[fan] Fold TurnOnAction fields into a single stateless lambda (#16122)

esphome/components/fan/__init__.py

@@ -31,17 +31,19 @@ from esphome.const import (
     CONF_TRIGGER_ID,
     CONF_WEB_SERVER,
 )
-from esphome.core import CORE, CoroPriority, coroutine_with_priority
+from esphome.core import CORE, CoroPriority, Lambda, coroutine_with_priority
 from esphome.core.entity_helpers import (
     entity_duplicate_validator,
     queue_entity_register,
     setup_entity,
 )
+from esphome.cpp_generator import LambdaExpression
 
 IS_PLATFORM_COMPONENT = True
 
 fan_ns = cg.esphome_ns.namespace("fan")
 Fan = fan_ns.class_("Fan", cg.EntityBase)
+FanCall = fan_ns.class_("FanCall")
 
 FanDirection = fan_ns.enum("FanDirection", is_class=True)
 FAN_DIRECTION_ENUM = {
@@ -347,17 +349,38 @@ async def fan_turn_off_to_code(config, action_id, template_arg, args):
 )
 async def fan_turn_on_to_code(config, action_id, template_arg, args):
     paren = await cg.get_variable(config[CONF_ID])
-    var = cg.new_Pvariable(action_id, template_arg, paren)
-    if (oscillating := config.get(CONF_OSCILLATING)) is not None:
-        template_ = await cg.templatable(oscillating, args, cg.bool_)
-        cg.add(var.set_oscillating(template_))
-    if (speed := config.get(CONF_SPEED)) is not None:
-        template_ = await cg.templatable(speed, args, cg.int_)
-        cg.add(var.set_speed(template_))
-    if (direction := config.get(CONF_DIRECTION)) is not None:
-        template_ = await cg.templatable(direction, args, FanDirection)
-        cg.add(var.set_direction(template_))
-    return var
+
+    # All configured fields are folded into a single stateless lambda whose
+    # constants live in flash; the action stores only a function pointer.
+    FIELDS = (
+        (CONF_OSCILLATING, "set_oscillating", cg.bool_),
+        (CONF_SPEED, "set_speed", cg.int_),
+        (CONF_DIRECTION, "set_direction", FanDirection),
+    )
+
+    fwd_args = ", ".join(name for _, name in args)
+    body_lines: list[str] = []
+    for conf_key, setter, type_ in FIELDS:
+        if (value := config.get(conf_key)) is None:
+            continue
+        if isinstance(value, Lambda):
+            inner = await cg.process_lambda(value, args, return_type=type_)
+            body_lines.append(f"call.{setter}(({inner})({fwd_args}));")
+        else:
+            body_lines.append(f"call.{setter}({cg.safe_exp(value)});")
+
+    # Match TurnOnAction::ApplyFn signature: const Ts &... for trigger args.
+    apply_args = [
+        (FanCall.operator("ref"), "call"),
+        *((t.operator("const").operator("ref"), n) for t, n in args),
+    ]
+    apply_lambda = LambdaExpression(
+        ["\n".join(body_lines)],
+        apply_args,
+        capture="",
+        return_type=cg.void,
+    )
+    return cg.new_Pvariable(action_id, template_arg, paren, apply_lambda)
 
 
 @automation.register_action(

esphome/components/fan/automation.h

@@ -7,29 +7,24 @@
 namespace esphome {
 namespace fan {
 
+// All configured fields are baked into a single stateless lambda whose
+// constants live in flash. The action only stores one function pointer
+// 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.
 template<typename... Ts> class TurnOnAction : public Action<Ts...> {
  public:
-  explicit TurnOnAction(Fan *state) : state_(state) {}
-
-  TEMPLATABLE_VALUE(bool, oscillating)
-  TEMPLATABLE_VALUE(int, speed)
-  TEMPLATABLE_VALUE(FanDirection, direction)
+  using ApplyFn = void (*)(FanCall &, const Ts &...);
+  TurnOnAction(Fan *state, ApplyFn apply) : state_(state), apply_(apply) {}
 
   void play(const Ts &...x) override {
     auto call = this->state_->turn_on();
-    if (this->oscillating_.has_value()) {
-      call.set_oscillating(this->oscillating_.value(x...));
-    }
-    if (this->speed_.has_value()) {
-      call.set_speed(this->speed_.value(x...));
-    }
-    if (this->direction_.has_value()) {
-      call.set_direction(this->direction_.value(x...));
-    }
+    this->apply_(call, x...);
     call.perform();
   }
 
   Fan *state_;
+  ApplyFn apply_;
 };
 
 template<typename... Ts> class TurnOffAction : public Action<Ts...> {