[cover] Fix ControlAction / CoverPublishAction trigger args with reference types (#16227)

esphome/components/cover/__init__.py

@@ -328,17 +328,28 @@ async def build_apply_lambda_action(
     Used by both `cover.control` and `cover.template.publish` (and shared
     with the template/cover platform). Constants are emitted as flash
     immediates; user lambdas are invoked inline so trigger args still flow.
-    The trigger arg types are wrapped as `const T &` to match the
-    `void (*)(..., const Ts &...)` ApplyFn signature.
+    Trigger arg types are normalized to `const std::remove_cvref_t<T> &`
+    to match the ApplyFn signature for any T (value, ref, or const-ref).
     """
     paren = await cg.get_variable(config[CONF_ID])
+    # 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.
+    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] = []
     for field in fields:
         if (value := config.get(field.conf_key)) is None:
             continue
         if isinstance(value, Lambda):
-            inner = await cg.process_lambda(value, args, return_type=field.type_)
+            inner = await cg.process_lambda(
+                value, normalized_args, return_type=field.type_
+            )
             value_expr = f"({inner})({fwd_args})"
         else:
             value_expr = str(cg.safe_exp(value))
@@ -346,7 +357,7 @@ async def build_apply_lambda_action(
 
     apply_args = [
         *prefix_args,
-        *((t.operator("const").operator("ref"), n) for t, n in args),
+        *normalized_args,
     ]
     apply_lambda = LambdaExpression(
         ["\n".join(body_lines)],

esphome/components/cover/automation.h

@@ -51,10 +51,17 @@ template<typename... Ts> class ToggleAction : public Action<Ts...> {
 // 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. `position: !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 (*)(CoverCall &, const Ts &...);
+  using ApplyFn = void (*)(CoverCall &, const std::remove_cvref_t<Ts> &...);
   ControlAction(Cover *cover, ApplyFn apply) : cover_(cover), apply_(apply) {}
 
   void play(const Ts &...x) override {
@@ -70,7 +77,7 @@ template<typename... Ts> class ControlAction : public Action<Ts...> {
 
 template<typename... Ts> class CoverPublishAction : public Action<Ts...> {
  public:
-  using ApplyFn = void (*)(Cover *, const Ts &...);
+  using ApplyFn = void (*)(Cover *, const std::remove_cvref_t<Ts> &...);
   CoverPublishAction(Cover *cover, ApplyFn apply) : cover_(cover), apply_(apply) {}
 
   void play(const Ts &...x) override {

tests/components/template/common-base.yaml

@@ -369,6 +369,19 @@ number:
         - valve.control:
             id: template_valve
             position: !lambda "return x / 100.0f;"
+  # Same regression test for cover.control: forces the apply-lambda
+  # codegen to handle a non-empty trigger Ts (float).
+  - platform: template
+    id: template_cover_position_number
+    optimistic: true
+    min_value: 0
+    max_value: 100
+    step: 1
+    on_value:
+      then:
+        - cover.control:
+            id: template_cover_with_triggers
+            position: !lambda "return x / 100.0f;"
 
 select:
   - platform: template