMP_QUERY_VAR ) ) {
+	if ( ! post_type_supports( $post_type, amp_get_slug() ) ) {
 		return null;
 	}
 

includes/amp-helper-functions.php

@@ -5,6 +5,36 @@
  * @package AMP
  */
 
+/**
+ * Get the slug used in AMP for the query var, endpoint, and post type support.
+ *
+ * The return value can be overridden by previously defining a AMP_QUERY_VAR
+ * constant or by adding a 'amp_query_var' filter, but *warning* this ability
+ * may be deprecated in the future. Normally the slug should be just 'amp'.
+ *
+ * @since 0.7
+ * @return string Slug used for query var, endpoint, and post type support.
+ */
+function amp_get_slug() {
+	if ( defined( 'AMP_QUERY_VAR' ) ) {
+		return AMP_QUERY_VAR;
+	}
+
+	/**
+	 * Filter the AMP query variable.
+	 *
+	 * Warning: This filter may become deprecated.
+	 *
+	 * @since 0.3.2
+	 * @param string $query_var The AMP query variable.
+	 */
+	$query_var = apply_filters( 'amp_query_var', 'amp' );
+
+	define( 'AMP_QUERY_VAR', $query_var );
+
+	return $query_var;
+}
+
 /**
  * Retrieves the full AMP-specific permalink for the given post ID.
  *
@@ -38,9 +68,9 @@ function amp_get_permalink( $post_id ) {
 		$parsed_url = wp_parse_url( get_permalink( $post_id ) );
 		$structure  = get_option( 'permalink_structure' );
 		if ( empty( $structure ) || ! empty( $parsed_url['query'] ) || is_post_type_hierarchical( get_post_type( $post_id ) ) ) {
-			$amp_url = add_query_arg( AMP_QUERY_VAR, '', get_permalink( $post_id ) );
+			$amp_url = add_query_arg( amp_get_slug(), '', get_permalink( $post_id ) );
 		} else {
-			$amp_url = trailingslashit( get_permalink( $post_id ) ) . user_trailingslashit( AMP_QUERY_VAR, 'single_amp' );
+			$amp_url = trailingslashit( get_permalink( $post_id ) ) . user_trailingslashit( amp_get_slug(), 'single_amp' );
 		}
 	}
 
@@ -66,10 +96,10 @@ function amp_get_permalink( $post_id ) {
 function amp_remove_endpoint( $url ) {
 
 	// Strip endpoint.
-	$url = preg_replace( ':/' . preg_quote( AMP_QUERY_VAR, ':' ) . '(?=/?(\?|#|$)):', '', $url );
+	$url = preg_replace( ':/' . preg_quote( amp_get_slug(), ':' ) . '(?=/?(\?|#|$)):', '', $url );
 
 	// Strip query var.
-	$url = remove_query_arg( AMP_QUERY_VAR, $url );
+	$url = remove_query_arg( amp_get_slug(), $url );
 
 	return $url;
 }
@@ -149,7 +179,7 @@ function is_amp_endpoint() {
 		_doing_it_wrong( __FUNCTION__, sprintf( esc_html__( "is_amp_endpoint() was called before the 'parse_query' hook was called. This function will always return 'false' before the 'parse_query' hook is called.", 'amp' ) ), '0.4.2' );
 	}
 
-	return false !== get_query_var( AMP_QUERY_VAR, false );
+	return false !== get_query_var( amp_get_slug(), false );
 }
 
 /**

includes/class-amp-post-type-support.php

@@ -54,7 +54,7 @@ public static function add_post_type_support() {
 			AMP_Options_Manager::get_option( 'supported_post_types', array() )
 		);
 		foreach ( $post_types as $post_type ) {
-			add_post_type_support( $post_type, AMP_QUERY_VAR );
+			add_post_type_support( $post_type, amp_get_slug() );
 		}
 	}
 
@@ -73,7 +73,7 @@ public static function get_support_errors( $post ) {
 		$errors = array();
 
 		// Because `add_rewrite_endpoint` doesn't let us target specific post_types.
-		if ( isset( $post->post_type ) && ! post_type_supports( $post->post_type, AMP_QUERY_VAR ) ) {
+		if ( isset( $post->post_type ) && ! post_type_supports( $post->post_type, amp_get_slug() ) ) {
 			$errors[] = 'post-type-support';
 		}
 

includes/class-amp-theme-support.php

@@ -130,7 +130,7 @@ public static function finish_init() {
 	 * @since 0.7
 	 */
 	public static function redirect_canonical_amp() {
-		if ( false !== get_query_var( AMP_QUERY_VAR, false ) ) { // Because is_amp_endpoint() now returns true if amp_is_canonical().
+		if ( false !== get_query_var( amp_get_slug(), false ) ) { // Because is_amp_endpoint() now returns true if amp_is_canonical().
 			$url = preg_replace( '#^(https?://.+?)(/.*)$#', '$1', home_url( '/' ) );
 			if ( isset( $_SERVER['REQUEST_URI'] ) ) {
 				$url .= wp_unslash( $_SERVER['REQUEST_URI'] );

includes/options/class-amp-options-manager.php

@@ -153,7 +153,7 @@ public static function check_supported_post_type_update_errors() {
 				continue;
 			}
 
-			$post_type_supported = post_type_supports( $post_type->name, AMP_QUERY_VAR );
+			$post_type_supported = post_type_supports( $post_type->name, amp_get_slug() );
 			$is_support_elected  = in_array( $post_type->name, $supported_types, true );
 
 			$error = null;

includes/options/class-amp-options-menu.php

@@ -94,7 +94,7 @@ public function render_post_types_support() {
 					id="<?php echo esc_attr( $element_id ); ?>"
 					name="<?php echo esc_attr( $element_name ); ?>"
 					value="<?php echo esc_attr( $post_type->name ); ?>"
-					<?php checked( true, amp_is_canonical() || post_type_supports( $post_type->name, AMP_QUERY_VAR ) ); ?>
+					<?php checked( true, amp_is_canonical() || post_type_supports( $post_type->name, amp_get_slug() ) ); ?>
 					<?php disabled( $is_builtin ); ?>
 					>
 				<label for="<?php echo esc_attr( $element_id ); ?>">

tests/test-amp-helper-functions.php

@@ -30,6 +30,15 @@ public function return_example_url( $url, $post_id ) {
 		return 'http://overridden.example.com/?' . build_query( compact( 'url', 'post_id', 'current_filter' ) );
 	}
 
+	/**
+	 * Test amp_get_slug().
+	 *
+	 * @covers amp_get_slug()
+	 */
+	public function test_amp_get_slug() {
+		$this->assertSame( 'amp', amp_get_slug() );
+	}
+
 	/**
 	 * Test amp_get_permalink() without pretty permalinks.
 	 *
@@ -261,7 +270,7 @@ public function test_amp_get_content_sanitizers_deprecated_param() {
 	 * @covers \post_supports_amp()
 	 */
 	public function test_post_supports_amp() {
-		add_post_type_support( 'page', AMP_QUERY_VAR );
+		add_post_type_support( 'page', amp_get_slug() );
 
 		// Test disabled by default for page for posts and show on front.
 		update_option( 'show_on_front', 'page' );
@@ -282,7 +291,7 @@ public function test_post_supports_amp() {
 		$this->assertFalse( post_supports_amp( $post ) );
 
 		// Reset.
-		remove_post_type_support( 'page', AMP_QUERY_VAR );
+		remove_post_type_support( 'page', amp_get_slug() );
 	}
 
 	/**

tests/test-class-amp-meta-box.php

@@ -93,13 +93,13 @@ public function test_render_status() {
 		$this->instance->render_status( $post );
 		$this->assertContains( $amp_status_markup, ob_get_clean() );
 
-		remove_post_type_support( 'post', AMP_QUERY_VAR );
+		remove_post_type_support( 'post', amp_get_slug() );
 
 		ob_start();
 		$this->instance->render_status( $post );
 		$this->assertEmpty( ob_get_clean() );
 
-		add_post_type_support( 'post', AMP_QUERY_VAR );
+		add_post_type_support( 'post', amp_get_slug() );
 		wp_set_current_user( $this->factory->user->create( array(
 			'role' => 'subscriber',
 		) ) );
@@ -160,7 +160,7 @@ public function test_preview_post_link() {
 		$link = 'https://foo.bar';
 		$this->assertEquals( 'https://foo.bar', $this->instance->preview_post_link( $link ) );
 		$_POST['amp-preview'] = 'do-preview';
-		$this->assertEquals( 'https://foo.bar?' . AMP_QUERY_VAR . '=1', $this->instance->preview_post_link( $link ) );
+		$this->assertEquals( 'https://foo.bar?' . amp_get_slug() . '=1', $this->instance->preview_post_link( $link ) );
 	}
 
 }

tests/test-class-amp-options-manager.php

@@ -171,7 +171,7 @@ public function test_check_supported_post_type_update_errors() {
 		$this->assertEmpty( get_settings_errors() );
 
 		// Activation error.
-		remove_post_type_support( 'foo', AMP_QUERY_VAR );
+		remove_post_type_support( 'foo', amp_get_slug() );
 		AMP_Options_Manager::check_supported_post_type_update_errors();
 		$errors = get_settings_errors();
 		$this->assertCount( 1, $errors );
@@ -181,7 +181,7 @@ public function test_check_supported_post_type_update_errors() {
 
 		// Deactivation error.
 		AMP_Options_Manager::update_option( 'supported_post_types', array() );
-		add_post_type_support( 'foo', AMP_QUERY_VAR );
+		add_post_type_support( 'foo', amp_get_slug() );
 		AMP_Options_Manager::check_supported_post_type_update_errors();
 		$errors = get_settings_errors();
 		$this->assertCount( 1, $errors );

tests/test-class-amp-post-type-support.php

@@ -73,9 +73,9 @@ public function test_add_post_type_support() {
 		AMP_Options_Manager::update_option( 'supported_post_types', array( 'poem' ) );
 
 		AMP_Post_Type_Support::add_post_type_support();
-		$this->assertTrue( post_type_supports( 'post', AMP_QUERY_VAR ) );
-		$this->assertTrue( post_type_supports( 'poem', AMP_QUERY_VAR ) );
-		$this->assertFalse( post_type_supports( 'book', AMP_QUERY_VAR ) );
+		$this->assertTrue( post_type_supports( 'post', amp_get_slug() ) );
+		$this->assertTrue( post_type_supports( 'poem', amp_get_slug() ) );
+		$this->assertFalse( post_type_supports( 'book', amp_get_slug() ) );
 	}
 
 	/**
@@ -92,7 +92,7 @@ public function test_get_support_error() {
 		// Post type support.
 		$book_id = $this->factory()->post->create( array( 'post_type' => 'book' ) );
 		$this->assertEquals( array( 'post-type-support' ), AMP_Post_Type_Support::get_support_errors( $book_id ) );
-		add_post_type_support( 'book', AMP_QUERY_VAR );
+		add_post_type_support( 'book', amp_get_slug() );
 		$this->assertEmpty( AMP_Post_Type_Support::get_support_errors( $book_id ) );
 
 		// Password-protected.