[PATCH 2/8] rust: pin-init: internal: init: set span location of guards

[Gary Guo <gary@garyguo.net>]

Set the span location of the guards to point to the identifier. The
generated diagnostic is still not ideal, as ideally it points the place
where the identifier is used rather than the identifier name in
initializer, but is still an improvement to status quo.

Before the change:

    error[E0505]: cannot move out of value because it is borrowed
      --> tests/ui/compile-fail/init/accessor_lifetime.rs:8:13
       |
     8 |       let _ = init!(Foo {
       |  _____________^
     9 | |         x: 0,
    10 | |         _: {
    11 | |             let _: &'static usize = x;
       | |                    -------------- type annotation requires that borrow lasts for `'static`
    12 | |         },
    13 | |     });
       | |      ^
       | |      |
       | |______move out of value occurs here
       |        borrow of value occurs here

After the change:

    error[E0505]: cannot move out of value because it is borrowed
      --> tests/ui/compile-fail/init/accessor_lifetime.rs:9:9
       |
     9 |         x: 0,
       |         ^
       |         |
       |         move out of value occurs here
       |         borrow of value occurs here
    10 |         _: {
    11 |             let _: &'static usize = x;
       |                    -------------- type annotation requires that borrow lasts for `'static`

Signed-off-by: Gary Guo <gary@garyguo.net>
---
 rust/pin-init/internal/src/init.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rust/pin-init/internal/src/init.rs b/rust/pin-init/internal/src/init.rs
index f0b23d0311ac..80e4dc068d2e 100644
--- a/rust/pin-init/internal/src/init.rs
+++ b/rust/pin-init/internal/src/init.rs
@@ -413,7 +413,7 @@ fn init_fields(fields: &Punctuated<InitializerField, Token![,]>, pinned: bool) -
         };
 
         // `mixed_site` ensures that the guard is not accessible to the user-controlled code.
-        let guard = format_ident!("__{ident}_guard", span = Span::mixed_site());
+        let guard = format_ident!("__{ident}_guard", span = span);
         let full_span = kind.span().resolved_at(Span::mixed_site());
 
         let init = match kind {

-- 
2.54.0