From c7747c42c1e30e4b084645cb44948f1f5be21813 Mon Sep 17 00:00:00 2001
From: Veetaha <gersoh3@gmail.com>
Date: Tue, 2 Sep 2025 10:48:15 +0000
Subject: [PATCH 1/2] Add missing lifetime replacement for generic param decls
 on `derive(IntoFuture)` impl block

---
 .../builder_derives/into_future.rs            |  4 ++
 .../integration/builder/attr_into_future.rs   | 51 +++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/bon-macros/src/builder/builder_gen/builder_derives/into_future.rs b/bon-macros/src/builder/builder_gen/builder_derives/into_future.rs
index ecd869ce..aa29ef22 100644
--- a/bon-macros/src/builder/builder_gen/builder_derives/into_future.rs
+++ b/bon-macros/src/builder/builder_gen/builder_derives/into_future.rs
@@ -163,6 +163,10 @@ impl BuilderGenCtx {
             original_lifetimes: &original_lifetimes,
         };
 
+        for decl in &mut new_generics_decl {
+            replace_lifetimes.visit_generic_param_mut(decl);
+        }
+
         let mut new_where_clause = where_clause.clone();
 
         if let Some(where_clause) = &mut new_where_clause {
diff --git a/bon/tests/integration/builder/attr_into_future.rs b/bon/tests/integration/builder/attr_into_future.rs
index 171c0bc1..ed095e62 100644
--- a/bon/tests/integration/builder/attr_into_future.rs
+++ b/bon/tests/integration/builder/attr_into_future.rs
@@ -151,6 +151,30 @@ mod tests {
 
             let &Dummy = assert_send(builder).await;
         }
+
+        #[tokio::test]
+        async fn complex_generics() {
+            struct Dummy;
+
+            #[builder(derive(IntoFuture(Box)))]
+            async fn sut<'a: 'b, 'b, T: Sync + 'a + 'b, U: Sync + 'a, const N: usize>(
+                x1: &'a T,
+                x2: &'b U,
+            ) -> (&'a T, &'b U, usize) {
+                async {}.await;
+                (x1, x2, N)
+            }
+
+            // Store the dummy struct in local variables to make sure no `'static`
+            // lifetime promotion happens
+            let local_x1 = Dummy;
+            let local_x2 = Dummy;
+
+            let builder = sut::<_, _, 42>().x1(&local_x1).x2(&local_x2);
+
+            let (&Dummy, &Dummy, usize) = assert_send(builder).await;
+            assert_eq!(usize, 42);
+        }
     }
 
     mod test_method {
@@ -253,5 +277,32 @@ mod tests {
 
             let _: &Dummy = assert_send(builder).await;
         }
+
+        #[tokio::test]
+        async fn complex_generics() {
+            struct Dummy;
+
+            #[bon]
+            impl Dummy {
+                #[builder(derive(IntoFuture(Box)))]
+                async fn sut<'a: 'b, 'b, T: Sync + 'a + 'b, U: Sync + 'a, const N: usize>(
+                    x1: &'a T,
+                    x2: &'b U,
+                ) -> (&'a T, &'b U, usize) {
+                    async {}.await;
+                    (x1, x2, N)
+                }
+            }
+
+            // Store the dummy struct in local variables to make sure no `'static`
+            // lifetime promotion happens
+            let local_x1 = Dummy;
+            let local_x2 = Dummy;
+
+            let builder = Dummy::sut().x1(&local_x1).x2(&local_x2);
+
+            let (&Dummy, &Dummy, usize) = assert_send(builder).await;
+            assert_eq!(usize, 42);
+        }
     }
 }

From be64fea9979ef8aee9ca42b0ae3ee52f38dd47a9 Mon Sep 17 00:00:00 2001
From: Veetaha <gersoh3@gmail.com>
Date: Tue, 2 Sep 2025 10:51:31 +0000
Subject: [PATCH 2/2] Fix test

---
 bon/tests/integration/builder/attr_into_future.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bon/tests/integration/builder/attr_into_future.rs b/bon/tests/integration/builder/attr_into_future.rs
index ed095e62..a8b6d1d2 100644
--- a/bon/tests/integration/builder/attr_into_future.rs
+++ b/bon/tests/integration/builder/attr_into_future.rs
@@ -299,7 +299,7 @@ mod tests {
             let local_x1 = Dummy;
             let local_x2 = Dummy;
 
-            let builder = Dummy::sut().x1(&local_x1).x2(&local_x2);
+            let builder = Dummy::sut::<_, _, 42>().x1(&local_x1).x2(&local_x2);
 
             let (&Dummy, &Dummy, usize) = assert_send(builder).await;
             assert_eq!(usize, 42);