real bugfix for #17170 (#18171)

* real bugfix for #17170

* better fix

compiler/closureiters.nim

@@ -414,8 +414,11 @@ proc exprToStmtList(n: PNode): tuple[s, res: PNode] =
 
 
 proc newEnvVarAsgn(ctx: Ctx, s: PSym, v: PNode): PNode =
-  result = newTree(nkFastAsgn, ctx.newEnvVarAccess(s), v)
-  result.info = v.info
+  if isEmptyType(v.typ):
+    result = v
+  else:
+    result = newTree(nkFastAsgn, ctx.newEnvVarAccess(s), v)
+    result.info = v.info
 
 proc addExprAssgn(ctx: Ctx, output, input: PNode, sym: PSym) =
   if input.kind == nkStmtListExpr:
@@ -427,8 +430,7 @@ proc addExprAssgn(ctx: Ctx, output, input: PNode, sym: PSym) =
 
 proc convertExprBodyToAsgn(ctx: Ctx, exprBody: PNode, res: PSym): PNode =
   result = newNodeI(nkStmtList, exprBody.info)
-  if exprBody.typ != nil:
-    ctx.addExprAssgn(result, exprBody, res)
+  ctx.addExprAssgn(result, exprBody, res)
 
 proc newNotCall(g: ModuleGraph; e: PNode): PNode =
   result = newTree(nkCall, newSymNode(g.getSysMagic(e.info, "not", mNot), e.info), e)

compiler/injectdestructors.nim

@@ -364,6 +364,7 @@ proc genMarkCyclic(c: var Con; result, dest: PNode) =
 proc genCopyNoCheck(c: var Con; dest, ri: PNode): PNode =
   let t = dest.typ.skipTypes({tyGenericInst, tyAlias, tySink})
   result = c.genOp(t, attachedAsgn, dest, ri)
+  assert ri.typ != nil
 
 proc genCopy(c: var Con; dest, ri: PNode): PNode =
   let t = dest.typ
@@ -371,6 +372,7 @@ proc genCopy(c: var Con; dest, ri: PNode): PNode =
     # try to improve the error message here:
     c.checkForErrorPragma(t, ri, "=copy")
   result = c.genCopyNoCheck(dest, ri)
+  assert ri.typ != nil
 
 proc genDiscriminantAsgn(c: var Con; s: var Scope; n: PNode): PNode =
   # discriminator is ordinal value that doesn't need sink destroy