From 8432aab597bc0ced32d888c980e67c5d3759c1be Mon Sep 17 00:00:00 2001
From: Catherine <whitequark@whitequark.org>
Date: Fri, 19 Jul 2024 01:10:59 +0000
Subject: [PATCH] hdl: truncate init value read from `Signal(...).init`.

We have a warning saying that the init value will be truncated to fit
the signal's shape (suppressed for common patterns of 0 and -1), but
the introspected via `.init` value is, confusingly, not truncated.
---
 amaranth/hdl/_ast.py  | 2 +-
 tests/test_hdl_ast.py | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/amaranth/hdl/_ast.py b/amaranth/hdl/_ast.py
index a490707bf..1293f871d 100644
--- a/amaranth/hdl/_ast.py
+++ b/amaranth/hdl/_ast.py
@@ -2052,7 +2052,7 @@ def __init__(self, shape=None, *, name=None, init=None, reset=None, reset_less=F
                             .format(orig_init, shape),
                     category=SyntaxWarning,
                     stacklevel=2)
-        self._init = init.value
+        self._init = Const(init.value, shape).value
         self._reset_less = bool(reset_less)
 
         if isinstance(orig_shape, range) and orig_init is not None and orig_init not in orig_shape:
diff --git a/tests/test_hdl_ast.py b/tests/test_hdl_ast.py
index d74ad773d..85d9ecfb6 100644
--- a/tests/test_hdl_ast.py
+++ b/tests/test_hdl_ast.py
@@ -1245,6 +1245,14 @@ def test_init_wrong_too_wide(self):
                 r"^Initial value -2 will be truncated to the signal shape signed\(1\)$"):
             Signal(signed(1), init=-2)
 
+    def test_init_truncated(self):
+        s1 = Signal(unsigned(2), init=-1)
+        self.assertEqual(s1.init, 0b11)
+        with warnings.catch_warnings():
+            warnings.filterwarnings(action="ignore", category=SyntaxWarning)
+            s2 = Signal(signed(2), init=-33)
+            self.assertEqual(s2.init, -1)
+
     def test_init_wrong_fencepost(self):
         with self.assertRaisesRegex(SyntaxError,
                 r"^Initial value 10 equals the non-inclusive end of the signal shape "