From 664b4bcb3ac2e4c688707677def1cb6b4075ea7b Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Sun, 13 Jan 2019 08:51:49 +0000
Subject: [PATCH] hdl.dsl: cases wider than switch test value are unreachable.

In 3083c1d6 they were erroneously fixed via truncation.
---
 nmigen/hdl/dsl.py           |  8 +++++---
 nmigen/test/test_hdl_dsl.py |  6 ++----
 nmigen/test/tools.py        | 10 ++++++----
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/nmigen/hdl/dsl.py b/nmigen/hdl/dsl.py
index de0231b..918e8e3 100644
--- a/nmigen/hdl/dsl.py
+++ b/nmigen/hdl/dsl.py
@@ -219,17 +219,19 @@ class Module(_ModuleBuilderRoot):
         if isinstance(value, str) and len(value) != len(switch_data["test"]):
             raise SyntaxError("Case value '{}' must have the same width as test (which is {})"
                               .format(value, len(switch_data["test"])))
+        omit_case = False
         if isinstance(value, int) and bits_for(value) > len(switch_data["test"]):
             warnings.warn("Case value '{:b}' is wider than test (which has width {}); "
-                          "comparison will be made against truncated value"
+                          "comparison will never be true"
                           .format(value, len(switch_data["test"])), SyntaxWarning, stacklevel=3)
-            value &= (1 << len(switch_data["test"])) - 1
+            omit_case = True
         try:
             _outer_case, self._statements = self._statements, []
             self._ctrl_context = None
             yield
             self._flush_ctrl()
-            switch_data["cases"][value] = self._statements
+            if not omit_case:
+                switch_data["cases"][value] = self._statements
         finally:
             self._ctrl_context = "Switch"
             self._statements = _outer_case
diff --git a/nmigen/test/test_hdl_dsl.py b/nmigen/test/test_hdl_dsl.py
index 3e3df1d..31753fd 100644
--- a/nmigen/test/test_hdl_dsl.py
+++ b/nmigen/test/test_hdl_dsl.py
@@ -289,14 +289,12 @@ class DSLTestCase(FHDLTestCase):
                     pass
             with self.assertWarns(SyntaxWarning,
                     msg="Case value '10110' is wider than test (which has width 4); comparison "
-                        "will be made against truncated value"):
+                        "will never be true"):
                 with m.Case(0b10110):
                     pass
         self.assertRepr(m._statements, """
         (
-            (switch (sig w1)
-                (case 0110 )
-            )
+            (switch (sig w1) )
         )
         """)
 
diff --git a/nmigen/test/tools.py b/nmigen/test/tools.py
index 7c89e88..e1b1a3d 100644
--- a/nmigen/test/tools.py
+++ b/nmigen/test/tools.py
@@ -12,10 +12,12 @@ __all__ = ["FHDLTestCase"]
 class FHDLTestCase(unittest.TestCase):
     def assertRepr(self, obj, repr_str):
         obj = Statement.wrap(obj)
-        repr_str = re.sub(r"\s+",   " ",  repr_str)
-        repr_str = re.sub(r"\( (?=\()", "(", repr_str)
-        repr_str = re.sub(r"\) (?=\))", ")", repr_str)
-        self.assertEqual(repr(obj), repr_str.strip())
+        def prepare_repr(repr_str):
+            repr_str = re.sub(r"\s+",   " ",  repr_str)
+            repr_str = re.sub(r"\( (?=\()", "(", repr_str)
+            repr_str = re.sub(r"\) (?=\))", ")", repr_str)
+            return repr_str.strip()
+        self.assertEqual(prepare_repr(repr(obj)), prepare_repr(repr_str))
 
     @contextmanager
     def assertRaises(self, exception, msg=None):
-- 
2.30.2