From 9c9ae190ee040b7eb97f7e82d74e73b7ea6cd7d6 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Tue, 24 Mar 2026 14:13:59 -1000
Subject: [PATCH] [core] Use compile-time HasElse parameter in IfAction
 (#15134)

---
 esphome/automation.py          |  7 +++++--
 esphome/core/base_automation.h | 27 ++++++++++++++-------------
 2 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/esphome/automation.py b/esphome/automation.py
index 36ab30b654..17966dc782 100644
--- a/esphome/automation.py
+++ b/esphome/automation.py
@@ -413,13 +413,16 @@ async def if_action_to_code(
     template_arg: cg.TemplateArguments,
     args: TemplateArgsType,
 ) -> MockObj:
+    has_else = CONF_ELSE in config
+    # Prepend HasElse bool to template arguments: IfAction<HasElse, Ts...>
+    if_template_arg = cg.TemplateArguments(has_else, *template_arg)
     cond_conf = next(el for el in config if el in (CONF_ANY, CONF_ALL, CONF_CONDITION))
     condition = await build_condition(config[cond_conf], template_arg, args)
-    var = cg.new_Pvariable(action_id, template_arg, condition)
+    var = cg.new_Pvariable(action_id, if_template_arg, condition)
     if CONF_THEN in config:
         actions = await build_action_list(config[CONF_THEN], template_arg, args)
         cg.add(var.add_then(actions))
-    if CONF_ELSE in config:
+    if has_else:
         actions = await build_action_list(config[CONF_ELSE], template_arg, args)
         cg.add(var.add_else(actions))
     return var
diff --git a/esphome/core/base_automation.h b/esphome/core/base_automation.h
index 985f26e711..efcffa8824 100644
--- a/esphome/core/base_automation.h
+++ b/esphome/core/base_automation.h
@@ -264,7 +264,7 @@ template<typename... Ts> class WhileLoopContinuation : public Action<Ts...> {
   WhileAction<Ts...> *parent_;
 };
 
-template<typename... Ts> class IfAction : public Action<Ts...> {
+template<bool HasElse, typename... Ts> class IfAction : public Action<Ts...> {
  public:
   explicit IfAction(Condition<Ts...> *condition) : condition_(condition) {}
 
@@ -273,27 +273,25 @@ template<typename... Ts> class IfAction : public Action<Ts...> {
     this->then_.add_action(new ContinuationAction<Ts...>(this));
   }
 
-  void add_else(const std::initializer_list<Action<Ts...> *> &actions) {
+  void add_else(const std::initializer_list<Action<Ts...> *> &actions) requires(HasElse) {
     this->else_.add_actions(actions);
     this->else_.add_action(new ContinuationAction<Ts...>(this));
   }
 
   void play_complex(const Ts &...x) override {
     this->num_running_++;
-    bool res = this->condition_->check(x...);
-    if (res) {
-      if (this->then_.empty()) {
-        this->play_next_(x...);
-      } else if (this->num_running_ > 0) {
+    if (this->condition_->check(x...)) {
+      if (!this->then_.empty() && this->num_running_ > 0) {
         this->then_.play(x...);
+        return;
       }
-    } else {
-      if (this->else_.empty()) {
-        this->play_next_(x...);
-      } else if (this->num_running_ > 0) {
+    } else if constexpr (HasElse) {
+      if (!this->else_.empty() && this->num_running_ > 0) {
         this->else_.play(x...);
+        return;
       }
     }
+    this->play_next_(x...);
   }
 
   void play(const Ts &...x) override { /* ignore - see play_complex */
@@ -301,13 +299,16 @@ template<typename... Ts> class IfAction : public Action<Ts...> {
 
   void stop() override {
     this->then_.stop();
-    this->else_.stop();
+    if constexpr (HasElse) {
+      this->else_.stop();
+    }
   }
 
  protected:
   Condition<Ts...> *condition_;
   ActionList<Ts...> then_;
-  ActionList<Ts...> else_;
+  struct NoElse {};
+  [[no_unique_address]] std::conditional_t<HasElse, ActionList<Ts...>, NoElse> else_;
 };
 
 template<typename... Ts> class WhileAction : public Action<Ts...> {