ENH: add 'filtered' polyMesh regionName() method

- in various situations with mesh regions it is also useful to
  filter out or remove the defaultRegion name (ie, "region0").

  Can now do that conveniently from the polyMesh itself or as a static
  function. Simply use this

      const word& regionDir = polyMesh::regionName(regionName);

  OR  mesh.regionName()

  instead of

      const word& regionDir =
      (
           regionName != polyMesh::defaultRegion
         ? regionName
         : word::null
      );

  Additionally, since the string '/' join operator filters out empty
  strings, the following will work correctly:

      (polyMesh::regionName(regionName)/polyMesh::meshSubDir)

      (mesh.regionName()/polyMesh::meshSubDir)

applications/utilities/mesh/generation/PDRblockMesh/PDRblockMesh.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019-2021 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -130,7 +130,6 @@ int main(int argc, char *argv[])
     const bool noOuterRegion = args.found("no-outer");
 
     const word regionName(polyMesh::defaultRegion);
-    const word regionPath;
 
 
     // Instance for resulting mesh

applications/utilities/mesh/generation/PDRblockMesh/cleanMeshDirectory.H

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2020 OpenCFD Ltd.
+    Copyright (C) 2020-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -18,10 +18,11 @@ Description
 {
     // Shadows enclosing parameter (dictName)
     const word blockMeshDictName("blockMeshDict");
+    const word& regionDir = polyMesh::regionName(regionName);
 
     const fileName polyMeshPath
     (
-        runTime.path()/meshInstance/regionPath/polyMesh::meshSubDir
+        runTime.path()/meshInstance/regionDir/polyMesh::meshSubDir
     );
 
     if (exists(polyMeshPath))

applications/utilities/mesh/generation/blockMesh/blockMesh.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2021 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -184,16 +184,13 @@ int main(int argc, char *argv[])
     );
 
     word regionName(polyMesh::defaultRegion);
-    word regionPath;
 
     // Check if the region is specified otherwise mesh the default region
     if (args.readIfPresent("region", regionName))
     {
         Info<< nl << "Generating mesh for region " << regionName << endl;
-        regionPath = regionName;
     }
 
-
     // Instance for resulting mesh
     bool useTime = false;
     word meshInstance(runTime.constant());

applications/utilities/mesh/generation/blockMesh/cleanMeshDirectory.H

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2020 OpenCFD Ltd.
+    Copyright (C) 2020-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -18,10 +18,11 @@ Description
 {
     // Shadows enclosing parameter (dictName)
     const word blockMeshDictName("blockMeshDict");
+    const word& regionDir = polyMesh::regionName(regionName);
 
     const fileName polyMeshPath
     (
-        runTime.path()/meshInstance/regionPath/polyMesh::meshSubDir
+        runTime.path()/meshInstance/regionDir/polyMesh::meshSubDir
     );
 
     if (exists(polyMeshPath))

applications/utilities/mesh/generation/blockMesh/findBlockMeshDict.H

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -22,6 +22,7 @@ autoPtr<IOdictionary> meshDictPtr;
 
 {
     fileName dictPath;
+    const word& regionDir = polyMesh::regionName(regionName);
 
     if (args.readIfPresent("dict", dictPath))
     {
@@ -37,15 +38,17 @@ autoPtr<IOdictionary> meshDictPtr;
         exists
         (
             runTime.path()/runTime.constant()
-            /regionPath/polyMesh::meshSubDir/dictName
+          / regionDir/polyMesh::meshSubDir/dictName
         )
     )
     {
         // Dictionary present in constant polyMesh directory (old-style)
 
         dictPath =
+        (
             runTime.constant()
-                /regionPath/polyMesh::meshSubDir/dictName;
+          / regionDir/polyMesh::meshSubDir/dictName
+        );
 
 
         // Warn that constant/polyMesh/blockMeshDict was used
@@ -54,14 +57,14 @@ autoPtr<IOdictionary> meshDictPtr;
             << "Using the old blockMeshDict location: "
             << dictPath << nl
             << "    instead of the default location:  "
-            << runTime.system()/regionPath/dictName << nl
+            << runTime.system()/regionDir/dictName << nl
             << endl;
     }
     else
     {
         // Assume dictionary is to be found in the system directory
 
-        dictPath = runTime.system()/regionPath/dictName;
+        dictPath = runTime.system()/regionDir/dictName;
     }
 
     IOobject meshDictIO

applications/utilities/mesh/generation/extrude/extrudeMesh/extrudeMesh.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2015-2021 OpenCFD Ltd.
+    Copyright (C) 2015-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -256,21 +256,19 @@ int main(int argc, char *argv[])
     #include "createTimeExtruded.H"
 
     // Get optional regionName
-    word regionName;
-    word regionDir;
+    word regionName(polyMesh::defaultRegion);
     if (args.readIfPresent("region", regionName))
     {
-        regionDir = regionName;
         Info<< "Create mesh " << regionName << " for time = "
             << runTimeExtruded.timeName() << nl << endl;
     }
     else
     {
-        regionName = fvMesh::defaultRegion;
         Info<< "Create mesh for time = "
             << runTimeExtruded.timeName() << nl << endl;
     }
 
+
     const IOdictionary dict
     (
         IOobject::selectIO
@@ -755,7 +753,12 @@ int main(int argc, char *argv[])
 
 
         // Create dummy fvSchemes, fvSolution
-        fvMeshTools::createDummyFvMeshFiles(mesh, regionDir, true);
+        fvMeshTools::createDummyFvMeshFiles
+        (
+            mesh,
+            polyMesh::regionName(regionName),
+            true
+        );
 
         // Create actual mesh from polyTopoChange container
         autoPtr<mapPolyMesh> map = meshMod().makeMesh

applications/utilities/mesh/generation/extrude2DMesh/extrude2DMeshApp.C

@@ -234,12 +234,12 @@ int main(int argc, char *argv[])
     {
         mesh = autoPtr<polyMesh>::New
         (
-            Foam::IOobject
+            IOobject
             (
-                Foam::polyMesh::defaultRegion,
+                polyMesh::defaultRegion,
                 runTimeExtruded.timeName(),
                 runTimeExtruded,
-                Foam::IOobject::MUST_READ
+                IOobject::MUST_READ
             )
         );
     }

applications/utilities/mesh/generation/foamyMesh/conformalVoronoiMesh/conformalVoronoiMesh/conformalVoronoiMeshIO.C

@@ -331,7 +331,7 @@ void Foam::conformalVoronoiMesh::writeMesh(const fileName& instance)
 //            (
 //                IOobject
 //                (
-//                    Foam::polyMesh::defaultRegion,
+//                    polyMesh::defaultRegion,
 //                    instance,
 //                    runTime_,
 //                    IOobject::MUST_READ