8000 Relax the limitations in `#[attr(key = value)]` when the values only accept literals · Issue #1331 · dbus2/zbus · GitHub
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Relax the limitations in #[attr(key = value)] when the values only accept literals #1331

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yuan-y-chang opened this issue Apr 12, 2025 · 3 comments
Open

Relax the limitations in #[attr(key = value)] when the values only accept literals #1331

yuan-y-chang opened this issue Apr 12, 2025 · 3 comments
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enhancement New feature or request zbus_macros

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@yuan-y-chang
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Sometimes we want to define and use some constant variables in many places.

const INTERFACE: &str = "org.zbus.MyGreeter1";
const SERVICE: &str = "org.zbus.MyGreeter";
const OBJ_PATH: &str = "/org/zbus/MyGreeter";

const VERSION_NAME: &str = "eVer";

#[zbus::proxy(
    interface = INTERFACE,
    default_service = SERVICE,
    default_path = OBJ_PATH
)]
trait Greeter {
    #[zbus(property, name = VERSION_NAME)]
    fn version(&self) -> zbus::Result<u32>;
}

But shows

error: attribute `interface`'s value must be a literal
 --> src\main.rs:2:17
  |
2 |     interface = INTERFACE,
  |                 ^^^^^^^^^

error: attribute `name`'s value must be a literal
  --> src\main.rs:12:29
   |
12 |     #[zbus(property, name = VERSION_NAME)]
   |                             ^^^^^^^^^^^^

Can we relax them to expr for string consistency?
@zeenix
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zeenix commented Apr 12, 2025

@yuan-y-chang sure thing. PR welcome!

@yuan-y-chang
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I guess the type-check mechanisms in the def_attrs macro should be removed?

Change

zbus/zvariant_utils/src/macros.rs

Lines 257 to 259 in 8fff8e2

(@attr_ty str) => {::std::option::Option<::std::string::String>};
(@attr_ty bool) => {::std::option::Option<bool>};
(@attr_ty [str]) => {::std::option::Option<::std::vec::Vec<::std::string::String>>};

to

(@attr_ty str) => {::std::option::Option<::syn::Expr>}; 
(@attr_ty bool) => {::std::option::Option<::syn::Expr>}; 
(@attr_ty [str]) => {::std::option::Option<::std::vec::Vec<::syn::Expr>>};

When parsing the attribute arguments,

zbus/zvariant_utils/src/macros.rs

Lines 267 to 279 in 8fff8e2

(@match_attr_with $attr_name:ident, $meta:ident, $self:ident, $matched:expr) => {
if let ::std::option::Option::Some(value) = $matched? {
if $self.$attr_name.is_some() {
return ::std::result::Result::Err(::syn::Error::new(
$meta.span(),
::std::concat!("duplicate `", ::std::stringify!($attr_name), 8FF8 "` attribute")
));
}
$self.$attr_name = ::std::option::Option::Some(value.value());
return Ok(());
}
};

The fragment $matched can store the Exprs directly and paste later. We can check the type with the Rust compiler.

@zeenix
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zeenix commented Apr 13, 2025

@yuan-y-chang I'm really sorry but I won't have to time to mentor you on this.

@zeenix zeenix added enhancement New feature or request zbus_macros labels May 4, 2025
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