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fix(derive): avoid higher-ranked bounds on plain-field WriteToAsyncRef #1

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fix(derive): avoid higher-ranked bounds on plain-field WriteToAsyncRef #1

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8 changes: 4 additions & 4 deletions dir-structure-macros/src/dir_structure_async/write_to_async_ref.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -93,13 +93,13 @@ pub(super) fn expand_dir_structure_for_field(
async_write_ref_future.clauses_ref_vfs = true;
let bound = vec![
parse_quote! {
for<'trivial> #actual_field_ty_perform: ::dir_structure::traits::asy::WriteToAsyncRef<'vfs, Vfs>

@dnbln dnbln Sep 9, 2026 •
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This bound is still necessary when #actual_field_ty_perform isn't a trivial type, as its part of the bounds that make it on the impl WriteToAsyncRef for YourStructure where ..., and if YourStructure has generics itself that might become a problem (edit: this comment applies to the other bound with the future, I see this one is still there).

I'd do this a bit differently:

diff --git a/dir-structure-macros/src/dir_structure_async/write_to_async_ref.rs b/dir-structure-macros/src/dir_structure_async/write_to_async_ref.rs
index 27754ac..fb397ef 100644
--- a/dir-structure-macros/src/dir_structure_async/write_to_async_ref.rs
+++ b/dir-structure-macros/src/dir_structure_async/write_to_async_ref.rs
@@ -91,18 +91,27 @@ pub(super) fn expand_dir_structure_for_field(
             }
             None => {
                 async_write_ref_future.clauses_ref_vfs = true;
+                let write_to_async_ref_bound: WherePredicate = parse_quote! {
+                    #actual_field_ty_perform: ::dir_structure::traits::asy::WriteToAsyncRef<'vfs, Vfs>
+                };
+                let fut_clause = quote! {
+                    <#actual_field_ty_perform as ::dir_structure::traits::asy::WriteToAsyncRef<'vfs, Vfs>>::Future<'fut>: ::std::future::Future<Output = ::dir_structure::error::VfsResult<(), Vfs>> + ::std::marker::Unpin + 'fut
+                };
                 let bound = vec![
+                    write_to_async_ref_bound.clone(),
                     parse_quote! {
-                        for<'trivial> #actual_field_ty_perform: ::dir_structure::traits::asy::WriteToAsyncRef<'vfs, Vfs>
+                        for<'fut> #fut_clause
                     },
+                ];
+                async_write_ref_future.clauses.extend([
+                    write_to_async_ref_bound,
                     parse_quote! {
-                        for<'trivial> <#actual_field_ty_perform as ::dir_structure::traits::asy::WriteToAsyncRef<'vfs, Vfs>>::Future<'fut>: ::std::future::Future<Output = ::dir_structure::error::VfsResult<(), Vfs>> + ::std::marker::Send + ::std::marker::Unpin + 'fut
+                        #fut_clause
                     },
-                ];
-                async_write_ref_future.clauses.extend(bound.clone());
-                async_write_ref_future.clauses.push(parse_quote! {
-                    'vfs: 'fut
-                });
+                    parse_quote! {
+                        'vfs: 'fut
+                    },
+                ]);
 
                 (
                     quote! {

@KiSetsuFu-PuLiN KiSetsuFu-PuLiN Sep 12, 2026

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Thanks for the review and the suggestions! This is my first PR, so I truly appreciate your guidance and apologize for any non-standard practices.
Also, I have to say this library is fantastic, it's been a huge help for my project's protocol design.

I've pushed the requested changes here.

One thing to note: in my real-world use case, this specific implementation causes compilation times to spike to ~20 minutes.
For comparison, the version in this branch finishes in under 1 minute.

I’ve included a test script to help you reproduce/verify this compilation bottleneck.
dir-structure.rs.sh

@dnbln dnbln Sep 23, 2026

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I'll have to look into this a bit more

},
parse_quote! {
for<'trivial> <#actual_field_ty_perform as ::dir_structure::traits::asy::WriteToAsyncRef<'vfs, Vfs>>::Future<'fut>: ::std::future::Future<Output = ::dir_structure::error::VfsResult<(), Vfs>> + ::std::marker::Send + ::std::marker::Unpin + 'fut
#actual_field_ty_perform: ::dir_structure::traits::asy::WriteToAsyncRef<'vfs, Vfs>
},
];
async_write_ref_future.clauses.extend(bound.clone());
async_write_ref_future.clauses.push(parse_quote! {
<#actual_field_ty_perform as ::dir_structure::traits::asy::WriteToAsyncRef<'vfs, Vfs>>::Future<'fut>: ::std::future::Future<Output = ::dir_structure::error::VfsResult<(), Vfs>> + ::std::marker::Unpin + 'fut
});
async_write_ref_future.clauses.push(parse_quote! {
'vfs: 'fut
});
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