agents: add pipeline reuse, type uniformity, and WORKSPACE parity rules (#4421) Agent implementations of WORKSPACE features (such as #4374 vs. #4416) previously invented parallel repository rules, format converters, and runtime union-type branches instead of reusing existing pipelines and canonical data types. This duplicated Bzlmod logic, broke host portability for vendored `requirements.bzl` files, and modified unrelated code. Codify the design and Starlark rules from #4416 so agents: * Trace existing call graphs and extend existing `WORKSPACE` rules and pipelines (`parse_requirements` -> `requirements.bzl.tmpl.workspace` -> `whl_library`) at the narrowest seam rather than adding parallel rules or format converters. * Extract pure helpers needed by both Bzlmod and `WORKSPACE` into standalone Bzlmod-agnostic `.bzl` files. * Preserve host portability in vendored `requirements.bzl` by emitting direct downloader attributes only when a package resolves to a single cross-platform distribution, falling back to `--hash` flags for platform-specific wheels. * Enforce uniform parameter, return, and collection types across callers and test fixtures without runtime union-type branches. * Leave working code untouched unless required and decompose multi-stage functions into focused helpers.
This repository is the home of the core Python rules -- py_library, py_binary, py_test, and related symbols that provide the basis for Python support in Bazel. It also contains package installation rules for integrating with PyPI and other indices.
Documentation for rules_python is at https://rules-python.readthedocs.io and in the Bazel Build Encyclopedia.
Examples live in the examples directory.
The core rules are stable. Their implementation is subject to Bazel's backward compatibility policy. This repository aims to follow semantic versioning.
The Bazel community maintains this repository. Neither Google nor the Bazel team provides support for the code. However, this repository is part of the test suite used to vet new Bazel releases. See How to contribute page for information on our development workflow.
requirements.txt is how users have been defining dependencies for a long time. We support this to support legacy usecases or package managers that we don't support directly. Any additional information that we need will be retrieved from the SimpleAPI during the bzlmod extension evaluation phase. Then it will be written to the MODULE.bazel.lock file for future reuse. We also support uv.lock files directly under bzlmod, which already contain cross-platform distribution URLs and hashes and do not require SimpleAPI queries or storing distribution hashes in MODULE.bazel.lock. uv is recommended for generating uv.lock or a fully locked requirements.txt file, and we provide a rule for it.py_binary, py_test rules should scale to large monorepos and we work hard to minimize the work done during analysis and build phase. What is more, the space requirements for should be minimal, so we strive to use symlinks rather than extracting wheels at build time. This means that for different configurations of the same build, we are not extracting the wheel multiple times thus scaling better over the time. From 2.0 onwards we are creating a virtual env for each target by creating an actual minimal virtual environment using symlinks. We plan on creating the traditional site-packages layout in the future by default.rules_python and this has resulted in a few PEPs supported within pure starlark - PEP440, PEP509.Common misconceptions:
rules_python has to keep backwards compatibility with google3. Whilst this might have been true in the past, rules_python is an open source project and any compatibility needs should come from the community - we have no requirement to keep this compatibility and are allowed to make our decisions. However, we do want to keep backwards compatibility as long as possible to not upset users with never ending migrations.rules_python is not caching pip downloads. With 2.0, we use Bazel's downloader by default and rely on bazel to provide the repository caching mechanisms. This means that for simpler setups this should result in transparent and scalable caching with the most recent bazel versions unless there are issues in the bazel itself.For detailed documentation, see https://rules-python.readthedocs.io
See Bzlmod support for more details.