From: whitequark <whitequark@whitequark.org>
Date: Thu, 27 Aug 2020 01:14:05 +0000 (+0000)
Subject: hdl.ast: clarify exception message for out of bounds indexing.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=2311c0592111988959a8c976b74422cf3ceba994;p=nmigen.git

hdl.ast: clarify exception message for out of bounds indexing.

Fixes #488.
---

diff --git a/nmigen/hdl/ast.py b/nmigen/hdl/ast.py
index 7d2efef..4a01bde 100644
--- a/nmigen/hdl/ast.py
+++ b/nmigen/hdl/ast.py
@@ -254,7 +254,7 @@ class Value(metaclass=ABCMeta):
         n = len(self)
         if isinstance(key, int):
             if key not in range(-n, n):
-                raise IndexError("Cannot index {} bits into {}-bit value".format(key, n))
+                raise IndexError(f"Index {key} is out of bounds for a {n}-bit value")
             if key < 0:
                 key += n
             return Slice(self, key, key + 1)
diff --git a/tests/test_hdl_ast.py b/tests/test_hdl_ast.py
index f14c07b..e6dfc49 100644
--- a/tests/test_hdl_ast.py
+++ b/tests/test_hdl_ast.py
@@ -187,7 +187,7 @@ class ValueTestCase(FHDLTestCase):
         self.assertEqual(s2.start, 3)
         self.assertEqual(s2.stop, 4)
         with self.assertRaisesRegex(IndexError,
-                r"^Cannot index 5 bits into 4-bit value$"):
+                r"^Index 5 is out of bounds for a 4-bit value$"):
             Const(10)[5]
 
     def test_getitem_slice(self):