Add an attribute that makes the spans from a macro edition 2021, and fix pin on edition 2024 with it

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -191,6 +191,7 @@ pub enum AttributeKind {
     },
     MacroTransparency(Transparency),
     Repr(ThinVec<(ReprAttr, Span)>),
+    RustcMacroEdition2021,
     Stability {
         stability: Stability,
         /// Span of the `#[stable(...)]` or `#[unstable(...)]` attribute

compiler/rustc_attr_data_structures/src/lib.rs

@@ -182,21 +182,18 @@ macro_rules! find_attr {
     }};
 
     ($attributes_list: expr, $pattern: pat $(if $guard: expr)? => $e: expr) => {{
-        fn check_attribute_iterator<'a>(_: &'_ impl IntoIterator<Item = &'a rustc_hir::Attribute>) {}
-        check_attribute_iterator(&$attributes_list);
-
-        let find_attribute = |iter| {
+        'done: {
             for i in $attributes_list {
+                let i: &rustc_hir::Attribute = i;
                 match i {
                     rustc_hir::Attribute::Parsed($pattern) $(if $guard)? => {
-                        return Some($e);
+                        break 'done Some($e);
                     }
                     _ => {}
                 }
             }
 
             None
-        };
-        find_attribute($attributes_list)
+        }
     }};
 }

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -28,6 +28,7 @@ pub(crate) mod cfg;
 pub(crate) mod confusables;
 pub(crate) mod deprecation;
 pub(crate) mod repr;
+pub(crate) mod rustc;
 pub(crate) mod stability;
 pub(crate) mod transparency;
 pub(crate) mod util;

compiler/rustc_attr_parsing/src/attributes/rustc.rs

@@ -0,0 +1,19 @@
+use rustc_attr_data_structures::AttributeKind;
+use rustc_span::sym;
+
+use super::{AcceptContext, SingleAttributeParser};
+use crate::parser::ArgParser;
+
+pub(crate) struct RustcMacroEdition2021Parser;
+
+// FIXME(jdonszelmann): make these proper diagnostics
+impl SingleAttributeParser for RustcMacroEdition2021Parser {
+    const PATH: &'static [rustc_span::Symbol] = &[sym::rustc_macro_edition_2021];
+
+    fn on_duplicate(_cx: &crate::context::AcceptContext<'_>, _first_span: rustc_span::Span) {}
+
+    fn convert(_cx: &AcceptContext<'_>, args: &ArgParser<'_>) -> Option<AttributeKind> {
+        assert!(args.no_args());
+        Some(AttributeKind::RustcMacroEdition2021)
+    }
+}

compiler/rustc_attr_parsing/src/context.rs

@@ -15,6 +15,7 @@ use crate::attributes::allow_unstable::{AllowConstFnUnstableParser, AllowInterna
 use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::deprecation::DeprecationParser;
 use crate::attributes::repr::ReprParser;
+use crate::attributes::rustc::RustcMacroEdition2021Parser;
 use crate::attributes::stability::{
     BodyStabilityParser, ConstStabilityIndirectParser, ConstStabilityParser, StabilityParser,
 };
@@ -76,6 +77,7 @@ attribute_groups!(
         // tidy-alphabetical-start
         Single<ConstStabilityIndirectParser>,
         Single<DeprecationParser>,
+        Single<RustcMacroEdition2021Parser>,
         Single<TransparencyParser>,
         // tidy-alphabetical-end
     ];

compiler/rustc_feature/src/builtin_attrs.rs

@@ -661,6 +661,14 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         "`rustc_never_type_options` is used to experiment with never type fallback and work on \
          never type stabilization, and will never be stable"
     ),
+    rustc_attr!(
+        rustc_macro_edition_2021,
+        Normal,
+        template!(Word),
+        ErrorFollowing,
+        EncodeCrossCrate::No,
+        "makes spans in this macro edition 2021"
+    ),
 
     // ==========================================================================
     // Internal attributes: Runtime related:

compiler/rustc_resolve/src/macros.rs

@@ -8,7 +8,7 @@ use std::sync::Arc;
 use rustc_ast::expand::StrippedCfgItem;
 use rustc_ast::{self as ast, Crate, NodeId, attr};
 use rustc_ast_pretty::pprust;
-use rustc_attr_parsing::StabilityLevel;
+use rustc_attr_parsing::{AttributeKind, StabilityLevel, find_attr};
 use rustc_data_structures::intern::Interned;
 use rustc_errors::{Applicability, StashKey};
 use rustc_expand::base::{
@@ -1125,6 +1125,13 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             edition,
         );
 
+        // The #[rustc_macro_edition_2021] attribute is used by the pin!() macro
+        // as a temporary workaround for a regression in expressiveness in Rust 2024.
+        // See https://github.com/rust-lang/rust/issues/138718.
+        if find_attr!(attrs.iter(), AttributeKind::RustcMacroEdition2021) {
+            ext.edition = Edition::Edition2021;
+        }
+
         if let Some(builtin_name) = ext.builtin_name {
             // The macro was marked with `#[rustc_builtin_macro]`.
             if let Some(builtin_macro) = self.builtin_macros.get_mut(&builtin_name) {

compiler/rustc_span/src/symbol.rs

@@ -1793,6 +1793,7 @@ symbols! {
         rustc_lint_opt_ty,
         rustc_lint_query_instability,
         rustc_lint_untracked_query_information,
+        rustc_macro_edition_2021,
         rustc_macro_transparency,
         rustc_main,
         rustc_mir,

library/core/src/pin.rs

@@ -1943,6 +1943,7 @@ unsafe impl<T: ?Sized> PinCoerceUnsized for *mut T {}
 #[stable(feature = "pin_macro", since = "1.68.0")]
 #[rustc_macro_transparency = "semitransparent"]
 #[allow_internal_unstable(unsafe_pin_internals)]
+#[cfg_attr(not(bootstrap), rustc_macro_edition_2021)]
 pub macro pin($value:expr $(,)?) {
     // This is `Pin::new_unchecked(&mut { $value })`, so, for starters, let's
     // review such a hypothetical macro (that any user-code could define):

library/coretests/tests/pin.rs

@@ -34,6 +34,9 @@ fn pin_const() {
     }
 
     pin_mut_const();
+
+    // Check that we accept a Rust 2024 $expr.
+    std::pin::pin!(const { 1 });
 }
 
 #[allow(unused)]
@@ -81,3 +84,14 @@ mod pin_coerce_unsized {
         arg
     }
 }
+
+#[test]
+#[cfg(not(bootstrap))]
+fn temp_lifetime() {
+    // Check that temporary lifetimes work as in Rust 2021.
+    // Regression test for https://github.com/rust-lang/rust/issues/138596
+    match std::pin::pin!(foo(&mut 0)) {
+        _ => {}
+    }
+    async fn foo(_: &mut usize) {}
+}