fixes #14159 [backport:1.2]

compiler/dfa.nim

@@ -639,8 +639,10 @@ proc isAnalysableFieldAccess*(orig: PNode; owner: PSym): bool =
     of nkHiddenDeref, nkDerefExpr:
       # We "own" sinkparam[].loc but not ourVar[].location as it is a nasty
       # pointer indirection.
+      # bug #14159, we cannot reason about sinkParam[].location as it can
+      # still be shared for tyRef.
       n = n[0]
-      return n.kind == nkSym and n.sym.owner == owner and (isSinkParam(n.sym) or
+      return n.kind == nkSym and n.sym.owner == owner and (
           n.sym.typ.skipTypes(abstractInst-{tyOwned}).kind in {tyOwned})
     else:
       break

tests/destructor/tcycle3.nim

@@ -2,6 +2,8 @@ discard """
   output: '''BEGIN
 END
 END 2
+cpu.nes false
+cpu step nes is nil? - false
 0'''
   cmd: '''nim c --gc:orc $file'''
 """
@@ -59,7 +61,38 @@ proc main =
   c.run
   echo "END 2"
 
+# bug #14159
+type
+  NES = ref object
+    cpu: CPU
+    apu: APU
+
+  CPU = ref object
+    nes: NES
+
+  APU = object
+    nes: NES
+    cpu: CPU
+
+proc initAPU(nes: sink NES): APU {.nosinks.} =
+  result.nes = nes
+  result.cpu = nes.cpu
+
+proc step(cpu: CPU): int =
+  echo "cpu.nes ", cpu.isNil
+  echo "cpu step nes is nil? - ", cpu.nes.isNil()
+
+proc newNES(): NES =
+  new result
+  result.cpu = CPU(nes: result)
+  result.apu = initAPU(result)
+
+proc bug14159 =
+  var nesConsole = newNES()
+  discard nesConsole.cpu.step()
+
 let mem = getOccupiedMem()
 main()
+bug14159()
 GC_fullCollect()
 echo getOccupiedMem() - mem