fixes #15361 (#15401)

* fixes #15361; better cursor inference

tests/destructor/tdestructor3.nim

@@ -23,17 +23,18 @@ joinable: false
 type T = object
 
 proc `=`(lhs: var T, rhs: T) =
-    echo "assign"
+  echo "assign"
 
 proc `=destroy`(v: var T) =
-    echo "destroy"
+  echo "destroy"
 
 proc use(x: T) = discard
 
 proc usedToBeBlock =
-    var v1 : T
-    var v2 : T = v1
-    use v1
+  var v1 = T()
+  var v2: T = v1
+  discard addr(v2) # prevent cursorfication
+  use v1
 
 usedToBeBlock()
 

tests/destructor/tmatrix.nim

@@ -96,14 +96,16 @@ proc info =
   allocCount = 0
   deallocCount = 0
 
+proc copy(a: Matrix): Matrix = a
+
 proc test1 =
   var a = matrix(5, 5, 1.0)
-  var b = a
+  var b = copy a
   var c = a + b
 
 proc test2 =
   var a = matrix(5, 5, 1.0)
-  var b = a
+  var b = copy a
   var c = -a
 
 proc test3 =