Code generation workflow for the Slint Python bindings #9834

GreyElaina · 2025-10-23T17:05:27Z

Summary

add the slint.codegen package with a CLI entry point to generate Python runtime and stub files from .slint
surface property and callback metadata from the interpreter, refine the callback decorator overloads, and generate modules/stubs with accurate type hints
document the generator, ship a counter example project, and cover the new flow with unit and integration tests while retaining the legacy import loader

Testing

pytest api/python/slint/tests/codegen -q

Follow-ups

update slint-ui/slint-python-template and slint-ui/material-python-template once codegen becomes the primary path

- introduce slint.codegen to emit runtime modules and stubs from .slint inputs via CLI or API - expose property/callback metadata in the bindings, extend callback decorator overloads, and add libcst-backed emitters for typed modules - document the workflow, add a counter example plus tests, and keep the legacy import-loader path for now

CLAassistant · 2025-10-23T17:05:34Z

All committers have signed the CLA.

…e utils.py

…nfiguration

- Drop nox cause we only rely on uv and maturin - Also drop unnessesary optional-dependencies group - Make ruff & mypy happy - `slint.{slint => core}`, `slint.{__init__ => api}`

GreyElaina · 2025-10-24T06:17:01Z

When i apply slint.codegen to ui-libraries/material then more problems occured... Let me see

GreyElaina · 2025-10-24T09:44:53Z

So, isn't it enough to distribute @material on PyPI directly using importlib.resources...?

tronical · 2025-10-24T13:09:17Z

Hi! Could you elaborate a bit what this PR does?

As part of #4136 we've been working on generating a .py file for .slint files (along with embedding typings) in https://github.com/slint-ui/slint/commits/simon/python-stubs/ . That's work I progress, but it can generate typings for all our test suite and the missing bits are verification of signature changes when the .slint files have changed as well as documentation. You can see an example of how the generated code looks like here: https://github.com/slint-ui/slint/blob/simon/python-stubs/demos/printerdemo/python/printerdemo.py

GreyElaina · 2025-10-24T16:18:00Z

Hi! Could you elaborate a bit what this PR does?

As part of #4136 we've been working on generating a .py file for .slint files (along with embedding typings) in simon/python-stubs/ (commits) . That's work I progress, but it can generate typings for all our test suite and the missing bits are verification of signature changes when the .slint files have changed as well as documentation. You can see an example of how the generated code looks like here: simon/python-stubs/demos/printerdemo/python/printerdemo.py

thx for taking a look. this PR is trying to accomplish:

It adds a Python-side code generator (slint.codegen) that walks one or more inputs (files or directories), preserves their package layout, and emits both the runnable module (.py) and a matching stub (.pyi). The generator can either drop the output next to the source or into an explicit target tree so the generated code can be checked into a wheel or vendor-ed alongside application code.
The runtime module we generate keeps loading the compiled component at execution time (so we still benefit from the flexibility the current loader gives us), but places the Python API surface in a normal module so editors can offer completions, go-to-definition, etc. without relying on import hooks.

the idea of checked load asserting that the generated artifact matches the .slint input... LGTM, but having to ship the JSON blob in every generated module. We’re experimenting with keying the tool.uv.cache-key via uv/pyproject metadata so that we can invalidate when the source changes; if that approach works out I’d be keen to wire it in here.

BTW, the python_type_name implementation is much better: supporting enums and user-defined structs/tuples directly. porting planned.

GreyElaina · 2025-10-25T10:55:15Z

WHY api/python/compiler is a downloader??

A maturin-powered pyproject.toml is enough for this case.

[build-system]
requires = ["maturin>=1.9,<2.0"]
build-backend = "maturin"

[project]
name = "slint-compiler"
requires-python = ">=3.10"
classifiers = [
    "Programming Language :: Rust",
    "Programming Language :: Python :: Implementation :: CPython",
]
dynamic = ["version"]

[tool.maturin]
bindings = "bin"
manifest-path = "Cargo.toml"

tronical · 2025-10-25T13:37:30Z

WHY api/python/compiler is a downloader??

A maturin-powered pyproject.toml is enough for this case.

The idea was to re-use the same binaries we've already built for the release, instead of doing another build for every host combination for Python.

I don't feel too strongly about this, but I like that this makes it a very low maintenance solution.

Are there any downsides we should address by using dedicated wheels?

GreyElaina · 2025-10-25T14:10:12Z

WHY api/python/compiler is a downloader??
A maturin-powered pyproject.toml is enough for this case.

The idea was to re-use the same binaries we've already built for the release, instead of doing another build for every host combination for Python.

I don't feel too strongly about this, but I like that this makes it a very low maintenance solution.

Are there any downsides we should address by using dedicated wheels?

No, but current downloader is not friendly to mirrors, which is important for poor network situation like in china mainland. And... personally, I like to follow the Occam's Razor principle, so if we can get it from PyPI, there's no need for our script to download it again from GitHub. In my opinion, this brings more trouble, like the current downloader has to manually concatenate URLs, etc... Anyway, maturin, cibuildwheel and other smart developers have already taken care of these for us, why not take advantage of that?

I have drafted 35b6b9d (#9834) for this improvement. ~~although it increased the carbon footprint, we all use Rust, so just don't worry about it.~~

GreyElaina · 2025-10-25T15:34:09Z

All enums in internal/common aren't wired...oh.

tronical · 2025-10-28T10:20:28Z

I don't think we expose these as-is in the other languages, so I don't think we should do so for Python.

Are you thinking that it's only necessary to let .slint access these APIs...?

Yes

Implementations of bindings in other languages perhaps should not involve the parts about layout or style control in .slint — these are all completed by callbacks that actually have similar ViewModel/Controller capabilities, is that right?

Yes

…t URLs in pyproject.toml

GreyElaina · 2025-10-28T12:58:24Z

Now, it can generate typing.Any for fields of built-in enum/struct types while still generating the correct types for user-defined enum/structs.

- Added `is_builtin` and `is_used` attributes to `StructMeta` and `EnumMeta` classes for better tracking of built-in types. - Updated the counter example to include a new property for text alignment and adjusted the generated Python code accordingly. - Introduced a new test module for optional types, including structures and enums, to validate their behavior. - Enhanced the test suite to ensure proper handling of enums and structures, including keyword-only arguments and unknown keywords. - Improved the handling of built-in enums in the Rust backend, ensuring they are correctly initialized and exposed to Python. - Refactored existing tests to use the new structure and ensure compatibility with the updated code generation logic. - Added tests for event loop handling, including SIGINT and quit events, to ensure robustness in asynchronous scenarios.

…efix

…ic_import path

- Recommend running the code generator as part of the build process - Instructions for using third-party component libraries

- Avoid rust-analyzer alarms and spinning

GreyElaina · 2025-10-30T12:39:57Z

@tronical SlintEventLoop always exit when the last window quit, even expose and use the run_event_loop_until_quit.

GreyElaina added 3 commits October 24, 2025 01:01

Merge branch 'master' of https://github.com/slint-ui/slint

3a63b47

Merge branch 'master' of https://github.com/slint-ui/slint

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autofix-ci bot and others added 10 commits October 23, 2025 17:07

[autofix.ci] apply automated fixes

4e68196

python: fix missing examples.counter.generated

b844bf4

Merge branch 'master' of https://github.com/GreyElaina/slint

67747d8

[autofix.ci] apply automated fixes

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refactor: replace normalize_identifier with _normalize_prop and remov…

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…e utils.py

[autofix.ci] apply automated fixes

646e92e

fix: python codegen circual import

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fix: ambignous slint.slint now slint.core via workable maturin co…

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…nfiguration

fix: cleanup slint.codegen.__init__

f8ece22

Refactor python binding module structure

6adb9de

- Drop nox cause we only rely on uv and maturin - Also drop unnessesary optional-dependencies group - Make ruff & mypy happy - `slint.{slint => core}`, `slint.{__init__ => api}`

GreyElaina force-pushed the master branch from 9d89d65 to 6adb9de Compare October 24, 2025 05:30

GreyElaina added 5 commits October 25, 2025 15:08

fix: nomalize identity with python keyword

11275c8

fix: missing hint for slint.Color

78ff39d

fix(python/cli): expect at least one input

a5ce4e6

fix(python): recorrect python identifier nomi in rust

d24f5dd

fix(python): missing inspect import

449d76a

refactor: restructure slint-compiler workflow

35b6b9d

fix(python/briefcase): improve code formatting

601faff

GreyElaina and others added 6 commits October 28, 2025 10:44

refactor: restructure slint-compiler workflow

daa997e

chore: update workflow to use specific Ubuntu versions and add projec…

2928dc5

…t URLs in pyproject.toml

ci: remove all related to api/python/compiler

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[autofix.ci] apply automated fixes

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Merge branch 'cherry-35b6b9d' into master

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[autofix.ci] apply automated fixes

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GreyElaina and others added 21 commits October 29, 2025 10:51

refactor(python): drop enums & structs export

a85b3c5

refactor: revert defination methods de-optional

687aa66

fix(python): adopt loop to standard selector loop behavior

2d0c9de

refactor: remove unused /undecided methods from ComponentInstance class

fe2c273

refactor(python): rename HasFileno and fd_for_fileobj to protected pr…

40e4c47

…efix

refactor(python): fix tests global_properties assertions and test_mag…

3103702

…ic_import path

fix(python): add type ignore for selector attribute in SlintEventLoop

9ae9f4d

test(python): add tests for emitters package code generation

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chore(python): add pytest-cov to development dependencies

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doc(python): update README.md

a300d54

- Recommend running the code generator as part of the build process - Instructions for using third-party component libraries

feat(build): implement stable library path copying in build script

64ea77e

- Avoid rust-analyzer alarms and spinning

feat(python): add stubgen script

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[autofix.ci] apply automated fixes

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fix(python): remove unused imports from interpreter.rs

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fix(python): mis-replaced repr(Path)

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fix(python): make mypy happy

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fix(python): ruff

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fix(python): mypy, ruff

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fix(python): alright then. run_until_complete() -> T | None

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Merge branch 'master' into master

9bee1ce

Code generation workflow for the Slint Python bindings #9834

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GreyElaina commented Oct 23, 2025

Summary

Testing

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