From fef37ecc78f58f459982bc247d47cd05790e29c5 Mon Sep 17 00:00:00 2001
From: Max Desiatov <m_desiatov@apple.com>
Date: Sat, 15 Apr 2023 10:25:28 +0100
Subject: [PATCH] TSCBasic: deprecate `localFileSystem` setter (#401)

This global should never be mutable, especially when using concurrency.
---
 Sources/TSCBasic/FileSystem.swift | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/Sources/TSCBasic/FileSystem.swift b/Sources/TSCBasic/FileSystem.swift
index c11fad16..9184e27d 100644
--- a/Sources/TSCBasic/FileSystem.swift
+++ b/Sources/TSCBasic/FileSystem.swift
@@ -1162,8 +1162,19 @@ public final class RerootedFileSystemView: FileSystem {
 // `underlyingFileSystem` is required to be `Sendable`.
 extension RerootedFileSystemView: @unchecked Sendable {}
 
+private var _localFileSystem: any FileSystem = LocalFileSystem()
+
 /// Public access to the local FS proxy.
-public var localFileSystem: FileSystem = LocalFileSystem()
+public var localFileSystem: any FileSystem {
+    get {
+         return _localFileSystem
+    }
+
+    @available(*, deprecated, message: "This global should never be mutable and is supposed to be read-only. Deprecated in Apr 2023.")
+    set {
+        _localFileSystem = newValue
+    }
+}
 
 // `LocalFileSystem` doesn't hold any internal state and all of its underlying operations are blocking.
 extension LocalFileSystem: @unchecked Sendable {}