derive(SmartPointer): rewrite bounds in where and generic bounds

compiler/rustc_builtin_macros/src/deriving/smart_ptr.rs

@@ -1,21 +1,30 @@
 use std::mem::swap;
 
 use ast::HasAttrs;
+use rustc_ast::mut_visit::MutVisitor;
+use rustc_ast::visit::BoundKind;
 use rustc_ast::{
     self as ast, GenericArg, GenericBound, GenericParamKind, ItemKind, MetaItem,
     TraitBoundModifiers, VariantData,
 };
 use rustc_attr as attr;
+use rustc_data_structures::flat_map_in_place::FlatMapInPlace;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident};
-use rustc_span::Span;
+use rustc_span::{Span, Symbol};
 use smallvec::{smallvec, SmallVec};
 use thin_vec::{thin_vec, ThinVec};
 
+type AstTy = ast::ptr::P<ast::Ty>;
+
 macro_rules! path {
     ($span:expr, $($part:ident)::*) => { vec![$(Ident::new(sym::$part, $span),)*] }
 }
 
+macro_rules! symbols {
+    ($($part:ident)::*) => { [$(sym::$part),*] }
+}
+
 pub fn expand_deriving_smart_ptr(
     cx: &ExtCtxt<'_>,
     span: Span,
@@ -143,31 +152,175 @@ pub fn expand_deriving_smart_ptr(
 
     // Find the `#[pointee]` parameter and add an `Unsize<__S>` bound to it.
     let mut impl_generics = generics.clone();
+    let pointee_ty_ident = generics.params[pointee_param_idx].ident;
+    let mut self_bounds;
     {
         let p = &mut impl_generics.params[pointee_param_idx];
+        self_bounds = p.bounds.clone();
         let arg = GenericArg::Type(s_ty.clone());
         let unsize = cx.path_all(span, true, path!(span, core::marker::Unsize), vec![arg]);
         p.bounds.push(cx.trait_bound(unsize, false));
         let mut attrs = thin_vec![];
         swap(&mut p.attrs, &mut attrs);
         p.attrs = attrs.into_iter().filter(|attr| !attr.has_name(sym::pointee)).collect();
     }
+    // We should not set default values to constant generic parameters
+    // and write out bounds that indirectly involves `#[pointee]`.
+    for (idx, (params, orig_params)) in
+        impl_generics.params.iter_mut().zip(&generics.params).enumerate()
+    {
+        if idx == pointee_param_idx {
+            continue;
+        }
+        match &mut params.kind {
+            ast::GenericParamKind::Const { default, .. } => *default = None,
+            ast::GenericParamKind::Type { default } => *default = None,
+            ast::GenericParamKind::Lifetime => {}
+        }
+        for bound in &orig_params.bounds {
+            let mut bound = bound.clone();
+            let mut substitution = TypeSubstitution {
+                from_name: pointee_ty_ident.name,
+                to_ty: &s_ty,
+                rewritten: false,
+            };
+            substitution.visit_param_bound(&mut bound, BoundKind::Bound);
+            if substitution.rewritten {
+                params.bounds.push(bound);
+            }
+        }
+    }
 
     // Add the `__S: ?Sized` extra parameter to the impl block.
+    // We should also write the bounds from `#[pointee]` to `__S` as required by `Unsize<__S>`.
     let sized = cx.path_global(span, path!(span, core::marker::Sized));
-    let bound = GenericBound::Trait(
-        cx.poly_trait_ref(span, sized),
-        TraitBoundModifiers {
-            polarity: ast::BoundPolarity::Maybe(span),
-            constness: ast::BoundConstness::Never,
-            asyncness: ast::BoundAsyncness::Normal,
-        },
-    );
-    let extra_param = cx.typaram(span, Ident::new(sym::__S, span), vec![bound], None);
-    impl_generics.params.push(extra_param);
+    if self_bounds.iter().all(|bound| {
+        if let GenericBound::Trait(
+            trait_ref,
+            TraitBoundModifiers { polarity: ast::BoundPolarity::Maybe(_), .. },
+        ) = bound
+        {
+            !is_sized_marker(&trait_ref.trait_ref.path)
+        } else {
+            false
+        }
+    }) {
+        self_bounds.push(GenericBound::Trait(
+            cx.poly_trait_ref(span, sized),
+            TraitBoundModifiers {
+                polarity: ast::BoundPolarity::Maybe(span),
+                constness: ast::BoundConstness::Never,
+                asyncness: ast::BoundAsyncness::Normal,
+            },
+        ));
+    }
+    {
+        let mut substitution =
+            TypeSubstitution { from_name: pointee_ty_ident.name, to_ty: &s_ty, rewritten: false };
+        for bound in &mut self_bounds {
+            substitution.visit_param_bound(bound, BoundKind::Bound);
+        }
+    }
+
+    // We should also commute the where bounds from `#[pointee]` to `__S`
+    // as well as any bound that indirectly involves the `#[pointee]` type.
+    for bound in &generics.where_clause.predicates {
+        if let ast::WherePredicate::BoundPredicate(bound) = bound {
+            let bound_on_pointee = bound
+                .bounded_ty
+                .kind
+                .is_simple_path()
+                .map_or(false, |name| name == pointee_ty_ident.name);
+
+            let bounds: Vec<_> = bound
+                .bounds
+                .iter()
+                .filter(|bound| {
+                    if let GenericBound::Trait(
+                        trait_ref,
+                        TraitBoundModifiers { polarity: ast::BoundPolarity::Maybe(_), .. },
+                    ) = bound
+                    {
+                        !bound_on_pointee || !is_sized_marker(&trait_ref.trait_ref.path)
+                    } else {
+                        true
+                    }
+                })
+                .cloned()
+                .collect();
+            let mut substitution = TypeSubstitution {
+                from_name: pointee_ty_ident.name,
+                to_ty: &s_ty,
+                rewritten: bounds.len() != bound.bounds.len(),
+            };
+            let mut predicate = ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
+                span: bound.span,
+                bound_generic_params: bound.bound_generic_params.clone(),
+                bounded_ty: bound.bounded_ty.clone(),
+                bounds,
+            });
+            substitution.visit_where_predicate(&mut predicate);
+            if substitution.rewritten {
+                impl_generics.where_clause.predicates.push(predicate);
+            }
+        }
+    }
+
+    let extra_param = cx.typaram(span, Ident::new(sym::__S, span), self_bounds, None);
+    impl_generics.params.insert(pointee_param_idx + 1, extra_param);
 
     // Add the impl blocks for `DispatchFromDyn` and `CoerceUnsized`.
     let gen_args = vec![GenericArg::Type(alt_self_type.clone())];
     add_impl_block(impl_generics.clone(), sym::DispatchFromDyn, gen_args.clone());
     add_impl_block(impl_generics.clone(), sym::CoerceUnsized, gen_args.clone());
 }
+
+fn is_sized_marker(path: &ast::Path) -> bool {
+    const CORE_UNSIZE: [Symbol; 3] = symbols!(core::marker::Sized);
+    const STD_UNSIZE: [Symbol; 3] = symbols!(std::marker::Sized);
+    if path.segments.len() == 3 {
+        path.segments.iter().zip(CORE_UNSIZE).all(|(segment, symbol)| segment.ident.name == symbol)
+            || path
+                .segments
+                .iter()
+                .zip(STD_UNSIZE)
+                .all(|(segment, symbol)| segment.ident.name == symbol)
+    } else {
+        *path == sym::Sized
+    }
+}
+
+struct TypeSubstitution<'a> {
+    from_name: Symbol,
+    to_ty: &'a AstTy,
+    rewritten: bool,
+}
+
+impl<'a> ast::mut_visit::MutVisitor for TypeSubstitution<'a> {
+    fn visit_ty(&mut self, ty: &mut AstTy) {
+        if let Some(name) = ty.kind.is_simple_path()
+            && name == self.from_name
+        {
+            *ty = self.to_ty.clone();
+            self.rewritten = true;
+        } else {
+            ast::mut_visit::walk_ty(self, ty);
+        }
+    }
+
+    fn visit_where_predicate(&mut self, where_predicate: &mut ast::WherePredicate) {
+        match where_predicate {
+            rustc_ast::WherePredicate::BoundPredicate(bound) => {
+                bound
+                    .bound_generic_params
+                    .flat_map_in_place(|param| self.flat_map_generic_param(param));
+                self.visit_ty(&mut bound.bounded_ty);
+                for bound in &mut bound.bounds {
+                    self.visit_param_bound(bound, BoundKind::Bound)
+                }
+            }
+            rustc_ast::WherePredicate::RegionPredicate(_)
+            | rustc_ast::WherePredicate::EqPredicate(_) => {}
+        }
+    }
+}

tests/ui/deriving/deriving-smart-pointer-expanded.rs

@@ -0,0 +1,22 @@
+//@ check-pass
+//@ compile-flags: -Zunpretty=expanded
+#![feature(derive_smart_pointer)]
+use std::marker::SmartPointer;
+
+pub trait MyTrait<T: ?Sized> {}
+
+#[derive(SmartPointer)]
+#[repr(transparent)]
+struct MyPointer<'a, #[pointee] T: ?Sized> {
+    ptr: &'a T,
+}
+
+#[derive(core::marker::SmartPointer)]
+#[repr(transparent)]
+pub struct MyPointer2<'a, Y, Z: MyTrait<T>, #[pointee] T: ?Sized + MyTrait<T>, X: MyTrait<T>>
+where
+    Y: MyTrait<T>,
+{
+    data: &'a mut T,
+    x: core::marker::PhantomData<X>,
+}

tests/ui/deriving/deriving-smart-pointer-expanded.stdout

@@ -0,0 +1,44 @@
+#![feature(prelude_import)]
+#![no_std]
+//@ check-pass
+//@ compile-flags: -Zunpretty=expanded
+#![feature(derive_smart_pointer)]
+#[prelude_import]
+use ::std::prelude::rust_2015::*;
+#[macro_use]
+extern crate std;
+use std::marker::SmartPointer;
+
+pub trait MyTrait<T: ?Sized> {}
+
+#[repr(transparent)]
+struct MyPointer<'a, #[pointee] T: ?Sized> {
+    ptr: &'a T,
+}
+#[automatically_derived]
+impl<'a, T: ?Sized + ::core::marker::Unsize<__S>, __S: ?Sized>
+    ::core::ops::DispatchFromDyn<MyPointer<'a, __S>> for MyPointer<'a, T> {
+}
+#[automatically_derived]
+impl<'a, T: ?Sized + ::core::marker::Unsize<__S>, __S: ?Sized>
+    ::core::ops::CoerceUnsized<MyPointer<'a, __S>> for MyPointer<'a, T> {
+}
+
+#[repr(transparent)]
+pub struct MyPointer2<'a, Y, Z: MyTrait<T>, #[pointee] T: ?Sized + MyTrait<T>,
+    X: MyTrait<T>> where Y: MyTrait<T> {
+    data: &'a mut T,
+    x: core::marker::PhantomData<X>,
+}
+#[automatically_derived]
+impl<'a, Y, Z: MyTrait<T> + MyTrait<__S>, T: ?Sized + MyTrait<T> +
+    ::core::marker::Unsize<__S>, __S: ?Sized + MyTrait<__S>, X: MyTrait<T> +
+    MyTrait<__S>> ::core::ops::DispatchFromDyn<MyPointer2<'a, Y, Z, __S, X>>
+    for MyPointer2<'a, Y, Z, T, X> where Y: MyTrait<T>, Y: MyTrait<__S> {
+}
+#[automatically_derived]
+impl<'a, Y, Z: MyTrait<T> + MyTrait<__S>, T: ?Sized + MyTrait<T> +
+    ::core::marker::Unsize<__S>, __S: ?Sized + MyTrait<__S>, X: MyTrait<T> +
+    MyTrait<__S>> ::core::ops::CoerceUnsized<MyPointer2<'a, Y, Z, __S, X>> for
+    MyPointer2<'a, Y, Z, T, X> where Y: MyTrait<T>, Y: MyTrait<__S> {
+}

tests/ui/deriving/smart-pointer-bounds-issue-127647.rs

@@ -0,0 +1,78 @@
+//@ check-pass
+
+#![feature(derive_smart_pointer)]
+
+#[derive(core::marker::SmartPointer)]
+#[repr(transparent)]
+pub struct Ptr<'a, #[pointee] T: OnDrop + ?Sized, X> {
+    data: &'a mut T,
+    x: core::marker::PhantomData<X>,
+}
+
+pub trait OnDrop {
+    fn on_drop(&mut self);
+}
+
+#[derive(core::marker::SmartPointer)]
+#[repr(transparent)]
+pub struct Ptr2<'a, #[pointee] T: ?Sized, X>
+where
+    T: OnDrop,
+{
+    data: &'a mut T,
+    x: core::marker::PhantomData<X>,
+}
+
+pub trait MyTrait<T: ?Sized> {}
+
+#[derive(core::marker::SmartPointer)]
+#[repr(transparent)]
+pub struct Ptr3<'a, #[pointee] T: ?Sized, X>
+where
+    T: MyTrait<T>,
+{
+    data: &'a mut T,
+    x: core::marker::PhantomData<X>,
+}
+
+#[derive(core::marker::SmartPointer)]
+#[repr(transparent)]
+pub struct Ptr4<'a, #[pointee] T: MyTrait<T> + ?Sized, X> {
+    data: &'a mut T,
+    x: core::marker::PhantomData<X>,
+}
+
+#[derive(core::marker::SmartPointer)]
+#[repr(transparent)]
+pub struct Ptr5<'a, #[pointee] T: ?Sized, X>
+where
+    Ptr5Companion<T>: MyTrait<T>,
+    Ptr5Companion2: MyTrait<T>,
+{
+    data: &'a mut T,
+    x: core::marker::PhantomData<X>,
+}
+
+pub struct Ptr5Companion<T: ?Sized>(core::marker::PhantomData<T>);
+pub struct Ptr5Companion2;
+
+#[derive(core::marker::SmartPointer)]
+#[repr(transparent)]
+pub struct Ptr6<'a, #[pointee] T: ?Sized, X: MyTrait<T>> {
+    data: &'a mut T,
+    x: core::marker::PhantomData<X>,
+}
+
+// a reduced example from https://lore.kernel.org/all/20240402-linked-list-v1-1-b1c59ba7ae3b@google.com/
+#[repr(transparent)]
+#[derive(core::marker::SmartPointer)]
+pub struct ListArc<#[pointee] T, const ID: u64 = 0>
+where
+    T: ListArcSafe<ID> + ?Sized,
+{
+    arc: *const T,
+}
+
+pub trait ListArcSafe<const ID: u64> {}
+
+fn main() {}