Move a lot of miscellaneous code related to extensions into a new module

ExtensionUtils is a new module that has a lot of miscellaneous things related
to loading extensions and the extension system put into a place that does not
depend on Shell or St.

Note that this will break extensions that have with multiple files by replacing
the old uuid-based importer with an object directly on the meta object.

https://bugzilla.gnome.org/show_bug.cgi?id=668429

js/misc/extensionUtils.js

@@ -0,0 +1,155 @@
+// -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
+
+// Common utils for the extension system and the extension
+// preferences tool
+
+const GLib = imports.gi.GLib;
+const Gio = imports.gi.Gio;
+const ShellJS = imports.gi.ShellJS;
+
+const Config = imports.misc.config;
+
+const ExtensionType = {
+    SYSTEM: 1,
+    PER_USER: 2
+};
+
+// GFile for user extensions
+var userExtensionsDir = null;
+
+/**
+ * versionCheck:
+ * @required: an array of versions we're compatible with
+ * @current: the version we have
+ *
+ * Check if a component is compatible for an extension.
+ * @required is an array, and at least one version must match.
+ * @current must be in the format <major>.<minor>.<point>.<micro>
+ * <micro> is always ignored
+ * <point> is ignored if <minor> is even (so you can target the
+ * whole stable release)
+ * <minor> and <major> must match
+ * Each target version must be at least <major> and <minor>
+ */
+function versionCheck(required, current) {
+    let currentArray = current.split('.');
+    let major = currentArray[0];
+    let minor = currentArray[1];
+    let point = currentArray[2];
+    for (let i = 0; i < required.length; i++) {
+        let requiredArray = required[i].split('.');
+        if (requiredArray[0] == major &&
+            requiredArray[1] == minor &&
+            (requiredArray[2] == point ||
+             (requiredArray[2] == undefined && parseInt(minor) % 2 == 0)))
+            return true;
+    }
+    return false;
+}
+
+function isOutOfDate(meta) {
+    if (!versionCheck(meta['shell-version'], Config.PACKAGE_VERSION))
+        return true;
+
+    if (meta['js-version'] && !versionCheck(meta['js-version'], Config.GJS_VERSION))
+        return true;
+
+    return false;
+}
+
+function loadMetadata(uuid, dir, type) {
+    let info;
+
+    let metadataFile = dir.get_child('metadata.json');
+    if (!metadataFile.query_exists(null)) {
+        throw new Error('Missing metadata.json');
+    }
+
+    let metadataContents, success, tag;
+    try {
+        [success, metadataContents, tag] = metadataFile.load_contents(null);
+    } catch (e) {
+        throw new Error('Failed to load metadata.json: ' + e);
+    }
+    let meta;
+    try {
+        meta = JSON.parse(metadataContents);
+    } catch (e) {
+        throw new Error('Failed to parse metadata.json: ' + e);
+    }
+
+    let requiredProperties = ['uuid', 'name', 'description', 'shell-version'];
+    for (let i = 0; i < requiredProperties.length; i++) {
+        let prop = requiredProperties[i];
+        if (!meta[prop]) {
+            throw new Error('missing "' + prop + '" property in metadata.json');
+        }
+    }
+
+    // Encourage people to add this
+    if (!meta.url) {
+        global.log('Warning: Missing "url" property in metadata.json');
+    }
+
+    if (uuid != meta.uuid) {
+        throw new Error('uuid "' + meta.uuid + '" from metadata.json does not match directory name "' + uuid + '"');
+    }
+
+    meta.type = type;
+    meta.dir = dir;
+    meta.path = dir.get_path();
+    meta.error = '';
+
+    return meta;
+}
+
+var _meta = null;
+
+function installImporter(meta) {
+    _meta = meta;
+    ShellJS.add_extension_importer('imports.misc.extensionUtils._meta', 'importer', meta.path);
+    _meta = null;
+}
+
+function init() {
+    let userExtensionsPath = GLib.build_filenamev([global.userdatadir, 'extensions']);
+    userExtensionsDir = Gio.file_new_for_path(userExtensionsPath);
+    try {
+        if (!userExtensionsDir.query_exists(null))
+            userExtensionsDir.make_directory_with_parents(null);
+    } catch (e) {
+        global.logError('' + e);
+    }
+}
+
+function scanExtensionsInDirectory(callback, dir, type) {
+    let fileEnum;
+    let file, info;
+    try {
+        fileEnum = dir.enumerate_children('standard::*', Gio.FileQueryInfoFlags.NONE, null);
+    } catch(e) {
+        global.logError('' + e);
+        return;
+    }
+
+    while ((info = fileEnum.next_file(null)) != null) {
+        let fileType = info.get_file_type();
+        if (fileType != Gio.FileType.DIRECTORY)
+            continue;
+        let uuid = info.get_name();
+        let extensionDir = dir.get_child(uuid);
+        callback(uuid, extensionDir, type);
+    }
+    fileEnum.close(null);
+}
+
+function scanExtensions(callback) {
+    let systemDataDirs = GLib.get_system_data_dirs();
+    for (let i = 0; i < systemDataDirs.length; i++) {
+        let dirPath = GLib.build_filenamev([systemDataDirs[i], 'gnome-shell', 'extensions']);
+        let dir = Gio.file_new_for_path(dirPath);
+        if (dir.query_exists(null))
+            scanExtensionsInDirectory(callback, dir, ExtensionType.SYSTEM);
+    }
+    scanExtensionsInDirectory(callback, userExtensionsDir, ExtensionType.PER_USER);
+}