From 6c3f782728f9ca3748bf91037c7508f355542e4b Mon Sep 17 00:00:00 2001
From: Segev Finer <segev@swimm.io>
Date: Mon, 10 Aug 2026 11:22:10 +0300
Subject: [PATCH] Make thenable plugins have the right name on errors

When an plugin registerd via an `import` without
await timeouts you got the useless `[object
Promise]` name in the error message. This PR fixes
that by setting name of the plugin earlier so that
it is used in the error message.
---
 index.js                          |  2 +-
 lib/plugin.js                     | 13 +++++++++++
 test/fixtures/esm-named.mjs       |  3 +++
 test/fixtures/esm-no-next.mjs     |  3 +++
 test/fixtures/esm-plugin-meta.mjs |  8 +++++++
 test/plugin-name.test.js          | 36 +++++++++++++++++++++++++++++++
 test/plugin-timeout.test.js       | 15 +++++++++++++
 7 files changed, 79 insertions(+), 1 deletion(-)
 create mode 100644 test/fixtures/esm-named.mjs
 create mode 100644 test/fixtures/esm-no-next.mjs
 create mode 100644 test/fixtures/esm-plugin-meta.mjs

diff --git a/index.js b/index.js
index 64449b31..ef70b39b 100644
--- a/index.js
+++ b/index.js
@@ -414,7 +414,7 @@ Boot.prototype._loadPlugin = function (plugin, callback) {
       if (typeof fn.default === 'function') {
         fn = fn.default
       }
-      plugin.func = fn
+      plugin.setFunc(fn)
       this._loadPlugin(plugin, callback)
     }, callback)
     return
diff --git a/lib/plugin.js b/lib/plugin.js
index a3f248d5..e4f8d10e 100644
--- a/lib/plugin.js
+++ b/lib/plugin.js
@@ -56,6 +56,19 @@ function Plugin (queue, func, options, isAfter, timeout) {
 
 inherits(Plugin, EventEmitter)
 
+/**
+ * Replaces the plugin function, keeping the derived name in sync.
+ *
+ * Used when a thenable plugin resolves to the actual plugin function, as the
+ * name derived from the thenable itself is meaningless.
+ *
+ * @param {function} func
+ */
+Plugin.prototype.setFunc = function (func) {
+  this.func = func
+  this.name = getPluginName(func, this.options)
+}
+
 /**
  * @callback ExecCallback
  * @param {Error|null} execErr
diff --git a/test/fixtures/esm-named.mjs b/test/fixtures/esm-named.mjs
new file mode 100644
index 00000000..3e00834a
--- /dev/null
+++ b/test/fixtures/esm-named.mjs
@@ -0,0 +1,3 @@
+export default async function esmNamedPlugin (app) {
+  app.loaded = true
+}
diff --git a/test/fixtures/esm-no-next.mjs b/test/fixtures/esm-no-next.mjs
new file mode 100644
index 00000000..77523755
--- /dev/null
+++ b/test/fixtures/esm-no-next.mjs
@@ -0,0 +1,3 @@
+export default function esmPluginNoNext (app, opts, next) {
+  // do not call next on purpose
+}
diff --git a/test/fixtures/esm-plugin-meta.mjs b/test/fixtures/esm-plugin-meta.mjs
new file mode 100644
index 00000000..31279e49
--- /dev/null
+++ b/test/fixtures/esm-plugin-meta.mjs
@@ -0,0 +1,8 @@
+async function plugin (app) {
+  app.loaded = true
+}
+
+// this symbol is assigned by fastify-plugin
+plugin[Symbol.for('plugin-meta')] = { name: 'esm-plugin-meta' }
+
+export default plugin
diff --git a/test/plugin-name.test.js b/test/plugin-name.test.js
index f5038196..193a5b4a 100644
--- a/test/plugin-name.test.js
+++ b/test/plugin-name.test.js
@@ -56,3 +56,39 @@ test('plugins get a name from the function source if theres no other option', as
   t.assert.strictEqual(jsonToCompare.label, 'root')
   t.assert.strictEqual(jsonToCompare.nodes[0].label, '(app, opts, next) => next()')
 })
+
+test('thenable plugins get a name from the resolved plugin metadata if it is set', async (t) => {
+  t.plan(2)
+  const app = boot()
+
+  app.use(import('./fixtures/esm-plugin-meta.mjs'))
+  await app.ready()
+
+  const jsonToCompare = app.toJSON()
+  t.assert.strictEqual(jsonToCompare.label, 'root')
+  t.assert.strictEqual(jsonToCompare.nodes[0].label, 'esm-plugin-meta')
+})
+
+test('thenable plugins get a name from the options if theres no metadata', async (t) => {
+  t.plan(2)
+  const app = boot()
+
+  app.use(import('./fixtures/esm-named.mjs'), { name: 'test registration options name' })
+  await app.ready()
+
+  const jsonToCompare = app.toJSON()
+  t.assert.strictEqual(jsonToCompare.label, 'root')
+  t.assert.strictEqual(jsonToCompare.nodes[0].label, 'test registration options name')
+})
+
+test('thenable plugins get a name from the resolved function name if theres no name in the options and no metadata', async (t) => {
+  t.plan(2)
+  const app = boot()
+
+  app.use(import('./fixtures/esm-named.mjs'))
+  await app.ready()
+
+  const jsonToCompare = app.toJSON()
+  t.assert.strictEqual(jsonToCompare.label, 'root')
+  t.assert.strictEqual(jsonToCompare.nodes[0].label, 'esmNamedPlugin')
+})
diff --git a/test/plugin-timeout.test.js b/test/plugin-timeout.test.js
index ebd59a46..ce2af3a4 100644
--- a/test/plugin-timeout.test.js
+++ b/test/plugin-timeout.test.js
@@ -74,6 +74,21 @@ test('timeout without calling next - use code as name', (t, done) => {
   })
 })
 
+test('timeout without calling next - use the name of the resolved thenable', (t, done) => {
+  t.plan(3)
+  const app = boot({}, {
+    timeout: 10 // 10 ms
+  })
+  app.use(import('./fixtures/esm-no-next.mjs'))
+
+  app.ready((err) => {
+    t.assert.ok(err)
+    t.assert.strictEqual(err.message, message('esmPluginNoNext'))
+    t.assert.strictEqual(err.code, 'AVV_ERR_PLUGIN_EXEC_TIMEOUT')
+    done()
+  })
+})
+
 test('does not keep going', (t, done) => {
   t.plan(2)
   const app = boot({}, {