rust: init: change the generated name of guard variables

The initializers created by the `[try_][pin_]init!` macros utilize the
guard pattern to drop already initialized fields, when initialization

rust: init: change the generated name of guard variables

The initializers created by the `[try_][pin_]init!` macros utilize the
guard pattern to drop already initialized fields, when initialization
fails mid-way. These guards are generated to have the same name as the
field that they handle. To prevent namespacing issues [1] when the
field name is the same as e.g. a constant name, add `__` as a prefix
and `_guard` as the suffix.

[ Gary says:

"Here's the simplified example:

```
macro_rules! f {
() => {
let a = 1;
let _: u32 = a;
}
}

const a: u64 = 1;

fn main() {
f!();
}
```

The `a` in `f` have a different hygiene so normally it is scoped to the
macro expansion and wouldn't escape. Interestingly a constant is still
preferred despite the hygiene so constants escaped into the macro,
leading to the error."

- Miguel ]

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/rust-for-linux/1e8a2a1f-abbf-44ba-8344-705a9cbb1627@proton.me/ [1]
Link: https://lore.kernel.org/r/20240403194321.88716-1-benno.lossin@proton.me
[ Added Benno's link and Gary's simplified example. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: macros: allow generic parameter default values in `#[pin_data]`

Add support for generic parameters defaults in `#[pin_data]` by using
the newly introduced `decl_generics` instead of the `impl_

rust: macros: allow generic parameter default values in `#[pin_data]`

Add support for generic parameters defaults in `#[pin_data]` by using
the newly introduced `decl_generics` instead of the `impl_generics`.

Before this would not compile:

#[pin_data]
struct Foo<const N: usize = 0> {
// ...
}

because it would be expanded to this:

struct Foo<const N: usize = 0> {
// ...
}

const _: () = {
struct __ThePinData<const N: usize = 0> {
__phantom: ::core::marker::PhantomData<fn(Foo<N>) -> Foo<N>>,
}
impl<const N: usize = 0> ::core::clone::Clone for __ThePinData<N> {
fn clone(&self) -> Self {
*self
}
}

// [...] rest of expansion omitted
};

The problem is with the `impl<const N: usize = 0>`, since that is
invalid Rust syntax. It should not mention the default value at all,
since default values only make sense on type definitions.

The new `impl_generics` do not contain the default values, thus
generating correct Rust code.

This is used by the next commit that puts `#[pin_data]` on
`kernel::workqueue::Work`.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240309155243.482334-2-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: update expanded macro explanation

The previous patches changed the internals of the macros resulting in
the example expanded code being outdated. This patch updates the example
and only

rust: init: update expanded macro explanation

The previous patches changed the internals of the macros resulting in
the example expanded code being outdated. This patch updates the example
and only changes documentation.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230814084602.25699-14-benno.lossin@proton.me
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: add support for arbitrary paths in init macros

Previously only `ident` and generic types were supported in the
`{try_}{pin_}init!` macros. This patch allows arbitrary path fragments,
so

rust: init: add support for arbitrary paths in init macros

Previously only `ident` and generic types were supported in the
`{try_}{pin_}init!` macros. This patch allows arbitrary path fragments,
so for example `Foo::Bar` but also very complex paths such as
`<Foo as Baz>::Bar::<0, i32>`.

Internally this is accomplished by using `path` fragments. Due to some
peculiar declarative macro limitations, we have to "forget" certain
additional parsing information in the token trees. This is achieved by
using the `paste!` proc macro. It does not actually modify the input,
since no `[< >]` will be present in the input, so it just strips the
information held by declarative macros. For example, if a declarative
macro takes `$t:path` as its input, it cannot sensibly propagate this to
a macro that takes `$($p:tt)*` as its input, since the `$t` token will
only be considered one `tt` token for the second macro. If we first pipe
the tokens through `paste!`, then it parses as expected.

Suggested-by: Asahi Lina <lina@asahilina.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230814084602.25699-10-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: add `..Zeroable::zeroed()` syntax for zeroing all missing fields

Add the struct update syntax to the init macros, but only for
`..Zeroable::zeroed()`. Adding this at the end of the struc

rust: init: add `..Zeroable::zeroed()` syntax for zeroing all missing fields

Add the struct update syntax to the init macros, but only for
`..Zeroable::zeroed()`. Adding this at the end of the struct initializer
allows one to omit fields from the initializer, these fields will be
initialized with 0x00 set to every byte. Only types that implement the
`Zeroable` trait can utilize this.

Suggested-by: Asahi Lina <lina@asahilina.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230814084602.25699-8-benno.lossin@proton.me
[ Rebased on `rust-next` and cleaned a few trivial nits. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: make initializer values inaccessible after initializing

Previously the init macros would create a local variable with the name
and hygiene of the field that is being initialized to store

rust: init: make initializer values inaccessible after initializing

Previously the init macros would create a local variable with the name
and hygiene of the field that is being initialized to store the value of
the field. This would override any user defined variables. For example:
```
struct Foo {
a: usize,
b: usize,
}
let a = 10;
let foo = init!(Foo{
a: a + 1, // This creates a local variable named `a`.
b: a, // This refers to that variable!
});
let foo = Box::init!(foo)?;
assert_eq!(foo.a, 11);
assert_eq!(foo.b, 11);
```

This patch changes this behavior, so the above code would panic at the
last assertion, since `b` would have value 10.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230814084602.25699-7-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: wrap type checking struct initializers in a closure

In the implementation of the init macros there is a `if false` statement
that type checks the initializer to ensure every field is ini

rust: init: wrap type checking struct initializers in a closure

In the implementation of the init macros there is a `if false` statement
that type checks the initializer to ensure every field is initialized.
Since the next patch has a stack variable to store the struct, the
function might allocate too much memory on debug builds. Putting the
struct into a closure that is never executed ensures that even in debug
builds no stack overflow error is caused. In release builds this was not
a problem since the code was optimized away due to the `if false`.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230814084602.25699-6-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: make guards in the init macros hygienic

Use hygienic identifiers for the guards instead of the field names. This
makes the init macros feel more like normal struct initializers, since
as

rust: init: make guards in the init macros hygienic

Use hygienic identifiers for the guards instead of the field names. This
makes the init macros feel more like normal struct initializers, since
assigning identifiers with the name of a field does not create
conflicts.

Also change the internals of the guards, no need to make the `forget`
function `unsafe`, since users cannot access the guards anyways. Now the
guards are carried directly on the stack and have no extra `Cell<bool>`
field that marks if they have been forgotten or not, instead they are
just forgotten via `mem::forget`.

Suggested-by: Asahi Lina <lina@asahilina.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230814084602.25699-5-benno.lossin@proton.me
[ Cleaned a few trivial nits. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: add derive macro for `Zeroable`

Add a derive proc-macro for the `Zeroable` trait. The macro supports
structs where every field implements the `Zeroable` trait. This way
`unsafe` implementation

rust: add derive macro for `Zeroable`

Add a derive proc-macro for the `Zeroable` trait. The macro supports
structs where every field implements the `Zeroable` trait. This way
`unsafe` implementations can be avoided.

The macro is split into two parts:
- a proc-macro to parse generics into impl and ty generics,
- a declarative macro that expands to the impl block.

Suggested-by: Asahi Lina <lina@asahilina.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Link: https://lore.kernel.org/r/20230814084602.25699-4-benno.lossin@proton.me
[ Added `ignore` to the `lib.rs` example and cleaned trivial nit. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: make `#[pin_data]` compatible with conditional compilation of fields

This patch allows one to write
```
#[pin_data]
pub struct Foo {
#[cfg(CONFIG_BAR)]
a: Bar,
#[cfg(not(CONF

rust: init: make `#[pin_data]` compatible with conditional compilation of fields

This patch allows one to write
```
#[pin_data]
pub struct Foo {
#[cfg(CONFIG_BAR)]
a: Bar,
#[cfg(not(CONFIG_BAR))]
a: Baz,
}
```
Before, this would result in a compile error, because `#[pin_data]`
would generate two functions named `a` for both fields unconditionally.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230814084602.25699-3-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: consolidate init macros

Merges the implementations of `try_init!` and `try_pin_init!`. These two
macros are very similar, but use different traits. The new macro
`__init_internal!` that

rust: init: consolidate init macros

Merges the implementations of `try_init!` and `try_pin_init!`. These two
macros are very similar, but use different traits. The new macro
`__init_internal!` that is now the implementation for both takes these
traits as parameters.

This change does not affect any users, as no public API has been
changed, but it should simplify maintaining the init macros.

Reviewed-by: Björn Roy Baron <bjorn3_gh@protonmail.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230814084602.25699-2-benno.lossin@proton.me
[ Cleaned a couple trivial nits. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: update macro expansion example in docs

Also improve the explaining comments.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: A

rust: init: update macro expansion example in docs

Also improve the explaining comments.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Link: https://lore.kernel.org/r/20230424081112.99890-4-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: add `PinnedDrop` trait and macros

The `PinnedDrop` trait that facilitates destruction of pinned types.
It has to be implemented via the `#[pinned_drop]` macro, since the
`drop` function

rust: init: add `PinnedDrop` trait and macros

The `PinnedDrop` trait that facilitates destruction of pinned types.
It has to be implemented via the `#[pinned_drop]` macro, since the
`drop` function should not be called by normal code, only by other
destructors. It also only works on structs that are annotated with
`#[pin_data(PinnedDrop)]`.

Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Link: https://lore.kernel.org/r/20230408122429.1103522-10-y86-dev@protonmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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rust: init: add initialization macros

Add the following initializer macros:
- `#[pin_data]` to annotate structurally pinned fields of structs,
needed for `pin_init!` and `try_pin_init!` to select

rust: init: add initialization macros

Add the following initializer macros:
- `#[pin_data]` to annotate structurally pinned fields of structs,
needed for `pin_init!` and `try_pin_init!` to select the correct
initializer of fields.
- `pin_init!` create a pin-initializer for a struct with the
`Infallible` error type.
- `try_pin_init!` create a pin-initializer for a struct with a custom
error type (`kernel::error::Error` is the default).
- `init!` create an in-place-initializer for a struct with the
`Infallible` error type.
- `try_init!` create an in-place-initializer for a struct with a custom
error type (`kernel::error::Error` is the default).

Also add their needed internal helper traits and structs.

Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Link: https://lore.kernel.org/r/20230408122429.1103522-8-y86-dev@protonmail.com
[ Fixed three typos. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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