Make SolverCategory non-const

* setSolverCategory is not allowed to alter a const value
* Adjust type of setSolverCategory's set
* Properly document deprecation of get/setSolverCategory

CHANGELOG.md

@@ -47,6 +47,12 @@
 
 - `SeqILU` can now be used with SIMD data types.
 
+- The method `setSolverCategory` of `OwnerOverlapCopyCommunication` is deprecated and
+  will be removed after Dune 2.7. The solver category can only be set in the constructor.
+
+- The method `getSolverCategory` of `OwnerOverlapCopyCommunication` is deprecated and
+  will be removed after Dune 2.7. Use `category()` instead.
+
 # Release 2.6
 
 - `BDMatrix` objects can now be constructed and assigned from `std::initializer_list`.

dune/istl/owneroverlapcopy.hh

@@ -289,13 +289,13 @@ namespace Dune {
      * @brief Set right Solver Category (default is overlapping).
      */
     void
-    DUNE_DEPRECATED_MSG("the solver category can only be set in the constructor")
-    setSolverCategory (SolverCategory set) {
+    DUNE_DEPRECATED_MSG("The solver category can only be set in the constructor. This method is deprecated and will be removed after Dune 2.7")
+    setSolverCategory (SolverCategory::Category set) {
       category_ = set;
     }
 
     SolverCategory::Category
-    DUNE_DEPRECATED_MSG("use category()")
+    DUNE_DEPRECATED_MSG("This method is deprecated and will be removed after Dune 2.7, use category() instead.")
     getSolverCategory () const {
       return category_;
     }
@@ -701,7 +701,8 @@ namespace Dune {
     mutable std::vector<double> mask;
     int oldseqNo;
     GlobalLookupIndexSet* globalLookup_;
-    const SolverCategory::Category category_;
+    // re-intruduce const qualifier once deprecated setCategory got removed after Dune 2.7
+    /* const */ SolverCategory::Category category_;
     bool freecomm;
   };