Set package index repository as non-canonical to allow Packagist to resolve newer versions

features/package-install.feature

@@ -45,12 +45,54 @@ Feature: Install WP-CLI packages
       """
       "url": "http://wp-cli.org/package-index/"
       """
+    And the composer.json file should contain:
+      """
+      "canonical": false
+      """
 
     When I run `WP_CLI_PACKAGES_DIR=. wp package is-installed wp-cli/restful`
     Then the return code should be 0
     And STDERR should be empty
     And STDOUT should be empty
 
+  Scenario: Install a package updates the package index repository to be non-canonical
+    Given an empty directory
+    And a composer.json file:
+      """
+      {
+        "repositories": {
+          "test" : {
+            "type": "path",
+            "url": "./dummy-package/"
+          },
+          "wp-cli": {
+            "type": "composer",
+            "url": "https://wp-cli.org/package-index/"
+          }
+        }
+      }
+      """
+    And a dummy-package/composer.json file:
+      """
+      {
+        "name": "wp-cli/restful",
+        "description": "This is a dummy package we will install instead of actually installing the real package. This prevents the test from hanging indefinitely for some reason, even though it passes. The 'name' must match a real package as it is checked against the package index."
+      }
+      """
+    When I run `WP_CLI_PACKAGES_DIR=. wp package install wp-cli/restful`
+    Then STDOUT should contain:
+      """
+      Updating package index repository url...
+      """
+    And STDOUT should contain:
+      """
+      Success: Package installed
+      """
+    And the composer.json file should contain:
+      """
+      "canonical": false
+      """
+
   @require-php-5.6
   Scenario: Install a package with 'wp-cli/wp-cli' as a dependency
     Given a WP install

src/Package_Command.php

@@ -92,8 +92,9 @@ class Package_Command extends WP_CLI_Command {
 	 * @var array
 	 */
 	private $composer_type_package = [
-		'type' => 'composer',
-		'url'  => self::PACKAGE_INDEX_URL,
+		'type'      => 'composer',
+		'url'       => self::PACKAGE_INDEX_URL,
+		'canonical' => false,
 	];
 
 	/**
@@ -365,7 +366,10 @@ public function install( $args, $assoc_args ) {
 			);
 		}
 		// If the composer file does not contain the current package index repository, refresh the repository definition.
-		if ( empty( $composer_backup_decoded['repositories']['wp-cli']['url'] ) || self::PACKAGE_INDEX_URL !== $composer_backup_decoded['repositories']['wp-cli']['url'] ) {
+		if ( empty( $composer_backup_decoded['repositories']['wp-cli']['url'] )
+			|| self::PACKAGE_INDEX_URL !== $composer_backup_decoded['repositories']['wp-cli']['url']
+			|| ! isset( $composer_backup_decoded['repositories']['wp-cli']['canonical'] )
+			|| false !== $composer_backup_decoded['repositories']['wp-cli']['canonical'] ) {
 			WP_CLI::log( 'Updating package index repository url...' );
 			$package_args = $this->composer_type_package;
 			$json_manipulator->addRepository(