closes #7590; add a test case (#21846)

tests/vm/tvmmisc.nim

@@ -668,3 +668,23 @@ block: # bug #10108
     discard y2
     reject:
       const c5 = deliver_x()
+
+block: # bug #7590
+  proc doInit[T]():auto=
+    var a: T
+    return a
+
+  proc fun2[T](tup1:T)=
+    const tup0=doInit[T]()
+
+    # var tup=tup0 #ok
+    const tup=tup0 #causes bug
+
+    doAssert tup is tuple
+    doAssert tup[0] is tuple
+    for ai in tup.fields:
+      doAssert ai is tuple, "BUG2"
+
+  # const c=(foo:(bar1: 0.0))
+  const c=(foo:(bar1:"foo1"))
+  fun2(c)