From 13b2af894152156ab04a4092cf1bc03ba7949ca5 Mon Sep 17 00:00:00 2001
From: joshua-maros <60271685+joshua-maros@users.noreply.github.com>
Date: Sat, 13 May 2023 23:15:05 -0700
Subject: [PATCH 1/8] Revert "This also does not work"

This reverts commit 3e269a742b860251900cd175eece7c54184c16d0.
---
 examples/src/ok_tests.rs                   | 10 +++++++
 ouroboros_macro/src/generate/into_heads.rs | 31 +++++++++++++++++++---
 ouroboros_macro/src/lib.rs                 | 12 ++++-----
 3 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/examples/src/ok_tests.rs b/examples/src/ok_tests.rs
index 48a81b1..61ae346 100644
--- a/examples/src/ok_tests.rs
+++ b/examples/src/ok_tests.rs
@@ -179,6 +179,16 @@ fn try_new_recover_heads() {
     }
 }
 
+#[test]
+fn into_heads() {
+    let bar = BoxAndRefBuilder {
+        data: 12,
+        dref_builder: |data| data,
+    }
+    .build();
+    assert!(bar.into_heads().data == 12);
+}
+
 #[test]
 fn box_and_mut_ref() {
     let mut bar = BoxAndMutRefBuilder {
diff --git a/ouroboros_macro/src/generate/into_heads.rs b/ouroboros_macro/src/generate/into_heads.rs
index 7b4b122..5784e46 100644
--- a/ouroboros_macro/src/generate/into_heads.rs
+++ b/ouroboros_macro/src/generate/into_heads.rs
@@ -3,8 +3,8 @@ use quote::quote;
 
 use crate::info_structures::{Options, StructInfo};
 
-/// Returns the Heads struct.
-pub fn make_heads(info: &StructInfo, options: Options) -> TokenStream {
+/// Returns the Heads struct and a function to convert the original struct into a Heads instance.
+pub fn make_into_heads(info: &StructInfo, options: Options) -> (TokenStream, TokenStream) {
     let visibility = if options.do_pub_extras {
         info.vis.clone()
     } else {
@@ -51,6 +51,31 @@ pub fn make_heads(info: &StructInfo, options: Options) -> TokenStream {
             #(#head_fields),*
         }
     };
+    let documentation = concat!(
+        "This function drops all internally referencing fields and returns only the ",
+        "[head fields](https://docs.rs/ouroboros/latest/ouroboros/attr.self_referencing.html#definitions) of this struct."
+    ).to_owned();
 
-    heads_struct_def
+    let documentation = if !options.do_no_doc {
+        quote! {
+            #[doc=#documentation]
+        }
+    } else {
+        quote! { #[doc(hidden)] }
+    };
+
+    let generic_args = info.generic_arguments();
+    let into_heads_fn = quote! {
+        #documentation
+        #[allow(clippy::drop_ref)]
+        #[allow(clippy::drop_copy)]
+        #[allow(clippy::drop_non_drop)]
+        #visibility fn into_heads(self) -> Heads<#(#generic_args),*> {
+            #(#code)*
+            Heads {
+                #(#field_initializers),*
+            }
+        }
+    };
+    (heads_struct_def, into_heads_fn)
 }
diff --git a/ouroboros_macro/src/lib.rs b/ouroboros_macro/src/lib.rs
index f531fb5..cd12419 100644
--- a/ouroboros_macro/src/lib.rs
+++ b/ouroboros_macro/src/lib.rs
@@ -9,7 +9,7 @@ mod utils;
 use crate::{
     generate::{
         constructor::create_builder_and_constructor, derives::create_derives,
-        into_heads::make_heads, struc::create_actual_struct_def,
+        into_heads::make_into_heads, struc::create_actual_struct_def,
         summon_checker::generate_checker_summoner,
         try_constructor::create_try_builder_and_constructor, type_asserts::make_type_asserts,
         with_all::make_with_all_function, with_each::make_with_functions,
@@ -50,15 +50,12 @@ fn self_referencing_impl(
         create_try_builder_and_constructor(&info, options, BuilderType::Sync)?;
     let (async_try_builder_struct_name, async_try_builder_def, async_try_constructor_def) =
         create_try_builder_and_constructor(&info, options, BuilderType::Async)?;
-    let (
-        async_send_try_builder_struct_name,
-        async_send_try_builder_def,
-        async_send_try_constructor_def,
-    ) = create_try_builder_and_constructor(&info, options, BuilderType::AsyncSend)?;
+    let (async_send_try_builder_struct_name, async_send_try_builder_def, async_send_try_constructor_def) =
+        create_try_builder_and_constructor(&info, options, BuilderType::AsyncSend)?;
 
     let with_defs = make_with_functions(&info, options)?;
     let (with_all_struct_defs, with_all_fn_defs) = make_with_all_function(&info, options)?;
-    let heads_struct_def = make_heads(&info, options);
+    let (heads_struct_def, into_heads_fn) = make_into_heads(&info, options);
 
     let impls = create_derives(&info)?;
 
@@ -100,6 +97,7 @@ fn self_referencing_impl(
                 #async_send_try_constructor_def
                 #(#with_defs)*
                 #with_all_fn_defs
+                #into_heads_fn
             }
             #type_asserts_def
         }

From c8891142dd2eb437f0dcf2c0ad170be6fbb73d9d Mon Sep 17 00:00:00 2001
From: joshua-maros <60271685+joshua-maros@users.noreply.github.com>
Date: Sat, 13 May 2023 23:15:11 -0700
Subject: [PATCH 2/8] Revert "Revert "Failed attempt to fix problems.""

This reverts commit b4d49cd874cfc74a3e6c496c61eaacf599330fa0.
---
 examples/Cargo.toml                           |  4 +--
 examples/src/ok_tests.rs                      |  3 ++
 ouroboros/Cargo.toml                          |  5 +--
 ouroboros/src/lib.rs                          |  1 +
 ouroboros_macro/Cargo.toml                    |  2 +-
 ouroboros_macro/src/generate/constructor.rs   | 15 +++++++--
 ouroboros_macro/src/generate/into_heads.rs    | 14 +++++----
 ouroboros_macro/src/generate/struc.rs         | 31 ++++++++++++++++---
 .../src/generate/try_constructor.rs           |  5 ++-
 ouroboros_macro/src/generate/with_all.rs      | 10 ++++--
 ouroboros_macro/src/generate/with_each.rs     | 17 +++++++---
 ouroboros_macro/src/info_structures.rs        | 11 +++++++
 ouroboros_macro/src/lib.rs                    |  5 ++-
 ouroboros_macro/src/parse.rs                  |  1 +
 14 files changed, 97 insertions(+), 27 deletions(-)

diff --git a/examples/Cargo.toml b/examples/Cargo.toml
index e8fa0fd..8243ddf 100644
--- a/examples/Cargo.toml
+++ b/examples/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros_examples"
-version = "0.15.7"
+version = "0.16.0"
 authors = ["Joshua Maros <joshua-maros@github.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
@@ -21,7 +21,7 @@ std = []
 __tokio = ["tokio", "std"]
 
 [dependencies]
-ouroboros = { version = "0.15.7", path = "../ouroboros" }
+ouroboros = { version = "0.16.0", path = "../ouroboros" }
 tokio = { version = "1.27.0", features = [ "macros", "rt" ], optional = true }
 
 [dev-dependencies]
diff --git a/examples/src/ok_tests.rs b/examples/src/ok_tests.rs
index 61ae346..db27303 100644
--- a/examples/src/ok_tests.rs
+++ b/examples/src/ok_tests.rs
@@ -1,6 +1,9 @@
 use alloc::borrow::ToOwned;
 use alloc::boxed::Box;
+use alloc::vec;
+use alloc::vec::Vec;
 use core::fmt::Debug;
+use ouroboros::macro_help::AliasableBox;
 
 use ouroboros::self_referencing;
 
diff --git a/ouroboros/Cargo.toml b/ouroboros/Cargo.toml
index 4ee1ca3..3c256b4 100644
--- a/ouroboros/Cargo.toml
+++ b/ouroboros/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros"
-version = "0.15.7"
+version = "0.16.0"
 authors = ["Joshua Maros <joshua-maros@github.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
@@ -11,7 +11,8 @@ repository = "https://github.com/joshua-maros/ouroboros"
 
 [dependencies]
 aliasable = "0.1.3"
-ouroboros_macro = { version = "0.15.7", path = "../ouroboros_macro" }
+ouroboros_macro = { version = "0.16.0", path = "../ouroboros_macro" }
+static_assertions = "1.1.0"
 
 [features]
 default = ["std"]
diff --git a/ouroboros/src/lib.rs b/ouroboros/src/lib.rs
index efd32e8..13870da 100644
--- a/ouroboros/src/lib.rs
+++ b/ouroboros/src/lib.rs
@@ -351,6 +351,7 @@ pub mod macro_help {
     pub extern crate alloc;
 
     pub use aliasable::boxed::AliasableBox;
+    pub use static_assertions::const_assert_eq;
     use aliasable::boxed::UniqueBox;
 
     pub struct CheckIfTypeIsStd<T>(core::marker::PhantomData<T>);
diff --git a/ouroboros_macro/Cargo.toml b/ouroboros_macro/Cargo.toml
index a350e81..5b2a56b 100644
--- a/ouroboros_macro/Cargo.toml
+++ b/ouroboros_macro/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros_macro"
-version = "0.15.7"
+version = "0.16.0"
 authors = ["Joshua Maros <joshua-maros@github.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
diff --git a/ouroboros_macro/src/generate/constructor.rs b/ouroboros_macro/src/generate/constructor.rs
index 6ab47bc..2ece184 100644
--- a/ouroboros_macro/src/generate/constructor.rs
+++ b/ouroboros_macro/src/generate/constructor.rs
@@ -154,12 +154,23 @@ pub fn create_builder_and_constructor(
         BuilderType::Sync => quote! { fn new },
     };
     let field_names: Vec<_> = info.fields.iter().map(|field| field.name.clone()).collect();
+    let internal_ident = &info.internal_ident;
     let constructor_def = quote! {
         #documentation
         #vis #constructor_fn(#(#params),*) -> #struct_name <#(#generic_args),*> {
+            ::ouroboros::macro_help::const_assert_eq!(
+                ::core::mem::size_of::<#struct_name<#(#generic_args),*>>(), 
+                ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()
+            );
+            ::ouroboros::macro_help::const_assert_eq!(
+                ::core::mem::align_of::<#struct_name<#(#generic_args),*>>(), 
+                ::core::mem::align_of::<#internal_ident<#(#generic_args),*>>()
+            );
             #(#code)*
-            Self {
-                #(#field_names),*
+            unsafe {
+                ::core::mem::transmute(#internal_ident<#(#generic_args),*> {
+                    #(#field_names),*
+                })
             }
         }
     };
diff --git a/ouroboros_macro/src/generate/into_heads.rs b/ouroboros_macro/src/generate/into_heads.rs
index 5784e46..12016a8 100644
--- a/ouroboros_macro/src/generate/into_heads.rs
+++ b/ouroboros_macro/src/generate/into_heads.rs
@@ -1,5 +1,5 @@
 use proc_macro2::TokenStream;
-use quote::quote;
+use quote::{format_ident, quote};
 
 use crate::info_structures::{Options, StructInfo};
 
@@ -13,12 +13,16 @@ pub fn make_into_heads(info: &StructInfo, options: Options) -> (TokenStream, Tok
     let mut code = Vec::new();
     let mut field_initializers = Vec::new();
     let mut head_fields = Vec::new();
+    let internal_struct = &info.internal_ident;
     // Drop everything in the reverse order of what it was declared in. Fields that come later
     // are only dependent on fields that came before them.
     for field in info.fields.iter().rev() {
         let field_name = &field.name;
-        if !field.self_referencing {
-            code.push(quote! { let #field_name = self.#field_name; });
+        if field.self_referencing {
+            // Heads are fields that do not borrow anything.
+            code.push(quote! { ::core::mem::drop(this.#field_name); });
+        } else {
+            code.push(quote! { let #field_name = this.#field_name; });
             if field.is_borrowed() {
                 field_initializers
                     .push(quote! { #field_name: ::ouroboros::macro_help::unbox(#field_name) });
@@ -27,9 +31,6 @@ pub fn make_into_heads(info: &StructInfo, options: Options) -> (TokenStream, Tok
             }
             let field_type = &field.typ;
             head_fields.push(quote! { #visibility #field_name: #field_type });
-        } else {
-            // Heads are fields that do not borrow anything.
-            code.push(quote! { ::core::mem::drop(self.#field_name); });
         }
     }
     for (ty, ident) in info.generic_consumers() {
@@ -71,6 +72,7 @@ pub fn make_into_heads(info: &StructInfo, options: Options) -> (TokenStream, Tok
         #[allow(clippy::drop_copy)]
         #[allow(clippy::drop_non_drop)]
         #visibility fn into_heads(self) -> Heads<#(#generic_args),*> {
+            let this: #internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
             #(#code)*
             Heads {
                 #(#field_initializers),*
diff --git a/ouroboros_macro/src/generate/struc.rs b/ouroboros_macro/src/generate/struc.rs
index 9b2ff51..8a7b9f4 100644
--- a/ouroboros_macro/src/generate/struc.rs
+++ b/ouroboros_macro/src/generate/struc.rs
@@ -6,12 +6,35 @@ use proc_macro2::TokenStream;
 use quote::quote;
 use syn::Error;
 
-/// Creates the struct that will actually store the data. This involves properly organizing the
-/// fields, collecting metadata about them, reversing the order everything is stored in, and
-/// converting any uses of 'this to 'static.
+/// Creates the struct that will actually store the data.
 pub fn create_actual_struct_def(info: &StructInfo) -> Result<TokenStream, Error> {
-    let vis = utils::submodule_contents_visiblity(&info.vis);
+    let visibility = utils::submodule_contents_visiblity(&info.vis);
+    let mut fields = Vec::new();
+    for (ty, ident) in info.generic_consumers() {
+        fields.push(quote! { #ident: ::core::marker::PhantomData<#ty> });
+    }
+    let generic_params = info.generic_params();
+    let generic_args = info.generic_arguments();
+    let generic_where = &info.generics.where_clause;
     let ident = &info.ident;
+    let internal_ident = &info.internal_ident;
+    Ok(quote! {
+        #visibility struct #ident <#generic_params> #generic_where {
+            actual_data: [u8; ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()],
+            _alignment: [#internal_ident<#(#generic_args),*>; 0],
+        }
+    })
+}
+
+/// Creates a struct with fields like the original struct. Instances of the
+/// "actual" struct are reinterpreted as instances of the "internal" struct
+/// whenever data needs to be accessed. (This gets around the problem that
+/// references passed to functions must be valid through the entire function,
+/// but references *created* inside a function can be considered invalid
+/// whenever, even during the duration of the function.)
+pub fn create_internal_struct_def(info: &StructInfo) -> Result<TokenStream, Error> {
+    let vis = quote! { pub(super) };
+    let ident = &info.internal_ident;
     let generics = &info.generics;
 
     let field_defs: Vec<_> = info
diff --git a/ouroboros_macro/src/generate/try_constructor.rs b/ouroboros_macro/src/generate/try_constructor.rs
index 4078c56..a5469d6 100644
--- a/ouroboros_macro/src/generate/try_constructor.rs
+++ b/ouroboros_macro/src/generate/try_constructor.rs
@@ -223,6 +223,7 @@ pub fn create_try_builder_and_constructor(
         quote! { #struct_name::#or_recover_ident(#(#builder_struct_field_names),*).map_err(|(error, _heads)| error) }
     };
     let field_names: Vec<_> = info.fields.iter().map(|field| field.name.clone()).collect();
+    let internal_ident = &info.internal_ident;
     let constructor_def = quote! {
         #documentation
         #visibility #constructor_fn<Error_>(#(#params),*) -> ::core::result::Result<#struct_name <#(#generic_args),*>, Error_> {
@@ -231,7 +232,9 @@ pub fn create_try_builder_and_constructor(
         #or_recover_documentation
         #visibility #or_recover_constructor_fn<Error_>(#(#params),*) -> ::core::result::Result<#struct_name <#(#generic_args),*>, (Error_, Heads<#(#generic_args),*>)> {
             #(#or_recover_code)*
-            ::core::result::Result::Ok(Self { #(#field_names),* })
+            ::core::result::Result::Ok(unsafe {
+                ::core::mem::transmute(#internal_ident { #(#field_names),* })
+            })
         }
     };
     builder_struct_generic_producers.push(quote! { Error_ });
diff --git a/ouroboros_macro/src/generate/with_all.rs b/ouroboros_macro/src/generate/with_all.rs
index e6a2665..03e3d59 100644
--- a/ouroboros_macro/src/generate/with_all.rs
+++ b/ouroboros_macro/src/generate/with_all.rs
@@ -16,19 +16,20 @@ pub fn make_with_all_function(
     let mut field_assignments = Vec::new();
     let mut mut_fields = Vec::new();
     let mut mut_field_assignments = Vec::new();
+    let internal_struct = &info.internal_ident;
     // I don't think the reverse is necessary but it does make the expanded code more uniform.
     for field in info.fields.iter().rev() {
         let field_name = &field.name;
         let field_type = &field.typ;
         if field.field_type == FieldType::Tail {
             fields.push(quote! { #visibility #field_name: &'outer_borrow #field_type });
-            field_assignments.push(quote! { #field_name: &self.#field_name });
+            field_assignments.push(quote! { #field_name: &this.#field_name });
             mut_fields.push(quote! { #visibility #field_name: &'outer_borrow mut #field_type });
-            mut_field_assignments.push(quote! { #field_name: &mut self.#field_name });
+            mut_field_assignments.push(quote! { #field_name: &mut this.#field_name });
         } else if field.field_type == FieldType::Borrowed {
             let ass = quote! { #field_name: unsafe {
                 ::ouroboros::macro_help::change_lifetime(
-                    &*self.#field_name
+                    &*this.#field_name
                 )
             } };
             fields.push(quote! { #visibility #field_name: &'this #field_type });
@@ -108,6 +109,7 @@ pub fn make_with_all_function(
     } else {
         quote! { #[doc(hidden)] }
     };
+    let generic_args = info.generic_arguments();
     let fn_defs = quote! {
         #documentation
         #[inline(always)]
@@ -115,6 +117,7 @@ pub fn make_with_all_function(
             &'outer_borrow self,
             user: impl for<'this> ::core::ops::FnOnce(#borrowed_fields_type) -> ReturnType
         ) -> ReturnType {
+            let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
             user(BorrowedFields {
                 #(#field_assignments),*
             })
@@ -125,6 +128,7 @@ pub fn make_with_all_function(
             &'outer_borrow mut self,
             user: impl for<'this> ::core::ops::FnOnce(#borrowed_mut_fields_type) -> ReturnType
         ) -> ReturnType {
+            let this: &mut #internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
             user(BorrowedMutFields {
                 #(#mut_field_assignments),*
             })
diff --git a/ouroboros_macro/src/generate/with_each.rs b/ouroboros_macro/src/generate/with_each.rs
index 8985857..15b0461 100644
--- a/ouroboros_macro/src/generate/with_each.rs
+++ b/ouroboros_macro/src/generate/with_each.rs
@@ -5,6 +5,8 @@ use syn::Error;
 
 pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<TokenStream>, Error> {
     let mut users = Vec::new();
+    let internal_struct = &info.internal_ident;
+    let generic_args = info.generic_arguments();
     for field in &info.fields {
         let visibility = &field.vis;
         let field_name = &field.name;
@@ -34,7 +36,8 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                     &'outer_borrow self,
                     user: impl for<'this> ::core::ops::FnOnce(&'outer_borrow #field_type) -> ReturnType,
                 ) -> ReturnType {
-                    user(&self. #field_name)
+                    let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
+                    user(&this. #field_name)
                 }
             });
             if field.covariant == Some(true) {
@@ -45,7 +48,8 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                     #visibility fn #borrower_name<'this>(
                         &'this self,
                     ) -> &'this #field_type {
-                        &self.#field_name
+                        let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
+                        &this.#field_name
                     }
                 });
             } else if field.covariant.is_none() {
@@ -76,7 +80,8 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                     &'outer_borrow mut self,
                     user: impl for<'this> ::core::ops::FnOnce(&'outer_borrow mut #field_type) -> ReturnType,
                 ) -> ReturnType {
-                    user(&mut self. #field_name)
+                    let this: &mut #internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
+                    user(&mut this. #field_name)
                 }
             });
         } else if field.field_type == FieldType::Borrowed {
@@ -102,7 +107,8 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                     &'outer_borrow self,
                     user: impl for<'this> ::core::ops::FnOnce(&'outer_borrow #field_type) -> ReturnType,
                 ) -> ReturnType {
-                    user(&*self.#field_name)
+                    let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
+                    user(&*this.#field_name)
                 }
             });
             if field.self_referencing {
@@ -120,7 +126,8 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                 #visibility fn #borrower_name<'this>(
                     &'this self,
                 ) -> &'this #field_type {
-                    &*self.#field_name
+                    let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
+                    &*this.#field_name
                 }
             });
         } else if field.field_type == FieldType::BorrowedMut {
diff --git a/ouroboros_macro/src/info_structures.rs b/ouroboros_macro/src/info_structures.rs
index 22e4cde..f2b0cc0 100644
--- a/ouroboros_macro/src/info_structures.rs
+++ b/ouroboros_macro/src/info_structures.rs
@@ -12,6 +12,16 @@ pub struct Options {
     pub do_pub_extras: bool,
 }
 
+impl Options {
+    pub fn documentation_to_tokens(&self, documentation: &str) -> TokenStream {
+        if self.do_no_doc {
+            quote! { #[doc(hidden)] }
+        } else {
+            quote! { #[doc=#documentation] }
+        }
+    }
+}
+
 #[derive(Clone, Copy, PartialEq)]
 pub enum FieldType {
     /// Not borrowed by other parts of the struct.
@@ -61,6 +71,7 @@ impl BuilderType {
 pub struct StructInfo {
     pub derives: Vec<Derive>,
     pub ident: Ident,
+    pub internal_ident: Ident,
     pub generics: Generics,
     pub vis: Visibility,
     pub fields: Vec<StructFieldInfo>,
diff --git a/ouroboros_macro/src/lib.rs b/ouroboros_macro/src/lib.rs
index cd12419..d0a6898 100644
--- a/ouroboros_macro/src/lib.rs
+++ b/ouroboros_macro/src/lib.rs
@@ -9,7 +9,7 @@ mod utils;
 use crate::{
     generate::{
         constructor::create_builder_and_constructor, derives::create_derives,
-        into_heads::make_into_heads, struc::create_actual_struct_def,
+        into_heads::make_into_heads, struc::create_internal_struct_def,
         summon_checker::generate_checker_summoner,
         try_constructor::create_try_builder_and_constructor, type_asserts::make_type_asserts,
         with_all::make_with_all_function, with_each::make_with_functions,
@@ -17,6 +17,7 @@ use crate::{
     info_structures::Options,
     parse::parse_struct,
 };
+use generate::struc::create_actual_struct_def;
 use inflector::Inflector;
 use info_structures::BuilderType;
 use proc_macro::TokenStream;
@@ -37,6 +38,7 @@ fn self_referencing_impl(
     let info = parse_struct(original_struct_def)?;
 
     let actual_struct_def = create_actual_struct_def(&info)?;
+    let internal_struct_def = create_internal_struct_def(&info)?;
 
     let borrowchk_summoner = generate_checker_summoner(&info)?;
 
@@ -78,6 +80,7 @@ fn self_referencing_impl(
             use super::*;
             #[doc="The self-referencing struct."]
             #actual_struct_def
+            #internal_struct_def
             #borrowchk_summoner
             #builder_def
             #async_builder_def
diff --git a/ouroboros_macro/src/parse.rs b/ouroboros_macro/src/parse.rs
index 546aa7c..8d5fd1a 100644
--- a/ouroboros_macro/src/parse.rs
+++ b/ouroboros_macro/src/parse.rs
@@ -262,6 +262,7 @@ pub fn parse_struct(def: &ItemStruct) -> Result<StructInfo, Error> {
     return Ok(StructInfo {
         derives,
         ident: def.ident.clone(),
+        internal_ident: format_ident!("{}Internal", def.ident),
         generics: def.generics.clone(),
         fields,
         vis,

From 30637694c97b231196e133b92da6a84336ee1216 Mon Sep 17 00:00:00 2001
From: joshua-maros <60271685+joshua-maros@users.noreply.github.com>
Date: Sun, 11 Jun 2023 18:23:55 -0500
Subject: [PATCH 3/8] Blah.

---
 examples/src/ok_tests.rs                    | 92 ++++++++++-----------
 ouroboros_macro/src/generate/constructor.rs | 11 +--
 ouroboros_macro/src/generate/drop.rs        | 28 +++++++
 ouroboros_macro/src/generate/into_heads.rs  |  2 +-
 ouroboros_macro/src/generate/mod.rs         |  1 +
 ouroboros_macro/src/generate/struc.rs       |  6 +-
 ouroboros_macro/src/info_structures.rs      | 24 +++++-
 ouroboros_macro/src/lib.rs                  |  4 +-
 ouroboros_macro/src/parse.rs                | 12 +++
 ouroboros_macro/src/utils.rs                |  4 +-
 10 files changed, 123 insertions(+), 61 deletions(-)
 create mode 100644 ouroboros_macro/src/generate/drop.rs

diff --git a/examples/src/ok_tests.rs b/examples/src/ok_tests.rs
index db27303..7a08614 100644
--- a/examples/src/ok_tests.rs
+++ b/examples/src/ok_tests.rs
@@ -1,9 +1,5 @@
-use alloc::borrow::ToOwned;
 use alloc::boxed::Box;
-use alloc::vec;
-use alloc::vec::Vec;
 use core::fmt::Debug;
-use ouroboros::macro_help::AliasableBox;
 
 use ouroboros::self_referencing;
 
@@ -54,32 +50,32 @@ struct AutoDetectCovarianceOnFieldsWithoutThis {
     self_reference: &'this (),
 }
 
-/// This test just makes sure that the macro copes with a ton of template parameters being thrown at
-/// it, specifically checking that the templates work fine even when a generated struct doesn't need
-/// all of them. (E.G. heads will only contain 'd, A, and B.)
-#[self_referencing]
-struct TemplateMess<'d, A, B: 'static, C: 'static>
-where
-    A: ?Sized,
-    B: 'static,
-    C: 'static,
-{
-    external: &'d A,
-    data1: B,
-    #[borrows(data1)]
-    data2: &'this C,
-    data3: B,
-    #[borrows(mut data3)]
-    data4: &'this mut C,
-}
+// /// This test just makes sure that the macro copes with a ton of template parameters being thrown at
+// /// it, specifically checking that the templates work fine even when a generated struct doesn't need
+// /// all of them. (E.G. heads will only contain 'd, A, and B.)
+// #[self_referencing]
+// struct TemplateMess<'d, A, B: 'static, C: 'static>
+// where
+//     A: ?Sized,
+//     B: 'static,
+//     C: 'static,
+// {
+//     external: &'d A,
+//     data1: B,
+//     #[borrows(data1)]
+//     data2: &'this C,
+//     data3: B,
+//     #[borrows(mut data3)]
+//     data4: &'this mut C,
+// }
 
-/// Regression test for #46
-#[self_referencing]
-struct PreviouslyBrokeAutoGeneratedChecker<T: 'static> {
-    x: T,
-    #[borrows(mut x)]
-    y: &'this (),
-}
+// /// Regression test for #46
+// #[self_referencing]
+// struct PreviouslyBrokeAutoGeneratedChecker<T: 'static> {
+//     x: T,
+//     #[borrows(mut x)]
+//     y: &'this (),
+// }
 
 #[test]
 fn box_and_ref() {
@@ -204,25 +200,25 @@ fn box_and_mut_ref() {
     assert!(bar.with_dref(|dref| **dref) == 34);
 }
 
-#[test]
-fn template_mess() {
-    let ext_str = "Hello World!".to_owned();
-    let mut instance = TemplateMessBuilder {
-        external: &ext_str[..],
-        data1: "asdf".to_owned(),
-        data2_builder: |data1_contents| data1_contents,
-        data3: "asdf".to_owned(),
-        data4_builder: |data3_contents| data3_contents,
-    }
-    .build();
-    instance.with_external(|ext| assert_eq!(*ext, "Hello World!"));
-    instance.with_data1(|data| assert_eq!(data, "asdf"));
-    instance.with_data4_mut(|con| **con = "Modified".to_owned());
-    instance.with(|fields| {
-        assert!(**fields.data1 == **fields.data2);
-        assert!(*fields.data4 == "Modified");
-    });
-}
+// #[test]
+// fn template_mess() {
+//     let ext_str = "Hello World!".to_owned();
+//     let mut instance = TemplateMessBuilder {
+//         external: &ext_str[..],
+//         data1: "asdf".to_owned(),
+//         data2_builder: |data1_contents| data1_contents,
+//         data3: "asdf".to_owned(),
+//         data4_builder: |data3_contents| data3_contents,
+//     }
+//     .build();
+//     instance.with_external(|ext| assert_eq!(*ext, "Hello World!"));
+//     instance.with_data1(|data| assert_eq!(data, "asdf"));
+//     instance.with_data4_mut(|con| **con = "Modified".to_owned());
+//     instance.with(|fields| {
+//         assert!(**fields.data1 == **fields.data2);
+//         assert!(*fields.data4 == "Modified");
+//     });
+// }
 
 const STATIC_INT: i32 = 456;
 #[test]
diff --git a/ouroboros_macro/src/generate/constructor.rs b/ouroboros_macro/src/generate/constructor.rs
index 2ece184..60583d8 100644
--- a/ouroboros_macro/src/generate/constructor.rs
+++ b/ouroboros_macro/src/generate/constructor.rs
@@ -13,6 +13,7 @@ pub fn create_builder_and_constructor(
 ) -> Result<(Ident, TokenStream, TokenStream), Error> {
     let struct_name = info.ident.clone();
     let generic_args = info.generic_arguments();
+    let generic_args_with_static_lifetimes = info.generic_arguments_with_static_lifetimes();
 
     let vis = if options.do_pub_extras {
         info.vis.clone()
@@ -159,16 +160,16 @@ pub fn create_builder_and_constructor(
         #documentation
         #vis #constructor_fn(#(#params),*) -> #struct_name <#(#generic_args),*> {
             ::ouroboros::macro_help::const_assert_eq!(
-                ::core::mem::size_of::<#struct_name<#(#generic_args),*>>(), 
-                ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()
+                ::core::mem::size_of::<#struct_name<#(#generic_args_with_static_lifetimes),*>>(),
+                ::core::mem::size_of::<#internal_ident<#(#generic_args_with_static_lifetimes),*>>()
             );
             ::ouroboros::macro_help::const_assert_eq!(
-                ::core::mem::align_of::<#struct_name<#(#generic_args),*>>(), 
-                ::core::mem::align_of::<#internal_ident<#(#generic_args),*>>()
+                ::core::mem::align_of::<#struct_name<#(#generic_args_with_static_lifetimes),*>>(),
+                ::core::mem::align_of::<#internal_ident<#(#generic_args_with_static_lifetimes),*>>()
             );
             #(#code)*
             unsafe {
-                ::core::mem::transmute(#internal_ident<#(#generic_args),*> {
+                ::core::mem::transmute(#internal_ident::<#(#generic_args),*> {
                     #(#field_names),*
                 })
             }
diff --git a/ouroboros_macro/src/generate/drop.rs b/ouroboros_macro/src/generate/drop.rs
new file mode 100644
index 0000000..a78d5e1
--- /dev/null
+++ b/ouroboros_macro/src/generate/drop.rs
@@ -0,0 +1,28 @@
+use crate::{
+    info_structures::StructInfo,
+    utils::{self, replace_this_with_lifetime},
+};
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::Error;
+
+pub fn create_drop_impl(info: &StructInfo) -> Result<TokenStream, Error> {
+    let ident = &info.ident;
+    let internal_ident = &info.internal_ident;
+    let generics = &info.generics;
+    let generic_args = info.generic_arguments();
+
+    let mut where_clause = quote! {};
+    if let Some(clause) = &generics.where_clause {
+        where_clause = quote! { #clause };
+    }
+    Ok(quote! {
+        impl #generics ::core::ops::Drop for #ident<#(#generic_args,)*> #where_clause {
+            fn drop(&mut self) {
+                unsafe {
+                    ::core::ptr::drop_in_place(::core::mem::transmute::<_, *mut #internal_ident <#(#generic_args,)*>>(self));
+                }
+            }
+        }
+    })
+}
diff --git a/ouroboros_macro/src/generate/into_heads.rs b/ouroboros_macro/src/generate/into_heads.rs
index 12016a8..2acb67d 100644
--- a/ouroboros_macro/src/generate/into_heads.rs
+++ b/ouroboros_macro/src/generate/into_heads.rs
@@ -1,5 +1,5 @@
 use proc_macro2::TokenStream;
-use quote::{format_ident, quote};
+use quote::quote;
 
 use crate::info_structures::{Options, StructInfo};
 
diff --git a/ouroboros_macro/src/generate/mod.rs b/ouroboros_macro/src/generate/mod.rs
index 0b229d1..4ba6a3e 100644
--- a/ouroboros_macro/src/generate/mod.rs
+++ b/ouroboros_macro/src/generate/mod.rs
@@ -1,5 +1,6 @@
 pub mod constructor;
 pub mod derives;
+pub mod drop;
 pub mod into_heads;
 pub mod struc;
 pub mod summon_checker;
diff --git a/ouroboros_macro/src/generate/struc.rs b/ouroboros_macro/src/generate/struc.rs
index 8a7b9f4..28f6197 100644
--- a/ouroboros_macro/src/generate/struc.rs
+++ b/ouroboros_macro/src/generate/struc.rs
@@ -14,7 +14,7 @@ pub fn create_actual_struct_def(info: &StructInfo) -> Result<TokenStream, Error>
         fields.push(quote! { #ident: ::core::marker::PhantomData<#ty> });
     }
     let generic_params = info.generic_params();
-    let generic_args = info.generic_arguments();
+    let generic_args = info.generic_arguments_with_static_lifetimes();
     let generic_where = &info.generics.where_clause;
     let ident = &info.ident;
     let internal_ident = &info.internal_ident;
@@ -22,6 +22,7 @@ pub fn create_actual_struct_def(info: &StructInfo) -> Result<TokenStream, Error>
         #visibility struct #ident <#generic_params> #generic_where {
             actual_data: [u8; ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()],
             _alignment: [#internal_ident<#(#generic_args),*>; 0],
+            #(#fields),*
         }
     })
 }
@@ -33,7 +34,6 @@ pub fn create_actual_struct_def(info: &StructInfo) -> Result<TokenStream, Error>
 /// but references *created* inside a function can be considered invalid
 /// whenever, even during the duration of the function.)
 pub fn create_internal_struct_def(info: &StructInfo) -> Result<TokenStream, Error> {
-    let vis = quote! { pub(super) };
     let ident = &info.internal_ident;
     let generics = &info.generics;
 
@@ -60,7 +60,7 @@ pub fn create_internal_struct_def(info: &StructInfo) -> Result<TokenStream, Erro
         where_clause = quote! { #clause };
     }
     let def = quote! {
-        #vis struct #ident #generics #where_clause {
+        struct #ident #generics #where_clause {
             #(#field_defs),*
         }
     };
diff --git a/ouroboros_macro/src/info_structures.rs b/ouroboros_macro/src/info_structures.rs
index f2b0cc0..f3e4a54 100644
--- a/ouroboros_macro/src/info_structures.rs
+++ b/ouroboros_macro/src/info_structures.rs
@@ -90,6 +90,20 @@ impl StructInfo {
         &self.generics.params
     }
 
+    pub fn generic_params_without_lifetimes(&self) -> Vec<&GenericParam> {
+        self.generics
+            .params
+            .iter()
+            .filter(|p| {
+                if let GenericParam::Lifetime(..) = p {
+                    false
+                } else {
+                    true
+                }
+            })
+            .collect()
+    }
+
     /// Same as generic_params but with 'this and 'outer_borrow prepended.
     pub fn borrowed_generic_params(&self) -> TokenStream {
         if self.generic_params().is_empty() {
@@ -115,7 +129,15 @@ impl StructInfo {
     }
 
     pub fn generic_arguments(&self) -> Vec<TokenStream> {
-        make_generic_arguments(&self.generics)
+        make_generic_arguments(self.generics.params.iter().collect())
+    }
+
+    pub fn generic_arguments_with_static_lifetimes(&self) -> Vec<TokenStream> {
+        let mut result = make_generic_arguments(self.generic_params_without_lifetimes());
+        for _ in 0..self.generics.lifetimes().count() {
+            result.insert(0, quote! { 'static });
+        }
+        result
     }
 
     /// Same as generic_arguments but with 'outer_borrow and 'this prepended.
diff --git a/ouroboros_macro/src/lib.rs b/ouroboros_macro/src/lib.rs
index d0a6898..c46584c 100644
--- a/ouroboros_macro/src/lib.rs
+++ b/ouroboros_macro/src/lib.rs
@@ -17,7 +17,7 @@ use crate::{
     info_structures::Options,
     parse::parse_struct,
 };
-use generate::struc::create_actual_struct_def;
+use generate::{struc::create_actual_struct_def, drop::create_drop_impl};
 use inflector::Inflector;
 use info_structures::BuilderType;
 use proc_macro::TokenStream;
@@ -39,6 +39,7 @@ fn self_referencing_impl(
 
     let actual_struct_def = create_actual_struct_def(&info)?;
     let internal_struct_def = create_internal_struct_def(&info)?;
+    let drop_impl = create_drop_impl(&info)?;
 
     let borrowchk_summoner = generate_checker_summoner(&info)?;
 
@@ -81,6 +82,7 @@ fn self_referencing_impl(
             #[doc="The self-referencing struct."]
             #actual_struct_def
             #internal_struct_def
+            #drop_impl
             #borrowchk_summoner
             #builder_def
             #async_builder_def
diff --git a/ouroboros_macro/src/parse.rs b/ouroboros_macro/src/parse.rs
index 8d5fd1a..a01d9a8 100644
--- a/ouroboros_macro/src/parse.rs
+++ b/ouroboros_macro/src/parse.rs
@@ -133,6 +133,18 @@ fn parse_derive_attribute(attr: &Attribute) -> Result<Vec<Derive>, Error> {
 pub fn parse_struct(def: &ItemStruct) -> Result<StructInfo, Error> {
     let vis = def.vis.clone();
     let generics = def.generics.clone();
+    if let Some(first_param) = generics.type_params().next() {
+        return Err(Error::new(
+            first_param.span(),
+            "Self-referencing structs currently cannot have type or constant parameters, only lifetime parameters.",
+        ));
+    }
+    if let Some(first_param) = generics.const_params().next() {
+        return Err(Error::new(
+            first_param.span(),
+            "Self-referencing structs currently cannot have type or constant parameters, only lifetime parameters.",
+        ));
+    }
     let mut actual_struct_def = def.clone();
     actual_struct_def.vis = vis.clone();
     let mut fields = Vec::new();
diff --git a/ouroboros_macro/src/utils.rs b/ouroboros_macro/src/utils.rs
index 5bbae6c..3b1f770 100644
--- a/ouroboros_macro/src/utils.rs
+++ b/ouroboros_macro/src/utils.rs
@@ -33,9 +33,9 @@ pub fn make_generic_consumers(generics: &Generics) -> impl Iterator<Item = (Toke
 }
 
 // Takes the generics parameters from the original struct and turns them into arguments.
-pub fn make_generic_arguments(generics: &Generics) -> Vec<TokenStream> {
+pub fn make_generic_arguments(generics: Vec<&GenericParam>) -> Vec<TokenStream> {
     let mut arguments = Vec::new();
-    for generic in generics.params.clone() {
+    for generic in generics {
         match generic {
             GenericParam::Type(typ) => {
                 let ident = &typ.ident;

From 71de8eb50cd9cab027f85fae7ce8caa04584aab5 Mon Sep 17 00:00:00 2001
From: joshua-maros <60271685+joshua-maros@users.noreply.github.com>
Date: Sun, 11 Jun 2023 18:24:07 -0500
Subject: [PATCH 4/8] Revert "Blah."

This reverts commit 30637694c97b231196e133b92da6a84336ee1216.
---
 examples/src/ok_tests.rs                    | 92 +++++++++++----------
 ouroboros_macro/src/generate/constructor.rs | 11 ++-
 ouroboros_macro/src/generate/drop.rs        | 28 -------
 ouroboros_macro/src/generate/into_heads.rs  |  2 +-
 ouroboros_macro/src/generate/mod.rs         |  1 -
 ouroboros_macro/src/generate/struc.rs       |  6 +-
 ouroboros_macro/src/info_structures.rs      | 24 +-----
 ouroboros_macro/src/lib.rs                  |  4 +-
 ouroboros_macro/src/parse.rs                | 12 ---
 ouroboros_macro/src/utils.rs                |  4 +-
 10 files changed, 61 insertions(+), 123 deletions(-)
 delete mode 100644 ouroboros_macro/src/generate/drop.rs

diff --git a/examples/src/ok_tests.rs b/examples/src/ok_tests.rs
index 7a08614..db27303 100644
--- a/examples/src/ok_tests.rs
+++ b/examples/src/ok_tests.rs
@@ -1,5 +1,9 @@
+use alloc::borrow::ToOwned;
 use alloc::boxed::Box;
+use alloc::vec;
+use alloc::vec::Vec;
 use core::fmt::Debug;
+use ouroboros::macro_help::AliasableBox;
 
 use ouroboros::self_referencing;
 
@@ -50,32 +54,32 @@ struct AutoDetectCovarianceOnFieldsWithoutThis {
     self_reference: &'this (),
 }
 
-// /// This test just makes sure that the macro copes with a ton of template parameters being thrown at
-// /// it, specifically checking that the templates work fine even when a generated struct doesn't need
-// /// all of them. (E.G. heads will only contain 'd, A, and B.)
-// #[self_referencing]
-// struct TemplateMess<'d, A, B: 'static, C: 'static>
-// where
-//     A: ?Sized,
-//     B: 'static,
-//     C: 'static,
-// {
-//     external: &'d A,
-//     data1: B,
-//     #[borrows(data1)]
-//     data2: &'this C,
-//     data3: B,
-//     #[borrows(mut data3)]
-//     data4: &'this mut C,
-// }
+/// This test just makes sure that the macro copes with a ton of template parameters being thrown at
+/// it, specifically checking that the templates work fine even when a generated struct doesn't need
+/// all of them. (E.G. heads will only contain 'd, A, and B.)
+#[self_referencing]
+struct TemplateMess<'d, A, B: 'static, C: 'static>
+where
+    A: ?Sized,
+    B: 'static,
+    C: 'static,
+{
+    external: &'d A,
+    data1: B,
+    #[borrows(data1)]
+    data2: &'this C,
+    data3: B,
+    #[borrows(mut data3)]
+    data4: &'this mut C,
+}
 
-// /// Regression test for #46
-// #[self_referencing]
-// struct PreviouslyBrokeAutoGeneratedChecker<T: 'static> {
-//     x: T,
-//     #[borrows(mut x)]
-//     y: &'this (),
-// }
+/// Regression test for #46
+#[self_referencing]
+struct PreviouslyBrokeAutoGeneratedChecker<T: 'static> {
+    x: T,
+    #[borrows(mut x)]
+    y: &'this (),
+}
 
 #[test]
 fn box_and_ref() {
@@ -200,25 +204,25 @@ fn box_and_mut_ref() {
     assert!(bar.with_dref(|dref| **dref) == 34);
 }
 
-// #[test]
-// fn template_mess() {
-//     let ext_str = "Hello World!".to_owned();
-//     let mut instance = TemplateMessBuilder {
-//         external: &ext_str[..],
-//         data1: "asdf".to_owned(),
-//         data2_builder: |data1_contents| data1_contents,
-//         data3: "asdf".to_owned(),
-//         data4_builder: |data3_contents| data3_contents,
-//     }
-//     .build();
-//     instance.with_external(|ext| assert_eq!(*ext, "Hello World!"));
-//     instance.with_data1(|data| assert_eq!(data, "asdf"));
-//     instance.with_data4_mut(|con| **con = "Modified".to_owned());
-//     instance.with(|fields| {
-//         assert!(**fields.data1 == **fields.data2);
-//         assert!(*fields.data4 == "Modified");
-//     });
-// }
+#[test]
+fn template_mess() {
+    let ext_str = "Hello World!".to_owned();
+    let mut instance = TemplateMessBuilder {
+        external: &ext_str[..],
+        data1: "asdf".to_owned(),
+        data2_builder: |data1_contents| data1_contents,
+        data3: "asdf".to_owned(),
+        data4_builder: |data3_contents| data3_contents,
+    }
+    .build();
+    instance.with_external(|ext| assert_eq!(*ext, "Hello World!"));
+    instance.with_data1(|data| assert_eq!(data, "asdf"));
+    instance.with_data4_mut(|con| **con = "Modified".to_owned());
+    instance.with(|fields| {
+        assert!(**fields.data1 == **fields.data2);
+        assert!(*fields.data4 == "Modified");
+    });
+}
 
 const STATIC_INT: i32 = 456;
 #[test]
diff --git a/ouroboros_macro/src/generate/constructor.rs b/ouroboros_macro/src/generate/constructor.rs
index 60583d8..2ece184 100644
--- a/ouroboros_macro/src/generate/constructor.rs
+++ b/ouroboros_macro/src/generate/constructor.rs
@@ -13,7 +13,6 @@ pub fn create_builder_and_constructor(
 ) -> Result<(Ident, TokenStream, TokenStream), Error> {
     let struct_name = info.ident.clone();
     let generic_args = info.generic_arguments();
-    let generic_args_with_static_lifetimes = info.generic_arguments_with_static_lifetimes();
 
     let vis = if options.do_pub_extras {
         info.vis.clone()
@@ -160,16 +159,16 @@ pub fn create_builder_and_constructor(
         #documentation
         #vis #constructor_fn(#(#params),*) -> #struct_name <#(#generic_args),*> {
             ::ouroboros::macro_help::const_assert_eq!(
-                ::core::mem::size_of::<#struct_name<#(#generic_args_with_static_lifetimes),*>>(),
-                ::core::mem::size_of::<#internal_ident<#(#generic_args_with_static_lifetimes),*>>()
+                ::core::mem::size_of::<#struct_name<#(#generic_args),*>>(), 
+                ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()
             );
             ::ouroboros::macro_help::const_assert_eq!(
-                ::core::mem::align_of::<#struct_name<#(#generic_args_with_static_lifetimes),*>>(),
-                ::core::mem::align_of::<#internal_ident<#(#generic_args_with_static_lifetimes),*>>()
+                ::core::mem::align_of::<#struct_name<#(#generic_args),*>>(), 
+                ::core::mem::align_of::<#internal_ident<#(#generic_args),*>>()
             );
             #(#code)*
             unsafe {
-                ::core::mem::transmute(#internal_ident::<#(#generic_args),*> {
+                ::core::mem::transmute(#internal_ident<#(#generic_args),*> {
                     #(#field_names),*
                 })
             }
diff --git a/ouroboros_macro/src/generate/drop.rs b/ouroboros_macro/src/generate/drop.rs
deleted file mode 100644
index a78d5e1..0000000
--- a/ouroboros_macro/src/generate/drop.rs
+++ /dev/null
@@ -1,28 +0,0 @@
-use crate::{
-    info_structures::StructInfo,
-    utils::{self, replace_this_with_lifetime},
-};
-use proc_macro2::TokenStream;
-use quote::quote;
-use syn::Error;
-
-pub fn create_drop_impl(info: &StructInfo) -> Result<TokenStream, Error> {
-    let ident = &info.ident;
-    let internal_ident = &info.internal_ident;
-    let generics = &info.generics;
-    let generic_args = info.generic_arguments();
-
-    let mut where_clause = quote! {};
-    if let Some(clause) = &generics.where_clause {
-        where_clause = quote! { #clause };
-    }
-    Ok(quote! {
-        impl #generics ::core::ops::Drop for #ident<#(#generic_args,)*> #where_clause {
-            fn drop(&mut self) {
-                unsafe {
-                    ::core::ptr::drop_in_place(::core::mem::transmute::<_, *mut #internal_ident <#(#generic_args,)*>>(self));
-                }
-            }
-        }
-    })
-}
diff --git a/ouroboros_macro/src/generate/into_heads.rs b/ouroboros_macro/src/generate/into_heads.rs
index 2acb67d..12016a8 100644
--- a/ouroboros_macro/src/generate/into_heads.rs
+++ b/ouroboros_macro/src/generate/into_heads.rs
@@ -1,5 +1,5 @@
 use proc_macro2::TokenStream;
-use quote::quote;
+use quote::{format_ident, quote};
 
 use crate::info_structures::{Options, StructInfo};
 
diff --git a/ouroboros_macro/src/generate/mod.rs b/ouroboros_macro/src/generate/mod.rs
index 4ba6a3e..0b229d1 100644
--- a/ouroboros_macro/src/generate/mod.rs
+++ b/ouroboros_macro/src/generate/mod.rs
@@ -1,6 +1,5 @@
 pub mod constructor;
 pub mod derives;
-pub mod drop;
 pub mod into_heads;
 pub mod struc;
 pub mod summon_checker;
diff --git a/ouroboros_macro/src/generate/struc.rs b/ouroboros_macro/src/generate/struc.rs
index 28f6197..8a7b9f4 100644
--- a/ouroboros_macro/src/generate/struc.rs
+++ b/ouroboros_macro/src/generate/struc.rs
@@ -14,7 +14,7 @@ pub fn create_actual_struct_def(info: &StructInfo) -> Result<TokenStream, Error>
         fields.push(quote! { #ident: ::core::marker::PhantomData<#ty> });
     }
     let generic_params = info.generic_params();
-    let generic_args = info.generic_arguments_with_static_lifetimes();
+    let generic_args = info.generic_arguments();
     let generic_where = &info.generics.where_clause;
     let ident = &info.ident;
     let internal_ident = &info.internal_ident;
@@ -22,7 +22,6 @@ pub fn create_actual_struct_def(info: &StructInfo) -> Result<TokenStream, Error>
         #visibility struct #ident <#generic_params> #generic_where {
             actual_data: [u8; ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()],
             _alignment: [#internal_ident<#(#generic_args),*>; 0],
-            #(#fields),*
         }
     })
 }
@@ -34,6 +33,7 @@ pub fn create_actual_struct_def(info: &StructInfo) -> Result<TokenStream, Error>
 /// but references *created* inside a function can be considered invalid
 /// whenever, even during the duration of the function.)
 pub fn create_internal_struct_def(info: &StructInfo) -> Result<TokenStream, Error> {
+    let vis = quote! { pub(super) };
     let ident = &info.internal_ident;
     let generics = &info.generics;
 
@@ -60,7 +60,7 @@ pub fn create_internal_struct_def(info: &StructInfo) -> Result<TokenStream, Erro
         where_clause = quote! { #clause };
     }
     let def = quote! {
-        struct #ident #generics #where_clause {
+        #vis struct #ident #generics #where_clause {
             #(#field_defs),*
         }
     };
diff --git a/ouroboros_macro/src/info_structures.rs b/ouroboros_macro/src/info_structures.rs
index f3e4a54..f2b0cc0 100644
--- a/ouroboros_macro/src/info_structures.rs
+++ b/ouroboros_macro/src/info_structures.rs
@@ -90,20 +90,6 @@ impl StructInfo {
         &self.generics.params
     }
 
-    pub fn generic_params_without_lifetimes(&self) -> Vec<&GenericParam> {
-        self.generics
-            .params
-            .iter()
-            .filter(|p| {
-                if let GenericParam::Lifetime(..) = p {
-                    false
-                } else {
-                    true
-                }
-            })
-            .collect()
-    }
-
     /// Same as generic_params but with 'this and 'outer_borrow prepended.
     pub fn borrowed_generic_params(&self) -> TokenStream {
         if self.generic_params().is_empty() {
@@ -129,15 +115,7 @@ impl StructInfo {
     }
 
     pub fn generic_arguments(&self) -> Vec<TokenStream> {
-        make_generic_arguments(self.generics.params.iter().collect())
-    }
-
-    pub fn generic_arguments_with_static_lifetimes(&self) -> Vec<TokenStream> {
-        let mut result = make_generic_arguments(self.generic_params_without_lifetimes());
-        for _ in 0..self.generics.lifetimes().count() {
-            result.insert(0, quote! { 'static });
-        }
-        result
+        make_generic_arguments(&self.generics)
     }
 
     /// Same as generic_arguments but with 'outer_borrow and 'this prepended.
diff --git a/ouroboros_macro/src/lib.rs b/ouroboros_macro/src/lib.rs
index c46584c..d0a6898 100644
--- a/ouroboros_macro/src/lib.rs
+++ b/ouroboros_macro/src/lib.rs
@@ -17,7 +17,7 @@ use crate::{
     info_structures::Options,
     parse::parse_struct,
 };
-use generate::{struc::create_actual_struct_def, drop::create_drop_impl};
+use generate::struc::create_actual_struct_def;
 use inflector::Inflector;
 use info_structures::BuilderType;
 use proc_macro::TokenStream;
@@ -39,7 +39,6 @@ fn self_referencing_impl(
 
     let actual_struct_def = create_actual_struct_def(&info)?;
     let internal_struct_def = create_internal_struct_def(&info)?;
-    let drop_impl = create_drop_impl(&info)?;
 
     let borrowchk_summoner = generate_checker_summoner(&info)?;
 
@@ -82,7 +81,6 @@ fn self_referencing_impl(
             #[doc="The self-referencing struct."]
             #actual_struct_def
             #internal_struct_def
-            #drop_impl
             #borrowchk_summoner
             #builder_def
             #async_builder_def
diff --git a/ouroboros_macro/src/parse.rs b/ouroboros_macro/src/parse.rs
index a01d9a8..8d5fd1a 100644
--- a/ouroboros_macro/src/parse.rs
+++ b/ouroboros_macro/src/parse.rs
@@ -133,18 +133,6 @@ fn parse_derive_attribute(attr: &Attribute) -> Result<Vec<Derive>, Error> {
 pub fn parse_struct(def: &ItemStruct) -> Result<StructInfo, Error> {
     let vis = def.vis.clone();
     let generics = def.generics.clone();
-    if let Some(first_param) = generics.type_params().next() {
-        return Err(Error::new(
-            first_param.span(),
-            "Self-referencing structs currently cannot have type or constant parameters, only lifetime parameters.",
-        ));
-    }
-    if let Some(first_param) = generics.const_params().next() {
-        return Err(Error::new(
-            first_param.span(),
-            "Self-referencing structs currently cannot have type or constant parameters, only lifetime parameters.",
-        ));
-    }
     let mut actual_struct_def = def.clone();
     actual_struct_def.vis = vis.clone();
     let mut fields = Vec::new();
diff --git a/ouroboros_macro/src/utils.rs b/ouroboros_macro/src/utils.rs
index 3b1f770..5bbae6c 100644
--- a/ouroboros_macro/src/utils.rs
+++ b/ouroboros_macro/src/utils.rs
@@ -33,9 +33,9 @@ pub fn make_generic_consumers(generics: &Generics) -> impl Iterator<Item = (Toke
 }
 
 // Takes the generics parameters from the original struct and turns them into arguments.
-pub fn make_generic_arguments(generics: Vec<&GenericParam>) -> Vec<TokenStream> {
+pub fn make_generic_arguments(generics: &Generics) -> Vec<TokenStream> {
     let mut arguments = Vec::new();
-    for generic in generics {
+    for generic in generics.params.clone() {
         match generic {
             GenericParam::Type(typ) => {
                 let ident = &typ.ident;

From 658ec36d8b41cc8820c12b1ca92e655127d6858a Mon Sep 17 00:00:00 2001
From: joshua-maros <60271685+joshua-maros@users.noreply.github.com>
Date: Sun, 11 Jun 2023 18:25:16 -0500
Subject: [PATCH 5/8] Revert "Revert "Revert "Failed attempt to fix
 problems."""

This reverts commit c8891142dd2eb437f0dcf2c0ad170be6fbb73d9d.
---
 examples/Cargo.toml                           |  4 +--
 examples/src/ok_tests.rs                      |  3 --
 ouroboros/Cargo.toml                          |  5 ++-
 ouroboros/src/lib.rs                          |  1 -
 ouroboros_macro/Cargo.toml                    |  2 +-
 ouroboros_macro/src/generate/constructor.rs   | 15 ++-------
 ouroboros_macro/src/generate/into_heads.rs    | 14 ++++-----
 ouroboros_macro/src/generate/struc.rs         | 31 +++----------------
 .../src/generate/try_constructor.rs           |  5 +--
 ouroboros_macro/src/generate/with_all.rs      | 10 ++----
 ouroboros_macro/src/generate/with_each.rs     | 17 +++-------
 ouroboros_macro/src/info_structures.rs        | 11 -------
 ouroboros_macro/src/lib.rs                    |  5 +--
 ouroboros_macro/src/parse.rs                  |  1 -
 14 files changed, 27 insertions(+), 97 deletions(-)

diff --git a/examples/Cargo.toml b/examples/Cargo.toml
index 8243ddf..e8fa0fd 100644
--- a/examples/Cargo.toml
+++ b/examples/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros_examples"
-version = "0.16.0"
+version = "0.15.7"
 authors = ["Joshua Maros <joshua-maros@github.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
@@ -21,7 +21,7 @@ std = []
 __tokio = ["tokio", "std"]
 
 [dependencies]
-ouroboros = { version = "0.16.0", path = "../ouroboros" }
+ouroboros = { version = "0.15.7", path = "../ouroboros" }
 tokio = { version = "1.27.0", features = [ "macros", "rt" ], optional = true }
 
 [dev-dependencies]
diff --git a/examples/src/ok_tests.rs b/examples/src/ok_tests.rs
index db27303..61ae346 100644
--- a/examples/src/ok_tests.rs
+++ b/examples/src/ok_tests.rs
@@ -1,9 +1,6 @@
 use alloc::borrow::ToOwned;
 use alloc::boxed::Box;
-use alloc::vec;
-use alloc::vec::Vec;
 use core::fmt::Debug;
-use ouroboros::macro_help::AliasableBox;
 
 use ouroboros::self_referencing;
 
diff --git a/ouroboros/Cargo.toml b/ouroboros/Cargo.toml
index 3c256b4..4ee1ca3 100644
--- a/ouroboros/Cargo.toml
+++ b/ouroboros/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros"
-version = "0.16.0"
+version = "0.15.7"
 authors = ["Joshua Maros <joshua-maros@github.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
@@ -11,8 +11,7 @@ repository = "https://github.com/joshua-maros/ouroboros"
 
 [dependencies]
 aliasable = "0.1.3"
-ouroboros_macro = { version = "0.16.0", path = "../ouroboros_macro" }
-static_assertions = "1.1.0"
+ouroboros_macro = { version = "0.15.7", path = "../ouroboros_macro" }
 
 [features]
 default = ["std"]
diff --git a/ouroboros/src/lib.rs b/ouroboros/src/lib.rs
index 13870da..efd32e8 100644
--- a/ouroboros/src/lib.rs
+++ b/ouroboros/src/lib.rs
@@ -351,7 +351,6 @@ pub mod macro_help {
     pub extern crate alloc;
 
     pub use aliasable::boxed::AliasableBox;
-    pub use static_assertions::const_assert_eq;
     use aliasable::boxed::UniqueBox;
 
     pub struct CheckIfTypeIsStd<T>(core::marker::PhantomData<T>);
diff --git a/ouroboros_macro/Cargo.toml b/ouroboros_macro/Cargo.toml
index 5b2a56b..a350e81 100644
--- a/ouroboros_macro/Cargo.toml
+++ b/ouroboros_macro/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros_macro"
-version = "0.16.0"
+version = "0.15.7"
 authors = ["Joshua Maros <joshua-maros@github.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
diff --git a/ouroboros_macro/src/generate/constructor.rs b/ouroboros_macro/src/generate/constructor.rs
index 2ece184..6ab47bc 100644
--- a/ouroboros_macro/src/generate/constructor.rs
+++ b/ouroboros_macro/src/generate/constructor.rs
@@ -154,23 +154,12 @@ pub fn create_builder_and_constructor(
         BuilderType::Sync => quote! { fn new },
     };
     let field_names: Vec<_> = info.fields.iter().map(|field| field.name.clone()).collect();
-    let internal_ident = &info.internal_ident;
     let constructor_def = quote! {
         #documentation
         #vis #constructor_fn(#(#params),*) -> #struct_name <#(#generic_args),*> {
-            ::ouroboros::macro_help::const_assert_eq!(
-                ::core::mem::size_of::<#struct_name<#(#generic_args),*>>(), 
-                ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()
-            );
-            ::ouroboros::macro_help::const_assert_eq!(
-                ::core::mem::align_of::<#struct_name<#(#generic_args),*>>(), 
-                ::core::mem::align_of::<#internal_ident<#(#generic_args),*>>()
-            );
             #(#code)*
-            unsafe {
-                ::core::mem::transmute(#internal_ident<#(#generic_args),*> {
-                    #(#field_names),*
-                })
+            Self {
+                #(#field_names),*
             }
         }
     };
diff --git a/ouroboros_macro/src/generate/into_heads.rs b/ouroboros_macro/src/generate/into_heads.rs
index 12016a8..5784e46 100644
--- a/ouroboros_macro/src/generate/into_heads.rs
+++ b/ouroboros_macro/src/generate/into_heads.rs
@@ -1,5 +1,5 @@
 use proc_macro2::TokenStream;
-use quote::{format_ident, quote};
+use quote::quote;
 
 use crate::info_structures::{Options, StructInfo};
 
@@ -13,16 +13,12 @@ pub fn make_into_heads(info: &StructInfo, options: Options) -> (TokenStream, Tok
     let mut code = Vec::new();
     let mut field_initializers = Vec::new();
     let mut head_fields = Vec::new();
-    let internal_struct = &info.internal_ident;
     // Drop everything in the reverse order of what it was declared in. Fields that come later
     // are only dependent on fields that came before them.
     for field in info.fields.iter().rev() {
         let field_name = &field.name;
-        if field.self_referencing {
-            // Heads are fields that do not borrow anything.
-            code.push(quote! { ::core::mem::drop(this.#field_name); });
-        } else {
-            code.push(quote! { let #field_name = this.#field_name; });
+        if !field.self_referencing {
+            code.push(quote! { let #field_name = self.#field_name; });
             if field.is_borrowed() {
                 field_initializers
                     .push(quote! { #field_name: ::ouroboros::macro_help::unbox(#field_name) });
@@ -31,6 +27,9 @@ pub fn make_into_heads(info: &StructInfo, options: Options) -> (TokenStream, Tok
             }
             let field_type = &field.typ;
             head_fields.push(quote! { #visibility #field_name: #field_type });
+        } else {
+            // Heads are fields that do not borrow anything.
+            code.push(quote! { ::core::mem::drop(self.#field_name); });
         }
     }
     for (ty, ident) in info.generic_consumers() {
@@ -72,7 +71,6 @@ pub fn make_into_heads(info: &StructInfo, options: Options) -> (TokenStream, Tok
         #[allow(clippy::drop_copy)]
         #[allow(clippy::drop_non_drop)]
         #visibility fn into_heads(self) -> Heads<#(#generic_args),*> {
-            let this: #internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
             #(#code)*
             Heads {
                 #(#field_initializers),*
diff --git a/ouroboros_macro/src/generate/struc.rs b/ouroboros_macro/src/generate/struc.rs
index 8a7b9f4..9b2ff51 100644
--- a/ouroboros_macro/src/generate/struc.rs
+++ b/ouroboros_macro/src/generate/struc.rs
@@ -6,35 +6,12 @@ use proc_macro2::TokenStream;
 use quote::quote;
 use syn::Error;
 
-/// Creates the struct that will actually store the data.
+/// Creates the struct that will actually store the data. This involves properly organizing the
+/// fields, collecting metadata about them, reversing the order everything is stored in, and
+/// converting any uses of 'this to 'static.
 pub fn create_actual_struct_def(info: &StructInfo) -> Result<TokenStream, Error> {
-    let visibility = utils::submodule_contents_visiblity(&info.vis);
-    let mut fields = Vec::new();
-    for (ty, ident) in info.generic_consumers() {
-        fields.push(quote! { #ident: ::core::marker::PhantomData<#ty> });
-    }
-    let generic_params = info.generic_params();
-    let generic_args = info.generic_arguments();
-    let generic_where = &info.generics.where_clause;
+    let vis = utils::submodule_contents_visiblity(&info.vis);
     let ident = &info.ident;
-    let internal_ident = &info.internal_ident;
-    Ok(quote! {
-        #visibility struct #ident <#generic_params> #generic_where {
-            actual_data: [u8; ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()],
-            _alignment: [#internal_ident<#(#generic_args),*>; 0],
-        }
-    })
-}
-
-/// Creates a struct with fields like the original struct. Instances of the
-/// "actual" struct are reinterpreted as instances of the "internal" struct
-/// whenever data needs to be accessed. (This gets around the problem that
-/// references passed to functions must be valid through the entire function,
-/// but references *created* inside a function can be considered invalid
-/// whenever, even during the duration of the function.)
-pub fn create_internal_struct_def(info: &StructInfo) -> Result<TokenStream, Error> {
-    let vis = quote! { pub(super) };
-    let ident = &info.internal_ident;
     let generics = &info.generics;
 
     let field_defs: Vec<_> = info
diff --git a/ouroboros_macro/src/generate/try_constructor.rs b/ouroboros_macro/src/generate/try_constructor.rs
index a5469d6..4078c56 100644
--- a/ouroboros_macro/src/generate/try_constructor.rs
+++ b/ouroboros_macro/src/generate/try_constructor.rs
@@ -223,7 +223,6 @@ pub fn create_try_builder_and_constructor(
         quote! { #struct_name::#or_recover_ident(#(#builder_struct_field_names),*).map_err(|(error, _heads)| error) }
     };
     let field_names: Vec<_> = info.fields.iter().map(|field| field.name.clone()).collect();
-    let internal_ident = &info.internal_ident;
     let constructor_def = quote! {
         #documentation
         #visibility #constructor_fn<Error_>(#(#params),*) -> ::core::result::Result<#struct_name <#(#generic_args),*>, Error_> {
@@ -232,9 +231,7 @@ pub fn create_try_builder_and_constructor(
         #or_recover_documentation
         #visibility #or_recover_constructor_fn<Error_>(#(#params),*) -> ::core::result::Result<#struct_name <#(#generic_args),*>, (Error_, Heads<#(#generic_args),*>)> {
             #(#or_recover_code)*
-            ::core::result::Result::Ok(unsafe {
-                ::core::mem::transmute(#internal_ident { #(#field_names),* })
-            })
+            ::core::result::Result::Ok(Self { #(#field_names),* })
         }
     };
     builder_struct_generic_producers.push(quote! { Error_ });
diff --git a/ouroboros_macro/src/generate/with_all.rs b/ouroboros_macro/src/generate/with_all.rs
index 03e3d59..e6a2665 100644
--- a/ouroboros_macro/src/generate/with_all.rs
+++ b/ouroboros_macro/src/generate/with_all.rs
@@ -16,20 +16,19 @@ pub fn make_with_all_function(
     let mut field_assignments = Vec::new();
     let mut mut_fields = Vec::new();
     let mut mut_field_assignments = Vec::new();
-    let internal_struct = &info.internal_ident;
     // I don't think the reverse is necessary but it does make the expanded code more uniform.
     for field in info.fields.iter().rev() {
         let field_name = &field.name;
         let field_type = &field.typ;
         if field.field_type == FieldType::Tail {
             fields.push(quote! { #visibility #field_name: &'outer_borrow #field_type });
-            field_assignments.push(quote! { #field_name: &this.#field_name });
+            field_assignments.push(quote! { #field_name: &self.#field_name });
             mut_fields.push(quote! { #visibility #field_name: &'outer_borrow mut #field_type });
-            mut_field_assignments.push(quote! { #field_name: &mut this.#field_name });
+            mut_field_assignments.push(quote! { #field_name: &mut self.#field_name });
         } else if field.field_type == FieldType::Borrowed {
             let ass = quote! { #field_name: unsafe {
                 ::ouroboros::macro_help::change_lifetime(
-                    &*this.#field_name
+                    &*self.#field_name
                 )
             } };
             fields.push(quote! { #visibility #field_name: &'this #field_type });
@@ -109,7 +108,6 @@ pub fn make_with_all_function(
     } else {
         quote! { #[doc(hidden)] }
     };
-    let generic_args = info.generic_arguments();
     let fn_defs = quote! {
         #documentation
         #[inline(always)]
@@ -117,7 +115,6 @@ pub fn make_with_all_function(
             &'outer_borrow self,
             user: impl for<'this> ::core::ops::FnOnce(#borrowed_fields_type) -> ReturnType
         ) -> ReturnType {
-            let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
             user(BorrowedFields {
                 #(#field_assignments),*
             })
@@ -128,7 +125,6 @@ pub fn make_with_all_function(
             &'outer_borrow mut self,
             user: impl for<'this> ::core::ops::FnOnce(#borrowed_mut_fields_type) -> ReturnType
         ) -> ReturnType {
-            let this: &mut #internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
             user(BorrowedMutFields {
                 #(#mut_field_assignments),*
             })
diff --git a/ouroboros_macro/src/generate/with_each.rs b/ouroboros_macro/src/generate/with_each.rs
index 15b0461..8985857 100644
--- a/ouroboros_macro/src/generate/with_each.rs
+++ b/ouroboros_macro/src/generate/with_each.rs
@@ -5,8 +5,6 @@ use syn::Error;
 
 pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<TokenStream>, Error> {
     let mut users = Vec::new();
-    let internal_struct = &info.internal_ident;
-    let generic_args = info.generic_arguments();
     for field in &info.fields {
         let visibility = &field.vis;
         let field_name = &field.name;
@@ -36,8 +34,7 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                     &'outer_borrow self,
                     user: impl for<'this> ::core::ops::FnOnce(&'outer_borrow #field_type) -> ReturnType,
                 ) -> ReturnType {
-                    let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
-                    user(&this. #field_name)
+                    user(&self. #field_name)
                 }
             });
             if field.covariant == Some(true) {
@@ -48,8 +45,7 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                     #visibility fn #borrower_name<'this>(
                         &'this self,
                     ) -> &'this #field_type {
-                        let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
-                        &this.#field_name
+                        &self.#field_name
                     }
                 });
             } else if field.covariant.is_none() {
@@ -80,8 +76,7 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                     &'outer_borrow mut self,
                     user: impl for<'this> ::core::ops::FnOnce(&'outer_borrow mut #field_type) -> ReturnType,
                 ) -> ReturnType {
-                    let this: &mut #internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
-                    user(&mut this. #field_name)
+                    user(&mut self. #field_name)
                 }
             });
         } else if field.field_type == FieldType::Borrowed {
@@ -107,8 +102,7 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                     &'outer_borrow self,
                     user: impl for<'this> ::core::ops::FnOnce(&'outer_borrow #field_type) -> ReturnType,
                 ) -> ReturnType {
-                    let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
-                    user(&*this.#field_name)
+                    user(&*self.#field_name)
                 }
             });
             if field.self_referencing {
@@ -126,8 +120,7 @@ pub fn make_with_functions(info: &StructInfo, options: Options) -> Result<Vec<To
                 #visibility fn #borrower_name<'this>(
                     &'this self,
                 ) -> &'this #field_type {
-                    let this: &#internal_struct<#(#generic_args),*> = unsafe { ::core::mem::transmute(self) };
-                    &*this.#field_name
+                    &*self.#field_name
                 }
             });
         } else if field.field_type == FieldType::BorrowedMut {
diff --git a/ouroboros_macro/src/info_structures.rs b/ouroboros_macro/src/info_structures.rs
index f2b0cc0..22e4cde 100644
--- a/ouroboros_macro/src/info_structures.rs
+++ b/ouroboros_macro/src/info_structures.rs
@@ -12,16 +12,6 @@ pub struct Options {
     pub do_pub_extras: bool,
 }
 
-impl Options {
-    pub fn documentation_to_tokens(&self, documentation: &str) -> TokenStream {
-        if self.do_no_doc {
-            quote! { #[doc(hidden)] }
-        } else {
-            quote! { #[doc=#documentation] }
-        }
-    }
-}
-
 #[derive(Clone, Copy, PartialEq)]
 pub enum FieldType {
     /// Not borrowed by other parts of the struct.
@@ -71,7 +61,6 @@ impl BuilderType {
 pub struct StructInfo {
     pub derives: Vec<Derive>,
     pub ident: Ident,
-    pub internal_ident: Ident,
     pub generics: Generics,
     pub vis: Visibility,
     pub fields: Vec<StructFieldInfo>,
diff --git a/ouroboros_macro/src/lib.rs b/ouroboros_macro/src/lib.rs
index d0a6898..cd12419 100644
--- a/ouroboros_macro/src/lib.rs
+++ b/ouroboros_macro/src/lib.rs
@@ -9,7 +9,7 @@ mod utils;
 use crate::{
     generate::{
         constructor::create_builder_and_constructor, derives::create_derives,
-        into_heads::make_into_heads, struc::create_internal_struct_def,
+        into_heads::make_into_heads, struc::create_actual_struct_def,
         summon_checker::generate_checker_summoner,
         try_constructor::create_try_builder_and_constructor, type_asserts::make_type_asserts,
         with_all::make_with_all_function, with_each::make_with_functions,
@@ -17,7 +17,6 @@ use crate::{
     info_structures::Options,
     parse::parse_struct,
 };
-use generate::struc::create_actual_struct_def;
 use inflector::Inflector;
 use info_structures::BuilderType;
 use proc_macro::TokenStream;
@@ -38,7 +37,6 @@ fn self_referencing_impl(
     let info = parse_struct(original_struct_def)?;
 
     let actual_struct_def = create_actual_struct_def(&info)?;
-    let internal_struct_def = create_internal_struct_def(&info)?;
 
     let borrowchk_summoner = generate_checker_summoner(&info)?;
 
@@ -80,7 +78,6 @@ fn self_referencing_impl(
             use super::*;
             #[doc="The self-referencing struct."]
             #actual_struct_def
-            #internal_struct_def
             #borrowchk_summoner
             #builder_def
             #async_builder_def
diff --git a/ouroboros_macro/src/parse.rs b/ouroboros_macro/src/parse.rs
index 8d5fd1a..546aa7c 100644
--- a/ouroboros_macro/src/parse.rs
+++ b/ouroboros_macro/src/parse.rs
@@ -262,7 +262,6 @@ pub fn parse_struct(def: &ItemStruct) -> Result<StructInfo, Error> {
     return Ok(StructInfo {
         derives,
         ident: def.ident.clone(),
-        internal_ident: format_ident!("{}Internal", def.ident),
         generics: def.generics.clone(),
         fields,
         vis,

From adb5763317ae1e6a3d6eacf9671e4435403c027a Mon Sep 17 00:00:00 2001
From: joshua-maros <60271685+joshua-maros@users.noreply.github.com>
Date: Tue, 13 Jun 2023 20:50:01 -0500
Subject: [PATCH 6/8] Fix

---
 ouroboros_macro/src/generate/struc.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ouroboros_macro/src/generate/struc.rs b/ouroboros_macro/src/generate/struc.rs
index 28f6197..bc9b5d4 100644
--- a/ouroboros_macro/src/generate/struc.rs
+++ b/ouroboros_macro/src/generate/struc.rs
@@ -20,7 +20,7 @@ pub fn create_actual_struct_def(info: &StructInfo) -> Result<TokenStream, Error>
     let internal_ident = &info.internal_ident;
     Ok(quote! {
         #visibility struct #ident <#generic_params> #generic_where {
-            actual_data: [u8; ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()],
+            actual_data: ::core::mem::MaybeUninit<[u8; ::core::mem::size_of::<#internal_ident<#(#generic_args),*>>()]>,
             _alignment: [#internal_ident<#(#generic_args),*>; 0],
             #(#fields),*
         }

From 79abb08555daf29372f540222af6df399f6f0457 Mon Sep 17 00:00:00 2001
From: joshua-maros <60271685+joshua-maros@users.noreply.github.com>
Date: Tue, 13 Jun 2023 21:06:21 -0500
Subject: [PATCH 7/8] Cleanup

---
 README.md                                     |  4 ++++
 examples/Cargo.toml                           |  4 ++--
 examples/src/fail_tests/auto_covariant.stderr |  7 ++++++-
 examples/src/ok_tests.rs                      | 10 ++++++++--
 ouroboros/Cargo.toml                          |  4 ++--
 ouroboros/src/lib.rs                          |  2 +-
 ouroboros_macro/Cargo.toml                    |  2 +-
 ouroboros_macro/src/generate/drop.rs          |  5 +----
 ouroboros_macro/src/info_structures.rs        | 14 +++++++-------
 9 files changed, 32 insertions(+), 20 deletions(-)

diff --git a/README.md b/README.md
index 8e5af71..77a90cf 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,10 @@ Dual licensed under MIT / Apache 2.0.
 While this crate is `no_std` compatible, it still requires the `alloc` crate.
 
 Version notes:
+- Version `0.17.0` fixed a potential soundness issue, but removed support for
+  template parameters in the process. Lifetime parameters are still supported.
+  As of 2023-06-13, the compiler is practically sound with 0.16 but this may
+  stop being the case at any time and without warning.
 - Version `0.13.0` and later contain checks for additional situations which
   cause undefined behavior if not caught.
 - Version `0.11.0` and later place restrictions on derive macros, earlier
diff --git a/examples/Cargo.toml b/examples/Cargo.toml
index 8243ddf..9f5739e 100644
--- a/examples/Cargo.toml
+++ b/examples/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros_examples"
-version = "0.16.0"
+version = "0.17.0"
 authors = ["Joshua Maros <joshua-maros@github.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
@@ -21,7 +21,7 @@ std = []
 __tokio = ["tokio", "std"]
 
 [dependencies]
-ouroboros = { version = "0.16.0", path = "../ouroboros" }
+ouroboros = { version = "0.17.0", path = "../ouroboros" }
 tokio = { version = "1.27.0", features = [ "macros", "rt" ], optional = true }
 
 [dev-dependencies]
diff --git a/examples/src/fail_tests/auto_covariant.stderr b/examples/src/fail_tests/auto_covariant.stderr
index 66b8ecf..54f2ae2 100644
--- a/examples/src/fail_tests/auto_covariant.stderr
+++ b/examples/src/fail_tests/auto_covariant.stderr
@@ -1,6 +1,11 @@
 error: Ouroboros cannot automatically determine if this type is covariant.
 
-       If it is covariant, it should be legal to convert any instance of that type to an instance of that type where all usages of 'this are replaced with a smaller lifetime. For example, Box<&'this i32> is covariant because it is legal to use it as a Box<&'a i32> where 'this: 'a. In contrast, Fn(&'this i32) cannot be used as Fn(&'a i32).
+       As an example, a Box<&'this ()> is covariant because it can be used as a
+       Box<&'smaller ()> for any lifetime smaller than 'this. In contrast,
+       a Fn(&'this ()) is not covariant because it cannot be used as a
+       Fn(&'smaller ()). In general, values that are safe to use with smaller
+       lifetimes than they were defined with are covariant, breaking this
+       guarantee means the value is not covariant.
 
        To resolve this error, add #[covariant] or #[not_covariant] to the field.
   --> src/fail_tests/auto_covariant.rs:11:12
diff --git a/examples/src/ok_tests.rs b/examples/src/ok_tests.rs
index 7a08614..78a04cb 100644
--- a/examples/src/ok_tests.rs
+++ b/examples/src/ok_tests.rs
@@ -1,4 +1,4 @@
-use alloc::boxed::Box;
+use alloc::{boxed::Box, borrow::ToOwned};
 use core::fmt::Debug;
 
 use ouroboros::self_referencing;
@@ -31,7 +31,7 @@ struct ChainedAndUndocumented {
     data: i32,
     #[borrows(data)]
     ref1: &'this i32,
-    #[borrows(data)]
+    #[borrows(ref1)]
     ref2: &'this &'this i32,
 }
 
@@ -245,6 +245,12 @@ fn single_lifetime() {
         #[borrows(external)]
         internal: &'this &'a str,
     }
+
+    let external = "Hello world!".to_owned();
+    let instance = Struct::new(&external, |field_ref| field_ref);
+    drop(instance.borrow_external());
+    drop(instance.borrow_internal());
+    drop(instance);
 }
 
 #[test]
diff --git a/ouroboros/Cargo.toml b/ouroboros/Cargo.toml
index 3c256b4..83845c5 100644
--- a/ouroboros/Cargo.toml
+++ b/ouroboros/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros"
-version = "0.16.0"
+version = "0.17.0"
 authors = ["Joshua Maros <joshua-maros@github.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
@@ -11,7 +11,7 @@ repository = "https://github.com/joshua-maros/ouroboros"
 
 [dependencies]
 aliasable = "0.1.3"
-ouroboros_macro = { version = "0.16.0", path = "../ouroboros_macro" }
+ouroboros_macro = { version = "0.17.0", path = "../ouroboros_macro" }
 static_assertions = "1.1.0"
 
 [features]
diff --git a/ouroboros/src/lib.rs b/ouroboros/src/lib.rs
index 13870da..db6d5c5 100644
--- a/ouroboros/src/lib.rs
+++ b/ouroboros/src/lib.rs
@@ -123,7 +123,7 @@
 ///         immutable: i32,
 ///         mutable: i32,
 ///         #[borrows(immutable, mut mutable)]
-///         #[covariant]
+///         #[not_covariant]
 ///         complex_data: ComplexData<'this, 'this>,
 ///     }
 ///
diff --git a/ouroboros_macro/Cargo.toml b/ouroboros_macro/Cargo.toml
index 5b2a56b..3d501b6 100644
--- a/ouroboros_macro/Cargo.toml
+++ b/ouroboros_macro/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros_macro"
-version = "0.16.0"
+version = "0.17.0"
 authors = ["Joshua Maros <joshua-maros@github.com>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"
diff --git a/ouroboros_macro/src/generate/drop.rs b/ouroboros_macro/src/generate/drop.rs
index a78d5e1..1cfb7f2 100644
--- a/ouroboros_macro/src/generate/drop.rs
+++ b/ouroboros_macro/src/generate/drop.rs
@@ -1,7 +1,4 @@
-use crate::{
-    info_structures::StructInfo,
-    utils::{self, replace_this_with_lifetime},
-};
+use crate::info_structures::StructInfo;
 use proc_macro2::TokenStream;
 use quote::quote;
 use syn::Error;
diff --git a/ouroboros_macro/src/info_structures.rs b/ouroboros_macro/src/info_structures.rs
index f3e4a54..7e7fd5c 100644
--- a/ouroboros_macro/src/info_structures.rs
+++ b/ouroboros_macro/src/info_structures.rs
@@ -13,13 +13,13 @@ pub struct Options {
 }
 
 impl Options {
-    pub fn documentation_to_tokens(&self, documentation: &str) -> TokenStream {
-        if self.do_no_doc {
-            quote! { #[doc(hidden)] }
-        } else {
-            quote! { #[doc=#documentation] }
-        }
-    }
+    // pub fn documentation_to_tokens(&self, documentation: &str) -> TokenStream {
+    //     if self.do_no_doc {
+    //         quote! { #[doc(hidden)] }
+    //     } else {
+    //         quote! { #[doc=#documentation] }
+    //     }
+    // }
 }
 
 #[derive(Clone, Copy, PartialEq)]

From 80b3e760a767a2525dfa79f17bdeaf284cd4485a Mon Sep 17 00:00:00 2001
From: joshua-maros <60271685+joshua-maros@users.noreply.github.com>
Date: Wed, 14 Jun 2023 18:29:54 -0500
Subject: [PATCH 8/8] Consistent tense

---
 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 77a90cf..c9763a3 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ Dual licensed under MIT / Apache 2.0.
 While this crate is `no_std` compatible, it still requires the `alloc` crate.
 
 Version notes:
-- Version `0.17.0` fixed a potential soundness issue, but removed support for
+- Version `0.17.0` fixes a potential soundness issue, but removes support for
   template parameters in the process. Lifetime parameters are still supported.
   As of 2023-06-13, the compiler is practically sound with 0.16 but this may
   stop being the case at any time and without warning.