hdl.ast: use keyword-only arguments as appropriate.

As a motivation/related refactor, make sure each AST node exposes
src_loc_at in the constructor.

nmigen/hdl/ast.py

@@ -41,7 +41,7 @@ class Value(metaclass=ABCMeta):
         else:
             raise TypeError("Object '{!r}' is not an nMigen value".format(obj))
 
-    def __init__(self, src_loc_at=0):
+    def __init__(self, *, src_loc_at=0):
         super().__init__()
         self.src_loc = tracer.get_src_loc(1 + src_loc_at)
 
@@ -242,6 +242,7 @@ class Const(Value):
         return value
 
     def __init__(self, value, shape=None):
+        # We deliberately do not call Value.__init__ here.
         self.value = int(value)
         if shape is None:
             shape = bits_for(self.value), self.value < 0
@@ -270,8 +271,8 @@ C = Const  # shorthand
 
 
 class AnyValue(Value, DUID):
-    def __init__(self, shape):
+    def __init__(self, shape, *, src_loc_at=0):
-        super().__init__(src_loc_at=0)
+        super().__init__(src_loc_at=src_loc_at)
         if isinstance(shape, int):
             shape = shape, False
         self.nbits, self.signed = shape
@@ -300,7 +301,7 @@ class AnySeq(AnyValue):
 
 @final
 class Operator(Value):
-    def __init__(self, op, operands, src_loc_at=0):
+    def __init__(self, op, operands, *, src_loc_at=0):
         super().__init__(src_loc_at=1 + src_loc_at)
         self.op = op
         self.operands = [Value.wrap(o) for o in operands]
@@ -395,7 +396,7 @@ def Mux(sel, val1, val0):
 
 @final
 class Slice(Value):
-    def __init__(self, value, start, end):
+    def __init__(self, value, start, end, *, src_loc_at=0):
         if not isinstance(start, int):
             raise TypeError("Slice start must be an integer, not '{!r}'".format(start))
         if not isinstance(end, int):
@@ -413,7 +414,7 @@ class Slice(Value):
         if start > end:
             raise IndexError("Slice start {} must be less than slice end {}".format(start, end))
 
-        super().__init__()
+        super().__init__(src_loc_at=src_loc_at)
         self.value = Value.wrap(value)
         self.start = start
         self.end   = end
@@ -433,11 +434,11 @@ class Slice(Value):
 
 @final
 class Part(Value):
-    def __init__(self, value, offset, width):
+    def __init__(self, value, offset, width, *, src_loc_at=0):
         if not isinstance(width, int) or width < 0:
             raise TypeError("Part width must be a non-negative integer, not '{!r}'".format(width))
 
-        super().__init__()
+        super().__init__(src_loc_at=src_loc_at)
         self.value  = value
         self.offset = Value.wrap(offset)
         self.width  = width
@@ -480,8 +481,8 @@ class Cat(Value):
     Value, inout
         Resulting ``Value`` obtained by concatentation.
     """
-    def __init__(self, *args):
+    def __init__(self, *args, src_loc_at=0):
-        super().__init__()
+        super().__init__(src_loc_at=src_loc_at)
         self.parts = [Value.wrap(v) for v in flatten(args)]
 
     def shape(self):
@@ -525,12 +526,12 @@ class Repl(Value):
     Repl, out
         Replicated value.
     """
-    def __init__(self, value, count):
+    def __init__(self, value, count, *, src_loc_at=0):
         if not isinstance(count, int) or count < 0:
             raise TypeError("Replication count must be a non-negative integer, not '{!r}'"
                             .format(count))
 
-        super().__init__()
+        super().__init__(src_loc_at=src_loc_at)
         self.value = Value.wrap(value)
         self.count = count
 
@@ -592,7 +593,7 @@ class Signal(Value, DUID):
     attrs : dict
     """
 
-    def __init__(self, shape=None, name=None, reset=0, reset_less=False, min=None, max=None,
+    def __init__(self, shape=None, name=None, *, reset=0, reset_less=False, min=None, max=None,
                  attrs=None, decoder=None, src_loc_at=0):
         super().__init__(src_loc_at=src_loc_at)
 
@@ -641,7 +642,7 @@ class Signal(Value, DUID):
             self.decoder = decoder
 
     @classmethod
-    def like(cls, other, name=None, name_suffix=None, src_loc_at=0, **kwargs):
+    def like(cls, other, *, name=None, name_suffix=None, src_loc_at=0, **kwargs):
         """Create Signal based on another.
 
         Parameters
@@ -688,8 +689,8 @@ class ClockSignal(Value):
     domain : str
         Clock domain to obtain a clock signal for. Defaults to ``"sync"``.
     """
-    def __init__(self, domain="sync"):
+    def __init__(self, domain="sync", *, src_loc_at=0):
-        super().__init__()
+        super().__init__(src_loc_at=src_loc_at)
         if not isinstance(domain, str):
             raise TypeError("Clock domain name must be a string, not '{!r}'".format(domain))
         self.domain = domain
@@ -722,8 +723,8 @@ class ResetSignal(Value):
     allow_reset_less : bool
         If the clock domain is reset-less, act as a constant ``0`` instead of reporting an error.
     """
-    def __init__(self, domain="sync", allow_reset_less=False):
+    def __init__(self, domain="sync", allow_reset_less=False, *, src_loc_at=0):
-        super().__init__()
+        super().__init__(src_loc_at=src_loc_at)
         if not isinstance(domain, str):
             raise TypeError("Clock domain name must be a string, not '{!r}'".format(domain))
         self.domain = domain
@@ -832,8 +833,8 @@ class Array(MutableSequence):
 
 @final
 class ArrayProxy(Value):
-    def __init__(self, elems, index):
+    def __init__(self, elems, index, *, src_loc_at=0):
-        super().__init__(src_loc_at=1)
+        super().__init__(src_loc_at=1 + src_loc_at)
         self.elems = elems
         self.index = Value.wrap(index)
 
@@ -885,7 +886,7 @@ class UserValue(Value):
         * Indexing or iterating through individual bits;
         * Adding an assignment to the value to a ``Module`` using ``m.d.<domain> +=``.
     """
-    def __init__(self, src_loc_at=1):
+    def __init__(self, *, src_loc_at=0):
         super().__init__(src_loc_at=1 + src_loc_at)
         self.__lowered = None
 
@@ -917,8 +918,8 @@ class Sample(Value):
     of the ``domain`` clock back. If that moment is before the beginning of time, it is equal
     to the value of the expression calculated as if each signal had its reset value.
     """
-    def __init__(self, expr, clocks, domain):
+    def __init__(self, expr, clocks, domain, *, src_loc_at=0):
-        super().__init__(src_loc_at=1)
+        super().__init__(src_loc_at=1 + src_loc_at)
         self.value  = Value.wrap(expr)
         self.clocks = int(clocks)
         self.domain = domain
@@ -962,6 +963,9 @@ class _StatementList(list):
 
 
 class Statement:
+    def __init__(self, *, src_loc_at=0):
+        self.src_loc = tracer.get_src_loc(1 + src_loc_at)
+
     @staticmethod
     def wrap(obj):
         if isinstance(obj, Iterable):
@@ -975,9 +979,8 @@ class Statement:
 
 @final
 class Assign(Statement):
-    def __init__(self, lhs, rhs, src_loc_at=0):
+    def __init__(self, lhs, rhs, *, src_loc_at=0):
-        self.src_loc = tracer.get_src_loc(src_loc_at)
+        super().__init__(src_loc_at=src_loc_at)
-
         self.lhs = Value.wrap(lhs)
         self.rhs = Value.wrap(rhs)
 
@@ -992,17 +995,14 @@ class Assign(Statement):
 
 
 class Property(Statement):
-    def __init__(self, test, _check=None, _en=None):
+    def __init__(self, test, *, _check=None, _en=None, src_loc_at=0):
-        self.src_loc = tracer.get_src_loc()
+        super().__init__(src_loc_at=src_loc_at)
-
         self.test   = Value.wrap(test)
-
         self._check = _check
+        self._en    = _en
         if self._check is None:
             self._check = Signal(reset_less=True, name="${}$check".format(self._kind))
             self._check.src_loc = self.src_loc
-
-        self._en = _en
         if _en is None:
             self._en = Signal(reset_less=True, name="${}$en".format(self._kind))
             self._en.src_loc = self.src_loc
@@ -1029,9 +1029,8 @@ class Assume(Property):
 
 # @final
 class Switch(Statement):
-    def __init__(self, test, cases, src_loc_at=0):
+    def __init__(self, test, cases, *, src_loc_at=0):
-        self.src_loc = tracer.get_src_loc(src_loc_at)
+        super().__init__(src_loc_at=src_loc_at)
-
         self.test  = Value.wrap(test)
         self.cases = OrderedDict()
         for keys, stmts in cases.items():
@@ -1081,7 +1080,8 @@ class Switch(Statement):
 
 @final
 class Delay(Statement):
-    def __init__(self, interval=None):
+    def __init__(self, interval=None, *, src_loc_at=0):
+        super().__init__(src_loc_at=src_loc_at)
         self.interval = None if interval is None else float(interval)
 
     def _rhs_signals(self):
@@ -1096,7 +1096,8 @@ class Delay(Statement):
 
 @final
 class Tick(Statement):
-    def __init__(self, domain="sync"):
+    def __init__(self, domain="sync", *, src_loc_at=0):
+        super().__init__(src_loc_at=src_loc_at)
         self.domain = str(domain)
 
     def _rhs_signals(self):
@@ -1108,6 +1109,9 @@ class Tick(Statement):
 
 @final
 class Passive(Statement):
+    def __init__(self, *, src_loc_at=0):
+        super().__init__(src_loc_at=src_loc_at)
+
     def _rhs_signals(self):
         return ValueSet()
 

nmigen/hdl/xfrm.py

@@ -207,7 +207,7 @@ class StatementVisitor(metaclass=ABCMeta):
             new_stmt = self.on_statements(stmt)
         else:
             new_stmt = self.on_unknown_statement(stmt)
-        if hasattr(stmt, "src_loc") and hasattr(new_stmt, "src_loc"):
+        if isinstance(new_stmt, Statement):
             new_stmt.src_loc = stmt.src_loc
         return new_stmt