Synthesize a TokenStream for StmtKind::Empty

Fixes #80760

compiler/rustc_parse/src/lib.rs

@@ -257,7 +257,16 @@ pub fn nt_to_tokenstream(
     let tokens = match *nt {
         Nonterminal::NtItem(ref item) => prepend_attrs(sess, &item.attrs, nt, item.tokens.as_ref()),
         Nonterminal::NtBlock(ref block) => convert_tokens(block.tokens.as_ref()),
-        Nonterminal::NtStmt(ref stmt) => prepend_attrs(sess, stmt.attrs(), nt, stmt.tokens()),
+        Nonterminal::NtStmt(ref stmt) => {
+            let do_prepend = |tokens| prepend_attrs(sess, stmt.attrs(), nt, tokens);
+            if let ast::StmtKind::Empty = stmt.kind {
+                let tokens: TokenStream =
+                    tokenstream::TokenTree::token(token::Semi, stmt.span).into();
+                do_prepend(Some(&LazyTokenStream::new(tokens)))
+            } else {
+                do_prepend(stmt.tokens())
+            }
+        }
         Nonterminal::NtPat(ref pat) => convert_tokens(pat.tokens.as_ref()),
         Nonterminal::NtTy(ref ty) => convert_tokens(ty.tokens.as_ref()),
         Nonterminal::NtIdent(ident, is_raw) => {

src/test/ui/proc-macro/issue-80760-empty-stmt.rs

@@ -0,0 +1,26 @@
+// check-pass
+// aux-build:test-macros.rs
+// compile-flags: -Z span-debug
+
+#![no_std] // Don't load unnecessary hygiene information from std
+extern crate std;
+
+#[macro_use]
+extern crate test_macros;
+
+macro_rules! empty_stmt {
+    ($s:stmt) => {
+        print_bang!($s);
+
+        // Currently, all attributes are ignored
+        // on an empty statement
+        #[print_attr]
+        #[rustc_dummy(first)]
+        #[rustc_dummy(second)]
+        $s
+    }
+}
+
+fn main() {
+    empty_stmt!(;);
+}

src/test/ui/proc-macro/issue-80760-empty-stmt.stdout

@@ -0,0 +1,14 @@
+PRINT-BANG INPUT (DISPLAY): ;
+PRINT-BANG INPUT (DEBUG): TokenStream [
+    Group {
+        delimiter: None,
+        stream: TokenStream [
+            Punct {
+                ch: ';',
+                spacing: Alone,
+                span: $DIR/issue-80760-empty-stmt.rs:25:17: 25:18 (#0),
+            },
+        ],
+        span: $DIR/issue-80760-empty-stmt.rs:13:21: 13:23 (#4),
+    },
+]