rust: pin-init: add code blocks to `[try_][pin_]init!` macros

Allow writing `_: { /* any number of statements */ }` in initializers to
run arbitrary code during initialization.

    try_init!(MyStruct {
        _: {
            if check_something() {
                return Err(MyError);
            }
        },
        foo: Foo::new(val),
        _: {
            println!("successfully initialized `MyStruct`");
        },
    })

Tested-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Benno Lossin <lossin@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/rust/pin-init/src/lib.rs b/rust/pin-init/src/lib.rs
index 2d0d9fd12524..dd553212836e 100644
--- a/rust/pin-init/src/lib.rs
+++ b/rust/pin-init/src/lib.rs
@@ -740,6 +740,8 @@ macro_rules! stack_try_pin_init {
 /// As already mentioned in the examples above, inside of `pin_init!` a `struct` initializer with
 /// the following modifications is expected:
 /// - Fields that you want to initialize in-place have to use `<-` instead of `:`.
+/// - You can use `_: { /* run any user-code here */ },` anywhere where you can place fields in
+///   order to run arbitrary code.
 /// - In front of the initializer you can write `&this in` to have access to a [`NonNull<Self>`]
 ///   pointer named `this` inside of the initializer.
 /// - Using struct update syntax one can place `..Zeroable::init_zeroed()` at the very end of the