Canonical: prevent "Undefined array key" PHP warnings when host is not set.

This change is necessary to prevent scanning tools from polluting debug/error logs of some hosting configurations with PHP warnings simply by omitting the Host header from their requests.

This commit makes sure that all of the required `host`, `path`, `query`, and `scheme` array keys inside of the `redirect_canonical()` function are always set after various operations have been performed on them.

It also includes 1 new test case and 2 additional tests, to verify the problem and its fix are working as intended, as well as a small modification to the `get_canonical()` phpunit helper specifically to account for `HTTP_HOST` maybe not being set.

Props artz91, johnjamesjacoby, mindctrl, sirlouen.

Fixes #63316.
Built from https://develop.svn.wordpress.org/trunk@61136


git-svn-id: http://core.svn.wordpress.org/trunk@60472 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/canonical.php

@@ -77,18 +77,18 @@ function redirect_canonical( $requested_url = null, $do_redirect = true ) {
 		return;
 	}
 
+	// Notice fixing.
+	$original += array(
+		'host'   => '',
+		'path'   => '',
+		'query'  => '',
+		'scheme' => '',
+	);
+
 	$redirect     = $original;
 	$redirect_url = false;
 	$redirect_obj = false;
 
-	// Notice fixing.
-	if ( ! isset( $redirect['path'] ) ) {
-		$redirect['path'] = '';
-	}
-	if ( ! isset( $redirect['query'] ) ) {
-		$redirect['query'] = '';
-	}
-
 	/*
 	 * If the original URL ended with non-breaking spaces, they were almost
 	 * certainly inserted by accident. Let's remove them, so the reader doesn't
@@ -616,12 +616,12 @@ function redirect_canonical( $requested_url = null, $do_redirect = true ) {
 	}
 
 	// Notice prevention after new parse_url( $redirect_url ) calls
-	if ( ! isset( $redirect['path'] ) ) {
-		$redirect['path'] = '';
-	}
-	if ( ! isset( $redirect['query'] ) ) {
-		$redirect['query'] = '';
-	}
+	$redirect += array(
+		'host'   => '',
+		'path'   => '',
+		'query'  => '',
+		'scheme' => '',
+	);
 
 	// Trailing /index.php.
 	$redirect['path'] = preg_replace( '|/' . preg_quote( $wp_rewrite->index, '|' ) . '/*?$|', '/', $redirect['path'] );

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.9-beta3-61135';
+$wp_version = '6.9-beta3-61136';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.