From 0d4c1431f58ca10300a323cb4a3b7e472da11551 Mon Sep 17 00:00:00 2001
From: Yacin Tmimi <yacintmimi@gmail.com>
Date: Fri, 11 Aug 2023 09:02:04 -0400
Subject: [PATCH] Improve formatting of empty macro_rules! definitions

Fixes 5882
---
 src/macros.rs              | 24 ++++++++++++++++++++++++
 tests/source/issue_5882.rs |  7 +++++++
 tests/target/issue_5882.rs |  7 +++++++
 3 files changed, 38 insertions(+)
 create mode 100644 tests/source/issue_5882.rs
 create mode 100644 tests/target/issue_5882.rs

diff --git a/src/macros.rs b/src/macros.rs
index e9a298a2769..88d26358b87 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -379,6 +379,23 @@ fn handle_vec_semi(
     }
 }
 
+fn rewrite_empty_macro_def_body(
+    context: &RewriteContext<'_>,
+    span: Span,
+    shape: Shape,
+) -> Option<String> {
+    // Create an empty, dummy `ast::Block` representing an empty macro body
+    let block = ast::Block {
+        stmts: vec![].into(),
+        id: rustc_ast::node_id::DUMMY_NODE_ID,
+        rules: ast::BlockCheckMode::Default,
+        span: span,
+        tokens: None,
+        could_be_bare_literal: false,
+    };
+    block.rewrite(context, shape)
+}
+
 pub(crate) fn rewrite_macro_def(
     context: &RewriteContext<'_>,
     shape: Shape,
@@ -419,6 +436,13 @@ pub(crate) fn rewrite_macro_def(
         shape
     };
 
+    if parsed_def.branches.len() == 0 {
+        let lo = context.snippet_provider.span_before(span, "{");
+        result += " ";
+        result += &rewrite_empty_macro_def_body(context, span.with_lo(lo), shape)?;
+        return Some(result);
+    }
+
     let branch_items = itemize_list(
         context.snippet_provider,
         parsed_def.branches.iter(),
diff --git a/tests/source/issue_5882.rs b/tests/source/issue_5882.rs
new file mode 100644
index 00000000000..e36f9965438
--- /dev/null
+++ b/tests/source/issue_5882.rs
@@ -0,0 +1,7 @@
+macro_rules!foo{}
+macro_rules!bar{/*comment*/}
+macro_rules!baz{//comment
+}
+macro_rules!foobar{
+//comment
+}
diff --git a/tests/target/issue_5882.rs b/tests/target/issue_5882.rs
new file mode 100644
index 00000000000..565fb434a6a
--- /dev/null
+++ b/tests/target/issue_5882.rs
@@ -0,0 +1,7 @@
+macro_rules! foo {}
+macro_rules! bar { /*comment*/ }
+macro_rules! baz { //comment
+}
+macro_rules! foobar {
+    //comment
+}