From d6b10ac4be0192d8aedff95b6559837e01031bf2 Mon Sep 17 00:00:00 2001
From: Chen-Yu Yang <chenyu@fastmail.com>
Date: Mon, 2 Mar 2026 17:18:27 -0500
Subject: [PATCH] test_derived_from_contiguous_before_assign

---
 test/unit/test_assign.py | 39 +++++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/test/unit/test_assign.py b/test/unit/test_assign.py
index b78855ad6e59c..2987e43ca23e4 100644
--- a/test/unit/test_assign.py
+++ b/test/unit/test_assign.py
@@ -685,21 +685,36 @@ def test_chained_slice_copies(self):
 
   def test_swap_slices(self):
     """Swap two non-overlapping slices - requires reading both before writing."""
-    # without .realize() on temps: values not captured before overwriting
+    # single realize: WAR detection orders contiguous reads before assign writes
     buf = Tensor([1, 2, 3, 4, 5, 6, 7, 8]).contiguous().realize()
-    left = buf[0:4].contiguous()  # lazy - not captured yet
-    right = buf[4:8].contiguous()  # lazy - not captured yet
-    buf[0:4].assign(right).realize()  # this works
-    buf[4:8].assign(left).realize()  # left now reads from modified buf!
-    np.testing.assert_equal(buf.numpy(), [5, 6, 7, 8, 5, 6, 7, 8])  # TODO: wrong! should be [5,6,7,8,1,2,3,4]
+    left = buf[0:4].contiguous()
+    right = buf[4:8].contiguous()
+    buf[0:4].assign(right)
+    buf[4:8].assign(left)
+    buf.realize()
+    np.testing.assert_equal(buf.numpy(), [5, 6, 7, 8, 1, 2, 3, 4])
 
-    # with .realize() on temps: values captured before writes
+  def test_derived_from_contiguous_before_assign(self):
+    """Tensors derived from a contiguous read should see pre-assign data, same as the contiguous itself."""
     buf = Tensor([1, 2, 3, 4, 5, 6, 7, 8]).contiguous().realize()
-    left = buf[0:4].contiguous().realize()
-    right = buf[4:8].contiguous().realize()
-    buf[0:4].assign(right).realize()
-    buf[4:8].assign(left).realize()
-    np.testing.assert_equal(buf.numpy(), [5, 6, 7, 8, 1, 2, 3, 4])
+    left = buf[0:4].contiguous()
+    derived = left + 10
+    right = buf[4:8].contiguous()
+    buf[0:4].assign(right)
+    Tensor.realize(buf, left, derived)
+    np.testing.assert_equal(left.numpy(), [1, 2, 3, 4])
+    np.testing.assert_equal(derived.numpy(), [11, 12, 13, 14])
+
+  def test_view_of_contiguous_before_assign(self):
+    """A view of a contiguous read should see the same pre-assign data as the contiguous."""
+    buf = Tensor([1, 2, 3, 4, 5, 6, 7, 8]).contiguous().realize()
+    c = buf[0:4].contiguous()
+    v = c[0:2]
+    right = buf[4:8].contiguous()
+    buf[0:4].assign(right)
+    Tensor.realize(buf, c, v)
+    np.testing.assert_equal(c.numpy(), [1, 2, 3, 4])
+    np.testing.assert_equal(v.numpy(), [1, 2])
 
   def test_reduction_after_partial_assign(self):
     """Reduction over buffer after partial assign - must see the assigned values."""