[light] Normalize trigger args to const remove_cvref_t<T> &

esphome/components/light/automation.h

@@ -37,16 +37,15 @@ template<bool HasTransitionLength, typename... Ts> class ToggleAction : public A
 // Trigger args are forwarded to the apply function so user lambdas
 // (e.g. `brightness: !lambda "return x;"`) keep working.
 //
-// Trigger args are forwarded as `Ts...`. The previous `const Ts &...`
-// form caused codegen to emit `const T &` for each arg in the apply
-// lambda's parameter list, which is invalid C++ source text when T is
-// already a reference (e.g. `const std::string & &` for triggers that
-// pass `std::string &`). Forwarding `Ts...` lets the codegen reuse the
-// trigger's `args` types unchanged for both the apply lambda and any
-// inner field lambdas, so they always type-match.
+// Trigger args are normalized to `const std::remove_cvref_t<Ts> &...` so
+// the codegen can emit a matching parameter list for both the apply lambda
+// and any inner field lambdas without producing invalid C++ source text
+// (e.g. `const T & &` if Ts already carries a reference, or `const const
+// T &` if Ts already carries a const). This keeps trigger args no-copy
+// regardless of whether the trigger supplies `T`, `T &`, or `const T &`.
 template<typename... Ts> class LightControlAction : public Action<Ts...> {
  public:
-  using ApplyFn = void (*)(LightState *, LightCall &, Ts...);
+  using ApplyFn = void (*)(LightState *, LightCall &, const std::remove_cvref_t<Ts> &...);
   LightControlAction(LightState *parent, ApplyFn apply) : parent_(parent), apply_(apply) {}
 
   void play(const Ts &...x) override {

esphome/components/light/automation.py

@@ -200,6 +200,15 @@ async def light_control_to_code(config, action_id, template_arg, args):
         (CONF_WARM_WHITE, "set_warm_white", cg.float_),
     )
 
+    # Normalize trigger args to `const std::remove_cvref_t<T> &` so the
+    # apply lambda and any inner field lambdas (generated below via
+    # `process_lambda`) share one parameter spelling that's well-formed for
+    # any T (value, ref, or const-ref). Matches LightControlAction::ApplyFn.
+    normalized_args = [
+        (cg.RawExpression(f"const std::remove_cvref_t<{cg.safe_exp(t)}> &"), n)
+        for t, n in args
+    ]
+
     fwd_args = ", ".join(name for _, name in args)
     body_lines: list[str] = []
 
@@ -208,7 +217,7 @@ async def light_control_to_code(config, action_id, template_arg, args):
             continue
         value = config[conf_key]
         if isinstance(value, Lambda):
-            inner = await cg.process_lambda(value, args, return_type=type_)
+            inner = await cg.process_lambda(value, normalized_args, return_type=type_)
             body_lines.append(f"call.{setter}(({inner})({fwd_args}));")
         else:
             body_lines.append(f"call.{setter}({cg.safe_exp(value)});")
@@ -216,7 +225,7 @@ async def light_control_to_code(config, action_id, template_arg, args):
     if CONF_EFFECT in config:
         if isinstance(config[CONF_EFFECT], Lambda):
             inner_lambda = await cg.process_lambda(
-                config[CONF_EFFECT], args, return_type=cg.std_string
+                config[CONF_EFFECT], normalized_args, return_type=cg.std_string
             )
             body_lines.append(
                 f"{{ auto __effect_s = ({inner_lambda})({fwd_args});\n"
@@ -230,13 +239,10 @@ 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: forward trigger args as Ts...
-    # so the apply lambda's parameter types match both ApplyFn and the
-    # inner field lambdas (which are generated from `args` directly).
     apply_args = [
         (LightState.operator("ptr"), "parent"),
         (LightCall.operator("ref"), "call"),
-        *args,
+        *normalized_args,
     ]
     apply_lambda = LambdaExpression(
         ["\n".join(body_lines)],