[template] Skip the switch optimistic and assumed state setters when they match the default (#19232)

esphome/components/template/switch/__init__.py

@@ -72,8 +72,11 @@ async def to_code(config):
         await automation.build_automation(
             var.get_turn_on_trigger(), [], config[CONF_TURN_ON_ACTION]
         )
-    cg.add(var.set_optimistic(config[CONF_OPTIMISTIC]))
-    cg.add(var.set_assumed_state(config[CONF_ASSUMED_STATE]))
+    # optimistic_ and assumed_state_ are false in C++; only emit setters to turn them on.
+    if config[CONF_OPTIMISTIC]:
+        cg.add(var.set_optimistic(True))
+    if config[CONF_ASSUMED_STATE]:
+        cg.add(var.set_assumed_state(True))
 
 
 @automation.register_action(

esphome/components/template/switch/template_switch.h

@@ -29,6 +29,7 @@ class TemplateSwitch final : public switch_::Switch, public Component {
   void write_state(bool state) override;
 
   TemplateLambda<bool> f_;
+  // Codegen only emits these setters to turn them on
   bool optimistic_{false};
   bool assumed_state_{false};
   Trigger<> turn_on_trigger_;

tests/component_tests/template/config/switch_defaults.yaml

@@ -0,0 +1,18 @@
+---
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+
+logger:
+
+switch:
+  - platform: template
+    id: plain_switch
+    turn_on_action:
+      - logger.log: "on"
+  - platform: template
+    id: enabled_switch
+    optimistic: true
+    assumed_state: true

tests/component_tests/template/test_template_switch.py

@@ -0,0 +1,17 @@
+"""Tests for the template switch codegen."""
+
+from collections.abc import Callable
+from pathlib import Path
+
+
+def test_default_flags_are_not_emitted(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """Only true optimistic and assumed_state are set; false is the C++ initializer."""
+    main_cpp = generate_main(component_config_path("switch_defaults.yaml"))
+
+    assert "plain_switch->set_optimistic(" not in main_cpp
+    assert "plain_switch->set_assumed_state(" not in main_cpp
+    assert "enabled_switch->set_optimistic(true);" in main_cpp
+    assert "enabled_switch->set_assumed_state(true);" in main_cpp