1 files changed, 41 insertions, 0 deletions
diff --git a/tests/arc/taliased_reassign.nim b/tests/arc/taliased_reassign.nim
new file mode 100644
index 000000000..5563fae8c
--- /dev/null
+++ b/tests/arc/taliased_reassign.nim
@@ -0,0 +1,41 @@
+discard """
+  matrix: "--mm:orc"
+"""
+
+# bug #20993
+
+type
+  Dual[int] = object # must be generic (even if fully specified)
+    p: int
+proc D(p: int): Dual[int] = Dual[int](p: p)
+proc `+`(x: Dual[int], y: Dual[int]): Dual[int] = D(x.p + y.p)
+
+type
+  Tensor[T] = object
+    buf: seq[T]
+proc newTensor*[T](s: int): Tensor[T] = Tensor[T](buf: newSeq[T](s))
+proc `[]`*[T](t: Tensor[T], idx: int): T = t.buf[idx]
+proc `[]=`*[T](t: var Tensor[T], idx: int, val: T) = t.buf[idx] = val
+
+proc `+.`[T](t1, t2: Tensor[T]): Tensor[T] =
+  let n = t1.buf.len
+  result = newTensor[T](n)
+  for i in 0 ..< n:
+    result[i] = t1[i] + t2[i]
+
+proc toTensor*[T](a: sink seq[T]): Tensor[T] =
+  ## This breaks it: Using `T` instead makes it work
+  type U = typeof(a[0])
+  var t: Tensor[U] # Tensor[T] works
+  t.buf = a
+  result = t
+
+proc loss() =
+  var B = toTensor(@[D(123)])
+  let a = toTensor(@[D(-10)])
+  B = B +. a
+  doAssert B[0].p == 113, "I want to be 113, but I am " & $B[0].p
+
+loss()
+
+