Revert "Revert "Failed attempt to fix problems.""

This reverts commit b4d49cd.
someguynamedjosh · May 14, 2023 · c889114 · c889114
1 parent 13b2af8
commit c889114
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Showing 14 changed files with 97 additions and 27 deletions.
diff --git 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 <[email protected]>"]
 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
@@ -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
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros"
-version = "0.15.7"
+version = "0.16.0"
 authors = ["Joshua Maros <[email protected]>"]
 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
@@ -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
@@ -1,6 +1,6 @@
 [package]
 name = "ouroboros_macro"
-version = "0.15.7"
+version = "0.16.0"
 authors = ["Joshua Maros <[email protected]>"]
 edition = "2018"
 license = "MIT OR Apache-2.0"

diff --git 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
@@ -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
@@ -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
@@ -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
@@ -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 });
@@ -108,13 +109,15 @@ pub fn make_with_all_function(
     } else {
         quote! { #[doc(hidden)] }
     };
+    let generic_args = info.generic_arguments();
     let fn_defs = quote! {
         #documentation
         #[inline(always)]
         #visibility fn with <'outer_borrow, ReturnType>(
             &'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
@@ -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
@@ -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
@@ -9,14 +9,15 @@ 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,
     },
     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
@@ -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,