COMP: suppress false positives from -Wdangling-reference (gcc)

- the number of false positives has reduced, but in a few remaining
  cases, the compiler cannot possibly "know" that the pointer stored
  on the registry will outlive the scope of the method (for example)

  gcc-13: suppressing these spurious warnings needs to be done at each
  caller, which is simply not worth it, since later compiler versions
  provide a cleaner solution.

  gcc-14: the [[gnu::no_dangling]] attribute on the declaration
  lets the compiler know the intent.

- additional FOAM_REAL_GNUC macro (defined in stdFoam.H) to define
  the "real" gcc version and ignoring other compilers masquerading
  as gcc.

COMP: rename MeshObject code to {cxx,txx}

- avoids issues on case-insensitive filesystems (#3316)

applications/utilities/parallelProcessing/decomposePar/decomposePar.C

@@ -210,6 +210,7 @@ autoPtr<labelIOList> faProcAddressing
 
 
 // Return cached or read proc addressing from facesInstance
+FOAM_NO_DANGLING_REFERENCE
 const labelIOList& procAddressing
 (
     const PtrList<fvMesh>& procMeshList,

src/OpenFOAM/Make/files

@@ -587,7 +587,7 @@ meshes/Identifiers/surface/geometricSurfacePatch.C
 meshes/Identifiers/surface/surfZoneIdentifier.C
 meshes/Identifiers/zone/zoneIdentifier.C
 
-meshes/MeshObject/meshObject.C
+meshes/MeshObject/meshObject.cxx
 
 polyMesh = meshes/polyMesh
 

src/OpenFOAM/include/stdFoam.H

@@ -71,6 +71,21 @@ Description
 #  define FOAM_LIKELY(cond)   (cond)
 #endif
 
+// Shadow macro for __GNUC__, excluding compilers masquerading as gcc
+#undef FOAM_REAL_GNUC
+#if defined(__GNUC__) && !defined(__llvm__)
+#  define FOAM_REAL_GNUC __GNUC__
+#endif
+
+// Suppress false positives from -Wdangling-reference (gcc >= 14)
+#if (FOAM_REAL_GNUC >= 14)
+#  define FOAM_NO_DANGLING_REFERENCE [[gnu::no_dangling]]
+#endif
+
+#ifndef FOAM_NO_DANGLING_REFERENCE
+#define FOAM_NO_DANGLING_REFERENCE
+#endif
+
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 

src/OpenFOAM/meshes/MeshObject/MeshObject.H

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2018-2024 OpenCFD Ltd.
+    Copyright (C) 2018-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -168,10 +168,12 @@ public:
 
         //- Get existing or create MeshObject registered with typeName
         template<class... Args>
+        FOAM_NO_DANGLING_REFERENCE  //< Reference stored in registry
         static const Type& New(const Mesh& mesh, Args&&... args);
 
         //- Get existing or create MeshObject with given registration name
         template<class... Args>
+        FOAM_NO_DANGLING_REFERENCE  //< Reference stored in registry
         static const Type& New
         (
             const word& objName,
@@ -320,7 +322,7 @@ public:
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 #ifdef NoRepository
-    #include "MeshObject.C"
+    #include "MeshObject.txx"
 #endif
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

src/mesh/snappyHexMesh/meshRefinement/meshRefinement.H

@@ -1927,6 +1927,7 @@ public:
             );
 
             //- Wrapper around dictionary::subDict which does not exit
+            FOAM_NO_DANGLING_REFERENCE
             static const dictionary& subDict
             (
                 const dictionary& dict,

src/meshTools/mappedPatches/mappedPolyPatch/mappedPatchBase.H

@@ -88,8 +88,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef mappedPatchBase_H
-#define mappedPatchBase_H
+#ifndef Foam_mappedPatchBase_H
+#define Foam_mappedPatchBase_H
 
 #include "pointField.H"
 #include "Tuple2.H"
@@ -103,6 +103,7 @@ SourceFiles
 namespace Foam
 {
 
+// Forward Declarations
 class polyPatch;
 class polyMesh;
 class mapDistribute;
@@ -405,6 +406,7 @@ protected:
 
             //- Lookup (sub)objectRegistry by following names of sub registries.
             //- Creates non-existing intermediate ones.
+            FOAM_NO_DANGLING_REFERENCE
             static const objectRegistry& subRegistry
             (
                 const objectRegistry& obr,
@@ -603,12 +605,12 @@ public:
 
         // For database storage
 
-            inline const fileName& sampleDatabasePath() const
+            const fileName& sampleDatabasePath() const
             {
                 return *sampleDatabasePtr_;
             }
 
-            inline bool sampleDatabase() const
+            bool sampleDatabase() const noexcept
             {
                 return bool(sampleDatabasePtr_);
             }
@@ -630,6 +632,7 @@ public:
 
             //- Lookup (sub)objectRegistry from '/' separated path (relative to
             //- objectRegistry). Creates non-existing intermediate ones.
+            FOAM_NO_DANGLING_REFERENCE
             static const objectRegistry& subRegistry
             (
                 const objectRegistry& obr,

src/parallel/decompose/decompositionMethods/decompositionMethod/decompositionMethod.H

@@ -105,6 +105,7 @@ protected:
         //  \return the coefficients dictionary found. If nothing was found,
         //  return the enclosing dictionary or
         //  dictionary::null (depending on the select parameter).
+        FOAM_NO_DANGLING_REFERENCE
         static const dictionary& findCoeffsDict
         (
             const dictionary& dict,
@@ -124,6 +125,7 @@ protected:
         //  \return the coefficients dictionary found. If nothing was found,
         //  return the top-level (non-region) dictionary or
         //  dictionary::null (depending on the select parameter).
+        FOAM_NO_DANGLING_REFERENCE
         const dictionary& findCoeffsDict
         (
             const word& coeffsName,