cleanup: factor reexports.bzl into the respective implementation files (#1137)

This helps avoid loading one rule requiring loading everything.

Within Google, this makes some Starlark testing frameworks avoid having
to mock far away dependencies of dependencies.

10 files changed, 159 insertions, 162 deletions

diff --git a/python/BUILD.bazel b/python/BUILD.bazel
index a524d2f..2582d73 100644
--- a/python/BUILD.bazel
+++ b/python/BUILD.bazel
@@ -56,9 +56,15 @@ bzl_library(
     visibility = ["//visibility:public"],
     deps = [
         ":current_py_toolchain_bzl",
+        ":py_binary_bzl",
         ":py_import_bzl",
+        ":py_info_bzl",
+        ":py_library_bzl",
+        ":py_runtime_bzl",
+        ":py_runtime_info_bzl",
+        ":py_runtime_pair_bzl",
+        ":py_test_bzl",
         "//python/private:bazel_tools_bzl",
-        "//python/private:reexports_bzl",
     ],
 )
 
@@ -76,7 +82,7 @@ bzl_library(
 bzl_library(
     name = "py_binary_bzl",
     srcs = ["py_binary.bzl"],
-    deps = ["//python/private:reexports_bzl"],
+    deps = ["//python/private:util_bzl"],
 )
 
 bzl_library(
@@ -99,19 +105,19 @@ bzl_library(
 bzl_library(
     name = "py_library_bzl",
     srcs = ["py_library.bzl"],
-    deps = ["//python/private:reexports_bzl"],
+    deps = ["//python/private:util_bzl"],
 )
 
 bzl_library(
     name = "py_runtime_bzl",
     srcs = ["py_runtime.bzl"],
-    deps = ["//python/private:reexports_bzl"],
+    deps = ["//python/private:util_bzl"],
 )
 
 bzl_library(
     name = "py_runtime_pair_bzl",
     srcs = ["py_runtime_pair.bzl"],
-    deps = ["//python/private:reexports_bzl"],
+    deps = ["//python/private:bazel_tools_bzl"],
 )
 
 bzl_library(
@@ -123,7 +129,7 @@ bzl_library(
 bzl_library(
     name = "py_test_bzl",
     srcs = ["py_test.bzl"],
-    deps = ["//python/private:reexports_bzl"],
+    deps = ["//python/private:util_bzl"],
 )
 
 # NOTE: Remember to add bzl_library targets to //tests:bzl_libraries
diff --git a/python/defs.bzl b/python/defs.bzl
index ec70c1b..6ded66a 100644
--- a/python/defs.bzl
+++ b/python/defs.bzl
@@ -14,16 +14,13 @@
 """Core rules for building Python projects."""
 
 load("@bazel_tools//tools/python:srcs_version.bzl", _find_requirements = "find_requirements")
-load(
-    "//python/private:reexports.bzl",
-    "internal_PyInfo",
-    "internal_PyRuntimeInfo",
-    _py_binary = "py_binary",
-    _py_library = "py_library",
-    _py_runtime = "py_runtime",
-    _py_runtime_pair = "py_runtime_pair",
-    _py_test = "py_test",
-)
+load("//python:py_binary.bzl", _py_binary = "py_binary")
+load("//python:py_info.bzl", internal_PyInfo = "PyInfo")
+load("//python:py_library.bzl", _py_library = "py_library")
+load("//python:py_runtime.bzl", _py_runtime = "py_runtime")
+load("//python:py_runtime_info.bzl", internal_PyRuntimeInfo = "PyRuntimeInfo")
+load("//python:py_runtime_pair.bzl", _py_runtime_pair = "py_runtime_pair")
+load("//python:py_test.bzl", _py_test = "py_test")
 load(":current_py_toolchain.bzl", _current_py_toolchain = "current_py_toolchain")
 load(":py_import.bzl", _py_import = "py_import")
 
diff --git a/python/private/BUILD.bazel b/python/private/BUILD.bazel
index 21e3c16..4068ea4 100644
--- a/python/private/BUILD.bazel
+++ b/python/private/BUILD.bazel
@@ -41,6 +41,12 @@ bzl_library(
     deps = [":bazel_tools_bzl"],
 )
 
+bzl_library(
+    name = "util_bzl",
+    srcs = ["util.bzl"],
+    visibility = ["//python:__subpackages__"],
+)
+
 # @bazel_tools can't define bzl_library itself, so we just put a wrapper around it.
 bzl_library(
     name = "bazel_tools_bzl",
diff --git a/python/private/reexports.bzl b/python/private/reexports.bzl
index 987187c..a300a20 100644
--- a/python/private/reexports.bzl
+++ b/python/private/reexports.bzl
@@ -37,20 +37,6 @@ different name. Then we can load it from defs.bzl and export it there under
 the original name.
 """
 
-load("@bazel_tools//tools/python:toolchain.bzl", _py_runtime_pair = "py_runtime_pair")
-
-# The implementation of the macros and tagging mechanism follows the example
-# set by rules_cc and rules_java.
-
-_MIGRATION_TAG = "__PYTHON_RULES_MIGRATION_DO_NOT_USE_WILL_BREAK__"
-
-def _add_tags(attrs):
-    if "tags" in attrs and attrs["tags"] != None:
-        attrs["tags"] = attrs["tags"] + [_MIGRATION_TAG]
-    else:
-        attrs["tags"] = [_MIGRATION_TAG]
-    return attrs
-
 # Don't use underscore prefix, since that would make the symbol local to this
 # file only. Use a non-conventional name to emphasize that this is not a public
 # symbol.
@@ -59,125 +45,3 @@ internal_PyInfo = PyInfo
 
 # buildifier: disable=name-conventions
 internal_PyRuntimeInfo = PyRuntimeInfo
-
-def py_library(**attrs):
-    """See the Bazel core [py_library](https://docs.bazel.build/versions/master/be/python.html#py_library) documentation.
-
-    Args:
-      **attrs: Rule attributes
-    """
-    if attrs.get("srcs_version") in ("PY2", "PY2ONLY"):
-        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
-
-    # buildifier: disable=native-python
-    native.py_library(**_add_tags(attrs))
-
-def py_binary(**attrs):
-    """See the Bazel core [py_binary](https://docs.bazel.build/versions/master/be/python.html#py_binary) documentation.
-
-    Args:
-      **attrs: Rule attributes
-    """
-    if attrs.get("python_version") == "PY2":
-        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
-    if attrs.get("srcs_version") in ("PY2", "PY2ONLY"):
-        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
-
-    # buildifier: disable=native-python
-    native.py_binary(**_add_tags(attrs))
-
-def py_test(**attrs):
-    """See the Bazel core [py_test](https://docs.bazel.build/versions/master/be/python.html#py_test) documentation.
-
-    Args:
-      **attrs: Rule attributes
-    """
-    if attrs.get("python_version") == "PY2":
-        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
-    if attrs.get("srcs_version") in ("PY2", "PY2ONLY"):
-        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
-
-    # buildifier: disable=native-python
-    native.py_test(**_add_tags(attrs))
-
-def py_runtime(**attrs):
-    """See the Bazel core [py_runtime](https://docs.bazel.build/versions/master/be/python.html#py_runtime) documentation.
-
-    Args:
-      **attrs: Rule attributes
-    """
-    if attrs.get("python_version") == "PY2":
-        fail("Python 2 is no longer supported: see https://github.com/bazelbuild/rules_python/issues/886")
-
-    # buildifier: disable=native-python
-    native.py_runtime(**_add_tags(attrs))
-
-# NOTE: This doc is copy/pasted from the builtin py_runtime_pair rule so our
-# doc generator gives useful API docs.
-def py_runtime_pair(name, py2_runtime = None, py3_runtime = None, **attrs):
-    """A toolchain rule for Python.
-
-    This used to wrap up to two Python runtimes, one for Python 2 and one for Python 3.
-    However, Python 2 is no longer supported, so it now only wraps a single Python 3
-    runtime.
-
-    Usually the wrapped runtimes are declared using the `py_runtime` rule, but any
-    rule returning a `PyRuntimeInfo` provider may be used.
-
-    This rule returns a `platform_common.ToolchainInfo` provider with the following
-    schema:
-
-    ```python
-    platform_common.ToolchainInfo(
-        py2_runtime = None,
-        py3_runtime = <PyRuntimeInfo or None>,
-    )
-    ```
-
-    Example usage:
-
-    ```python
-    # In your BUILD file...
-
-    load("@rules_python//python:defs.bzl", "py_runtime_pair")
-
-    py_runtime(
-        name = "my_py3_runtime",
-        interpreter_path = "/system/python3",
-        python_version = "PY3",
-    )
-
-    py_runtime_pair(
-        name = "my_py_runtime_pair",
-        py3_runtime = ":my_py3_runtime",
-    )
-
-    toolchain(
-        name = "my_toolchain",
-        target_compatible_with = <...>,
-        toolchain = ":my_py_runtime_pair",
-        toolchain_type = "@rules_python//python:toolchain_type",
-    )
-    ```
-
-    ```python
-    # In your WORKSPACE...
-
-    register_toolchains("//my_pkg:my_toolchain")
-    ```
-
-    Args:
-        name: str, the name of the target
-        py2_runtime: optional Label; must be unset or None; an error is raised
-            otherwise.
-        py3_runtime: Label; a target with `PyRuntimeInfo` for Python 3.
-        **attrs: Extra attrs passed onto the native rule
-    """
-    if attrs.get("py2_runtime"):
-        fail("PYthon 2 is no longer supported: see https://github.com/bazelbuild/rules_python/issues/886")
-    _py_runtime_pair(
-        name = name,
-        py2_runtime = py2_runtime,
-        py3_runtime = py3_runtime,
-        **attrs
-    )
diff --git a/python/private/util.bzl b/python/private/util.bzl
index 8ea1f49..25a50aa 100644
--- a/python/private/util.bzl
+++ b/python/private/util.bzl
@@ -29,3 +29,15 @@ def copy_propagating_kwargs(from_kwargs, into_kwargs = None):
         if attr in from_kwargs and attr not in into_kwargs:
             into_kwargs[attr] = from_kwargs[attr]
     return into_kwargs
+
+# The implementation of the macros and tagging mechanism follows the example
+# set by rules_cc and rules_java.
+
+_MIGRATION_TAG = "__PYTHON_RULES_MIGRATION_DO_NOT_USE_WILL_BREAK__"
+
+def add_migration_tag(attrs):
+    if "tags" in attrs and attrs["tags"] != None:
+        attrs["tags"] = attrs["tags"] + [_MIGRATION_TAG]
+    else:
+        attrs["tags"] = [_MIGRATION_TAG]
+    return attrs
diff --git a/python/py_binary.bzl b/python/py_binary.bzl
index 9d145d8..6b6f7e0 100644
--- a/python/py_binary.bzl
+++ b/python/py_binary.bzl
@@ -14,6 +14,18 @@
 
 """Public entry point for py_binary."""
 
-load("//python/private:reexports.bzl", _py_binary = "py_binary")
+load("//python/private:util.bzl", "add_migration_tag")
 
-py_binary = _py_binary
+def py_binary(**attrs):
+    """See the Bazel core [py_binary](https://docs.bazel.build/versions/master/be/python.html#py_binary) documentation.
+
+    Args:
+      **attrs: Rule attributes
+    """
+    if attrs.get("python_version") == "PY2":
+        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
+    if attrs.get("srcs_version") in ("PY2", "PY2ONLY"):
+        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
+
+    # buildifier: disable=native-python
+    native.py_binary(**add_migration_tag(attrs))
diff --git a/python/py_library.bzl b/python/py_library.bzl
index 1aff68c..d54cbb2 100644
--- a/python/py_library.bzl
+++ b/python/py_library.bzl
@@ -14,6 +14,16 @@
 
 """Public entry point for py_library."""
 
-load("//python/private:reexports.bzl", _py_library = "py_library")
+load("//python/private:util.bzl", "add_migration_tag")
 
-py_library = _py_library
+def py_library(**attrs):
+    """See the Bazel core [py_library](https://docs.bazel.build/versions/master/be/python.html#py_library) documentation.
+
+    Args:
+      **attrs: Rule attributes
+    """
+    if attrs.get("srcs_version") in ("PY2", "PY2ONLY"):
+        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
+
+    # buildifier: disable=native-python
+    native.py_library(**add_migration_tag(attrs))
diff --git a/python/py_runtime.bzl b/python/py_runtime.bzl
index 5e80308..b70f9d4 100644
--- a/python/py_runtime.bzl
+++ b/python/py_runtime.bzl
@@ -14,6 +14,16 @@
 
 """Public entry point for py_runtime."""
 
-load("//python/private:reexports.bzl", _py_runtime = "py_runtime")
+load("//python/private:util.bzl", "add_migration_tag")
 
-py_runtime = _py_runtime
+def py_runtime(**attrs):
+    """See the Bazel core [py_runtime](https://docs.bazel.build/versions/master/be/python.html#py_runtime) documentation.
+
+    Args:
+      **attrs: Rule attributes
+    """
+    if attrs.get("python_version") == "PY2":
+        fail("Python 2 is no longer supported: see https://github.com/bazelbuild/rules_python/issues/886")
+
+    # buildifier: disable=native-python
+    native.py_runtime(**add_migration_tag(attrs))
diff --git a/python/py_runtime_pair.bzl b/python/py_runtime_pair.bzl
index 3f3ecf4..951c606 100644
--- a/python/py_runtime_pair.bzl
+++ b/python/py_runtime_pair.bzl
@@ -14,6 +14,74 @@
 
 """Public entry point for py_runtime_pair."""
 
-load("//python/private:reexports.bzl", _py_runtime_pair = "py_runtime_pair")
+load("@bazel_tools//tools/python:toolchain.bzl", _py_runtime_pair = "py_runtime_pair")
 
-py_runtime_pair = _py_runtime_pair
+# NOTE: This doc is copy/pasted from the builtin py_runtime_pair rule so our
+# doc generator gives useful API docs.
+def py_runtime_pair(name, py2_runtime = None, py3_runtime = None, **attrs):
+    """A toolchain rule for Python.
+
+    This used to wrap up to two Python runtimes, one for Python 2 and one for Python 3.
+    However, Python 2 is no longer supported, so it now only wraps a single Python 3
+    runtime.
+
+    Usually the wrapped runtimes are declared using the `py_runtime` rule, but any
+    rule returning a `PyRuntimeInfo` provider may be used.
+
+    This rule returns a `platform_common.ToolchainInfo` provider with the following
+    schema:
+
+    ```python
+    platform_common.ToolchainInfo(
+        py2_runtime = None,
+        py3_runtime = <PyRuntimeInfo or None>,
+    )
+    ```
+
+    Example usage:
+
+    ```python
+    # In your BUILD file...
+
+    load("@rules_python//python:defs.bzl", "py_runtime_pair")
+
+    py_runtime(
+        name = "my_py3_runtime",
+        interpreter_path = "/system/python3",
+        python_version = "PY3",
+    )
+
+    py_runtime_pair(
+        name = "my_py_runtime_pair",
+        py3_runtime = ":my_py3_runtime",
+    )
+
+    toolchain(
+        name = "my_toolchain",
+        target_compatible_with = <...>,
+        toolchain = ":my_py_runtime_pair",
+        toolchain_type = "@rules_python//python:toolchain_type",
+    )
+    ```
+
+    ```python
+    # In your WORKSPACE...
+
+    register_toolchains("//my_pkg:my_toolchain")
+    ```
+
+    Args:
+        name: str, the name of the target
+        py2_runtime: optional Label; must be unset or None; an error is raised
+            otherwise.
+        py3_runtime: Label; a target with `PyRuntimeInfo` for Python 3.
+        **attrs: Extra attrs passed onto the native rule
+    """
+    if attrs.get("py2_runtime"):
+        fail("PYthon 2 is no longer supported: see https://github.com/bazelbuild/rules_python/issues/886")
+    _py_runtime_pair(
+        name = name,
+        py2_runtime = py2_runtime,
+        py3_runtime = py3_runtime,
+        **attrs
+    )
diff --git a/python/py_test.bzl b/python/py_test.bzl
index 84470bc..09580c0 100644
--- a/python/py_test.bzl
+++ b/python/py_test.bzl
@@ -14,6 +14,18 @@
 
 """Public entry point for py_test."""
 
-load("//python/private:reexports.bzl", _py_test = "py_test")
+load("//python/private:util.bzl", "add_migration_tag")
 
-py_test = _py_test
+def py_test(**attrs):
+    """See the Bazel core [py_test](https://docs.bazel.build/versions/master/be/python.html#py_test) documentation.
+
+    Args:
+      **attrs: Rule attributes
+    """
+    if attrs.get("python_version") == "PY2":
+        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
+    if attrs.get("srcs_version") in ("PY2", "PY2ONLY"):
+        fail("Python 2 is no longer supported: https://github.com/bazelbuild/rules_python/issues/886")
+
+    # buildifier: disable=native-python
+    native.py_test(**add_migration_tag(attrs))