Suboptimal diagnostic spans for macros that regurgitate attributes

Code

macro_rules! tuple_const {
    ($(#[$attr:meta])* $vis:vis const $NAME:ident: $ty:ty = $expr:expr;) => {
        $(#[$attr])* $vis const $NAME: ($ty,) = ($expr,);
    }
}

tuple_const! {
    #[inline]
    pub const FOO: u32 = 17;
}

Current output

error[E0518]: attribute should be applied to function or closure
  --> src/lib.rs:3:11
   |
3  |           $(#[$attr])* $vis const $NAME: ($ty,) = ($expr,);
   |             ^^^^^^^^   ------------------------------------ not a function or closure
...
7  | / tuple_const! {
8  | |     #[inline]
9  | |     pub const FOO: u32 = 17;
10 | | }
   | |_- in this macro invocation
   |
   = note: this error originates in the macro `tuple_const` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0518`.

Desired output

error: `#[inline]` attribute cannot be used on constants
 --> src/lib.rs:8:5
  |
8 |     #[inline]
  |       ^^^^^^
  |
  = help: `#[inline]` can only be applied to functions

Rationale and extra context

It’s common for macro_rules! macros that parse and emit items to contain a matcher of the form $(#[$attr:meta])* in order to parse the attributes, and then to re-emit the attributes using $(#[$attr])* in the macro body. The standard library’s thread_local! is an example of such a macro.

Diagnostic messages involving attributes generally point to the entire attribute span, including the surrounding #[…]. However, for invocations of macros that use the technique described above, the #[ and ] are considered to originate from the macro. This means that diagnostic messages relating to these macro invocations will point to the entire macro invocation, not the specific attribute that the diagnostic is concerned with.

If the compiler were to use a slightly smaller span for attribute diagnostics (excluding the outer #[…]`) whenever possible, or at least in cases like this one, that would resolve the issue.

Rust Version

rustc 1.91.0-nightly (02c7b1a7a 2025-09-13)
binary: rustc
commit-hash: 02c7b1a7ac1d739663878030510508372e46f254
commit-date: 2025-09-13
host: x86_64-unknown-linux-gnu
release: 1.91.0-nightly
LLVM version: 21.1.1

@rustbot label A-attributes A-macros D-imprecise-spans

Reproduce the diagnostic using the macro_rules! example in src/lib.rs, then trace the compiler's attribute diagnostic span handling for attributes regurgitated by macros. Done means the error points to the invocation's #[inline] attribute and reports that it cannot be used on constants, rather than pointing to the macro definition.