From 993c96875cfd7e016c48d190cef23c519bc397ea Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Thu, 24 Sep 2026 14:05:24 +0100
Subject: [PATCH] [core][select] Pass the select.set option as a plain literal
 (#19568)

---
 esphome/automation.py                  |  9 +++++++++
 esphome/components/climate/__init__.py | 10 ++--------
 esphome/components/select/__init__.py  |  7 ++++++-
 tests/unit_tests/test_automation.py    | 18 ++++++++++++++++++
 4 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/esphome/automation.py b/esphome/automation.py
index 850ac554af..a8c421f065 100644
--- a/esphome/automation.py
+++ b/esphome/automation.py
@@ -224,6 +224,15 @@ def flash_string(config: ConfigType, value: str) -> str:
     return str(cg.safe_exp(value))
 
 
+def literal_with_length(config: ConfigType, value: str) -> str:
+    """Renderer for a ``(const char *, size_t)`` target: a plain literal plus its byte length.
+
+    The target compares or copies the bytes in place, so it needs the RAM literal rather than
+    the PROGMEM rendering on ESP8266, and the length saves a strlen.
+    """
+    return f"{cg.safe_exp(value)}, {len(value.encode('utf-8'))}"
+
+
 @dataclass(frozen=True)
 class ApplyCall:
     """One statement from config keys, e.g. ``"set_range({}, {})"`` with ``((CONF_LOW, cg.float_), ...)``.
diff --git a/esphome/components/climate/__init__.py b/esphome/components/climate/__init__.py
index 4c9f58c7a4..e64092d30e 100644
--- a/esphome/components/climate/__init__.py
+++ b/esphome/components/climate/__init__.py
@@ -494,12 +494,6 @@ CLIMATE_CONTROL_ACTION_SCHEMA = cv.Schema(
 )
 
 
-def _literal_with_length(config: ConfigType, value: str) -> str:
-    # The (const char *, size_t) overload compares bytes in place, so it needs a plain
-    # literal rather than the default PROGMEM rendering on ESP8266, and skips a strlen.
-    return f"{cg.safe_exp(value)}, {len(value.encode('utf-8'))}"
-
-
 automation.register_apply_action(
     "climate.control",
     CLIMATE_CONTROL_ACTION_SCHEMA,
@@ -517,14 +511,14 @@ automation.register_apply_action(
         CONF_CUSTOM_FAN_MODE,
         "set_fan_mode",
         cg.std_string,
-        const_fn=_literal_with_length,
+        const_fn=automation.literal_with_length,
     ),
     automation.ApplyField(CONF_PRESET, "set_preset", ClimatePreset),
     automation.ApplyField(
         CONF_CUSTOM_PRESET,
         "set_preset",
         cg.std_string,
-        const_fn=_literal_with_length,
+        const_fn=automation.literal_with_length,
     ),
     automation.ApplyField(CONF_SWING_MODE, "set_swing_mode", ClimateSwingMode),
     call="make_call",
diff --git a/esphome/components/select/__init__.py b/esphome/components/select/__init__.py
index 2db4c8cc34..6b7461bfa8 100644
--- a/esphome/components/select/__init__.py
+++ b/esphome/components/select/__init__.py
@@ -142,7 +142,12 @@ automation.register_apply_action(
             cv.Required(CONF_OPTION): cv.templatable(cv.string_strict),
         }
     ),
-    automation.ApplyField(CONF_OPTION, "set_option", cg.std_string),
+    automation.ApplyField(
+        CONF_OPTION,
+        "set_option",
+        cg.std_string,
+        const_fn=automation.literal_with_length,
+    ),
     call="make_call",
 )
 
diff --git a/tests/unit_tests/test_automation.py b/tests/unit_tests/test_automation.py
index c4265a7888..f6aaff3d92 100644
--- a/tests/unit_tests/test_automation.py
+++ b/tests/unit_tests/test_automation.py
@@ -18,6 +18,7 @@ from esphome.automation import (
     TriggerOnTrueForwarder,
     build_callback_automations,
     has_non_synchronous_actions,
+    literal_with_length,
     maybe_simple_id,
     register_apply_action,
     register_apply_condition,
@@ -838,6 +839,23 @@ async def test_apply_string_constant_stays_in_flash_on_esp8266(
     )
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize("platform", ["esp32", "esp8266"])
+async def test_apply_literal_with_length_is_plain_on_every_platform(
+    registries: tuple[Registry, Registry], mock_cg: MockCodegen, platform: str
+) -> None:
+    """A (const char *, size_t) target gets the RAM literal and its byte length, never a flash copy."""
+    fields = (
+        ApplyField("option", "set_option", cg.std_string, const_fn=literal_with_length),
+    )
+    await _run_apply_action(
+        registries, fields, {"option": "h\u00e9llo"}, platform=platform
+    )
+    text = _apply_lambda(mock_cg)
+    assert f'::{PARENT_OBJ}->set_option("h\\303\\251llo", 6);' in text
+    assert "progmem_string" not in text
+
+
 @pytest.mark.asyncio
 async def test_register_apply_condition_predicate(
     registries: tuple[Registry, Registry], mock_cg: MockCodegen