2 files changed, 51 insertions, 4 deletions

diff --git a/Source/cmOutputConverter.cxx b/Source/cmOutputConverter.cxx
index 3d61743f35..e62e0cd328 100644
--- a/Source/cmOutputConverter.cxx
+++ b/Source/cmOutputConverter.cxx
@@ -34,6 +34,7 @@ cmOutputConverter::cmOutputConverter(cmStateSnapshot const& snapshot)
   assert(this->StateSnapshot.IsValid());
   this->ComputeRelativePathTopSource();
   this->ComputeRelativePathTopBinary();
+  this->ComputeRelativePathTopRelation();
 }
 
 void cmOutputConverter::ComputeRelativePathTopSource()
@@ -69,6 +70,22 @@ void cmOutputConverter::ComputeRelativePathTopBinary()
   this->RelativePathTopBinary = snapshot.GetDirectory().GetCurrentBinary();
 }
 
+void cmOutputConverter::ComputeRelativePathTopRelation()
+{
+  if (cmSystemTools::ComparePath(this->RelativePathTopSource,
+                                 this->RelativePathTopBinary)) {
+    this->RelativePathTopRelation = TopRelation::InSource;
+  } else if (cmSystemTools::IsSubDirectory(this->RelativePathTopBinary,
+                                           this->RelativePathTopSource)) {
+    this->RelativePathTopRelation = TopRelation::BinInSrc;
+  } else if (cmSystemTools::IsSubDirectory(this->RelativePathTopSource,
+                                           this->RelativePathTopBinary)) {
+    this->RelativePathTopRelation = TopRelation::SrcInBin;
+  } else {
+    this->RelativePathTopRelation = TopRelation::Separate;
+  }
+}
+
 std::string const& cmOutputConverter::GetRelativePathTopSource() const
 {
   return this->RelativePathTopSource;
@@ -84,19 +101,40 @@ void cmOutputConverter::SetRelativePathTop(std::string const& topSource,
 {
   this->RelativePathTopSource = topSource;
   this->RelativePathTopBinary = topBinary;
+  this->ComputeRelativePathTopRelation();
 }
 
 std::string cmOutputConverter::MaybeRelativeTo(
   std::string const& local_path, std::string const& remote_path) const
 {
-  bool bothInBinary =
-    PathEqOrSubDir(local_path, this->RelativePathTopBinary) &&
+  bool localInBinary = PathEqOrSubDir(local_path, this->RelativePathTopBinary);
+  bool remoteInBinary =
     PathEqOrSubDir(remote_path, this->RelativePathTopBinary);
 
-  bool bothInSource =
-    PathEqOrSubDir(local_path, this->RelativePathTopSource) &&
+  bool localInSource = PathEqOrSubDir(local_path, this->RelativePathTopSource);
+  bool remoteInSource =
     PathEqOrSubDir(remote_path, this->RelativePathTopSource);
 
+  switch (this->RelativePathTopRelation) {
+    case TopRelation::Separate:
+      // Checks are independent.
+      break;
+    case TopRelation::BinInSrc:
+      localInSource = localInSource && !localInBinary;
+      remoteInSource = remoteInSource && !remoteInBinary;
+      break;
+    case TopRelation::SrcInBin:
+      localInBinary = localInBinary && !localInSource;
+      remoteInBinary = remoteInBinary && !remoteInSource;
+      break;
+    case TopRelation::InSource:
+      // Checks are identical.
+      break;
+  };
+
+  bool const bothInBinary = localInBinary && remoteInBinary;
+  bool const bothInSource = localInSource && remoteInSource;
+
   if (bothInBinary || bothInSource) {
     return cmSystemTools::ForceToRelativePath(local_path, remote_path);
   }
diff --git a/Source/cmOutputConverter.h b/Source/cmOutputConverter.h
index 290809fd92..d19bccc186 100644
--- a/Source/cmOutputConverter.h
+++ b/Source/cmOutputConverter.h
@@ -147,8 +147,17 @@ private:
   // safely by the build tools.
   std::string RelativePathTopSource;
   std::string RelativePathTopBinary;
+  enum class TopRelation
+  {
+    Separate,
+    BinInSrc,
+    SrcInBin,
+    InSource,
+  };
+  TopRelation RelativePathTopRelation = TopRelation::Separate;
   void ComputeRelativePathTopSource();
   void ComputeRelativePathTopBinary();
+  void ComputeRelativePathTopRelation();
   std::string MaybeRelativeTo(std::string const& local_path,
                               std::string const& remote_path) const;
 };