pyosys: tox for non-wheel builds, update instructions

[donn]

What are the reasons/motivation for this change?

@Ravenslofty noted that unlike the previous setup, users may have to manually manage a virtual environment to get the new Python build dependencies (pybind11 and cxxheaderparser,) and that is cumbersome.

While pybind11 can in fact be installed via package managers, it tends to be out of date more often than not. cxxheaderparser is not in any package manager that isn't Nix.

I considered just handling the ImportError to instruct the user on creating a venv but that's also just kind of cumbersome.

Explain how this is achieved.

• add tox to list of dependencies: saves builders from manually having to manage a venv for python build dependencies
  • when building wheels, pip automatically creates the environment with those dependencies, so no need for tox
  • when running simply make ENABLE_PYOSYS=1, this is not the case. people attempting to pip3 install --upgrade pybind11 cxxheaderparser to add it to their system packages will be met with a scare message about "breaking system packages"
  • tox is available from all major package managers all the way back to ubuntu 20.04 and resolves this issue
  • if someone really prefers to provide their own dependencies (such as within Nix,) passing PYOSYS_USE_TOX=0 suppresses this behavior
• update installation instructions to drop boost and add tox instead

Naturally, tox is not required if you're not building Yosys with Python support.

Make sure your change comes with tests. If not possible, share how a reviewer might evaluate it.

On an Ubuntu 22.04 installation (Ubuntu 20.04 also in theory but the Bison on there is out of date so you have to build that on your own), apt-get install build-essential clang lld bison flex libfl-dev libreadline-dev gawk tcl-dev libffi-dev graphviz xdot pkg-config python3-dev tox zlib1g-dev should be enough to allow make ENABLE_PYOSYS=1 to build successfully without further intervention.

I validated that statement as follows:

podman run --rm -ti docker.io/ubuntu:22.04 bash -c "
    apt-get update &&
    DEBIAN_FRONTEND=noninteractive apt-get install -y git build-essential clang lld bison flex libfl-dev libreadline-dev gawk tcl-dev libffi-dev graphviz xdot pkg-config python3-dev tox zlib1g-dev &&
    git clone --recursive --branch pyosys_tweaks https://github.com/donn/yosys &&
    cd yosys &&
    make ENABLE_PYOSYS=1 -j\$(nproc) &&
    ./yosys -H
"

---

• Also bec macos-13 is being sunset by EOY, I updated the wheels CI script to use macos-15 and macos-15-intel before I forget about them, and for consistency updated the other CI scripts as well. https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down/

[Ravenslofty]

$ git reset --hard
HEAD is now at 7193598fb pyosys: `tox` for non-wheels builds, update instructions
$ make clean
[...]
$ git diff --stat
 kernel/binding.h   |   60 -----
 kernel/celltypes.h |  556 --------------------------------------------
 kernel/consteval.h |  426 ----------------------------------
 kernel/cost.h      |   99 --------
 kernel/log.h       |  528 ------------------------------------------
 kernel/register.h  |  179 ---------------
 kernel/rtlil.h     | 2447 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 kernel/yosys.h     |  103 ---------
 libs/sha1/sha1.h   |   57 -----
 9 files changed, 4455 deletions(-)

(we're discussing this privately, but I want to clarify I don't think this is presently ready to merge)

[donn]

Rebased on main to pull in #5435

[Ravenslofty]

It builds now; might wait for a JF to get more eyes on this though.

(now working after #5435)

[Ravenslofty]

in the JF it was decided that we'd prefer uv over tox for this process.