Amaranth bitwise negation `~` compiles to Python bitwise negation `~` in
simulation; the same holds for comparison operators such as `==`. Thus
an expression such as `~(a == b)` in simulation will compile to Python
that takes the bitwise negation of the comparison result, which will be
an actual bool.
On 3.12, the result is a `DeprecationWarning` emitted only at simulation
run-time.
When negating in simulation, coerce the value to an int. `mask` is
sufficient as we do no further arithmetic here.
This fixes the following issues:
- on Python 3.10 and earlier, storing to free variables is now handled
correctly
- on Python 3.11, `_varname_from_oparg` is now used, fixing problems
with cell variables that are also arguments
- on all supported versions, EXTENDED_ARG is now parsed, ensuring proper
handling for long functions
Fixes#792.
This is actually an existing correctness requirement (for the similar
reasons that ValueCastable.as_value() must always return the same
value every time) that for some reason wasn't respected.
See amaranth-lang/rfcs#15 and #784.
Note that this RFC breaks the existing syntax for initializing a view
with a new signal. Instances of `View(layout)` *must* be changed to
`Signal(layout)`.
The __init_subclass__ method fires on class definition rather than use.
It also has the bonus impact that no __new__ method is defined, so the
classes can be correctly detected as mix-in classes by modules such as
enum.
See amaranth-lang/rfcs#4.
This functionality was not explicitly specified in the RFC but it
falls under "anywhere an integer or an enumeration is accepted".
* Reject union initialization with more than one reset value.
* Replace the reset value specified in the class definition with
the one provided during initalization instead of merging.
* Annotations like `s: unsigned(4) = 1` are recognized and
the assigned value is used as the reset value for the implicitly
created `Signal`.
* Base classes inheriting from `Struct` and `Union` without
specifying a layout are recognized.
* Classes that both inherit from a base class with a layout and
specify a layout are rejected.
Mutability of Field isn't specified by the RFC and can cause issues
if the objects stored in Layout subclasses are mutated. There isn't
any reason to do that (the subclasses themselves are mutable and
handle that correctly), so disallow it.
These operators are ignored when they are encountered on LHS, as
the signedness of the assignment target does not matter in Amaranth.
.as_signed() appears on LHS of assigns to signed aggregate fields.
