Allow other attributes in #[pin_data] structs

When using a macro with custom attributes in a `#[pin_data]` struct it
can mess up the generated `__Unpin` struct.

This commit catches all other (not just `#[pin]`) attributes, moves the
`#[cfg]` one in `$accum` (so that it is used for both the original
struct and the generated `__Unpin` one), and keeps all other (custom,
documentation, etc.) only in the original struct.

With this commit a struct can use both #[pin] and other custom
attributes, allowing combining multiple attribute macros without
clashing.

To keep this functionality this commit also adds a test with a custom
attribute that fails without this fix.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>

Author: mkletzan

Cargo.lock

@@ -32,6 +32,7 @@ trybuild = { version = "1.0", features = ["diff"] }
 macrotest = "1.0"
 # needed for macrotest, have to enable verbatim feature to be able to format `&raw` expressions.
 prettyplease = { version = "0.2", features = ["verbatim"] }
+dummy = { path = "tests/dummy" }
 
 [lints.rust]
 non_ascii_idents = "deny"

Cargo.toml

@@ -779,8 +779,9 @@ macro_rules! __pin_data {
         @ty_generics($($ty_generics:tt)*),
         @decl_generics($($decl_generics:tt)*),
         @where($($whr:tt)*),
-        // Some other attribute, just put it into `$accum`.
-        @fields_munch(#[$($attr:tt)*] $($rest:tt)*),
+        // The #[cfg] attributes are kept for those members that are not
+        // removed, so we need to keep them.
+        @fields_munch(#[cfg $($attr:tt)*] $($rest:tt)*),
         @pinned($($pinned:tt)*),
         @not_pinned($($not_pinned:tt)*),
         @fields($($fields:tt)*),
@@ -800,7 +801,41 @@ macro_rules! __pin_data {
             @pinned($($pinned)*),
             @not_pinned($($not_pinned)*),
             @fields($($fields)*),
-            @accum($($accum)* #[$($attr)*]),
+            @accum($($accum)* #[cfg $($attr)*]),
+            @is_pinned($($is_pinned)?),
+            @pinned_drop($($pinned_drop)?),
+        );
+    };
+    (find_pinned_fields:
+        @struct_attrs($($struct_attrs:tt)*),
+        @vis($vis:vis),
+        @name($name:ident),
+        @impl_generics($($impl_generics:tt)*),
+        @ty_generics($($ty_generics:tt)*),
+        @decl_generics($($decl_generics:tt)*),
+        @where($($whr:tt)*),
+        // Some other attribute, just put it into `$fields`
+        @fields_munch(#[$($attr:tt)*] $($rest:tt)*),
+        @pinned($($pinned:tt)*),
+        @not_pinned($($not_pinned:tt)*),
+        @fields($($fields:tt)*),
+        @accum($($accum:tt)*),
+        @is_pinned($($is_pinned:ident)?),
+        @pinned_drop($($pinned_drop:ident)?),
+    ) => {
+        $crate::__pin_data!(find_pinned_fields:
+            @struct_attrs($($struct_attrs)*),
+            @vis($vis),
+            @name($name),
+            @impl_generics($($impl_generics)*),
+            @ty_generics($($ty_generics)*),
+            @decl_generics($($decl_generics)*),
+            @where($($whr)*),
+            @fields_munch($($rest)*),
+            @pinned($($pinned)*),
+            @not_pinned($($not_pinned)*),
+            @fields($($fields)* #[$($attr)*]),
+            @accum($($accum)*),
             @is_pinned($($is_pinned)?),
             @pinned_drop($($pinned_drop)?),
         );

src/macros.rs

@@ -0,0 +1,12 @@
+[package]
+name = "dummy"
+version = "0.0.0"
+edition = "2024"
+
+license = "MIT OR Apache-2.0"
+description = "Proc macro only for test reproduction."
+
+publish = false
+
+[lib]
+proc-macro = true

tests/dummy/Cargo.lock

@@ -0,0 +1,4 @@
+#[proc_macro_derive(Dummy, attributes(dummy_attr))]
+pub fn derive_device(_: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    proc_macro::TokenStream::new()
+}

tests/dummy/Cargo.toml

@@ -0,0 +1,23 @@
+#![cfg_attr(not(RUSTC_LINT_REASONS_IS_STABLE), feature(lint_reasons))]
+
+use pinned_init::*;
+use dummy::Dummy;
+
+#[pin_data]
+#[derive(Dummy)]
+struct Pointless {
+    #[pin]
+    #[dummy_attr]
+    #[cfg(test)]
+    member: i8,
+    #[pin]
+    #[dummy_attr]
+    #[cfg(not(test))]
+    member: u8,
+}
+
+#[test]
+fn multiple_attributes() {
+    stack_pin_init!(let p = init!(Pointless { member: 0 }));
+    println!("{}", p.member);
+}