hdl.rec: implement Record.connect.

Fixes #31.

nmigen/hdl/rec.py

@@ -1,5 +1,6 @@
 from enum import Enum
 from collections import OrderedDict
+from functools import reduce
 
 from .. import tracer
 from ..tools import union
@@ -119,3 +120,53 @@ class Record(Value):
         if name is None:
             name = "<unnamed>"
         return "(rec {} {})".format(name, " ".join(fields))
+
+    def connect(self, *subordinates, include=None, exclude=None):
+        def rec_name(record):
+            if record.name is None:
+                return "unnamed record"
+            else:
+                return "record '{}'".format(record.name)
+
+        for field in include or {}:
+            if field not in self.fields:
+                raise AttributeError("Cannot include field '{}' because it is not present in {}"
+                                     .format(field, rec_name(self)))
+        for field in exclude or {}:
+            if field not in self.fields:
+                raise AttributeError("Cannot exclude field '{}' because it is not present in {}"
+                                     .format(field, rec_name(self)))
+
+        stmts = []
+        for field in self.fields:
+            if include is not None and field not in include:
+                continue
+            if exclude is not None and field in exclude:
+                continue
+
+            shape, direction = self.layout[field]
+            if not isinstance(shape, Layout) and direction == DIR_NONE:
+                raise TypeError("Cannot connect field '{}' of {} because it does not have "
+                                "a direction"
+                                .format(field, rec_name(self)))
+
+            item = self.fields[field]
+            subord_items = []
+            for subord in subordinates:
+                if field not in subord.fields:
+                    raise AttributeError("Cannot connect field '{}' of {} to subordinate {} "
+                                         "because the subordinate record does not have this field"
+                                         .format(field, rec_name(self), rec_name(subord)))
+                subord_items.append(subord.fields[field])
+
+            if isinstance(shape, Layout):
+                sub_include = include[field] if include and field in include else None
+                sub_exclude = exclude[field] if exclude and field in exclude else None
+                stmts += item.connect(*subord_items, include=sub_include, exclude=sub_exclude)
+            else:
+                if direction == DIR_FANOUT:
+                    stmts += [sub_item.eq(item) for sub_item in subord_items]
+                if direction == DIR_FANIN:
+                    stmts += [item.eq(reduce(lambda a, b: a | b, subord_items))]
+
+        return stmts