Making CSR act as a rectangular domain map

CSRtoRectangular.patch

diff --git a/modules/layouts/LayoutCSR.chpl b/modules/layouts/LayoutCSR.chpl
index a388bfc..8d46293 100644
--- a/modules/layouts/LayoutCSR.chpl
+++ b/modules/layouts/LayoutCSR.chpl
@@ -52,6 +52,10 @@ class CSR: BaseDist {
     return new CSRDom(rank=rank, idxType=idxType, dist=this, parentDom=dom);
   }
 
+  proc dsiNewRectangularDom(param rank: int, type idxType, param stridable: bool, inds) {
+    return new CSRDom(rank=rank, idxType=idxType, dist=this, parentDom={(...inds)});
+  }
+
   proc dsiClone() return new CSR();
 
   proc dsiEqualDMaps(that: CSR) param {
@@ -63,9 +67,20 @@ class CSR: BaseDist {
   }
 }
 
-class CSRDom: BaseSparseDomImpl {
+class CSRDom: BaseRectangularDom {
+  // rank and idxType will be moved to BaseDom
+  param rank: int;
+  type idxType;
+  var parentDom;
+
+  proc stridable param return parentDom.stridable;
+
   var dist: CSR;
 
+  var nnz = 0; //: int;
+  var nnzDom = {1..nnz};
+
+
   var rowRange: range(idxType);
   var colRange: range(idxType);
 
@@ -458,7 +473,17 @@ class CSRDom: BaseSparseDomImpl {
 }
 
 
-class CSRArr: BaseSparseArrImpl {
+class CSRArr: BaseArr {
+    type eltType;
+    param rank : int;
+    type idxType;
+
+    var dom; /* : DefaultSparseDom(?); */
+
+    // NOTE I tried to put `data` in `BaseSparseArrImpl`. However, it wasn't
+    // clear how to initialize this in that class.
+    var data: [dom.nnzDom] eltType;
+    var irv: eltType;
 
   proc dsiAccess(ind: rank*idxType) ref {
     // make sure we're in the dense bounding box