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[core] Emit deprecation warning on TemplatableFn return type mismatch

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J. Nick Koston
2026-04-07 14:37:54 -10:00
parent 05011a28a0
commit 4cc6624cb0
1 changed files with 3 additions and 1 deletions
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esphome/core/automation.h
+3 -1
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@@ -47,8 +47,10 @@ template<typename T, typename... X> class TemplatableFn {
// Convertible return type (e.g., int -> uint8_t) — casting trampoline.
// Stateless lambdas are default-constructible in C++20, so F{} recreates the lambda inside
// the trampoline without capturing. This compiles to the same code as a direct call + cast.
// Deprecated: codegen should use the correct output type to avoid the trampoline.
template<typename F>
TemplatableFn(F) requires(!std::convertible_to<F, T (*)(X...)>) &&
[[deprecated("Lambda return type does not match TemplatableFn<T> — use the correct type in "
"codegen")]] TemplatableFn(F) requires(!std::convertible_to<F, T (*)(X...)>) &&
std::invocable<F, X...> &&std::convertible_to<std::invoke_result_t<F, X...>, T> &&std::is_empty_v<F>
&&std::default_initializable<F> : f_([](X... x) -> T { return static_cast<T>(F{}(x...)); }) {}