refactor: use usr flags instead of platforms in transition

Signed-off-by: Thulio Ferraz Assis <3149049+f0rmiga@users.noreply.github.com>

examples/multi_python_versions/WORKSPACE

@@ -1,5 +1,16 @@
 workspace(name = "rules_python_multi_python_versions")
 
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "bazel_skylib",
+    sha256 = "c6966ec828da198c5d9adbaa94c05e3a1c7f21bd012a0b29ba8ddbccb2c93b0d",
+    urls = [
+        "https://github.com/bazelbuild/bazel-skylib/releases/download/1.1.1/bazel-skylib-1.1.1.tar.gz",
+        "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.1.1/bazel-skylib-1.1.1.tar.gz",
+    ],
+)
+
 local_repository(
     name = "rules_python",
     path = "../..",

python/BUILD

@@ -34,7 +34,7 @@ filegroup(
     name = "distribution",
     srcs = glob(["**"]) + [
         "//python/constraints:distribution",
-        "//python/platforms:distribution",
+        "//python/config_settings:distribution",
         "//python/private:distribution",
         "//python/runfiles:distribution",
     ],

python/config_settings/BUILD.bazel

@@ -0,0 +1,12 @@
+load("//python:versions.bzl", "TOOL_VERSIONS")
+load(":config_settings.bzl", "construct_config_settings")
+
+filegroup(
+    name = "distribution",
+    srcs = glob(["*.bzl"]) + [
+        "BUILD.bazel",
+    ],
+    visibility = ["//python:__pkg__"],
+)
+
+construct_config_settings(python_versions = TOOL_VERSIONS.keys())

python/config_settings/config_settings.bzl

@@ -0,0 +1,26 @@
+"""This module is used to construct the config settings in the BUILD file in this same package.
+"""
+
+load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
+
+# buildifier: disable=unnamed-macro
+def construct_config_settings(python_versions):
+    """Constructs a set of configs for all Python versions.
+
+    Args:
+        python_versions: The Python versions supported by rules_python.
+    """
+    string_flag(
+        name = "python_version",
+        build_setting_default = python_versions[0],
+        values = python_versions,
+        visibility = ["//visibility:public"],
+    )
+
+    for python_version in python_versions:
+        python_version_constraint_setting = "is_python_" + python_version
+        native.config_setting(
+            name = python_version_constraint_setting,
+            flag_values = {":python_version": python_version},
+            visibility = ["//visibility:public"],
+        )

python/platforms/transition.bzl → python/config_settings/transition.bzl

@@ -4,13 +4,13 @@ them to the desired target platform.
 
 load("//python:defs.bzl", _py_binary = "py_binary", _py_test = "py_test")
 
-def _transition_platform_impl(_, attr):
-    return {"//command_line_option:platforms": str(attr.target_platform)}
+def _transition_python_version_impl(_, attr):
+    return {"//python/config_settings:python_version": str(attr.python_version)}
 
-_transition_platform = transition(
-    implementation = _transition_platform_impl,
+_transition_python_version = transition(
+    implementation = _transition_python_version_impl,
     inputs = [],
-    outputs = ["//command_line_option:platforms"],
+    outputs = ["//python/config_settings:python_version"],
 )
 
 def _transition_py_impl(ctx):
@@ -61,15 +61,15 @@ _COMMON_ATTRS = {
     "is_windows": attr.bool(
         mandatory = True,
     ),
+    "python_version": attr.string(
+        mandatory = True,
+    ),
     "target": attr.label(
         executable = True,
-        cfg = _transition_platform,
+        cfg = _transition_python_version,
         mandatory = True,
         providers = [PyInfo],
     ),
-    "target_platform": attr.label(
-        mandatory = True,
-    ),
     # "tools" is a hack here. It should be "data" but "data" is not included by default in the
     # location expansion in the same way it is in the native Python rules. The difference on how
     # the Bazel deals with those special attributes differ on the LocationExpander, e.g.:
@@ -102,7 +102,7 @@ _transition_py_test = rule(
     test = True,
 )
 
-def _py_rule(rule, transition_rule, name, target_platform, **kwargs):
+def _py_rule(rule, transition_rule, name, python_version, **kwargs):
     args = kwargs.pop("args", None)
     data = kwargs.pop("data", None)
     env = kwargs.pop("env", None)
@@ -154,9 +154,9 @@ def _py_rule(rule, transition_rule, name, target_platform, **kwargs):
             "//conditions:default": False,
         }),
         target = ":_" + name,
+        python_version = python_version,
 
         # Attributes common to all build rules.
-        target_platform = target_platform,
         compatible_with = compatible_with,
         deprecation = deprecation,
         distribs = distribs,
@@ -171,8 +171,8 @@ def _py_rule(rule, transition_rule, name, target_platform, **kwargs):
         visibility = visibility,
     )
 
-def py_binary(name, target_platform, **kwargs):
-    return _py_rule(_py_binary, _transition_py_binary, name, target_platform, **kwargs)
+def py_binary(name, python_version, **kwargs):
+    return _py_rule(_py_binary, _transition_py_binary, name, python_version, **kwargs)
 
-def py_test(name, target_platform, **kwargs):
-    return _py_rule(_py_test, _transition_py_test, name, target_platform, **kwargs)
+def py_test(name, python_version, **kwargs):
+    return _py_rule(_py_test, _transition_py_test, name, python_version, **kwargs)

python/pip.bzl

@@ -16,7 +16,7 @@
 load("//python/pip_install:pip_repository.bzl", "pip_repository", _package_annotation = "package_annotation")
 load("//python/pip_install:repositories.bzl", "pip_install_dependencies")
 load("//python/pip_install:requirements.bzl", _compile_pip_requirements = "compile_pip_requirements")
-load(":versions.bzl", "MINOR_MAPPING", "PLATFORMS")
+load(":versions.bzl", "MINOR_MAPPING")
 
 compile_pip_requirements = _compile_pip_requirements
 package_annotation = _package_annotation
@@ -285,19 +285,17 @@ def _whl_library_render_alias_target(
 alias(
     name = "{alias_name}",
     actual = select({{""".format(alias_name = alias_name)]
-    for [platform_name, meta] in PLATFORMS.items():
-        for [python_version, repo_prefix] in version_map:
-            alias.append("""\
-        "@{rules_python}//python/platforms:{platform_name}_{full_python_version}_config": "{actual}",""".format(
-                full_python_version = MINOR_MAPPING[python_version] if python_version in MINOR_MAPPING else python_version,
-                platform_name = platform_name,
-                actual = "@{repo_prefix}{wheel_name}//:{alias_name}".format(
-                    repo_prefix = repo_prefix,
-                    wheel_name = wheel_name,
-                    alias_name = alias_name,
-                ),
-                rules_python = rules_python,
-            ))
+    for [python_version, repo_prefix] in version_map:
+        alias.append("""\
+        "@{rules_python}//python/config_settings:is_python_{full_python_version}": "{actual}",""".format(
+            full_python_version = MINOR_MAPPING[python_version] if python_version in MINOR_MAPPING else python_version,
+            actual = "@{repo_prefix}{wheel_name}//:{alias_name}".format(
+                repo_prefix = repo_prefix,
+                wheel_name = wheel_name,
+                alias_name = alias_name,
+            ),
+            rules_python = rules_python,
+        ))
     alias.append("""\
         "//conditions:default": "{default_actual}",
     }}),

python/private/toolchains_repo.bzl

@@ -33,7 +33,7 @@ load(
 
 def _toolchains_repo_impl(rctx):
     rules_python_repository_name = rctx.attr._rules_python_workspace.workspace_name
-    python_version_constraint = "@{rules_python}//python/platforms:is_python_{python_version}".format(
+    python_version_constraint = "@{rules_python}//python/config_settings:is_python_{python_version}".format(
         rules_python = rules_python_repository_name,
         python_version = rctx.attr.python_version,
     )
@@ -54,7 +54,8 @@ def _toolchains_repo_impl(rctx):
 # for executing build actions.
 toolchain(
     name = "{platform}_toolchain",
-    target_compatible_with = {compatible_with} + (["{python_version_constraint}"] if {set_python_version_constraint} else []),
+    target_compatible_with = {compatible_with},
+    target_settings = ["{python_version_constraint}"] if {set_python_version_constraint} else [],
     toolchain = "@{user_repository_name}_{platform}//:python_runtimes",
     toolchain_type = "@bazel_tools//tools/python:toolchain_type",
 )
@@ -103,13 +104,10 @@ alias(name = "py3_runtime",     actual = "@{py_repository}_{host_platform}//:py3
 alias(name = "python_headers",  actual = "@{py_repository}_{host_platform}//:python_headers")
 alias(name = "python_runtimes", actual = "@{py_repository}_{host_platform}//:python_runtimes")
 alias(name = "python3",         actual = "@{py_repository}_{host_platform}//:{python3_binary_path}")
-alias(name = "platform",        actual = "@{rules_python_repository_name}//:{host_platform}_{python_version}_platform")
 """.format(
         py_repository = rctx.attr.user_repository_name,
         host_platform = host_platform,
         python3_binary_path = python3_binary_path,
-        python_version = rctx.attr.python_version,
-        rules_python_repository_name = rules_python_repository_name,
     )
     if not is_windows:
         build_contents += """\
@@ -125,22 +123,40 @@ alias(name = "pip",             actual = "@{py_repository}_{host_platform}//:bin
     rctx.file("defs.bzl", content = """\
 # Generated by python/private/toolchains_repo.bzl
 
-load(
-    "@{py_repository}_{host_platform}//:defs.bzl",
-    _compile_pip_requirements = "compile_pip_requirements",
-    _py_binary = "py_binary",
-    _py_test = "py_test",
-)
+load("@{rules_python}//python/config_settings:transition.bzl", _py_binary = "py_binary", _py_test = "py_test")
+load("@{rules_python}//python:pip.bzl", _compile_pip_requirements = "compile_pip_requirements")
 
-compile_pip_requirements = _compile_pip_requirements
 host_platform = "{host_platform}"
 interpreter = "@{py_repository}_{host_platform}//:{python3_binary_path}"
-py_binary = _py_binary
-py_test = _py_test
+
+def py_binary(name, **kwargs):
+    return _py_binary(
+        name = name,
+        python_version = "{python_version}",
+        **kwargs
+    )
+
+def py_test(name, **kwargs):
+    return _py_test(
+        name = name,
+        python_version = "{python_version}",
+        **kwargs
+    )
+
+def compile_pip_requirements(name, **kwargs):
+    return _compile_pip_requirements(
+        name = name,
+        py_binary = py_binary,
+        py_test = py_test,
+        **kwargs
+    )
+
 """.format(
-        py_repository = rctx.attr.user_repository_name,
         host_platform = host_platform,
+        py_repository = rctx.attr.user_repository_name,
+        python_version = rctx.attr.python_version,
         python3_binary_path = python3_binary_path,
+        rules_python = rules_python_repository_name,
     ))
 
 toolchain_aliases = repository_rule(

python/repositories.bzl

@@ -260,43 +260,6 @@ py_runtime_pair(
     rctx.file(STANDALONE_INTERPRETER_FILENAME, "# File intentionally left blank. Indicates that this is an interpreter repo created by rules_python.")
     rctx.file("BUILD.bazel", build_content)
 
-    rules_python_repository_name = rctx.attr._rules_python_workspace.workspace_name
-
-    defs_content = """\
-# Generated by python/repositories.bzl
-
-load("@{rules_python}//python/platforms:transition.bzl", _py_binary = "py_binary", _py_test = "py_test")
-load("@{rules_python}//python:pip.bzl", _compile_pip_requirements = "compile_pip_requirements")
-
-def py_binary(name, **kwargs):
-    return _py_binary(
-        name = name,
-        target_platform = "@{rules_python}//python/platforms:{platform}_{python_version}_platform",
-        **kwargs
-    )
-
-def py_test(name, **kwargs):
-    return _py_test(
-        name = name,
-        target_platform = "@{rules_python}//python/platforms:{platform}_{python_version}_platform",
-        **kwargs
-    )
-
-def compile_pip_requirements(name, **kwargs):
-    return _compile_pip_requirements(
-        name = name,
-        py_binary = py_binary,
-        py_test = py_test,
-        **kwargs
-    )
-""".format(
-        platform = platform,
-        python_version = python_version,
-        rules_python = rules_python_repository_name,
-    )
-
-    rctx.file("defs.bzl", defs_content)
-
     return {
         "distutils": rctx.attr.distutils,
         "distutils_content": rctx.attr.distutils_content,
@@ -364,9 +327,6 @@ python_repository = repository_rule(
         "zstd_version": attr.string(
             default = "1.5.2",
         ),
-        "_rules_python_workspace": attr.label(
-            default = Label("//:WORKSPACE"),
-        ),
     },
 )