Fix bitwise hex count values and array of zero

In the parser "count" has always allowed hex values (0x12) but we
would not actually interpret those properly. Also, arrays of zero
are useful sometimes so add a test to make sure those work (with hex
counts only to make them stand out as intentional).

chirp/bitwise.py

@@ -854,6 +854,13 @@ def items(self):
             yield key, self._generators[key]
 
 
+def parse_count(string):
+    if string.startswith('0x'):
+        return int(string, 16)
+    else:
+        return int(string)
+
+
 class Processor:
     _types = {
         "u8":    u8DataElement,
@@ -956,7 +963,7 @@ def parse_defn(self, defn):
         else:
             if defn[1][0] == "array":
                 sym = defn[1][1][0]
-                count = int(defn[1][1][1][1])
+                count = parse_count(defn[1][1][1][1])
             else:
                 count = 1
                 sym = defn[1]
@@ -997,7 +1004,7 @@ def parse_struct_decl(self, struct):
         deftype = struct[-1]
         if deftype[0] == "array":
             name = deftype[1][0][1]
-            count = int(deftype[1][1][1])
+            count = parse_count(deftype[1][1][1])
         elif deftype[0] == "symbol":
             name = deftype[1]
             count = 1

tests/unit/test_bitwise.py

@@ -104,6 +104,14 @@ def test_int_array_of_one(self):
         obj.foo[0] = 1
         self.assertEqual(b'\x01\x01\x02\x03', data.get_packed())
 
+    def test_int_array_of_zero(self):
+        data = memmap.MemoryMapBytes(bytes(b'\x00\x01\x02\x03'))
+        obj = bitwise.parse('u8 foo[0x0]; u8 bar;', data)
+        # Make sure we can't access any elements of zero-length foo
+        self.assertRaises(IndexError, lambda: obj.foo[0])
+        # Make sure bar is still at the front, unaffected by zero-length foo
+        self.assertEqual(0, obj.bar)
+
     def test_int_array_set_raw(self):
         data = memmap.MemoryMapBytes(bytes(b'\x00\x01\x02\x03'))
         obj = bitwise.parse('u8 foo[4];', data)