Add a Starlark flag to select() on to get the Python mode
This adds @bazel_tools//tools/python:python_version, whose value is always either "PY2" or "PY3" (never undefined), and which works regardless of the value of --experimental_better_python_version_mixing. Users who need to select() on the Python version should use this label in their `config_setting`s. Users should not select() on "force_python" or "python_version" because these flags may not always represent the true Python version state, and can lead to action conflict errors.
Work toward #6583.
RELNOTES: None
PiperOrigin-RevId: 226235967
diff --git a/tools/python/BUILD b/tools/python/BUILD
index a344b44..62c1b80 100644
--- a/tools/python/BUILD
+++ b/tools/python/BUILD
@@ -1,3 +1,5 @@
+load(":python_version.bzl", "define_python_version_flag")
+
package(default_visibility = ["//visibility:public"])
sh_binary(
@@ -6,27 +8,15 @@
)
filegroup(
- name = "srcs_and_embedded_tools",
- srcs = [
- # Tools are build from the workspace for tests.
- "2to3.sh",
- "BUILD",
- ],
- visibility = ["//visibility:private"],
-)
-
-filegroup(
name = "srcs",
- srcs = [
- ":srcs_and_embedded_tools",
+ srcs = glob(["**"]) + [
"//tools/python/runfiles:srcs",
],
)
filegroup(
name = "embedded_tools",
- srcs = [
- ":srcs_and_embedded_tools",
+ srcs = glob(["**"]) + [
"//tools/python/runfiles:embedded_tools",
],
visibility = ["//tools:__pkg__"],
@@ -39,3 +29,48 @@
],
visibility = ["//tools:__pkg__"],
)
+
+# This target can be used to inspect the current Python major version. To use,
+# put it in the `flag_values` attribute of a `config_setting` and test it
+# against the values "PY2" or "PY3". It will always match one or the other.
+#
+# If you do not need to test any other flags in combination with the Python
+# version, then as a convenience you may use the predefined `config_setting`s
+# `@bazel_tools//python:PY2` and `@bazel_tools//python:PY3`.
+#
+# Example usage:
+#
+# config_setting(
+# name = "py3_on_arm",
+# values = {"cpu": "arm"},
+# flag_values = {"@bazel_tools//python:python_version": "PY3"},
+# )
+#
+# my_target(
+# ...
+# some_attr = select({
+# ":py3_on_arm": ...,
+# ...
+# }),
+# ...
+# )
+#
+# Caution: Do not `select()` on the built-in command-line flags `--force_python`
+# or `--python_version`, as they do not always reflect the true Python version
+# of the current target. `select()`-ing on them can lead to action conflicts and
+# will be disallowed.
+define_python_version_flag(
+ name = "python_version",
+)
+
+config_setting(
+ name = "PY2",
+ flag_values = {":python_version": "PY2"},
+ visibility = ["//visibility:public"],
+)
+
+config_setting(
+ name = "PY3",
+ flag_values = {":python_version": "PY3"},
+ visibility = ["//visibility:public"],
+)
