From 989cf27554bc9c80693c91b564eeb1688e9dea2e Mon Sep 17 00:00:00 2001
From: Henry Weller <http://cfd.direct>
Date: Thu, 10 Feb 2022 14:47:07 +0000
Subject: [PATCH] snappyHexMesh, createPatch: Keep all constraint patches even
 if zero size

This change ensures that special constraint type patches, like internal used for
load-balancing, are not deleted by snappyHexMesh or createPatch.
---
 .../generation/snappyHexMesh/snappyHexMesh.C  | 35 +++++--------------
 .../manipulation/createPatch/createPatch.C    | 16 ++++-----
 2 files changed, 15 insertions(+), 36 deletions(-)

diff --git a/applications/utilities/mesh/generation/snappyHexMesh/snappyHexMesh.C b/applications/utilities/mesh/generation/snappyHexMesh/snappyHexMesh.C
index cf09bb1132..fd9e452b8c 100644
--- a/applications/utilities/mesh/generation/snappyHexMesh/snappyHexMesh.C
+++ b/applications/utilities/mesh/generation/snappyHexMesh/snappyHexMesh.C
@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     | Website:  https://openfoam.org
-    \\  /    A nd           | Copyright (C) 2011-2021 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2022 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -565,12 +565,8 @@ scalar getMergeDistance(const polyMesh& mesh, const scalar mergeTol)
 
 void removeZeroSizedPatches(fvMesh& mesh)
 {
-    // Remove any zero-sized ones. Assumes
-    // - processor patches are already only there if needed
-    // - all other patches are available on all processors
-    // - but coupled ones might still be needed, even if zero-size
-    //   (e.g. processorCyclic)
-    // See also logic in createPatch.
+    // Remove non-constraint zero-sized patches
+
     const polyBoundaryMesh& pbm = mesh.boundaryMesh();
 
     labelList oldToNew(pbm.size(), -1);
@@ -579,31 +575,16 @@ void removeZeroSizedPatches(fvMesh& mesh)
     {
         const polyPatch& pp = pbm[patchi];
 
-        if (!isA<processorPolyPatch>(pp))
-        {
-            if
-            (
-                isA<coupledPolyPatch>(pp)
-             || returnReduce(pp.size(), sumOp<label>())
-            )
-            {
-                // Coupled (and unknown size) or uncoupled and used
-                oldToNew[patchi] = newPatchi++;
-            }
-        }
-    }
-
-    forAll(pbm, patchi)
-    {
-        const polyPatch& pp = pbm[patchi];
-
-        if (isA<processorPolyPatch>(pp))
+        if
+        (
+            polyPatch::constraintType(pp.type())
+         || returnReduce(pp.size(), sumOp<label>())
+        )
         {
             oldToNew[patchi] = newPatchi++;
         }
     }
 
-
     const label nKeepPatches = newPatchi;
 
     // Shuffle unused ones to end
diff --git a/applications/utilities/mesh/manipulation/createPatch/createPatch.C b/applications/utilities/mesh/manipulation/createPatch/createPatch.C
index f240c642e9..3b9d2b9325 100644
--- a/applications/utilities/mesh/manipulation/createPatch/createPatch.C
+++ b/applications/utilities/mesh/manipulation/createPatch/createPatch.C
@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     | Website:  https://openfoam.org
-    \\  /    A nd           | Copyright (C) 2011-2021 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2022 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -32,7 +32,7 @@ Description
     - creates new patches (from selected boundary faces). Synchronise faces
       on coupled patches.
     - synchronises points on coupled boundaries
-    - remove patches with 0 faces in them
+    - remove non-constraint patches with 0 faces
 
 \*---------------------------------------------------------------------------*/
 
@@ -115,18 +115,15 @@ void filterPatches(polyMesh& mesh, const HashSet<word>& addedPatchNames)
         // Note: reduce possible since non-proc patches guaranteed in same order
         if (!isA<processorPolyPatch>(pp))
         {
-
             // Add if
-            // - non zero size
-            // - or added from the createPatchDict
-            // - or cyclic (since referred to by other cyclic half or
-            //   proccyclic)
-
+            // - listed in createPatchDict
+            // - or constraint type
+            // - or non zero size
             if
             (
                 addedPatchNames.found(pp.name())
+             || polyPatch::constraintType(pp.type())
              || returnReduce(pp.size(), sumOp<label>()) > 0
-             || isA<coupledPolyPatch>(pp)
             )
             {
                 allPatches.append
@@ -148,6 +145,7 @@ void filterPatches(polyMesh& mesh, const HashSet<word>& addedPatchNames)
             }
         }
     }
+
     // Copy non-empty processor patches
     forAll(patches, patchi)
     {