Alternative fix for #4910 that covers #6892; fixes #6892 (#6938)

compiler/semexprs.nim

@@ -1290,13 +1290,10 @@ proc takeImplicitAddr(c: PContext, n: PNode): PNode =
 proc asgnToResultVar(c: PContext, n, le, ri: PNode) {.inline.} =
   if le.kind == nkHiddenDeref:
     var x = le.sons[0]
-    if x.typ.kind == tyVar and x.kind == nkSym:
-      if x.sym.kind == skResult:
-        n.sons[0] = x # 'result[]' --> 'result'
-        n.sons[1] = takeImplicitAddr(c, ri)
-      if x.sym.kind != skParam:
-        # XXX This is hacky. See bug #4910.
-        x.typ.flags.incl tfVarIsPtr
+    if x.typ.kind == tyVar and x.kind == nkSym and x.sym.kind == skResult:
+      n.sons[0] = x # 'result[]' --> 'result'
+      n.sons[1] = takeImplicitAddr(c, ri)
+      x.typ.flags.incl tfVarIsPtr
       #echo x.info, " setting it for this type ", typeToString(x.typ), " ", n.info
 
 template resultTypeIsInferrable(typ: PType): untyped =
@@ -1449,14 +1446,15 @@ proc semYieldVarResult(c: PContext, n: PNode, restype: PType) =
   var t = skipTypes(restype, {tyGenericInst, tyAlias})
   case t.kind
   of tyVar:
+    t.flags.incl tfVarIsPtr # bugfix for #4048, #4910, #6892
     if n.sons[0].kind in {nkHiddenStdConv, nkHiddenSubConv}:
       n.sons[0] = n.sons[0].sons[1]
-
     n.sons[0] = takeImplicitAddr(c, n.sons[0])
   of tyTuple:
     for i in 0..<t.sonsLen:
       var e = skipTypes(t.sons[i], {tyGenericInst, tyAlias})
       if e.kind == tyVar:
+        e.flags.incl tfVarIsPtr # bugfix for #4048, #4910, #6892
         if n.sons[0].kind == nkPar:
           n.sons[0].sons[i] = takeImplicitAddr(c, n.sons[0].sons[i])
         elif n.sons[0].kind in {nkHiddenStdConv, nkHiddenSubConv} and

tests/cpp/tget_subsystem.nim

@@ -22,10 +22,18 @@ proc getSubsystem*[T](): ptr T {.
 let input: ptr Input = getSubsystem[Input]()
 
 
-# bug #4910
+# bugs #4910, #6892 
+proc modify(x: var int) = 
+  x = 123
 
 proc foo() =
-  var ts: array[10, int]
+  var ts: array[2, int]
   for t in mitems(ts):
-     t = 123
+    discard
+
+  for t in mitems(ts):
+     modify(t)
+
+  for i, t in mpairs(ts):
+    modify(t)