[fan] Use const remove_reference_t<T> & to avoid copies of non-ref Ts

esphome/components/fan/__init__.py

@@ -369,11 +369,15 @@ 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: trigger args forwarded
-    # by-value as Ts...
+    # Match TurnOnAction::ApplyFn signature: `const std::remove_reference_t<T> &`
+    # for each trigger arg so non-reference Ts stay no-copy (`const T &`) and
+    # reference Ts collapse correctly without producing `const T & &`.
     apply_args = [
         (FanCall.operator("ref"), "call"),
-        *args,
+        *(
+            (cg.RawExpression(f"const std::remove_reference_t<{cg.safe_exp(t)}> &"), n)
+            for t, n in args
+        ),
     ]
     apply_lambda = LambdaExpression(
         ["\n".join(body_lines)],

esphome/components/fan/automation.h

@@ -13,11 +13,13 @@ namespace fan {
 // 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 &`).
+// Trigger args are forwarded as `const std::remove_reference_t<Ts> &...`
+// (instead of `const Ts &...`) so codegen can emit the same form in the
+// apply lambda's parameter list without producing `const T & &` for
+// triggers whose Ts already carries a reference (e.g. `std::string &`).
 template<typename... Ts> class TurnOnAction : public Action<Ts...> {
  public:
-  using ApplyFn = void (*)(FanCall &, Ts...);
+  using ApplyFn = void (*)(FanCall &, const std::remove_reference_t<Ts> &...);
   TurnOnAction(Fan *state, ApplyFn apply) : state_(state), apply_(apply) {}
 
   void play(const Ts &...x) override {