Fix plugin version not being loaded

Load the version of the plugin from its package.json file and document
this requirement in the writing plugins document.

docs/writing-plugins.md

@@ -39,8 +39,21 @@ The basic file structure of a plugin is the following.
          +- module.json
          +- plugin.lua
 
-The most important file is the `info.js` file.  Without it the plugin
-will not recognized by Clusterio.  Here's an example of it:
+Clusterio plugins are Node.js packages that can be published on npm for
+ease of installation and distribution.  The usual guides for creating
+such packages apply.  At minimum the `package.json` file must contain a
+version entry.
+
+A possible workflow for developing plugins is to place the plugin in a
+sub-directory of where clusterio has been installed, and rely on Node.js
+searching up the folder heirarchy for it to find `@clusterio/lib`.  To
+add it to `plugin-list.json` so that it gets loaded use the `plugin add
+<path>` sub-command to either clusteriomaster, clusterioslave or
+clusterioctl.  Note that it's important that the path starts with ./ or
+../ (use .\ or ..\ on Windows).
+
+For a plugin the most important file is the `info.js` file.  Without it
+the plugin will not recognized by Clusterio.  Here's an example of it:
 
     const link = require('@clusterio/lib/link'); // For messages
 
@@ -48,7 +61,6 @@ will not recognized by Clusterio.  Here's an example of it:
         name: "foo_frobber",
         title: "Foo Frobber",
         description: "Does advanced frobnication",
-        version: "0.8.1",
         instanceEntrypoint: "instance",
         masterEntrypoint: "master",
         messages: {
@@ -68,11 +80,6 @@ The following properties are recognized:
 **description**:
     Brief description of what the plugin does.  Currently not used.
 
-**version**:
-    Semver compatible version string of the plugin.  Currently only
-    servers as the default for the Clusterio module embedded in the
-    plugin, if any.
-
 **instanceEntrypoint**:
     Path to a Node.js module relative to the plugin directory which
     contains the InstancePlugin class definition for this plugin.  This

packages/lib/plugin.js

@@ -402,9 +402,11 @@ async function loadPluginInfos(pluginList) {
 	let plugins = [];
 	for (let [pluginName, pluginPath] of pluginList) {
 		let pluginInfo;
+		let pluginPackage;
 
 		try {
 			pluginInfo = require(path.posix.join(pluginPath, "info"));
+			pluginPackage = require(path.posix.join(pluginPath, "package.json"));
 
 		} catch (err) {
 			throw new errors.PluginError(pluginName, err);
@@ -417,6 +419,7 @@ async function loadPluginInfos(pluginList) {
 		}
 
 		pluginInfo.requirePath = pluginPath;
+		pluginInfo.version = pluginPackage.version;
 		plugins.push(pluginInfo);
 	}
 	return plugins;

test/lib/plugin.js

@@ -54,6 +54,10 @@ describe("lib/plugin", function() {
 					path.join(pluginPath, "info.js"),
 					`module.exports = { name: "${infoName}" };`
 				);
+				await fs.outputFile(
+					path.join(pluginPath, "package.json"),
+					'{ "version": "0.0.1" }'
+				);
 			}
 
 			await writePlugin(testPlugin, "test");
@@ -71,7 +75,7 @@ describe("lib/plugin", function() {
 		it("should load test plugin", async function() {
 			assert.deepEqual(
 				await plugin.loadPluginInfos(new Map([["test", path.resolve(testPlugin)]])),
-				[{ name: "test", requirePath: path.resolve(testPlugin) }]
+				[{ name: "test", version: "0.0.1", requirePath: path.resolve(testPlugin) }]
 			);
 		});
 		it("should reject on broken plugin", async function() {