fixes #15361 (#15401)

* fixes #15361; better cursor inference

tests/arc/top_no_cursor2.nim

@@ -0,0 +1,53 @@
+discard """
+  output: '''true
+true
+true
+true
+true'''
+  cmd: "nim c --gc:arc $file"
+"""
+# bug #15361
+
+type
+  ErrorNodeKind = enum Branch, Leaf
+  Error = ref object
+    case kind: ErrorNodeKind
+      of Branch:
+        left: Error
+        right: Error
+      of Leaf:
+        leafError: string
+    input: string
+
+proc ret(input: string, lefterr, righterr: Error): Error =
+  result = Error(kind: Branch, left: lefterr, right: righterr, input: input)
+
+proc parser() =
+  var rerrors: Error
+  let lerrors = Error(
+    kind: Leaf,
+    leafError: "first error",
+    input: "123 ;"
+  )
+  # If you remove "block" - everything works
+  block:
+    let rresult = Error(
+      kind: Leaf,
+      leafError: "second error",
+      input: ";"
+    )
+    # this assignment is needed too
+    rerrors = rresult
+
+  # Returns Error(kind: Branch, left: lerrors, right: rerrors, input: "some val")
+  # needs to be a proc call for some reason, can't inline the result
+  var data = ret(input = "some val", lefterr = lerrors, righterr = rerrors)
+
+  echo data.left.leafError == "first error"
+  echo data.left.input == "123 ;"
+  # stacktrace shows this line
+  echo data.right.leafError == "second error"
+  echo data.right.input == ";"
+  echo data.input == "some val"
+
+parser()

tests/arc/topt_no_cursor.nim

@@ -52,7 +52,7 @@ _ = (
   blitTmp, ";")
 lvalue = _[0]
 lnext_cursor = _[1]
-`=sink`(result.value, lvalue)
+`=sink`(result.value, move lvalue)
 -- end of expandArc ------------------------
 --expandArc: tt
 
@@ -148,7 +148,7 @@ proc p1(): Maybe =
   var lnext: string
   (lvalue, lnext) = (lresult, ";")
 
-  result.value = lvalue
+  result.value = move lvalue
 
 proc tissue15130 =
   doAssert p1().value == @[123]

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 =