plugin.needs to assert dependencies (#89)

* plugin.needs to assert dependencies

* tweak error msg

* support async needs check

* update documentation on plugins regarding `needs`

PLUGINS.md

@@ -12,6 +12,7 @@ Plugins are simply NodeJS modules that export an `object` of form `{ name, versi
 
 module.exports = {
   name: 'bluetooth',
+  needs: ['conn'],
   version: '5.0.1',
   manifest: {
     localPeers: 'async',
@@ -87,6 +88,15 @@ will be available at `node.fooBar`.
 A `plugin.name` can also be an `'object`. This object will be merged
 directly with the
 
+### `plugin.needs` (Array) _optional_
+
+An array of strings which are the names of other plugins that this plugin
+depends on. If those plugins are not present, then secret-stack will throw
+an error indicating that the dependency is missing.
+
+Use this field to declare dependencies on other plugins, and this should
+facilitate the correct usage of your plugin.
+
 ### `plugin.version` (String) _optional_
 
 NOTE - not currently used anywhere functionally

lib/api.js

@@ -141,6 +141,18 @@ function Api (plugins, defaultConfig) {
       }
 
       const name = plugin.name
+
+      if (plugin.needs) {
+        queueMicrotask(() => {
+          for (const needed of plugin.needs) {
+            const found = create.plugins.some((p) => p.name === needed)
+            if (!found) {
+              throw new Error(`secret-stack plugin "${name ?? '?'}" needs plugin "${needed}" but not found`)
+            }
+          }
+        })
+      }
+
       if (plugin.manifest) {
         create.manifest = u.merge.manifest(
           create.manifest,

test/api.js

@@ -140,6 +140,47 @@ tape('plugin cannot be named global', function (t) {
   t.end()
 })
 
+tape('plugin needs another plugin', function (t) {
+  // core, not a plugin.
+  var Create = Api([{
+    manifest: {},
+    init: function (api) {
+      return {}
+    }
+  }])
+
+  function uncaughtExceptionListener(err) {
+    t.equals(err.message, 'secret-stack plugin "x" needs plugin "y" but not found')
+
+    // Wait for potentially other errors
+    setTimeout(() => {
+      process.off('uncaughtException', uncaughtExceptionListener)
+      t.end()
+    }, 100)
+  }
+
+  process.on('uncaughtException', uncaughtExceptionListener)
+
+  // Should throw
+  Create.use({
+    name: 'x',
+    needs: ['y'],
+    init: function () { }
+  })
+
+  // Should NOT throw, even though 'foo' is loaded after 'bar'
+  Create.use({
+    name: 'bar',
+    needs: ['foo'],
+    init: function () { }
+  })
+
+  Create.use({
+    name: 'foo',
+    init: function () { }
+  })
+})
+
 tape('compound (array) plugins', function (t) {
   // core, not a plugin.
   var Create = Api([{