1 files changed, 887 insertions, 0 deletions
diff --git a/third_party/rust/pin-project/tests/pin_project.rs b/third_party/rust/pin-project/tests/pin_project.rs
new file mode 100644
index 0000000000..aa08056e81
--- /dev/null
+++ b/third_party/rust/pin-project/tests/pin_project.rs
@@ -0,0 +1,887 @@
+#![warn(rust_2018_idioms, single_use_lifetimes)]
+#![allow(dead_code)]
+
+#[macro_use]
+mod auxiliary;
+
+use std::{
+    marker::{PhantomData, PhantomPinned},
+    panic,
+    pin::Pin,
+};
+
+use pin_project::{pin_project, pinned_drop, UnsafeUnpin};
+
+#[test]
+fn projection() {
+    #[pin_project(
+        project = StructProj,
+        project_ref = StructProjRef,
+        project_replace = StructProjOwn,
+    )]
+    struct Struct<T, U> {
+        #[pin]
+        f1: T,
+        f2: U,
+    }
+
+    let mut s = Struct { f1: 1, f2: 2 };
+    let mut s_orig = Pin::new(&mut s);
+    let s = s_orig.as_mut().project();
+
+    let _: Pin<&mut i32> = s.f1;
+    assert_eq!(*s.f1, 1);
+    let _: &mut i32 = s.f2;
+    assert_eq!(*s.f2, 2);
+
+    assert_eq!(s_orig.as_ref().f1, 1);
+    assert_eq!(s_orig.as_ref().f2, 2);
+
+    let mut s = Struct { f1: 1, f2: 2 };
+    let mut s = Pin::new(&mut s);
+    {
+        let StructProj { f1, f2 } = s.as_mut().project();
+        let _: Pin<&mut i32> = f1;
+        let _: &mut i32 = f2;
+    }
+    {
+        let StructProjRef { f1, f2 } = s.as_ref().project_ref();
+        let _: Pin<&i32> = f1;
+        let _: &i32 = f2;
+    }
+    {
+        let StructProjOwn { f1, f2 } = s.as_mut().project_replace(Struct { f1: 3, f2: 4 });
+        let _: PhantomData<i32> = f1;
+        let _: i32 = f2;
+        assert_eq!(f2, 2);
+        assert_eq!(s.f1, 3);
+        assert_eq!(s.f2, 4);
+    }
+
+    #[pin_project(project_replace)]
+    struct TupleStruct<T, U>(#[pin] T, U);
+
+    let mut s = TupleStruct(1, 2);
+    let s = Pin::new(&mut s).project();
+
+    let _: Pin<&mut i32> = s.0;
+    assert_eq!(*s.0, 1);
+    let _: &mut i32 = s.1;
+    assert_eq!(*s.1, 2);
+
+    #[pin_project(project = EnumProj, project_ref = EnumProjRef, project_replace = EnumProjOwn)]
+    #[derive(Eq, PartialEq, Debug)]
+    enum Enum<A, B, C, D> {
+        Tuple(#[pin] A, B),
+        Struct {
+            #[pin]
+            f1: C,
+            f2: D,
+        },
+        Unit,
+    }
+
+    let mut e = Enum::Tuple(1, 2);
+    let mut e = Pin::new(&mut e);
+
+    match e.as_mut().project() {
+        EnumProj::Tuple(x, y) => {
+            let x: Pin<&mut i32> = x;
+            assert_eq!(*x, 1);
+            let y: &mut i32 = y;
+            assert_eq!(*y, 2);
+        }
+        EnumProj::Struct { f1, f2 } => {
+            let _: Pin<&mut i32> = f1;
+            let _: &mut i32 = f2;
+            unreachable!();
+        }
+        EnumProj::Unit => unreachable!(),
+    }
+
+    assert_eq!(&*e, &Enum::Tuple(1, 2));
+
+    let mut e = Enum::Struct { f1: 3, f2: 4 };
+    let mut e = Pin::new(&mut e);
+
+    match e.as_mut().project() {
+        EnumProj::Tuple(x, y) => {
+            let _: Pin<&mut i32> = x;
+            let _: &mut i32 = y;
+            unreachable!();
+        }
+        EnumProj::Struct { f1, f2 } => {
+            let _: Pin<&mut i32> = f1;
+            assert_eq!(*f1, 3);
+            let _: &mut i32 = f2;
+            assert_eq!(*f2, 4);
+        }
+        EnumProj::Unit => unreachable!(),
+    }
+
+    if let EnumProj::Struct { f1, f2 } = e.as_mut().project() {
+        let _: Pin<&mut i32> = f1;
+        assert_eq!(*f1, 3);
+        let _: &mut i32 = f2;
+        assert_eq!(*f2, 4);
+    }
+}
+
+#[test]
+fn enum_project_set() {
+    #[pin_project(project = EnumProj, project_ref = EnumProjRef, project_replace = EnumProjOwn)]
+    #[derive(Eq, PartialEq, Debug)]
+    enum Enum {
+        V1(#[pin] u8),
+        V2(bool),
+    }
+
+    let mut e = Enum::V1(25);
+    let mut e_orig = Pin::new(&mut e);
+    let e_proj = e_orig.as_mut().project();
+
+    match e_proj {
+        EnumProj::V1(val) => {
+            let new_e = Enum::V2(val.as_ref().get_ref() == &25);
+            e_orig.set(new_e);
+        }
+        EnumProj::V2(_) => unreachable!(),
+    }
+
+    assert_eq!(e, Enum::V2(true));
+}
+
+#[test]
+fn where_clause() {
+    #[pin_project]
+    struct Struct<T>
+    where
+        T: Copy,
+    {
+        f: T,
+    }
+
+    #[pin_project]
+    struct TupleStruct<T>(T)
+    where
+        T: Copy;
+
+    #[pin_project(project = EnumProj, project_ref = EnumProjRef, project_replace = EnumProjOwn)]
+    enum Enum<T>
+    where
+        T: Copy,
+    {
+        V(T),
+    }
+}
+
+#[test]
+fn where_clause_and_associated_type_field() {
+    #[pin_project(project_replace)]
+    struct Struct1<I>
+    where
+        I: Iterator,
+    {
+        #[pin]
+        f1: I,
+        f2: I::Item,
+    }
+
+    #[pin_project(project_replace)]
+    struct Struct2<I, J>
+    where
+        I: Iterator<Item = J>,
+    {
+        #[pin]
+        f1: I,
+        f2: J,
+    }
+
+    #[pin_project(project_replace)]
+    struct Struct3<T>
+    where
+        T: 'static,
+    {
+        f: T,
+    }
+
+    trait Static: 'static {}
+
+    impl<T> Static for Struct3<T> {}
+
+    #[pin_project(project_replace)]
+    struct TupleStruct<I>(#[pin] I, I::Item)
+    where
+        I: Iterator;
+
+    #[pin_project(project = EnumProj, project_ref = EnumProjRef, project_replace = EnumProjOwn)]
+    enum Enum<I>
+    where
+        I: Iterator,
+    {
+        V1(#[pin] I),
+        V2(I::Item),
+    }
+}
+
+#[test]
+fn derive_copy() {
+    #[pin_project(project_replace)]
+    #[derive(Clone, Copy)]
+    struct Struct<T> {
+        f: T,
+    }
+
+    fn is_copy<T: Copy>() {}
+
+    is_copy::<Struct<u8>>();
+}
+
+#[test]
+fn move_out() {
+    struct NotCopy;
+
+    #[pin_project(project_replace)]
+    struct Struct {
+        f: NotCopy,
+    }
+
+    let x = Struct { f: NotCopy };
+    let _val: NotCopy = x.f;
+
+    #[pin_project(project = EnumProj, project_ref = EnumProjRef, project_replace = EnumProjOwn)]
+    enum Enum {
+        V(NotCopy),
+    }
+
+    let x = Enum::V(NotCopy);
+    #[allow(clippy::infallible_destructuring_match)]
+    let _val: NotCopy = match x {
+        Enum::V(val) => val,
+    };
+}
+
+#[test]
+fn trait_bounds_on_type_generics() {
+    #[pin_project(project_replace)]
+    pub struct Struct1<'a, T: ?Sized> {
+        f: &'a mut T,
+    }
+
+    #[pin_project(project_replace)]
+    pub struct Struct2<'a, T: ::core::fmt::Debug> {
+        f: &'a mut T,
+    }
+
+    #[pin_project(project_replace)]
+    pub struct Struct3<'a, T: core::fmt::Debug> {
+        f: &'a mut T,
+    }
+
+    #[pin_project(project_replace)]
+    pub struct Struct4<'a, T: core::fmt::Debug + core::fmt::Display> {
+        f: &'a mut T,
+    }
+
+    #[pin_project(project_replace)]
+    pub struct Struct5<'a, T: core::fmt::Debug + ?Sized> {
+        f: &'a mut T,
+    }
+
+    #[pin_project(project_replace)]
+    pub struct Struct6<'a, T: core::fmt::Debug = [u8; 16]> {
+        f: &'a mut T,
+    }
+
+    let _: Struct6<'_> = Struct6 { f: &mut [0_u8; 16] };
+
+    #[pin_project(project_replace)]
+    pub struct Struct7<T: 'static> {
+        f: T,
+    }
+
+    trait Static: 'static {}
+
+    impl<T> Static for Struct7<T> {}
+
+    #[pin_project(project_replace)]
+    pub struct Struct8<'a, 'b: 'a> {
+        f1: &'a u8,
+        f2: &'b u8,
+    }
+
+    #[pin_project(project_replace)]
+    pub struct TupleStruct<'a, T: ?Sized>(&'a mut T);
+
+    #[pin_project(project = EnumProj, project_ref = EnumProjRef, project_replace = EnumProjOwn)]
+    enum Enum<'a, T: ?Sized> {
+        V(&'a mut T),
+    }
+}
+
+#[test]
+fn overlapping_lifetime_names() {
+    #[pin_project(project_replace)]
+    pub struct Struct1<'pin, T> {
+        #[pin]
+        f: &'pin mut T,
+    }
+
+    #[pin_project(project_replace)]
+    pub struct Struct2<'pin, 'pin_, 'pin__> {
+        #[pin]
+        f: &'pin &'pin_ &'pin__ (),
+    }
+
+    pub trait Trait<'a> {}
+
+    #[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
+    #[pin_project(project_replace)]
+    pub struct Hrtb<'pin___, T>
+    where
+        for<'pin> &'pin T: Unpin,
+        T: for<'pin> Trait<'pin>,
+        for<'pin, 'pin_, 'pin__> &'pin &'pin_ &'pin__ T: Unpin,
+    {
+        #[pin]
+        f: &'pin___ mut T,
+    }
+
+    #[pin_project(PinnedDrop)]
+    pub struct PinnedDropStruct<'pin> {
+        #[pin]
+        f: &'pin (),
+    }
+
+    #[pinned_drop]
+    impl PinnedDrop for PinnedDropStruct<'_> {
+        fn drop(self: Pin<&mut Self>) {}
+    }
+
+    #[pin_project(UnsafeUnpin)]
+    pub struct UnsafeUnpinStruct<'pin> {
+        #[pin]
+        f: &'pin (),
+    }
+
+    unsafe impl UnsafeUnpin for UnsafeUnpinStruct<'_> {}
+
+    #[pin_project(!Unpin)]
+    pub struct NotUnpinStruct<'pin> {
+        #[pin]
+        f: &'pin (),
+    }
+}
+
+#[test]
+fn combine() {
+    #[pin_project(PinnedDrop, UnsafeUnpin)]
+    pub struct PinnedDropWithUnsafeUnpin<T> {
+        #[pin]
+        f: T,
+    }
+
+    #[pinned_drop]
+    impl<T> PinnedDrop for PinnedDropWithUnsafeUnpin<T> {
+        fn drop(self: Pin<&mut Self>) {}
+    }
+
+    unsafe impl<T: Unpin> UnsafeUnpin for PinnedDropWithUnsafeUnpin<T> {}
+
+    #[pin_project(PinnedDrop, !Unpin)]
+    pub struct PinnedDropWithNotUnpin<T> {
+        #[pin]
+        f: T,
+    }
+
+    #[pinned_drop]
+    impl<T> PinnedDrop for PinnedDropWithNotUnpin<T> {
+        fn drop(self: Pin<&mut Self>) {}
+    }
+
+    #[pin_project(UnsafeUnpin, project_replace)]
+    pub struct UnsafeUnpinWithReplace<T> {
+        #[pin]
+        f: T,
+    }
+
+    unsafe impl<T: Unpin> UnsafeUnpin for UnsafeUnpinWithReplace<T> {}
+
+    #[pin_project(!Unpin, project_replace)]
+    pub struct NotUnpinWithReplace<T> {
+        #[pin]
+        f: T,
+    }
+}
+
+#[test]
+fn private_type_in_public_type() {
+    #[pin_project(project_replace)]
+    pub struct PublicStruct<T> {
+        #[pin]
+        inner: PrivateStruct<T>,
+    }
+
+    struct PrivateStruct<T>(T);
+}
+
+#[allow(clippy::needless_lifetimes)]
+#[test]
+fn lifetime_project() {
+    #[pin_project(project_replace)]
+    struct Struct1<T, U> {
+        #[pin]
+        pinned: T,
+        unpinned: U,
+    }
+
+    #[pin_project(project_replace)]
+    struct Struct2<'a, T, U> {
+        #[pin]
+        pinned: &'a T,
+        unpinned: U,
+    }
+
+    #[pin_project(project = EnumProj, project_ref = EnumProjRef, project_replace = EnumProjOwn)]
+    enum Enum<T, U> {
+        V {
+            #[pin]
+            pinned: T,
+            unpinned: U,
+        },
+    }
+
+    impl<T, U> Struct1<T, U> {
+        fn get_pin_ref<'a>(self: Pin<&'a Self>) -> Pin<&'a T> {
+            self.project_ref().pinned
+        }
+        fn get_pin_mut<'a>(self: Pin<&'a mut Self>) -> Pin<&'a mut T> {
+            self.project().pinned
+        }
+        fn get_pin_ref_elided(self: Pin<&Self>) -> Pin<&T> {
+            self.project_ref().pinned
+        }
+        fn get_pin_mut_elided(self: Pin<&mut Self>) -> Pin<&mut T> {
+            self.project().pinned
+        }
+    }
+
+    impl<'b, T, U> Struct2<'b, T, U> {
+        fn get_pin_ref<'a>(self: Pin<&'a Self>) -> Pin<&'a &'b T> {
+            self.project_ref().pinned
+        }
+        fn get_pin_mut<'a>(self: Pin<&'a mut Self>) -> Pin<&'a mut &'b T> {
+            self.project().pinned
+        }
+        fn get_pin_ref_elided(self: Pin<&Self>) -> Pin<&&'b T> {
+            self.project_ref().pinned
+        }
+        fn get_pin_mut_elided(self: Pin<&mut Self>) -> Pin<&mut &'b T> {
+            self.project().pinned
+        }
+    }
+
+    impl<T, U> Enum<T, U> {
+        fn get_pin_ref<'a>(self: Pin<&'a Self>) -> Pin<&'a T> {
+            match self.project_ref() {
+                EnumProjRef::V { pinned, .. } => pinned,
+            }
+        }
+        fn get_pin_mut<'a>(self: Pin<&'a mut Self>) -> Pin<&'a mut T> {
+            match self.project() {
+                EnumProj::V { pinned, .. } => pinned,
+            }
+        }
+        fn get_pin_ref_elided(self: Pin<&Self>) -> Pin<&T> {
+            match self.project_ref() {
+                EnumProjRef::V { pinned, .. } => pinned,
+            }
+        }
+        fn get_pin_mut_elided(self: Pin<&mut Self>) -> Pin<&mut T> {
+            match self.project() {
+                EnumProj::V { pinned, .. } => pinned,
+            }
+        }
+    }
+}
+
+mod visibility {
+    use pin_project::pin_project;
+
+    #[pin_project(project_replace)]
+    pub(crate) struct S {
+        pub f: u8,
+    }
+}
+
+#[test]
+fn visibility() {
+    let mut x = visibility::S { f: 0 };
+    let x = Pin::new(&mut x);
+    let y = x.as_ref().project_ref();
+    let _: &u8 = y.f;
+    let y = x.project();
+    let _: &mut u8 = y.f;
+}
+
+#[test]
+fn trivial_bounds() {
+    #[pin_project(project_replace)]
+    pub struct NoGenerics {
+        #[pin]
+        f: PhantomPinned,
+    }
+
+    assert_not_unpin!(NoGenerics);
+}
+
+#[test]
+fn dst() {
+    #[pin_project]
+    struct Struct1<T: ?Sized> {
+        f: T,
+    }
+
+    let mut x = Struct1 { f: 0_u8 };
+    let x: Pin<&mut Struct1<dyn core::fmt::Debug>> = Pin::new(&mut x as _);
+    let _: &mut (dyn core::fmt::Debug) = x.project().f;
+
+    #[pin_project]
+    struct Struct2<T: ?Sized> {
+        #[pin]
+        f: T,
+    }
+
+    let mut x = Struct2 { f: 0_u8 };
+    let x: Pin<&mut Struct2<dyn core::fmt::Debug + Unpin>> = Pin::new(&mut x as _);
+    let _: Pin<&mut (dyn core::fmt::Debug + Unpin)> = x.project().f;
+
+    #[allow(explicit_outlives_requirements)] // https://github.com/rust-lang/rust/issues/60993
+    #[pin_project]
+    struct Struct3<T>
+    where
+        T: ?Sized,
+    {
+        f: T,
+    }
+
+    #[allow(explicit_outlives_requirements)] // https://github.com/rust-lang/rust/issues/60993
+    #[pin_project]
+    struct Struct4<T>
+    where
+        T: ?Sized,
+    {
+        #[pin]
+        f: T,
+    }
+
+    #[pin_project(UnsafeUnpin)]
+    struct Struct5<T: ?Sized> {
+        f: T,
+    }
+
+    #[pin_project(UnsafeUnpin)]
+    struct Struct6<T: ?Sized> {
+        #[pin]
+        f: T,
+    }
+
+    #[pin_project(PinnedDrop)]
+    struct Struct7<T: ?Sized> {
+        f: T,
+    }
+
+    #[pinned_drop]
+    impl<T: ?Sized> PinnedDrop for Struct7<T> {
+        fn drop(self: Pin<&mut Self>) {}
+    }
+
+    #[pin_project(PinnedDrop)]
+    struct Struct8<T: ?Sized> {
+        #[pin]
+        f: T,
+    }
+
+    #[pinned_drop]
+    impl<T: ?Sized> PinnedDrop for Struct8<T> {
+        fn drop(self: Pin<&mut Self>) {}
+    }
+
+    #[pin_project(!Unpin)]
+    struct Struct9<T: ?Sized> {
+        f: T,
+    }
+
+    #[pin_project(!Unpin)]
+    struct Struct10<T: ?Sized> {
+        #[pin]
+        f: T,
+    }
+
+    #[pin_project]
+    struct Struct11<'a, T: ?Sized, U: ?Sized> {
+        f1: &'a mut T,
+        f2: U,
+    }
+
+    #[pin_project]
+    struct TupleStruct1<T: ?Sized>(T);
+
+    #[pin_project]
+    struct TupleStruct2<T: ?Sized>(#[pin] T);
+
+    #[allow(explicit_outlives_requirements)] // https://github.com/rust-lang/rust/issues/60993
+    #[pin_project]
+    struct TupleStruct3<T>(T)
+    where
+        T: ?Sized;
+
+    #[allow(explicit_outlives_requirements)] // https://github.com/rust-lang/rust/issues/60993
+    #[pin_project]
+    struct TupleStruct4<T>(#[pin] T)
+    where
+        T: ?Sized;
+
+    #[pin_project(UnsafeUnpin)]
+    struct TupleStruct5<T: ?Sized>(T);
+
+    #[pin_project(UnsafeUnpin)]
+    struct TupleStruct6<T: ?Sized>(#[pin] T);
+
+    #[pin_project(PinnedDrop)]
+    struct TupleStruct7<T: ?Sized>(T);
+
+    #[pinned_drop]
+    impl<T: ?Sized> PinnedDrop for TupleStruct7<T> {
+        fn drop(self: Pin<&mut Self>) {}
+    }
+
+    #[pin_project(PinnedDrop)]
+    struct TupleStruct8<T: ?Sized>(#[pin] T);
+
+    #[pinned_drop]
+    impl<T: ?Sized> PinnedDrop for TupleStruct8<T> {
+        fn drop(self: Pin<&mut Self>) {}
+    }
+
+    #[pin_project(!Unpin)]
+    struct TupleStruct9<T: ?Sized>(T);
+
+    #[pin_project(!Unpin)]
+    struct TupleStruct10<T: ?Sized>(#[pin] T);
+
+    #[pin_project]
+    struct TupleStruct11<'a, T: ?Sized, U: ?Sized>(&'a mut T, U);
+}
+
+#[test]
+fn dyn_type() {
+    #[pin_project]
+    struct Struct1 {
+        f: dyn core::fmt::Debug,
+    }
+
+    #[pin_project]
+    struct Struct2 {
+        #[pin]
+        f: dyn core::fmt::Debug,
+    }
+
+    #[pin_project]
+    struct Struct3 {
+        f: dyn core::fmt::Debug + Send,
+    }
+
+    #[pin_project]
+    struct Struct4 {
+        #[pin]
+        f: dyn core::fmt::Debug + Send,
+    }
+
+    #[pin_project]
+    struct TupleStruct1(dyn core::fmt::Debug);
+
+    #[pin_project]
+    struct TupleStruct2(#[pin] dyn core::fmt::Debug);
+
+    #[pin_project]
+    struct TupleStruct3(dyn core::fmt::Debug + Send);
+
+    #[pin_project]
+    struct TupleStruct4(#[pin] dyn core::fmt::Debug + Send);
+}
+
+#[test]
+fn parse_self() {
+    macro_rules! mac {
+        ($($tt:tt)*) => {
+            $($tt)*
+        };
+    }
+
+    pub trait Trait {
+        type Assoc;
+    }
+
+    #[allow(clippy::type_repetition_in_bounds)]
+    #[pin_project(project_replace)]
+    pub struct Generics<T: Trait<Assoc = Self>>
+    where
+        Self: Trait<Assoc = Self>,
+        <Self as Trait>::Assoc: Sized,
+        mac!(Self): Trait<Assoc = mac!(Self)>,
+    {
+        _f: T,
+    }
+
+    impl<T: Trait<Assoc = Self>> Trait for Generics<T> {
+        type Assoc = Self;
+    }
+
+    #[pin_project(project_replace)]
+    pub struct Struct {
+        _f1: Box<Self>,
+        _f2: Box<<Self as Trait>::Assoc>,
+        _f3: Box<mac!(Self)>,
+        _f4: [(); Self::ASSOC],
+        _f5: [(); Self::assoc()],
+        _f6: [(); mac!(Self::assoc())],
+    }
+
+    impl Struct {
+        const ASSOC: usize = 1;
+        const fn assoc() -> usize {
+            0
+        }
+    }
+
+    impl Trait for Struct {
+        type Assoc = Self;
+    }
+
+    #[pin_project(project_replace)]
+    struct Tuple(
+        Box<Self>,
+        Box<<Self as Trait>::Assoc>,
+        Box<mac!(Self)>,
+        [(); Self::ASSOC],
+        [(); Self::assoc()],
+        [(); mac!(Self::assoc())],
+    );
+
+    impl Tuple {
+        const ASSOC: usize = 1;
+        const fn assoc() -> usize {
+            0
+        }
+    }
+
+    impl Trait for Tuple {
+        type Assoc = Self;
+    }
+
+    #[pin_project(project = EnumProj, project_ref = EnumProjRef, project_replace = EnumProjOwn)]
+    enum Enum {
+        Struct {
+            _f1: Box<Self>,
+            _f2: Box<<Self as Trait>::Assoc>,
+            _f3: Box<mac!(Self)>,
+            _f4: [(); Self::ASSOC],
+            _f5: [(); Self::assoc()],
+            _f6: [(); mac!(Self::assoc())],
+        },
+        Tuple(
+            Box<Self>,
+            Box<<Self as Trait>::Assoc>,
+            Box<mac!(Self)>,
+            [(); Self::ASSOC],
+            [(); Self::assoc()],
+            [(); mac!(Self::assoc())],
+        ),
+    }
+
+    impl Enum {
+        const ASSOC: usize = 1;
+        const fn assoc() -> usize {
+            0
+        }
+    }
+
+    impl Trait for Enum {
+        type Assoc = Self;
+    }
+}
+
+#[test]
+fn no_infer_outlives() {
+    trait Trait<X> {
+        type Y;
+    }
+
+    struct Struct1<A>(A);
+
+    impl<X, T> Trait<X> for Struct1<T> {
+        type Y = Option<T>;
+    }
+
+    #[pin_project(project_replace)]
+    struct Struct2<A, B> {
+        _f: <Struct1<A> as Trait<B>>::Y,
+    }
+}
+
+// https://github.com/rust-lang/rust/issues/47949
+// https://github.com/taiki-e/pin-project/pull/194#discussion_r419098111
+#[allow(clippy::many_single_char_names)]
+#[test]
+fn project_replace_panic() {
+    #[pin_project(project_replace)]
+    struct S<T, U> {
+        #[pin]
+        pinned: T,
+        unpinned: U,
+    }
+
+    struct D<'a>(&'a mut bool, bool);
+    impl Drop for D<'_> {
+        fn drop(&mut self) {
+            *self.0 = true;
+            if self.1 {
+                panic!();
+            }
+        }
+    }
+
+    let (mut a, mut b, mut c, mut d) = (false, false, false, false);
+    let res = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        let mut x = S { pinned: D(&mut a, true), unpinned: D(&mut b, false) };
+        let _y = Pin::new(&mut x)
+            .project_replace(S { pinned: D(&mut c, false), unpinned: D(&mut d, false) });
+        // Previous `x.pinned` was dropped and panicked when `project_replace` is
+        // called, so this is unreachable.
+        unreachable!();
+    }));
+    assert!(res.is_err());
+    assert!(a);
+    assert!(b);
+    assert!(c);
+    assert!(d);
+
+    let (mut a, mut b, mut c, mut d) = (false, false, false, false);
+    let res = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        let mut x = S { pinned: D(&mut a, false), unpinned: D(&mut b, true) };
+        {
+            let _y = Pin::new(&mut x)
+                .project_replace(S { pinned: D(&mut c, false), unpinned: D(&mut d, false) });
+            // `_y` (previous `x.unpinned`) live to the end of this scope, so
+            // this is not unreachable.
+            // unreachable!();
+        }
+        unreachable!();
+    }));
+    assert!(res.is_err());
+    assert!(a);
+    assert!(b);
+    assert!(c);
+    assert!(d);
+}