Correctly generate `impl` blocks for traits with generics

diff --git a/c-bindings-gen/src/main.rs b/c-bindings-gen/src/main.rs
index 536e4420bda0faa405636ce4452c60750b57dee5..279424e1fde81e07ed9de1d64138ee7a3cbb5764 100644 (file)
--- a/c-bindings-gen/src/main.rs
+++ b/c-bindings-gen/src/main.rs
@@ -597,7 +597,16 @@ fn writeln_trait<'a, 'b, W: std::io::Write>(w: &mut W, t: &'a syn::ItemTrait, ty
                (s, i) => {
                        if let Some(supertrait) = types.crate_types.traits.get(s) {
                                let resolver = get_module_type_resolver!(s, types.crate_libs, types.crate_types);
-                               writeln!(w, "impl {} for {} {{", s, trait_name).unwrap();
+
+                               // Blindly assume that the same imports where `supertrait` is defined are also
+                               // imported here. This will almost certainly break at some point, but it should be
+                               // a compilation failure when it does so.
+                               write!(w, "impl").unwrap();
+                               maybe_write_lifetime_generics(w, &supertrait.generics, types);
+                               write!(w, " {}", s).unwrap();
+                               maybe_write_generics(w, &supertrait.generics, types, false);
+                               writeln!(w, " for {} {{", trait_name).unwrap();
+
                                impl_trait_for_c!(supertrait, format!(".{}", i), &resolver);
                                writeln!(w, "}}").unwrap();
                        } else {