From cf223674e51cff65ed9c71b46b434c9c48dd8b72 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Sun, 3 May 2026 19:43:49 -0500
Subject: [PATCH] [climate] Fix ControlAction trigger args with reference types
 (#16221)

---
 esphome/components/climate/__init__.py  | 14 +++++++++++---
 esphome/components/climate/automation.h |  9 ++++++++-
 tests/components/climate/common.yaml    | 15 +++++++++++++++
 3 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/esphome/components/climate/__init__.py b/esphome/components/climate/__init__.py
index 7c9002d6dc..fc1b0f368e 100644
--- a/esphome/components/climate/__init__.py
+++ b/esphome/components/climate/__init__.py
@@ -506,6 +506,15 @@ async def climate_control_to_code(config, action_id, template_arg, args):
         (CONF_SWING_MODE, "set_swing_mode", ClimateSwingMode),
     )
 
+    # Normalize trigger args to `const std::remove_cvref_t<T> &` so the
+    # apply lambda and any inner field lambdas (generated below via
+    # `process_lambda`) share one parameter spelling that's well-formed for
+    # any T (value, ref, or const-ref). Matches ControlAction::ApplyFn.
+    normalized_args = [
+        (cg.RawExpression(f"const std::remove_cvref_t<{cg.safe_exp(t)}> &"), n)
+        for t, n in args
+    ]
+
     fwd_args = ", ".join(name for _, name in args)
     body_lines: list[str] = []
 
@@ -513,7 +522,7 @@ async def climate_control_to_code(config, action_id, template_arg, args):
         if (value := config.get(conf_key)) is None:
             continue
         if isinstance(value, Lambda):
-            inner = await cg.process_lambda(value, args, return_type=type_)
+            inner = await cg.process_lambda(value, normalized_args, return_type=type_)
             body_lines.append(f"call.{setter}(({inner})({fwd_args}));")
         elif type_ is cg.std_string:
             # Static custom strings: emit a flash literal and pass the
@@ -526,10 +535,9 @@ async def climate_control_to_code(config, action_id, template_arg, args):
         else:
             body_lines.append(f"call.{setter}({cg.safe_exp(value)});")
 
-    # Match ControlAction::ApplyFn signature: const Ts &... for trigger args.
     apply_args = [
         (ClimateCall.operator("ref"), "call"),
-        *((t.operator("const").operator("ref"), n) for t, n in args),
+        *normalized_args,
     ]
     apply_lambda = LambdaExpression(
         ["\n".join(body_lines)],
diff --git a/esphome/components/climate/automation.h b/esphome/components/climate/automation.h
index 71d23fd6b6..6ac9bd8bae 100644
--- a/esphome/components/climate/automation.h
+++ b/esphome/components/climate/automation.h
@@ -10,9 +10,16 @@ namespace esphome::climate {
 // 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. `target_temperature: !lambda "return x;"`) keep working.
+//
+// Trigger args are normalized to `const std::remove_cvref_t<Ts> &...` so
+// the codegen can emit a matching parameter list for both the apply lambda
+// and any inner field lambdas without producing invalid C++ source text
+// (e.g. `const T & &` if Ts already carries a reference, or `const const
+// T &` if Ts already carries a const). This keeps trigger args no-copy
+// regardless of whether the trigger supplies `T`, `T &`, or `const T &`.
 template<typename... Ts> class ControlAction : public Action<Ts...> {
  public:
-  using ApplyFn = void (*)(ClimateCall &, const Ts &...);
+  using ApplyFn = void (*)(ClimateCall &, const std::remove_cvref_t<Ts> &...);
   ControlAction(Climate *climate, ApplyFn apply) : climate_(climate), apply_(apply) {}
 
   void play(const Ts &...x) override {
diff --git a/tests/components/climate/common.yaml b/tests/components/climate/common.yaml
index 2d35438afd..c28fde8eeb 100644
--- a/tests/components/climate/common.yaml
+++ b/tests/components/climate/common.yaml
@@ -85,3 +85,18 @@ button:
       - climate.control:
           id: climate_test_thermostat
           mode: "OFF"
+
+# Exercise climate.control inside a trigger with non-empty Ts (number on_value
+# passes float).
+number:
+  - platform: template
+    id: climate_target_temp_number
+    optimistic: true
+    min_value: 16
+    max_value: 28
+    step: 0.5
+    on_value:
+      then:
+        - climate.control:
+            id: climate_test_thermostat
+            target_temperature_high: !lambda "return x;"