From d481d0cb4a5dff5e0b2ad64cd98f2ce86c2852db Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Sun, 3 May 2026 16:10:03 -0500
Subject: [PATCH] [fan] Fix TurnOnAction trigger args with reference types

`const Ts &...` is ill-formed when Ts is already a reference (e.g. a
trigger that passes `std::string &`). Forward Ts by-value so the
generated lambda matches ApplyFn for any valid trigger arg type.
---
 esphome/components/fan/__init__.py  |  5 +++--
 esphome/components/fan/automation.h |  5 ++++-
 tests/components/fan/common.yaml    | 15 +++++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/esphome/components/fan/__init__.py b/esphome/components/fan/__init__.py
index f47fc06b3d..bc006a6602 100644
--- a/esphome/components/fan/__init__.py
+++ b/esphome/components/fan/__init__.py
@@ -369,10 +369,11 @@ async def fan_turn_on_to_code(config, action_id, template_arg, args):
         else:
             body_lines.append(f"call.{setter}({cg.safe_exp(value)});")
 
-    # Match TurnOnAction::ApplyFn signature: const Ts &... for trigger args.
+    # Match TurnOnAction::ApplyFn signature: trigger args forwarded
+    # by-value as Ts...
     apply_args = [
         (FanCall.operator("ref"), "call"),
-        *((t.operator("const").operator("ref"), n) for t, n in args),
+        *args,
     ]
     apply_lambda = LambdaExpression(
         ["\n".join(body_lines)],
diff --git a/esphome/components/fan/automation.h b/esphome/components/fan/automation.h
index d8eda41b27..a5ed80aec6 100644
--- a/esphome/components/fan/automation.h
+++ b/esphome/components/fan/automation.h
@@ -12,9 +12,12 @@ namespace fan {
 // plus one parent pointer, regardless of how many fields the user set.
 // Trigger args are forwarded to the apply function so user lambdas
 // (e.g. `speed: !lambda "return x;"`) keep working.
+//
+// Ts... must be forwarded by-value: `const T &` is ill-formed when T is
+// already a reference type (some triggers pass `std::string &`).
 template<typename... Ts> class TurnOnAction : public Action<Ts...> {
  public:
-  using ApplyFn = void (*)(FanCall &, const Ts &...);
+  using ApplyFn = void (*)(FanCall &, Ts...);
   TurnOnAction(Fan *state, ApplyFn apply) : state_(state), apply_(apply) {}
 
   void play(const Ts &...x) override {
diff --git a/tests/components/fan/common.yaml b/tests/components/fan/common.yaml
index 6cabbd24f8..91f799432c 100644
--- a/tests/components/fan/common.yaml
+++ b/tests/components/fan/common.yaml
@@ -88,3 +88,18 @@ button:
       - fan.turn_on:
           id: test_fan
           speed: !lambda 'return 1;'
+
+# Exercise fan.turn_on inside a trigger with non-empty Ts (number on_value
+# passes float).
+number:
+  - platform: template
+    id: fan_speed_number
+    optimistic: true
+    min_value: 1
+    max_value: 3
+    step: 1
+    on_value:
+      then:
+        - fan.turn_on:
+            id: test_fan
+            speed: !lambda "return (int) x;"