[PATCH 1/3] rust: pin-init: internal: init: allow reborrow of `Pin<&mut T>` bindings

[Gary Guo]

Use `let mut` for created bindings of initialized field, so `Pin<&mut T>`
bindings may be reborrowed in subsequent initializers or code blocks.

Without `let mut`, attempt to reborrow can produce error (and also a
confusing fix):

    error[E0596]: cannot borrow `gpu` as mutable, as it is not declared as mutable
       --> drivers/gpu/nova-core/driver.rs:129:17
        |
    129 |                 gpu.as_mut().run_selftests(pdev);
        |                 ^^^ cannot borrow as mutable
        |
    help: consider changing this to be mutable                                                                                                                                                                                  |
    119 |             mut gpu <- Gpu::new(
        |             +++

    error: aborting due to 1 previous error

Reported-by: Danilo Krummrich <dakr@xxxxxxxxxx>
Closes: https://lore.kernel.org/nova-gpu/DLQXWXRP3P1J.28SLFOJJQ2EDK@xxxxxxxxxx/
Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
---
 rust/pin-init/internal/src/init.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/rust/pin-init/internal/src/init.rs b/rust/pin-init/internal/src/init.rs
index c5b5a0ce5c4e..4e77c7af86f9 100644
--- a/rust/pin-init/internal/src/init.rs
+++ b/rust/pin-init/internal/src/init.rs
@@ -446,7 +446,8 @@ fn init_fields(fields: &Punctuated<InitializerField, Token![,]>, pinned: bool) -
                 // Allow `non_snake_case` since the same warning is going to be reported for the
                 // struct field.
                 #[allow(unused_variables, non_snake_case)]
-                let #ident = #guard.let_binding();
+                // Include `mut` so that `Pin<&mut T>` bindings can be reborrowed via `.as_mut()`.
+                let mut #ident = #guard.let_binding();
             },
             Member::Unnamed(_) => quote!(),
         };

-- 
2.54.0