Rollup merge of #133080 - ehuss:edition-desugar-span, r=compiler-errors

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/auxiliary/no-use-macro.rs

@@ -0,0 +1,20 @@
+// A macro_rules macro in 2015 that has an RPIT without `use<>` that would
+// cause a problem with 2024 capturing rules.
+
+#[macro_export]
+macro_rules! macro_rpit {
+    () => {
+        fn test_mbe(x: &Vec<i32>) -> impl std::fmt::Display {
+            x[0]
+        }
+
+        pub fn from_mbe() {
+            let mut x = vec![];
+            x.push(1);
+
+            let element = test_mbe(&x);
+            x.push(2);
+            println!("{element}");
+        }
+    };
+}

tests/ui/impl-trait/precise-capturing/auxiliary/no-use-pm.rs

@@ -0,0 +1,29 @@
+// A proc-macro in 2015 that has an RPIT without `use<>` that would cause a
+// problem with 2024 capturing rules.
+
+//@ force-host
+//@ no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro]
+pub fn pm_rpit(input: TokenStream) -> TokenStream {
+    "fn test_pm(x: &Vec<i32>) -> impl std::fmt::Display {
+    x[0]
+}
+
+pub fn from_pm() {
+    let mut x = vec![];
+    x.push(1);
+
+    let element = test_pm(&x);
+    x.push(2);
+    println!(\"{element}\");
+}
+"
+    .parse()
+    .unwrap()
+}

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

@@ -0,0 +1,26 @@
+// Tests that code generated from an external macro (MBE and proc-macro) that
+// has an RPIT will not fail when the call-site is 2024.
+// https://github.com/rust-lang/rust/issues/132917
+
+//@ aux-crate: no_use_pm=no-use-pm.rs
+//@ aux-crate: no_use_macro=no-use-macro.rs
+//@ edition: 2024
+//@ compile-flags:-Z unstable-options
+//@ check-pass
+
+no_use_pm::pm_rpit!{}
+
+no_use_macro::macro_rpit!{}
+
+fn main() {
+    let mut x = vec![];
+    x.push(1);
+
+    let element = test_pm(&x);
+    x.push(2);
+    println!("{element}");
+
+    let element = test_mbe(&x);
+    x.push(2);
+    println!("{element}");
+}