From 5c336a16448bdb923102e5e72c14e7f3c2780133 Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 09:00:01 +0900
Subject: [PATCH 01/13] chore: stop exposing host platform in the toolchain
 aliases defs

---
 python/private/toolchains_repo.bzl | 1 -
 1 file changed, 1 deletion(-)

diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index d21fb53a41..f2c76e0269 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -181,7 +181,6 @@ load(
 )
 load("{rules_python}//python:pip.bzl", _compile_pip_requirements = "compile_pip_requirements")
 
-host_platform = "{host_platform}"
 interpreter = "@{py_repository}_{host_platform}//:{python3_binary_path}"
 
 def py_binary(name, **kwargs):

From 44a172090681c2463ea558a64995de62cbf2dfbc Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 09:00:47 +0900
Subject: [PATCH 02/13] chore: stop exposing the interpreter - use
 python_3_x_host//:python instead

---
 python/private/toolchains_repo.bzl | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index f2c76e0269..b0e38952b9 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -132,7 +132,6 @@ def _toolchain_aliases_impl(rctx):
     host_platform = _get_host_platform(os_name, arch)
 
     is_windows = (os_name == WINDOWS_NAME)
-    python3_binary_path = "python.exe" if is_windows else "bin/python3"
 
     # Base BUILD file for this repository.
     build_contents = """\
@@ -181,8 +180,6 @@ load(
 )
 load("{rules_python}//python:pip.bzl", _compile_pip_requirements = "compile_pip_requirements")
 
-interpreter = "@{py_repository}_{host_platform}//:{python3_binary_path}"
-
 def py_binary(name, **kwargs):
     return _py_binary(
         name = name,
@@ -213,10 +210,7 @@ def compile_pip_requirements(name, **kwargs):
     )
 
 """.format(
-        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 = get_repository_name(rctx.attr._rules_python_workspace),
     ))
 

From ba6fc876eeff9d35240b0b5054b18ab512d23106 Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 09:02:37 +0900
Subject: [PATCH 03/13] chore: remove uname calling from toolchain aliases repo

---
 python/private/toolchains_repo.bzl | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index b0e38952b9..14002fc645 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -127,9 +127,7 @@ toolchains_repo = repository_rule(
 
 def _toolchain_aliases_impl(rctx):
     logger = repo_utils.logger(rctx)
-    (os_name, arch) = _get_host_os_arch(rctx, logger)
-
-    host_platform = _get_host_platform(os_name, arch)
+    (os_name, _) = _get_host_os_arch(rctx, logger)
 
     is_windows = (os_name == WINDOWS_NAME)
 
@@ -160,7 +158,6 @@ alias(name = "python3",         actual = select({{":" + item: "@{py_repository}_
 alias(name = "pip",             actual = select({{":" + item: "@{py_repository}_" + item + "//:python_runtimes" for item in PLATFORMS if "windows" not in item}}))
 """.format(
             py_repository = rctx.attr.user_repository_name,
-            host_platform = host_platform,
         )
     rctx.file("BUILD.bazel", build_contents)
 

From f373be6613dfcdd4834818a2f661a82b4e9bbb32 Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 09:09:58 +0900
Subject: [PATCH 04/13] chore: stop exposing config settings in the toolchain
 aliases repo

---
 python/private/toolchain_aliases.bzl | 45 ++++++++++++++++++++++++++++
 python/private/toolchains_repo.bzl   | 14 ++++-----
 2 files changed, 50 insertions(+), 9 deletions(-)
 create mode 100644 python/private/toolchain_aliases.bzl

diff --git a/python/private/toolchain_aliases.bzl b/python/private/toolchain_aliases.bzl
new file mode 100644
index 0000000000..8943267896
--- /dev/null
+++ b/python/private/toolchain_aliases.bzl
@@ -0,0 +1,45 @@
+# Copyright 2024 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Create toolchain alias targets."""
+
+load("@rules_python//python:versions.bzl", "PLATFORMS")
+
+def toolchain_aliases(*, name, platforms, native = native):
+    """Cretae toolchain aliases for the python toolchains.
+
+    Args:
+        name: {type}`str` The name of the current repository.
+        platforms: {type}`platforms` The list of platforms that are supported
+            for the current toolchain repository.
+        native: The native struct used in the macro, useful for testing.
+    """
+    for platform in PLATFORMS.keys():
+        if platform not in platforms:
+            continue
+
+        native.config_setting(
+            name = platform,
+            flag_values = PLATFORMS[platform].flag_values,
+            constraint_values = PLATFORMS[platform].compatible_with,
+            visibility = ["//visibility:private"],
+        )
+
+    native.alias(name = "files", actual = select({{":" + item: "@" + name + "_" + item + "//:files" for item in platforms}}))
+    native.alias(name = "includes", actual = select({{":" + item: "@" + name + "_" + item + "//:includes" for item in platforms}}))
+    native.alias(name = "libpython", actual = select({{":" + item: "@" + name + "_" + item + "//:libpython" for item in platforms}}))
+    native.alias(name = "py3_runtime", actual = select({{":" + item: "@" + name + "_" + item + "//:py3_runtime" for item in platforms}}))
+    native.alias(name = "python_headers", actual = select({{":" + item: "@" + name + "_" + item + "//:python_headers" for item in platforms}}))
+    native.alias(name = "python_runtimes", actual = select({{":" + item: "@" + name + "_" + item + "//:python_runtimes" for item in platforms}}))
+    native.alias(name = "python3", actual = select({{":" + item: "@" + name + "_" + item + "//:" + ("python.exe" if "windows" in item else "bin/python3") for item in platforms}}))
diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index 14002fc645..9dc24a817b 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -135,20 +135,16 @@ def _toolchain_aliases_impl(rctx):
     build_contents = """\
 # Generated by python/private/toolchains_repo.bzl
 package(default_visibility = ["//visibility:public"])
-load("@rules_python//python:versions.bzl", "gen_python_config_settings")
-gen_python_config_settings()
+load("@rules_python//python/private:toolchain_aliases.bzl", "toolchain_aliases")
 exports_files(["defs.bzl"])
 
 PLATFORMS = [
 {loaded_platforms}
 ]
-alias(name = "files",           actual = select({{":" + item: "@{py_repository}_" + item + "//:files" for item in PLATFORMS}}))
-alias(name = "includes",        actual = select({{":" + item: "@{py_repository}_" + item + "//:includes" for item in PLATFORMS}}))
-alias(name = "libpython",       actual = select({{":" + item: "@{py_repository}_" + item + "//:libpython" for item in PLATFORMS}}))
-alias(name = "py3_runtime",     actual = select({{":" + item: "@{py_repository}_" + item + "//:py3_runtime" for item in PLATFORMS}}))
-alias(name = "python_headers",  actual = select({{":" + item: "@{py_repository}_" + item + "//:python_headers" for item in PLATFORMS}}))
-alias(name = "python_runtimes", actual = select({{":" + item: "@{py_repository}_" + item + "//:python_runtimes" for item in PLATFORMS}}))
-alias(name = "python3",         actual = select({{":" + item: "@{py_repository}_" + item + "//:" + ("python.exe" if "windows" in item else "bin/python3") for item in PLATFORMS}}))
+toolchain_aliases(
+    name = "{py_repository}",
+    platforms = PLATFORMS,
+)
 """.format(
         py_repository = rctx.attr.user_repository_name,
         loaded_platforms = "\n".join(["    \"{}\",".format(p) for p in rctx.attr.platforms]),

From 45de4ac944dc96a9520e306ffc998b942ec3d43b Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 10:24:19 +0900
Subject: [PATCH 05/13] move all of the alias setting to the new macro

---
 python/private/toolchain_aliases.bzl | 45 +++++++++++++++++++++++-----
 python/private/toolchains_repo.bzl   | 15 ++--------
 2 files changed, 40 insertions(+), 20 deletions(-)

diff --git a/python/private/toolchain_aliases.bzl b/python/private/toolchain_aliases.bzl
index 8943267896..953172cb4e 100644
--- a/python/private/toolchain_aliases.bzl
+++ b/python/private/toolchain_aliases.bzl
@@ -16,13 +16,14 @@
 
 load("@rules_python//python:versions.bzl", "PLATFORMS")
 
-def toolchain_aliases(*, name, platforms, native = native):
+def toolchain_aliases(*, name, platforms, visibility = None, native = native):
     """Cretae toolchain aliases for the python toolchains.
 
     Args:
         name: {type}`str` The name of the current repository.
         platforms: {type}`platforms` The list of platforms that are supported
             for the current toolchain repository.
+        visibility: {type}`list[Target] | None` The visibility of the aliases.
         native: The native struct used in the macro, useful for testing.
     """
     for platform in PLATFORMS.keys():
@@ -36,10 +37,38 @@ def toolchain_aliases(*, name, platforms, native = native):
             visibility = ["//visibility:private"],
         )
 
-    native.alias(name = "files", actual = select({{":" + item: "@" + name + "_" + item + "//:files" for item in platforms}}))
-    native.alias(name = "includes", actual = select({{":" + item: "@" + name + "_" + item + "//:includes" for item in platforms}}))
-    native.alias(name = "libpython", actual = select({{":" + item: "@" + name + "_" + item + "//:libpython" for item in platforms}}))
-    native.alias(name = "py3_runtime", actual = select({{":" + item: "@" + name + "_" + item + "//:py3_runtime" for item in platforms}}))
-    native.alias(name = "python_headers", actual = select({{":" + item: "@" + name + "_" + item + "//:python_headers" for item in platforms}}))
-    native.alias(name = "python_runtimes", actual = select({{":" + item: "@" + name + "_" + item + "//:python_runtimes" for item in platforms}}))
-    native.alias(name = "python3", actual = select({{":" + item: "@" + name + "_" + item + "//:" + ("python.exe" if "windows" in item else "bin/python3") for item in platforms}}))
+    prefix = name
+    for name in [
+        "files",
+        "includes",
+        "libpython",
+        "py3_runtime",
+        "python_headers",
+        "python_runtimes",
+    ]:
+        native.alias(
+            name = name,
+            actual = select({
+                ":" + platform: "@{}_{}//:{}".format(prefix, platform, name)
+                for platform in platforms
+            }),
+            visibility = visibility,
+        )
+
+    native.alias(
+        name = "python3",
+        actual = select({
+            ":" + platform: "@{}_{}//:{}".format(prefix, platform, "python.exe" if "windows" in platform else "bin/python3")
+            for platform in platforms
+        }),
+        visibility = visibility,
+    )
+    native.alias(
+        name = "pip",
+        actual = select({
+            ":" + platform: "@{}_{}//:python_runtimes".format(prefix, platform)
+            for platform in platforms
+            if "windows" not in platform
+        }),
+        visibility = visibility,
+    )
diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index 9dc24a817b..ae55ba2af3 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -126,16 +126,13 @@ toolchains_repo = repository_rule(
 )
 
 def _toolchain_aliases_impl(rctx):
-    logger = repo_utils.logger(rctx)
-    (os_name, _) = _get_host_os_arch(rctx, logger)
-
-    is_windows = (os_name == WINDOWS_NAME)
-
     # Base BUILD file for this repository.
     build_contents = """\
 # Generated by python/private/toolchains_repo.bzl
-package(default_visibility = ["//visibility:public"])
 load("@rules_python//python/private:toolchain_aliases.bzl", "toolchain_aliases")
+
+package(default_visibility = ["//visibility:public"])
+
 exports_files(["defs.bzl"])
 
 PLATFORMS = [
@@ -149,12 +146,6 @@ toolchain_aliases(
         py_repository = rctx.attr.user_repository_name,
         loaded_platforms = "\n".join(["    \"{}\",".format(p) for p in rctx.attr.platforms]),
     )
-    if not is_windows:
-        build_contents += """\
-alias(name = "pip",             actual = select({{":" + item: "@{py_repository}_" + item + "//:python_runtimes" for item in PLATFORMS if "windows" not in item}}))
-""".format(
-            py_repository = rctx.attr.user_repository_name,
-        )
     rctx.file("BUILD.bazel", build_contents)
 
     # Expose a Starlark file so rules can know what host platform we used and where to find an interpreter

From 6269dc34586a6a1b9a52c2bc2a2ffd8b36b58f5a Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 10:46:24 +0900
Subject: [PATCH 06/13] chore: use identifiers used in platforms package for
 arch and os names and get rid of uname dep

---
 python/private/python_register_toolchains.bzl |  5 +-
 python/private/toolchains_repo.bzl            | 87 ++++++++-----------
 python/versions.bzl                           | 33 ++++---
 3 files changed, 58 insertions(+), 67 deletions(-)

diff --git a/python/private/python_register_toolchains.bzl b/python/private/python_register_toolchains.bzl
index 98c8e5bfc3..467540ec0d 100644
--- a/python/private/python_register_toolchains.bzl
+++ b/python/private/python_register_toolchains.bzl
@@ -160,7 +160,10 @@ def python_register_toolchains(
                 platform = platform,
             ))
 
-    host_toolchain(name = name + "_host")
+    host_toolchain(
+        name = name + "_host",
+        platforms = loaded_platforms,
+    )
 
     toolchain_aliases(
         name = name,
diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index ae55ba2af3..7b8780d5d1 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -25,8 +25,6 @@ platform-specific repositories.
 
 load(
     "//python:versions.bzl",
-    "LINUX_NAME",
-    "MACOS_NAME",
     "PLATFORMS",
     "WINDOWS_NAME",
 )
@@ -220,15 +218,15 @@ actions.""",
 )
 
 def _host_toolchain_impl(rctx):
-    logger = repo_utils.logger(rctx)
     rctx.file("BUILD.bazel", """\
 # Generated by python/private/toolchains_repo.bzl
 
 exports_files(["python"], visibility = ["//visibility:public"])
 """)
 
-    (os_name, arch) = _get_host_os_arch(rctx, logger)
-    host_platform = _get_host_platform(os_name, arch)
+    os_name = repo_utils.get_platforms_os_name(rctx)
+    cpu_name = repo_utils.get_platforms_cpu_name(rctx)
+    host_platform = _get_host_platform(rctx, os_name, cpu_name, rctx.attr.platforms)
     repo = "@@{py_repository}_{host_platform}".format(
         py_repository = rctx.attr.name[:-len("_host")],
         host_platform = host_platform,
@@ -297,6 +295,7 @@ toolchain_aliases repo because referencing the `python` interpreter target from
 this repo causes an eager fetch of the toolchain for the host platform.
     """,
     attrs = {
+        "platforms": attr.string_list(mandatory = True),
         "_rule_name": attr.string(default = "host_toolchain"),
         "_rules_python_workspace": attr.label(default = Label("//:WORKSPACE")),
     },
@@ -365,57 +364,47 @@ multi_toolchain_aliases = repository_rule(
 def sanitize_platform_name(platform):
     return platform.replace("-", "_")
 
-def _get_host_platform(os_name, arch):
+def _get_host_platform(rctx, os_name, cpu_name, platforms):
     """Gets the host platform.
 
     Args:
-        os_name: the host OS name.
-        arch: the host arch.
+        rctx: {type}`repository_ctx`.
+        os_name: {type}`str` the host OS name.
+        cpu_name: {type}`str` the host CPU name.
+        platforms: {type}`list[str]` the list of loaded platforms.
     Returns:
         The host platform.
     """
-    host_platform = None
-    for platform, meta in PLATFORMS.items():
-        if "freethreaded" in platform:
-            continue
-
-        if meta.os_name == os_name and meta.arch == arch:
-            host_platform = platform
-    if not host_platform:
-        fail("No platform declared for host OS {} on arch {}".format(os_name, arch))
-    return host_platform
+    candidates = []
+    for platform in platforms:
+        meta = PLATFORMS[platform]
 
-def _get_host_os_arch(rctx, logger):
-    """Infer the host OS name and arch from a repository context.
+        if meta.os_name == os_name and meta.arch == cpu_name:
+            candidates.append(platform)
 
-    Args:
-        rctx: Bazel's repository_ctx.
-        logger: Logger to use for operations.
+    if len(candidates) == 1:
+        return candidates[0]
 
-    Returns:
-        A tuple with the host OS name and arch.
-    """
-    os_name = rctx.os.name
-
-    # We assume the arch for Windows is always x86_64.
-    if "windows" in os_name.lower():
-        arch = "x86_64"
-
-        # Normalize the os_name. E.g. os_name could be "OS windows server 2019".
-        os_name = WINDOWS_NAME
-    else:
-        # This is not ideal, but bazel doesn't directly expose arch.
-        arch = repo_utils.execute_unchecked(
+    if candidates:
+        preference = repo_utils.getenv(
             rctx,
-            op = "GetUname",
-            arguments = [repo_utils.which_checked(rctx, "uname"), "-m"],
-            logger = logger,
-        ).stdout.strip()
-
-        # Normalize the os_name.
-        if "mac" in os_name.lower():
-            os_name = MACOS_NAME
-        elif "linux" in os_name.lower():
-            os_name = LINUX_NAME
-
-    return (os_name, arch)
+            "RULES_PYTHON_{}_{}_USE_HOST_PYTHON".format(
+                os_name.upper(),
+                cpu_name.upper(),
+            ),
+        )
+        if preference == None:
+            candidates = sorted(candidates, lambda k: ("freethreaded" in k, k))
+        elif preference not in candidates:
+            fail("Please choose a prefrered interpreter out of the following platforms: {}".format(candidates))
+        else:
+            candidates = [preference]
+
+    if candidates:
+        return candidates[0]
+
+    fail("Could not find a compatible 'host' python for '{os_name}', '{cpu_name}' from the loaded platforms: {platforms}".format(
+        os_name = os_name,
+        cpu_name = cpu_name,
+        platforms = platforms,
+    ))
diff --git a/python/versions.bzl b/python/versions.bzl
index 774c24d1b9..5f62d01f79 100644
--- a/python/versions.bzl
+++ b/python/versions.bzl
@@ -15,8 +15,8 @@
 """The Python versions we use for the toolchains.
 """
 
-# Values returned by https://bazel.build/rules/lib/repository_os.
-MACOS_NAME = "mac os"
+# Values present in the @platforms//os package
+MACOS_NAME = "osx"
 LINUX_NAME = "linux"
 WINDOWS_NAME = "windows"
 FREETHREADED = "freethreaded"
@@ -604,9 +604,8 @@ def _generate_platforms():
             ],
             flag_values = {},
             os_name = MACOS_NAME,
-            # Matches the value returned from:
-            # repository_ctx.execute(["uname", "-m"]).stdout.strip()
-            arch = "arm64",
+            # Matches the value in @platforms//cpu package
+            arch = "aarch64",
         ),
         "aarch64-unknown-linux-gnu": struct(
             compatible_with = [
@@ -617,9 +616,7 @@ def _generate_platforms():
                 libc: "glibc",
             },
             os_name = LINUX_NAME,
-            # Note: this string differs between OSX and Linux
-            # Matches the value returned from:
-            # repository_ctx.execute(["uname", "-m"]).stdout.strip()
+            # Matches the value in @platforms//cpu package
             arch = "aarch64",
         ),
         "armv7-unknown-linux-gnu": struct(
@@ -631,7 +628,8 @@ def _generate_platforms():
                 libc: "glibc",
             },
             os_name = LINUX_NAME,
-            arch = "armv7",
+            # Matches the value in @platforms//cpu package
+            arch = "arm",
         ),
         "i386-unknown-linux-gnu": struct(
             compatible_with = [
@@ -642,7 +640,8 @@ def _generate_platforms():
                 libc: "glibc",
             },
             os_name = LINUX_NAME,
-            arch = "i386",
+            # Matches the value in @platforms//cpu package
+            arch = "x86_32",
         ),
         "ppc64le-unknown-linux-gnu": struct(
             compatible_with = [
@@ -653,10 +652,8 @@ def _generate_platforms():
                 libc: "glibc",
             },
             os_name = LINUX_NAME,
-            # Note: this string differs between OSX and Linux
-            # Matches the value returned from:
-            # repository_ctx.execute(["uname", "-m"]).stdout.strip()
-            arch = "ppc64le",
+            # Matches the value in @platforms//cpu package
+            arch = "ppc",
         ),
         "riscv64-unknown-linux-gnu": struct(
             compatible_with = [
@@ -667,6 +664,7 @@ def _generate_platforms():
                 Label("//python/config_settings:py_linux_libc"): "glibc",
             },
             os_name = LINUX_NAME,
+            # Matches the value in @platforms//cpu package
             arch = "riscv64",
         ),
         "s390x-unknown-linux-gnu": struct(
@@ -678,9 +676,7 @@ def _generate_platforms():
                 Label("//python/config_settings:py_linux_libc"): "glibc",
             },
             os_name = LINUX_NAME,
-            # Note: this string differs between OSX and Linux
-            # Matches the value returned from:
-            # repository_ctx.execute(["uname", "-m"]).stdout.strip()
+            # Matches the value in @platforms//cpu package
             arch = "s390x",
         ),
         "x86_64-apple-darwin": struct(
@@ -690,6 +686,7 @@ def _generate_platforms():
             ],
             flag_values = {},
             os_name = MACOS_NAME,
+            # Matches the value in @platforms//cpu package
             arch = "x86_64",
         ),
         "x86_64-pc-windows-msvc": struct(
@@ -699,6 +696,7 @@ def _generate_platforms():
             ],
             flag_values = {},
             os_name = WINDOWS_NAME,
+            # Matches the value in @platforms//cpu package
             arch = "x86_64",
         ),
         "x86_64-unknown-linux-gnu": struct(
@@ -710,6 +708,7 @@ def _generate_platforms():
                 libc: "glibc",
             },
             os_name = LINUX_NAME,
+            # Matches the value in @platforms//cpu package
             arch = "x86_64",
         ),
     }

From 2fa2f40ad0296fb301726a005c02d206546b4082 Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 10:53:46 +0900
Subject: [PATCH 07/13] add nice log messages

---
 python/private/python_register_toolchains.bzl |  1 +
 python/private/toolchains_repo.bzl            | 36 +++++++++++++------
 2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/python/private/python_register_toolchains.bzl b/python/private/python_register_toolchains.bzl
index 467540ec0d..cd3e9cbed7 100644
--- a/python/private/python_register_toolchains.bzl
+++ b/python/private/python_register_toolchains.bzl
@@ -163,6 +163,7 @@ def python_register_toolchains(
     host_toolchain(
         name = name + "_host",
         platforms = loaded_platforms,
+        python_version = python_version,
     )
 
     toolchain_aliases(
diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index 7b8780d5d1..4bea802c97 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -225,8 +225,14 @@ exports_files(["python"], visibility = ["//visibility:public"])
 """)
 
     os_name = repo_utils.get_platforms_os_name(rctx)
-    cpu_name = repo_utils.get_platforms_cpu_name(rctx)
-    host_platform = _get_host_platform(rctx, os_name, cpu_name, rctx.attr.platforms)
+    host_platform = _get_host_platform(
+        rctx = rctx,
+        logger = repo_utils.logger(rctx),
+        python_version = rctx.attr.python_version,
+        os_name = os_name,
+        cpu_name = repo_utils.get_platforms_cpu_name(rctx),
+        platforms = rctx.attr.platforms,
+    )
     repo = "@@{py_repository}_{host_platform}".format(
         py_repository = rctx.attr.name[:-len("_host")],
         host_platform = host_platform,
@@ -296,6 +302,7 @@ this repo causes an eager fetch of the toolchain for the host platform.
     """,
     attrs = {
         "platforms": attr.string_list(mandatory = True),
+        "python_version": attr.string(mandatory = True),
         "_rule_name": attr.string(default = "host_toolchain"),
         "_rules_python_workspace": attr.label(default = Label("//:WORKSPACE")),
     },
@@ -364,11 +371,13 @@ multi_toolchain_aliases = repository_rule(
 def sanitize_platform_name(platform):
     return platform.replace("-", "_")
 
-def _get_host_platform(rctx, os_name, cpu_name, platforms):
+def _get_host_platform(*, rctx, logger, python_version, os_name, cpu_name, platforms):
     """Gets the host platform.
 
     Args:
         rctx: {type}`repository_ctx`.
+        logger: {type}`struct`.
+        python_version: {type}`string`.
         os_name: {type}`str` the host OS name.
         cpu_name: {type}`str` the host CPU name.
         platforms: {type}`list[str]` the list of loaded platforms.
@@ -386,25 +395,30 @@ def _get_host_platform(rctx, os_name, cpu_name, platforms):
         return candidates[0]
 
     if candidates:
-        preference = repo_utils.getenv(
-            rctx,
-            "RULES_PYTHON_{}_{}_USE_HOST_PYTHON".format(
-                os_name.upper(),
-                cpu_name.upper(),
-            ),
+        env_var = "RULES_PYTHON_HERMETIC_PYTHON_{}_{}_{}".format(
+            python_version.replace(".", "_"),
+            os_name.upper(),
+            cpu_name.upper(),
         )
+        logger.warn("Please use '{}' to select one of the candidates: {}".format(
+            env_var,
+            candidates,
+        ))
+        preference = repo_utils.getenv(rctx, env_var)
         if preference == None:
             candidates = sorted(candidates, lambda k: ("freethreaded" in k, k))
         elif preference not in candidates:
-            fail("Please choose a prefrered interpreter out of the following platforms: {}".format(candidates))
+            logger.fail("Please choose a prefrered interpreter out of the following platforms: {}".format(candidates))
+            return None
         else:
             candidates = [preference]
 
     if candidates:
         return candidates[0]
 
-    fail("Could not find a compatible 'host' python for '{os_name}', '{cpu_name}' from the loaded platforms: {platforms}".format(
+    logger.fail("Could not find a compatible 'host' python for '{os_name}', '{cpu_name}' from the loaded platforms: {platforms}".format(
         os_name = os_name,
         cpu_name = cpu_name,
         platforms = platforms,
     ))
+    return None

From 8799dc3c1304ac8261f4e47849c0c6716fe1da89 Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 11:14:59 +0900
Subject: [PATCH 08/13] fixup

---
 python/private/toolchains_repo.bzl | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index 4bea802c97..764975b618 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -395,20 +395,19 @@ def _get_host_platform(*, rctx, logger, python_version, os_name, cpu_name, platf
         return candidates[0]
 
     if candidates:
-        env_var = "RULES_PYTHON_HERMETIC_PYTHON_{}_{}_{}".format(
+        env_var = "RULES_PYTHON_REPO_TOOLCHAIN_{}_{}_{}".format(
             python_version.replace(".", "_"),
             os_name.upper(),
             cpu_name.upper(),
         )
-        logger.warn("Please use '{}' to select one of the candidates: {}".format(
-            env_var,
-            candidates,
-        ))
         preference = repo_utils.getenv(rctx, env_var)
         if preference == None:
-            candidates = sorted(candidates, lambda k: ("freethreaded" in k, k))
+            logger.info("Consider using '{}' to select from one of the platforms: {}".format(
+                env_var,
+                candidates,
+            ))
         elif preference not in candidates:
-            logger.fail("Please choose a prefrered interpreter out of the following platforms: {}".format(candidates))
+            logger.fail("Please choose a preferred interpreter out of the following platforms: {}".format(candidates))
             return None
         else:
             candidates = [preference]

From 73a8aa6eaa9fda9f4fb8abd52c8d8df3f546d87c Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 11:21:00 +0900
Subject: [PATCH 09/13] doc: changelog

---
 CHANGELOG.md | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c351487605..f9dd06e6ba 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -52,15 +52,28 @@ Unreleased changes template.
 
 {#v0-0-0-changed}
 ### Changed
-* Nothing yet.
+
+**Breaking**:
+* (toolchains) stop exposing config settings in python toolchain alias repos.
+* (toolchains) consumers who were depending on the `MACOS_NAME` and the `arch`
+  attribute in the `PLATFORMS` list, please update your code to respect the new
+  values. The values now correspond to the values available in the
+  `@platforms//` package constraint values.
+
+Other changes:
+* Nothing yet
 
 {#v0-0-0-fixed}
 ### Fixed
-* Nothing yet.
+* (toolchains) stop depending on `uname` to get the value of the host platform.
 
 {#v0-0-0-added}
 ### Added
-* Nothing yet.
+* (toolchains) allow users to select which variant of the support host toolchain
+  they would like to use through
+  `RULES_PYTHON_REPO_TOOLCHAIN_{VERSION}_{OS}_{ARCH}` env variable setting. For
+  example, this allows one to use `freethreaded` python interpreter in the
+  `repository_rule` to build a wheel from `sdist`.
 
 {#v0-0-0-removed}
 ### Removed

From 87eea0716b185947a65ea745e87125f70ce8f417 Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 11:31:02 +0900
Subject: [PATCH 10/13] fixup

---
 CHANGELOG.md                       | 9 +++++++++
 python/private/toolchains_repo.bzl | 4 ----
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f9dd06e6ba..761e208209 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -55,10 +55,19 @@ Unreleased changes template.
 
 **Breaking**:
 * (toolchains) stop exposing config settings in python toolchain alias repos.
+  Please consider depending on the flags defined in
+  `//python/config_setting/...` and the `@platforms` package instead.
 * (toolchains) consumers who were depending on the `MACOS_NAME` and the `arch`
   attribute in the `PLATFORMS` list, please update your code to respect the new
   values. The values now correspond to the values available in the
   `@platforms//` package constraint values.
+* (toolchains) `host_platform` and `interpreter` constants are no longer created
+  in the `toolchain` generated alias `.bzl` files. If you need to access the
+  host interpreter during the `repository_rule` evaluation, please use the
+  `@python_{version}_host//:python` targets created by
+  {bzl:obj}`python_register_toolchains` and
+  {bzl:obj}`python_register_multi_toolchains` macros or the {bzl:obj}`python`
+  bzlmod extension.
 
 Other changes:
 * Nothing yet
diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index 764975b618..ccec957180 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -319,16 +319,12 @@ def _multi_toolchain_aliases_impl(rctx):
 load(
     "@{repository_name}//:defs.bzl",
     _compile_pip_requirements = "compile_pip_requirements",
-    _host_platform = "host_platform",
-    _interpreter = "interpreter",
     _py_binary = "py_binary",
     _py_console_script_binary = "py_console_script_binary",
     _py_test = "py_test",
 )
 
 compile_pip_requirements = _compile_pip_requirements
-host_platform = _host_platform
-interpreter = _interpreter
 py_binary = _py_binary
 py_console_script_binary = _py_console_script_binary
 py_test = _py_test

From c5b8b169027ce697c29c776c6b207a060f84c37b Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Thu, 14 Nov 2024 11:53:50 +0900
Subject: [PATCH 11/13] migrate away from using the interpreter const

---
 WORKSPACE                                                      | 2 +-
 .../compile_pip_requirements_test_from_external_repo/WORKSPACE | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/WORKSPACE b/WORKSPACE
index b77918f5ef..46ebbc8cde 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -86,7 +86,7 @@ load("@rules_python_gazelle_plugin//:deps.bzl", _py_gazelle_deps = "gazelle_deps
 _py_gazelle_deps()
 
 # This interpreter is used for various rules_python dev-time tools
-load("@python//3.11.9:defs.bzl", "interpreter")
+interpreter = "@python_3_11_9_host//:python"
 
 #####################
 # Install twine for our own runfiles wheel publishing.
diff --git a/tests/integration/compile_pip_requirements_test_from_external_repo/WORKSPACE b/tests/integration/compile_pip_requirements_test_from_external_repo/WORKSPACE
index 48caeb442f..7834000854 100644
--- a/tests/integration/compile_pip_requirements_test_from_external_repo/WORKSPACE
+++ b/tests/integration/compile_pip_requirements_test_from_external_repo/WORKSPACE
@@ -12,7 +12,6 @@ python_register_toolchains(
     python_version = "3.9",
 )
 
-load("@python39//:defs.bzl", "interpreter")
 load("@rules_python//python:pip.bzl", "pip_parse")
 
 local_repository(
@@ -22,7 +21,7 @@ local_repository(
 
 pip_parse(
     name = "pypi",
-    python_interpreter_target = interpreter,
+    python_interpreter_target = "@python39_host//:python",
     requirements_lock = "@compile_pip_requirements//:requirements_lock.txt",
 )
 

From e90040aa6d09eb39c6cb1ca2e298f224242a5633 Mon Sep 17 00:00:00 2001
From: Richard Levasseur <richardlev@gmail.com>
Date: Sun, 17 Nov 2024 16:59:28 -0800
Subject: [PATCH 12/13] Fix doc typoe

---
 python/private/toolchain_aliases.bzl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/python/private/toolchain_aliases.bzl b/python/private/toolchain_aliases.bzl
index 953172cb4e..31ac4a8fdf 100644
--- a/python/private/toolchain_aliases.bzl
+++ b/python/private/toolchain_aliases.bzl
@@ -17,7 +17,7 @@
 load("@rules_python//python:versions.bzl", "PLATFORMS")
 
 def toolchain_aliases(*, name, platforms, visibility = None, native = native):
-    """Cretae toolchain aliases for the python toolchains.
+    """Create toolchain aliases for the python toolchains.
 
     Args:
         name: {type}`str` The name of the current repository.

From 919b8b9b7e29ad0890ec5851b29e896d585cad36 Mon Sep 17 00:00:00 2001
From: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
Date: Mon, 18 Nov 2024 10:22:44 +0900
Subject: [PATCH 13/13] doc: add docs for the toolchain selection env var

---
 docs/environment-variables.md      | 10 ++++++++++
 examples/bzlmod/MODULE.bazel.lock  |  4 ++--
 python/private/repo_utils.bzl      |  6 +++++-
 python/private/toolchains_repo.bzl |  6 ++----
 4 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/docs/environment-variables.md b/docs/environment-variables.md
index 2a0052923c..906281d56f 100644
--- a/docs/environment-variables.md
+++ b/docs/environment-variables.md
@@ -15,6 +15,16 @@ Determines the verbosity of logging output for repo rules. Valid values:
 * `TRACE`
 :::
 
+:::{envvar} RULES_PYTHON_REPO_TOOLCHAIN_VERSION_OS_ARCH
+
+Determines the python interpreter platform to be used for a particular
+interpreter `(version, os, arch)` triple to be used in repository rules.
+Replace the `VERSION_OS_ARCH` part with actual values when using, e.g.
+`3_13_0_linux_x86_64`. The version values must have `_` instead of `.` and the
+os, arch values are the same as the ones mentioned in the
+`//python:versions.bzl` file.
+:::
+
 :::{envvar} RULES_PYTHON_PIP_ISOLATED
 
 Determines if `--isolated` is used with pip.
diff --git a/examples/bzlmod/MODULE.bazel.lock b/examples/bzlmod/MODULE.bazel.lock
index 5a546c2f7a..8bad32a07b 100644
--- a/examples/bzlmod/MODULE.bazel.lock
+++ b/examples/bzlmod/MODULE.bazel.lock
@@ -1562,7 +1562,7 @@
     },
     "@@rules_python~//python/extensions:pip.bzl%pip": {
       "general": {
-        "bzlTransitiveDigest": "MwmpiMn2qoAVC+3E9MF3E98fB8v1utYBfMa0frXyi7g=",
+        "bzlTransitiveDigest": "mCwiXbsZmReVgs884fZHYfxaZaL9mFG+prEnH/lpE9g=",
         "usagesDigest": "VmrNvB/4EhzsYieLDka9584M+pYKPpjNLl3Wcb5rx/c=",
         "recordedFileInputs": {
           "@@//requirements_lock_3_10.txt": "5e7083982a7e60f34998579a0ae83b520d46ab8f2552cc51337217f024e6def5",
@@ -7035,7 +7035,7 @@
     },
     "@@rules_python~//python/private/pypi:pip.bzl%pip_internal": {
       "general": {
-        "bzlTransitiveDigest": "Kx383BMHUpAHEjRiU5aWU4QTRQVg+Uu+Mgi7jVxuz0c=",
+        "bzlTransitiveDigest": "Xu1N6572iHVqGChH12PpMhprC21k3CpjRZVpm3FmE2c=",
         "usagesDigest": "/lZXl/ZgP+u5PE8WkeWTyYBsvX9XQWFn1antj5qrBzQ=",
         "recordedFileInputs": {
           "@@rules_python~//tools/publish/requirements_linux.txt": "8175b4c8df50ae2f22d1706961884beeb54e7da27bd2447018314a175981997d",
diff --git a/python/private/repo_utils.bzl b/python/private/repo_utils.bzl
index e0bf69acac..0e3f7b024b 100644
--- a/python/private/repo_utils.bzl
+++ b/python/private/repo_utils.bzl
@@ -41,6 +41,10 @@ def _logger(mrctx, name = None):
 
     Returns:
         A struct with attributes logging: trace, debug, info, warn, fail.
+        Please use `return logger.fail` when using the `fail` method, because
+        it makes `buildifier` happy and ensures that other implementation of
+        the logger injected into the function work as expected by terminating
+        on the given line.
     """
     if _is_repo_debug_enabled(mrctx):
         verbosity_level = "DEBUG"
@@ -140,7 +144,7 @@ def _execute_internal(
     result = mrctx.execute(arguments, environment = environment, **kwargs)
 
     if fail_on_error and result.return_code != 0:
-        logger.fail((
+        return logger.fail((
             "repo.execute: {op}: end: failure:\n" +
             "  command: {cmd}\n" +
             "  return code: {return_code}\n" +
diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index ccec957180..7e9a0c7ff9 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -403,17 +403,15 @@ def _get_host_platform(*, rctx, logger, python_version, os_name, cpu_name, platf
                 candidates,
             ))
         elif preference not in candidates:
-            logger.fail("Please choose a preferred interpreter out of the following platforms: {}".format(candidates))
-            return None
+            return logger.fail("Please choose a preferred interpreter out of the following platforms: {}".format(candidates))
         else:
             candidates = [preference]
 
     if candidates:
         return candidates[0]
 
-    logger.fail("Could not find a compatible 'host' python for '{os_name}', '{cpu_name}' from the loaded platforms: {platforms}".format(
+    return logger.fail("Could not find a compatible 'host' python for '{os_name}', '{cpu_name}' from the loaded platforms: {platforms}".format(
         os_name = os_name,
         cpu_name = cpu_name,
         platforms = platforms,
     ))
-    return None