From 7aa9f0d796397171cb130b033ea9e63b455791b8 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Sun, 3 May 2026 16:06:54 -0500
Subject: [PATCH] [light] Fix LightControlAction 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/light/automation.h  |  5 ++++-
 esphome/components/light/automation.py |  5 +++--
 tests/components/light/common.yaml     | 15 +++++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/esphome/components/light/automation.h b/esphome/components/light/automation.h
index a5c73997b0..620ea3aca9 100644
--- a/esphome/components/light/automation.h
+++ b/esphome/components/light/automation.h
@@ -36,9 +36,12 @@ template<bool HasTransitionLength, typename... Ts> class ToggleAction : public A
 // 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. `brightness: !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 LightControlAction : public Action<Ts...> {
  public:
-  using ApplyFn = void (*)(LightState *, LightCall &, const Ts &...);
+  using ApplyFn = void (*)(LightState *, LightCall &, Ts...);
   LightControlAction(LightState *parent, ApplyFn apply) : parent_(parent), apply_(apply) {}
 
   void play(const Ts &...x) override {
diff --git a/esphome/components/light/automation.py b/esphome/components/light/automation.py
index ca4018a975..370489770d 100644
--- a/esphome/components/light/automation.py
+++ b/esphome/components/light/automation.py
@@ -230,11 +230,12 @@ async def light_control_to_code(config, action_id, template_arg, args):
                 f"call.set_effect(static_cast<uint32_t>({_resolve_effect_index(config)}));"
             )
 
-    # Match LightControlAction::ApplyFn signature: const Ts &... for trigger args.
+    # Match LightControlAction::ApplyFn signature: trigger args forwarded
+    # by-value as Ts...
     apply_args = [
         (LightState.operator("ptr"), "parent"),
         (LightCall.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/tests/components/light/common.yaml b/tests/components/light/common.yaml
index e58f7baee4..044a8144fa 100644
--- a/tests/components/light/common.yaml
+++ b/tests/components/light/common.yaml
@@ -127,6 +127,21 @@ esphome:
           blue: 0%
           transition_length: 1s
 
+# Exercise light actions inside a trigger with non-empty Ts (number on_value
+# passes float).
+number:
+  - platform: template
+    id: test_number_brightness
+    optimistic: true
+    min_value: 0
+    max_value: 100
+    step: 1
+    on_value:
+      then:
+        - light.turn_on:
+            id: test_monochromatic_light
+            brightness: !lambda "return x / 100.0;"
+
 light:
   - platform: binary
     id: test_binary_light