Fix ICE when combining #[eii] with #[core::contracts::ensures]

compiler/rustc_expand/src/expand.rs

@@ -814,6 +814,27 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         {
                             rustc_parse::fake_token_stream_for_item(&self.cx.sess.psess, item_inner)
                         }
+                        Annotatable::Item(item_inner) if item_inner.tokens.is_none() => {
+                            rustc_parse::fake_token_stream_for_item(&self.cx.sess.psess, item_inner)
+                        }
+                        // When a function has EII implementations attached (via `eii_impls`),
+                        // use fake tokens so the pretty-printer re-emits the EII attribute
+                        // (e.g. `#[hello]`) in the token stream. Without this, the EII
+                        // attribute is lost during the token roundtrip performed by
+                        // `AttrProcMacro` expanders like `contracts::requires/ensures`,
+                        // breaking the EII link on the resulting re-parsed item.
+                        Annotatable::Item(item_inner)
+                            if matches!(&item_inner.kind,
+                                ItemKind::Fn(f) if !f.eii_impls.is_empty()) =>
+                        {
+                            rustc_parse::fake_token_stream_for_item(&self.cx.sess.psess, item_inner)
+                        }
+                        Annotatable::ForeignItem(item_inner) if item_inner.tokens.is_none() => {
+                            rustc_parse::fake_token_stream_for_foreign_item(
+                                &self.cx.sess.psess,
+                                item_inner,
+                            )
+                        }
                         _ => item.to_tokens(),
                     };
                     let attr_item = attr.get_normal_item();

compiler/rustc_parse/src/lib.rs

@@ -257,6 +257,15 @@ pub fn fake_token_stream_for_item(psess: &ParseSess, item: &ast::Item) -> TokenS
     unwrap_or_emit_fatal(source_str_to_stream(psess, filename, source, Some(item.span)))
 }
 
+pub fn fake_token_stream_for_foreign_item(
+    psess: &ParseSess,
+    item: &ast::ForeignItem,
+) -> TokenStream {
+    let source = pprust::foreign_item_to_string(item);
+    let filename = FileName::macro_expansion_source_code(&source);
+    unwrap_or_emit_fatal(source_str_to_stream(psess, filename, source, Some(item.span)))
+}
+
 pub fn fake_token_stream_for_crate(psess: &ParseSess, krate: &ast::Crate) -> TokenStream {
     let source = pprust::crate_to_string_for_macros(krate);
     let filename = FileName::macro_expansion_source_code(&source);

tests/ui/eii/eii_impl_with_contract.rs

@@ -0,0 +1,20 @@
+//@ run-pass
+//@ ignore-backends: gcc
+//@ ignore-windows
+
+#![feature(extern_item_impls)]
+#![feature(contracts)]
+#![allow(incomplete_features)]
+
+#[eii(hello)]
+fn hello(x: u64);
+
+#[hello]
+#[core::contracts::requires(x > 0)]
+fn hello_impl(x: u64) {
+    println!("{x:?}")
+}
+
+fn main() {
+    hello(42);
+}

tests/ui/eii/ice_contract_attr_on_eii_generated_item.rs

@@ -0,0 +1,11 @@
+//@ compile-flags: --crate-type rlib
+
+#![feature(extern_item_impls)]
+#![feature(contracts)]
+#![allow(incomplete_features)]
+
+#[eii]
+#[core::contracts::ensures]
+//~^ ERROR contract annotations is only supported in functions with bodies
+//~| ERROR contract annotations can only be used on functions
+fn implementation();

tests/ui/eii/ice_contract_attr_on_eii_generated_item.stderr

@@ -0,0 +1,14 @@
+error: contract annotations is only supported in functions with bodies
+  --> $DIR/ice_contract_attr_on_eii_generated_item.rs:8:1
+   |
+LL | #[core::contracts::ensures]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: contract annotations can only be used on functions
+  --> $DIR/ice_contract_attr_on_eii_generated_item.rs:8:1
+   |
+LL | #[core::contracts::ensures]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+