Compser: Read once, fail gracefully (and more) (#12442)

* Read once, fail gracefully

* Improve inline comment

* Adding more inline documentation on the loading process.

* run composer install on build scripts

* Remove extra slash

`JETPACK__PLUGIN_DIR` already has a trailing slash.

* Restore @jeherve's original soft fallback for unbuilt Jetpack.

This reverts commit 77ee45f.

* Update inline docs at 0238eab

jetpack.php

@@ -149,6 +149,17 @@ function jetpack_admin_missing_autoloader() { ?>
 	<?php
 }
 
+/**
+ * This is where the loading of Jetpack begins.
+ *
+ * First, we check for our supported version of PHP and load our composer autoloader. If either of these fail,
+ * we "pause" Jetpack by ending the loading process and displaying an admin_notice to inform the site owner.
+ *
+ * After both those things happen successfully, we require the legacy files, then add on to various hooks that we expect
+ * to always run.
+ *
+ * Lastly, we fire Jetpack::init() to fire up the engines.
+ */
 if ( version_compare( phpversion(), JETPACK__MINIMUM_PHP_VERSION, '<' ) ) {
 	if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
 		error_log(
@@ -164,8 +175,13 @@ function jetpack_admin_missing_autoloader() { ?>
 	return;
 }
 
-// Load all the packages.
-$jetpack_autoloader = JETPACK__PLUGIN_DIR . '/vendor/autoload.php';
+/**
+ * Load all the packages.
+ *
+ * We want to fail gracefully if `composer install` has not been executed yet, so we are checking for the autoloader.
+ * If the autoloader is not present, let's log the failure, pause Jetpack, and display a nice admin notice.
+ */
+$jetpack_autoloader = JETPACK__PLUGIN_DIR . 'vendor/autoload.php';
 if ( is_readable( $jetpack_autoloader ) ) {
 	require $jetpack_autoloader;
 } else {

tools/build-jetpack.sh

@@ -56,6 +56,15 @@ if [[ $ADD_BETA_VERSION -eq 1 ]]; then
     echo "Now at version $CURRENT_VERSION!"
 fi
 
+# Checking for composer
+hash composer 2>/dev/null || {
+    echo >&2 "This script requires you to have composer package manager installed."
+    echo >&2 "Please install it following the instructions on https://getcomposer.org/. Aborting.";
+    exit 1;
+}
+
+composer --cwd $TARGET_DIR install
+
 # Checking for yarn
 hash yarn 2>/dev/null || {
     echo >&2 "This script requires you to have yarn package manager installed."

tools/build-release-branch.sh

@@ -204,6 +204,15 @@ echo ""
 
 echo "Building Jetpack"
 
+# Checking for composer
+hash composer 2>/dev/null || {
+    echo >&2 "This script requires you to have composer package manager installed."
+    echo >&2 "Please install it following the instructions on https://getcomposer.org/. Aborting.";
+    exit 1;
+}
+
+composer install
+
 # Checking for yarn
 hash yarn 2>/dev/null || {
 	echo >&2 "This script requires you to have yarn package manager installed."

tools/deploy-to-master-stable-branch.sh

@@ -41,6 +41,15 @@ echo ""
 
 echo "Building Jetpack"
 
+# Checking for composer
+hash composer 2>/dev/null || {
+    echo >&2 "This script requires you to have composer package manager installed."
+    echo >&2 "Please install it following the instructions on https://getcomposer.org/. Aborting.";
+    exit 1;
+}
+
+composer install
+
 # Checking for yarn
 hash yarn 2>/dev/null || {
     echo >&2 "This script requires you to have yarn package manager installed."