From 7cee8ba40d91923b1771c998f719cb3020100129 Mon Sep 17 00:00:00 2001
From: Rintaro Ishizaki <rishizaki@apple.com>
Date: Fri, 10 Oct 2025 14:48:50 -0700
Subject: [PATCH] [Macros] Termination signal for executable plugin

Exit the plugin when it receives an empty message.

rdar://160820381
---
 .../StandardIOMessageConnection.swift                         | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Sources/SwiftCompilerPluginMessageHandling/StandardIOMessageConnection.swift b/Sources/SwiftCompilerPluginMessageHandling/StandardIOMessageConnection.swift
index 9ad7cc46542..74bb6768d38 100644
--- a/Sources/SwiftCompilerPluginMessageHandling/StandardIOMessageConnection.swift
+++ b/Sources/SwiftCompilerPluginMessageHandling/StandardIOMessageConnection.swift
@@ -152,6 +152,10 @@ public struct StandardIOMessageConnection: MessageConnection {
 
     // Read the JSON payload.
     let count = Int(UInt64(littleEndian: header))
+    // Empty message is a termination signal.
+    if count == 0 {
+      return nil
+    }
     let data = UnsafeMutableRawBufferPointer.allocate(byteCount: count, alignment: 1)
     defer { data.deallocate() }
     try _read(into: data)