Flag: --incompatible_load_python_rules_from_bzl
Available since: 0.29
Will be flipped in: 2.0
Feature tracking issue: #8893

Motivation

The "core" Python rule logic is currently bundled with Bazel as a combination of native symbols and symbols loaded from @bazel_tools//tools/python. Eventually the native rules will be ported to Starlark, and all symbols will live in bazelbuild/rules_python. In the meantime, we're making it so the user loads these symbols from the rules_python repository, even though they're largely still implemented inside of Bazel itself. This will help make future migration of rule logic to rules_python less painful.

Change

Enabling this flag causes the four native Python rules,

• py_library
• py_binary
• py_test
• py_runtime

to fail at analysis time when they are used directly instead of via rules_python.

Migration

Any usage of the these rules as a built-in symbol should be replaced with a use of the macros defined in rules_python as follows. (All four macros are defined in defs.bzl.)

# My BUILD file

py_binary(
    ...
)

should become

# My BUILD file

load("@rules_python//python:defs.bzl", "py_binary")

py_binary(
    ...
)

In the case of macros in .bzl files,

# My .bzl file

def my_macro(...):
    native.py_binary(
        ...
    )

should become

# My .bzl file

load("@rules_python//python:defs.bzl", "py_binary")

def my_macro(...):
    py_binary(
        ...
    )

To access the @rules_python repo you'll need to make sure you have the following in your WORKSPACE file:

# My WORKSPACE file

load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")

git_repository(
    name = "rules_python",
    remote = "https://github.com/bazelbuild/rules_python.git",
    commit = "4b84ad270387a7c439ebdccfd530e2339601ef27",  # (2019-08-02 or later)
)

load("@rules_python//python:repositories.bzl", "py_repositories")
py_repositories()

If you're using rules_python for pip support (which is separate from the core Python rules), you'll also need to call the pip_repositories() function.

Note that until recently, @rules_python went by the workspace name @io_bazel_rules_python. If you have a definition for the old name in your WORKSPACE file then you'll need to rename it, and ensure your commit is updated to a recent version.