From 9d6a7526de63bdb19453ff9aa80a2a3ca36703fc Mon Sep 17 00:00:00 2001
From: vmarchaud <contact@vmarchaud.fr>
Date: Sun, 29 Dec 2019 22:12:51 +0100
Subject: [PATCH] feat: warn user when a instrumented package was already
 required #636

---
 .../src/instrumentation/PluginLoader.ts       | 10 ++++++++
 .../test/instrumentation/PluginLoader.test.ts | 24 +++++++++++++++++++
 .../already-require-module/index.js           |  4 ++++
 .../already-require-module/package.json       |  4 ++++
 4 files changed, 42 insertions(+)
 create mode 100644 packages/opentelemetry-node/test/instrumentation/node_modules/already-require-module/index.js
 create mode 100644 packages/opentelemetry-node/test/instrumentation/node_modules/already-require-module/package.json

diff --git a/packages/opentelemetry-node/src/instrumentation/PluginLoader.ts b/packages/opentelemetry-node/src/instrumentation/PluginLoader.ts
index 3eb8881e6fd..23f910b3bb3 100644
--- a/packages/opentelemetry-node/src/instrumentation/PluginLoader.ts
+++ b/packages/opentelemetry-node/src/instrumentation/PluginLoader.ts
@@ -78,6 +78,16 @@ export class PluginLoader {
         return this;
       }
 
+      const alreadyRequiredModules = Object.keys(require.cache);
+      const requiredModulesToHook = modulesToHook.filter(name =>
+        alreadyRequiredModules.some(cached => cached.includes(name))
+      );
+      if (requiredModulesToHook.length > 0) {
+        this.logger.warn(
+          `Some modules (${requiredModulesToHook}) were already required when their respective plugin were loaded, some plugins might not work. Make sure the SDK is setup before you require in other modules.`
+        );
+      }
+
       // Enable the require hook.
       hook(modulesToHook, (exports, name, baseDir) => {
         if (this._hookState !== HookState.ENABLED) return exports;
diff --git a/packages/opentelemetry-node/test/instrumentation/PluginLoader.test.ts b/packages/opentelemetry-node/test/instrumentation/PluginLoader.test.ts
index af6ca193e7e..b5c53ca5362 100644
--- a/packages/opentelemetry-node/test/instrumentation/PluginLoader.test.ts
+++ b/packages/opentelemetry-node/test/instrumentation/PluginLoader.test.ts
@@ -85,6 +85,13 @@ const notSupportedVersionPlugins: Plugins = {
   },
 };
 
+const alreadyRequiredPlugins: Plugins = {
+  'already-require-module': {
+    enabled: true,
+    path: '@opentelemetry/plugin-supported-module',
+  },
+};
+
 describe('PluginLoader', () => {
   const tracer = new NoopTracer();
   const logger = new NoopLogger();
@@ -218,6 +225,23 @@ describe('PluginLoader', () => {
       assert.strictEqual(require('simple-module').value(), 0);
       pluginLoader.unload();
     });
+
+    it(`should warn when module was already loaded`, callback => {
+      const verifyWarnLogger = {
+        error: logger.error,
+        info: logger.info,
+        debug: logger.debug,
+        warn: (message: string, ...args: unknown[]) => {
+          assert(message.match(/were already required when/));
+          assert(message.match(/(already-require-module)/));
+          return callback();
+        },
+      };
+      require('already-require-module');
+      const pluginLoader = new PluginLoader(tracer, verifyWarnLogger);
+      pluginLoader.load(alreadyRequiredPlugins);
+      pluginLoader.unload();
+    });
   });
 
   describe('.unload()', () => {
diff --git a/packages/opentelemetry-node/test/instrumentation/node_modules/already-require-module/index.js b/packages/opentelemetry-node/test/instrumentation/node_modules/already-require-module/index.js
new file mode 100644
index 00000000000..18c0f69a3b9
--- /dev/null
+++ b/packages/opentelemetry-node/test/instrumentation/node_modules/already-require-module/index.js
@@ -0,0 +1,4 @@
+module.exports = {
+    name: () => 'already-module',
+    value: () => 0,
+};
diff --git a/packages/opentelemetry-node/test/instrumentation/node_modules/already-require-module/package.json b/packages/opentelemetry-node/test/instrumentation/node_modules/already-require-module/package.json
new file mode 100644
index 00000000000..7ae0ab8f096
--- /dev/null
+++ b/packages/opentelemetry-node/test/instrumentation/node_modules/already-require-module/package.json
@@ -0,0 +1,4 @@
+{
+  "name": "already-module",
+  "version": "0.1.0"
+}