From 5eaf1e1be289245267263536f5464e40d2a677c0 Mon Sep 17 00:00:00 2001
From: Rolf Eike Beer <eb@emlix.com>
Date: Mon, 9 Sep 2019 09:09:48 +0200
Subject: cmSystemTools: introduce MoveFileIfDifferent()

---
 Source/cmSystemTools.cxx | 12 ++++++++++++
 Source/cmSystemTools.h   |  4 ++++
 2 files changed, 16 insertions(+)

diff --git a/Source/cmSystemTools.cxx b/Source/cmSystemTools.cxx
index b7287d9..074faa5 100644
--- a/Source/cmSystemTools.cxx
+++ b/Source/cmSystemTools.cxx
@@ -855,6 +855,18 @@ bool cmSystemTools::RenameFile(const std::string& oldname,
 #endif
 }
 
+void cmSystemTools::MoveFileIfDifferent(const std::string& source,
+                                        const std::string& destination)
+{
+  if (FilesDiffer(source, destination)) {
+    if (RenameFile(source, destination)) {
+      return;
+    }
+    CopyFileAlways(source, destination);
+  }
+  RemoveFile(source);
+}
+
 std::string cmSystemTools::ComputeFileHash(const std::string& source,
                                            cmCryptoHash::Algo algo)
 {
diff --git a/Source/cmSystemTools.h b/Source/cmSystemTools.h
index 863db3f..8ca4939 100644
--- a/Source/cmSystemTools.h
+++ b/Source/cmSystemTools.h
@@ -131,6 +131,10 @@ public:
   static bool RenameFile(const std::string& oldname,
                          const std::string& newname);
 
+  //! Rename a file if contents are different, delete the source otherwise
+  static void MoveFileIfDifferent(const std::string& source,
+                                  const std::string& destination);
+
   //! Compute the hash of a file
   static std::string ComputeFileHash(const std::string& source,
                                      cmCryptoHash::Algo algo);
-- 
cgit v0.12


From 5b96fd5b81bde4655e471a31bf0fc579c1d10136 Mon Sep 17 00:00:00 2001
From: Rolf Eike Beer <eb@emlix.com>
Date: Mon, 9 Sep 2019 10:34:08 +0200
Subject: use cmSystemTools::MoveFileIfDifferent()

This is better than doing CopyFileIfDifferent() followed by RemoveFile() in
two ways:

 - it is more efficient, as it avoids disk I/O for the data, even if the
   files here are usually small
 - it is atomic, so an abort during the copy will not leave a destination file
   with partial data behind
---
 Source/cmGeneratorTarget.cxx       | 6 ++----
 Source/cmLocalGenerator.cxx        | 3 +--
 Source/cmUseMangledMesaCommand.cxx | 3 +--
 3 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index b4706a3..f1c48cc 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -3417,8 +3417,7 @@ std::string cmGeneratorTarget::GetPchHeader(const std::string& config,
         file << pchEpilogue << "\n";
       }
     }
-    cmSystemTools::CopyFileIfDifferent(filename_tmp, filename);
-    cmSystemTools::RemoveFile(filename_tmp);
+    cmSystemTools::MoveFileIfDifferent(filename_tmp, filename);
   }
   return inserted.first->second;
 }
@@ -3451,8 +3450,7 @@ std::string cmGeneratorTarget::GetPchSource(const std::string& config,
       cmGeneratedFileStream file(filename_tmp);
       file << "/* generated by CMake */\n";
     }
-    cmSystemTools::CopyFileIfDifferent(filename_tmp, filename);
-    cmSystemTools::RemoveFile(filename_tmp);
+    cmSystemTools::MoveFileIfDifferent(filename_tmp, filename);
   }
   return inserted.first->second;
 }
diff --git a/Source/cmLocalGenerator.cxx b/Source/cmLocalGenerator.cxx
index 9152e94..3d8c3fb 100644
--- a/Source/cmLocalGenerator.cxx
+++ b/Source/cmLocalGenerator.cxx
@@ -2275,8 +2275,7 @@ void cmLocalGenerator::AddUnityBuild(cmGeneratorTarget* target,
           }
         }
       }
-      cmSystemTools::CopyFileIfDifferent(filename_tmp, filename);
-      cmSystemTools::RemoveFile(filename_tmp);
+      cmSystemTools::MoveFileIfDifferent(filename_tmp, filename);
 
       target->AddSource(filename, true);
 
diff --git a/Source/cmUseMangledMesaCommand.cxx b/Source/cmUseMangledMesaCommand.cxx
index cfc00e8..1fd386b 100644
--- a/Source/cmUseMangledMesaCommand.cxx
+++ b/Source/cmUseMangledMesaCommand.cxx
@@ -98,7 +98,6 @@ void CopyAndFullPathMesaHeader(const std::string& source,
   // close the files before attempting to copy
   fin.close();
   fout.close();
-  cmSystemTools::CopyFileIfDifferent(tempOutputFile, outFile);
-  cmSystemTools::RemoveFile(tempOutputFile);
+  cmSystemTools::MoveFileIfDifferent(tempOutputFile, outFile);
 }
 }
-- 
cgit v0.12