fixes #12989 (#12992)

* fixes #12989
* Revert "remove unwanted changes"

This reverts commit 5018297.

compiler/injectdestructors.nim

@@ -133,10 +133,10 @@ proc initialized(code: ControlFlowGraph; pc: int,
       inc pc
   return pc
 
-template isUnpackedTuple(s: PSym): bool =
+template isUnpackedTuple(n: PNode): bool =
   ## we move out all elements of unpacked tuples,
   ## hence unpacked tuples themselves don't need to be destroyed
-  s.kind == skTemp and s.typ.kind == tyTuple
+  (n.kind == nkSym and n.sym.kind == skTemp and n.sym.typ.kind == tyTuple)
 
 proc checkForErrorPragma(c: Con; t: PType; ri: PNode; opname: string) =
   var m = "'" & opname & "' is not available for type <" & typeToString(t) & ">"
@@ -542,7 +542,7 @@ proc p(n: PNode; c: var Con; mode: ProcessMode): PNode =
               # move the variable declaration to the top of the frame:
               c.addTopVar v
               # make sure it's destroyed at the end of the proc:
-              if not isUnpackedTuple(it[0].sym):
+              if not isUnpackedTuple(v):
                 c.destroys.add genDestroy(c, v)
             if ri.kind == nkEmpty and c.inLoop > 0:
               ri = genDefaultCall(v.typ, c, v.info)
@@ -612,13 +612,15 @@ proc p(n: PNode; c: var Con; mode: ProcessMode): PNode =
 proc moveOrCopy(dest, ri: PNode; c: var Con): PNode =
   case ri.kind
   of nkCallKinds:
-    result = genSink(c, dest, ri)
-    result.add p(ri, c, consumed)
-  of nkBracketExpr:
-    if ri[0].kind == nkSym and isUnpackedTuple(ri[0].sym):
-      # unpacking of tuple: move out the elements
+    if isUnpackedTuple(dest):
+      result = newTree(nkFastAsgn, dest, p(ri, c, consumed))
+    else:
       result = genSink(c, dest, ri)
       result.add p(ri, c, consumed)
+  of nkBracketExpr:
+    if isUnpackedTuple(ri[0]):
+      # unpacking of tuple: take over elements
+      result = newTree(nkFastAsgn, dest, p(ri, c, consumed))
     elif isAnalysableFieldAccess(ri, c.owner) and isLastRead(ri, c):
       # Rule 3: `=sink`(x, z); wasMoved(z)
       var snk = genSink(c, dest, ri)

compiler/lowerings.nim

@@ -60,7 +60,6 @@ proc lowerTupleUnpacking*(g: ModuleGraph; n: PNode; owner: PSym): PNode =
   var temp = newSym(skTemp, getIdent(g.cache, genPrefix), owner, value.info, g.config.options)
   temp.typ = skipTypes(value.typ, abstractInst)
   incl(temp.flags, sfFromGeneric)
-  incl(temp.flags, sfCursor)
 
   var v = newNodeI(nkVarSection, value.info)
   let tempAsNode = newSymNode(temp)

tests/destructor/t12037.nim

@@ -23,3 +23,12 @@ test()
 import tables
 var t = initTable[string, seq[ptr int]]()
 discard t.hasKeyOrPut("f1", @[])
+
+
+#############################################
+### bug #12989
+proc bug(start: (seq[int], int)) =
+  let (s, i) = start
+
+let input = @[0]
+bug((input, 0))

tests/destructor/tmisc_destructors.nim

@@ -28,7 +28,7 @@ proc test(): auto =
 var (a, b, _) = test()
 
 doAssert assign_counter == 0
-doAssert sink_counter == 9 # XXX this is still silly and needs to be investigated
+doAssert sink_counter == 6
 
 # bug #11510
 proc main =