Fix span edition for 2024 RPIT coming from an external macro

This fixes a problem where code generated by an external macro with an
RPIT would end up using the call-site edition instead of the macro's
edition for the RPIT. When used from a 2024 crate, this caused the code
to change behavior to the 2024 capturing rules, which we don't want.

This was caused by the impl-trait lowering code would replace the span
with one marked with `DesugaringKind::OpaqueTy` desugaring. However, it
was also overriding the edition of the span with the edition of the
local crate. Instead it should be using the edition of the span itself.

Fixes https://github.com/rust-lang/rust/issues/132917

compiler/rustc_ast_lowering/src/lib.rs

@@ -738,7 +738,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         allow_internal_unstable: Option<Lrc<[Symbol]>>,
     ) -> Span {
         self.tcx.with_stable_hashing_context(|hcx| {
-            span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
+            span.mark_with_reason(allow_internal_unstable, reason, span.edition(), hcx)
         })
     }
 

tests/ui/impl-trait/precise-capturing/external-macro.rs

@@ -6,12 +6,11 @@
 //@ aux-crate: no_use_macro=no-use-macro.rs
 //@ edition: 2024
 //@ compile-flags:-Z unstable-options
+//@ check-pass
 
 no_use_pm::pm_rpit!{}
-//~^ ERROR: cannot borrow `x` as mutable
 
 no_use_macro::macro_rpit!{}
-//~^ ERROR: cannot borrow `x` as mutable
 
 fn main() {
     let mut x = vec![];
@@ -19,11 +18,9 @@ fn main() {
 
     let element = test_pm(&x);
     x.push(2);
-    //~^ ERROR: cannot borrow `x` as mutable
     println!("{element}");
 
     let element = test_mbe(&x);
     x.push(2);
-    //~^ ERROR: cannot borrow `x` as mutable
     println!("{element}");
 }

tests/ui/impl-trait/precise-capturing/external-macro.stderr

@@ -1,89 +0,0 @@
-error[E0502]: cannot borrow `x` as mutable because it is also borrowed as immutable
-  --> $DIR/external-macro.rs:10:1
-   |
-LL | no_use_pm::pm_rpit!{}
-   | ^^^^^^^^^^^^^^^^^^^^^
-   | |
-   | mutable borrow occurs here
-   | immutable borrow occurs here
-   | immutable borrow later used here
-   |
-note: this call may capture more lifetimes than intended, because Rust 2024 has adjusted the `impl Trait` lifetime capture rules
-  --> $DIR/external-macro.rs:10:1
-   |
-LL | no_use_pm::pm_rpit!{}
-   | ^^^^^^^^^^^^^^^^^^^^^
-   = note: this error originates in the macro `no_use_pm::pm_rpit` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: use the precise capturing `use<...>` syntax to make the captures explicit
-   |
-LL | no_use_pm::pm_rpit!{} + use<>
-   |                       +++++++
-
-error[E0502]: cannot borrow `x` as mutable because it is also borrowed as immutable
-  --> $DIR/external-macro.rs:13:1
-   |
-LL | no_use_macro::macro_rpit!{}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   | |
-   | mutable borrow occurs here
-   | immutable borrow occurs here
-   | immutable borrow later used here
-   |
-note: this call may capture more lifetimes than intended, because Rust 2024 has adjusted the `impl Trait` lifetime capture rules
-  --> $DIR/external-macro.rs:13:1
-   |
-LL | no_use_macro::macro_rpit!{}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: this error originates in the macro `no_use_macro::macro_rpit` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: use the precise capturing `use<...>` syntax to make the captures explicit
-  --> $DIR/auxiliary/no-use-macro.rs:7:60
-   |
-LL |         fn test_mbe(x: &Vec<i32>) -> impl std::fmt::Display + use<> {
-   |                                                             +++++++
-
-error[E0502]: cannot borrow `x` as mutable because it is also borrowed as immutable
-  --> $DIR/external-macro.rs:21:5
-   |
-LL |     let element = test_pm(&x);
-   |                           -- immutable borrow occurs here
-LL |     x.push(2);
-   |     ^^^^^^^^^ mutable borrow occurs here
-LL |
-LL |     println!("{element}");
-   |               --------- immutable borrow later used here
-   |
-note: this call may capture more lifetimes than intended, because Rust 2024 has adjusted the `impl Trait` lifetime capture rules
-  --> $DIR/external-macro.rs:20:19
-   |
-LL |     let element = test_pm(&x);
-   |                   ^^^^^^^^^^^
-help: use the precise capturing `use<...>` syntax to make the captures explicit
-   |
-LL | no_use_pm::pm_rpit!{} + use<>
-   |                       +++++++
-
-error[E0502]: cannot borrow `x` as mutable because it is also borrowed as immutable
-  --> $DIR/external-macro.rs:26:5
-   |
-LL |     let element = test_pm(&x);
-   |                           -- immutable borrow occurs here
-...
-LL |     x.push(2);
-   |     ^^^^^^^^^ mutable borrow occurs here
-...
-LL | }
-   | - immutable borrow might be used here, when `element` is dropped and runs the destructor for type `impl std::fmt::Display`
-   |
-note: this call may capture more lifetimes than intended, because Rust 2024 has adjusted the `impl Trait` lifetime capture rules
-  --> $DIR/external-macro.rs:20:19
-   |
-LL |     let element = test_pm(&x);
-   |                   ^^^^^^^^^^^
-help: use the precise capturing `use<...>` syntax to make the captures explicit
-   |
-LL | no_use_pm::pm_rpit!{} + use<>
-   |                       +++++++
-
-error: aborting due to 4 previous errors
-
-For more information about this error, try `rustc --explain E0502`.