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lib.wiring.connect: diagnostic when no connection made.

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If a connect() call results in no connections being made, and it's
because there were no outputs specified at all, issue an error.
Tests enumerate cases per
https://github.com/amaranth-lang/amaranth/pull/1153#issuecomment-1962810678.

Co-authored-by: Catherine <whitequark@whitequark.org>
This commit is contained in:
Amelia Cuss 2024-02-23 16:26:46 +11:00 • committed by Catherine
parent 09029cdd91
commit a586df89ad
2 changed files with 77 additions and 1 deletions
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19
amaranth/lib/wiring.py
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@ -1371,6 +1371,7 @@ def connect(m, *args, **kwargs):
* For a given path, if any of the interface objects has an input port member corresponding
to a constant value, then the rest of the interface objects must have output port members
corresponding to the same constant value.
* When connecting multiple interface objects, at least one connection must be made.
For example, if :py:`obj1` is being connected to :py:`obj2` and :py:`obj3`, and :py:`obj1.a.b`
is an output, then :py:`obj2.a.b` and :py:`obj2.a.b` must exist and be inputs. If :py:`obj2.c`
@ -1420,10 +1421,15 @@ def connect(m, *args, **kwargs):
reasons_as_string)
signatures[handle] = obj.signature
# Collate signatures and build connections.
# Connecting zero or one signatures is OK.
if len(signatures) <= 1:
return
# Collate signatures, build connections, track whether we see any input or output.
flattens = {handle: iter(sorted(signature.members.flatten()))
for handle, signature in signatures.items()}
connections = []
any_in, any_out = False, False
# Each iteration of the outer loop is intended to connect several (usually a pair) members
# to each other, e.g. an out member `[0].a` to an in member `[1].a`. However, because we
# do not just check signatures for equality (in order to improve diagnostics), it is possible
@ -1437,6 +1443,7 @@ def connect(m, *args, **kwargs):
# implied in the flow of each port member, so the signature members are only classified
# here to ensure they are not connected to port members.
is_first = True
first_path = None
sig_kind, out_kind, in_kind = [], [], []
for handle, flattened_members in flattens.items():
path_for_handle, member = next(flattened_members, (None, None))
@ -1499,6 +1506,8 @@ def connect(m, *args, **kwargs):
# There are no port members at this point; we're done with this path.
continue
# There are only port members after this point.
any_in = any_in or bool(in_kind)
any_out = any_out or bool(out_kind)
is_first = True
for (path, member) in in_kind + out_kind:
member_shape = member.shape
@ -1574,6 +1583,14 @@ def connect(m, *args, **kwargs):
out_path=(*out_path, index), in_path=(*in_path, index))
assert out_member.dimensions == in_member.dimensions
connect_dimensions(out_member.dimensions, out_path=out_path, in_path=in_path)
# If no connections were made, and there were inputs but no outputs in the
# signatures, issue a diagnostic as this is most likely in error.
if len(connections) == 0 and any_in and not any_out:
raise ConnectionError(f"Only input to input connections have been made between several "
f"interfaces; should one of them have been flipped?")
# Now that we know all of the connections are legal, add them to the module. This is done
# instead of returning them because adding them to a non-comb domain would subtly violate
# assumptions that `connect()` is intended to provide.