From 3017b3e7d4da702c8b1e2dbfb9657b7517e108b8 Mon Sep 17 00:00:00 2001
From: Brad King <brad.king@kitware.com>
Date: Wed, 10 Nov 2021 11:25:12 -0500
Subject: cmLocalGenerator: Simplify unity source copy-if-different logic

---
 Source/cmLocalGenerator.cxx | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/Source/cmLocalGenerator.cxx b/Source/cmLocalGenerator.cxx
index 66b49e0..2b5b711 100644
--- a/Source/cmLocalGenerator.cxx
+++ b/Source/cmLocalGenerator.cxx
@@ -2813,20 +2813,15 @@ std::string cmLocalGenerator::WriteUnitySource(
   cmValue beforeInclude, cmValue afterInclude, std::string filename) const
 {
   cmValue uniqueIdName = target->GetProperty("UNITY_BUILD_UNIQUE_ID");
-  const std::string filename_tmp = cmStrCat(filename, ".tmp");
-  {
-    cmGeneratedFileStream file(
-      filename_tmp, false,
-      target->GetGlobalGenerator()->GetMakefileEncoding());
-    file << "/* generated by CMake */\n\n";
-
-    for (cmSourceFile* sf : sources) {
-      RegisterUnitySources(target, sf, filename);
-      IncludeFileInUnitySources(file, sf->ResolveFullPath(), beforeInclude,
-                                afterInclude, uniqueIdName);
-    }
+  cmGeneratedFileStream file(
+    filename, false, target->GetGlobalGenerator()->GetMakefileEncoding());
+  file.SetCopyIfDifferent(true);
+  file << "/* generated by CMake */\n\n";
+  for (cmSourceFile* sf : sources) {
+    RegisterUnitySources(target, sf, filename);
+    IncludeFileInUnitySources(file, sf->ResolveFullPath(), beforeInclude,
+                              afterInclude, uniqueIdName);
   }
-  cmSystemTools::MoveFileIfDifferent(filename_tmp, filename);
   return filename;
 }
 
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