Use Probe

Author: Tpt

pyo3-macros-backend/src/type_hint.rs

@@ -148,11 +148,10 @@ impl PythonTypeHint {
                 }
             }
             PythonTypeHintVariant::ReturnType(t) => {
-                // Use https://github.com/GoldsteinE/gh-blog/blob/master/const_deref_specialization/src/lib.md to detect empty tuple
                 quote! {{
-                    const TYPE: #pyo3_crate_path::inspect::TypeHint = if #pyo3_crate_path::impl_::introspection::is_empty_tuple_from_closure(&|| {
-                        #pyo3_crate_path::impl_::introspection::IsEmptyTupleChecker::<#t>::new().check()
-                    }) {
+                    #[allow(unused_imports)]
+                    use #pyo3_crate_path::impl_::pyclass::Probe as _;
+                    const TYPE: #pyo3_crate_path::inspect::TypeHint = if #pyo3_crate_path::impl_::pyclass::IsReturningEmptyTuple::<#t>::VALUE {
                         #pyo3_crate_path::inspect::TypeHint::builtin("None")
                     } else {
                         <#t as #pyo3_crate_path::impl_::introspection::PyReturnType>::OUTPUT_TYPE

src/impl_/introspection.rs

@@ -1,8 +1,5 @@
 use crate::conversion::IntoPyObject;
 use crate::inspect::TypeHint;
-use crate::pyclass::boolean_struct::{private::Boolean, False, True};
-use std::marker::PhantomData;
-use std::ops::Deref;
 
 /// Trait to guess a function Python return type
 ///
@@ -20,57 +17,6 @@ impl<T: PyReturnType, E> PyReturnType for Result<T, E> {
     const OUTPUT_TYPE: TypeHint = T::OUTPUT_TYPE;
 }
 
-/// Hack to guess if the output type is the empty tuple
-///
-/// Inspiration: <https://github.com/GoldsteinE/gh-blog/blob/master/const_deref_specialization/src/lib.md>
-/// TL;DR: with closure we can get the compiler to return us the output type of the usual deref-based specialization
-pub const fn is_empty_tuple_from_closure<B: Boolean>(
-    _closure_returning_bool: &impl FnOnce() -> B,
-) -> bool {
-    B::VALUE
-}
-
-pub struct IsEmptyTupleChecker<T> {
-    _marker: PhantomData<T>,
-}
-
-impl<T> IsEmptyTupleChecker<T> {
-    #[allow(clippy::new_without_default)]
-    pub const fn new() -> Self {
-        Self {
-            _marker: PhantomData,
-        }
-    }
-}
-
-impl IsEmptyTupleChecker<()> {
-    pub fn check(&self) -> True {
-        True
-    }
-}
-
-impl<E> IsEmptyTupleChecker<Result<(), E>> {
-    pub fn check(&self) -> True {
-        True
-    }
-}
-
-impl<T> Deref for IsEmptyTupleChecker<T> {
-    type Target = IsEmptyTupleCheckerFalse;
-
-    fn deref(&self) -> &IsEmptyTupleCheckerFalse {
-        &IsEmptyTupleCheckerFalse
-    }
-}
-
-pub struct IsEmptyTupleCheckerFalse;
-
-impl IsEmptyTupleCheckerFalse {
-    pub fn check(&self) -> False {
-        False
-    }
-}
-
 #[repr(C)]
 pub struct SerializedIntrospectionFragment<const LEN: usize> {
     pub length: u32,

src/impl_/pyclass/probes.rs

@@ -79,6 +79,16 @@ impl<T: Clone> IsClone<T> {
     pub const VALUE: bool = true;
 }
 
+probe!(IsReturningEmptyTuple);
+
+impl IsReturningEmptyTuple<()> {
+    pub const VALUE: bool = true;
+}
+
+impl<E> IsReturningEmptyTuple<Result<(), E>> {
+    pub const VALUE: bool = true;
+}
+
 #[cfg(test)]
 macro_rules! value_of {
     ($probe:ident, $ty:ty) => {{