feat(toolchain): use py_linux_libc flag value

With this we start using the `py_linux_libc` flag value in toolchains as
well and ensure that no hermetic toolchain will be matched when we
specify to pull the `musl` wheels. In that case the user will need to
supply their own toolchain that is the expected behaviour.

However, I am not sure how we could fail due to no available toolchain
in that case because the autodetecting toolchain will just use the host
interpreter.

Author: aignas

python/private/BUILD.bazel

@@ -252,6 +252,8 @@ bzl_library(
     name = "py_toolchain_suite_bzl",
     srcs = ["py_toolchain_suite.bzl"],
     deps = [
+        ":config_settings_bzl",
+        ":text_util_bzl",
         ":toolchain_types_bzl",
         "@bazel_skylib//lib:selects",
     ],

python/private/py_toolchain_suite.bzl

@@ -15,21 +15,23 @@
 """Create the toolchain defs in a BUILD.bazel file."""
 
 load("@bazel_skylib//lib:selects.bzl", "selects")
+load(":config_settings.bzl", "is_python_config_setting")
 load(
     ":toolchain_types.bzl",
     "EXEC_TOOLS_TOOLCHAIN_TYPE",
     "PY_CC_TOOLCHAIN_TYPE",
     "TARGET_TOOLCHAIN_TYPE",
 )
 
-def py_toolchain_suite(*, prefix, user_repository_name, python_version, set_python_version_constraint, **kwargs):
+def py_toolchain_suite(*, prefix, user_repository_name, python_version, set_python_version_constraint, flag_values, **kwargs):
     """For internal use only.
 
     Args:
         prefix: Prefix for toolchain target names.
         user_repository_name: The name of the user repository.
         python_version: The full (X.Y.Z) version of the interpreter.
         set_python_version_constraint: True or False as a string.
+        flag_values: Extra flag values to match for this toolchain.
         **kwargs: extra args passed to the `toolchain` calls.
 
     """
@@ -38,23 +40,54 @@ def py_toolchain_suite(*, prefix, user_repository_name, python_version, set_pyth
     # string as we cannot have list of bools in build rule attribues.
     # This if statement does not appear to work unless it is in the
     # toolchain file.
-    if set_python_version_constraint == "True":
+    if set_python_version_constraint in ["True", "False"]:
         major_minor, _, _ = python_version.rpartition(".")
 
+        match_any = []
+        for i, v in enumerate([major_minor, python_version]):
+            name = "{prefix}_{python_version}_{i}".format(
+                prefix = prefix,
+                python_version = python_version,
+                i = i,
+            )
+            match_any.append(name)
+            if flag_values:
+                is_python_config_setting(
+                    name = name,
+                    python_version = v,
+                    flag_values = flag_values,
+                    visibility = ["//visibility:private"],
+                )
+            else:
+                native.alias(
+                    name = name,
+                    actual = Label("//python/config_settings:is_python_%s" % v),
+                    visibility = ["//visibility:private"],
+                )
+
+        if set_python_version_constraint == "False":
+            name = "{prefix}_version_setting_no_python_version".format(prefix = prefix)
+            match_any.append(name)
+            native.config_setting(
+                name = name,
+                flag_values = flag_values | {
+                    str(Label("//python/config_settings:python_version")): "",
+                },
+                visibility = ["//visibility:private"],
+            )
+
+        name = "{prefix}_version_setting_{python_version}".format(
+            prefix = prefix,
+            python_version = python_version,
+            visibility = ["//visibility:private"],
+        )
         selects.config_setting_group(
-            name = prefix + "_version_setting",
-            match_any = [
-                Label("//python/config_settings:is_python_%s" % v)
-                for v in [
-                    major_minor,
-                    python_version,
-                ]
-            ],
+            name = name,
+            match_any = match_any,
             visibility = ["//visibility:private"],
         )
-        target_settings = [prefix + "_version_setting"]
-    elif set_python_version_constraint == "False":
-        target_settings = []
+
+        target_settings = [name]
     else:
         fail(("Invalid set_python_version_constraint value: got {} {}, wanted " +
               "either the string 'True' or the string 'False'; " +

python/private/toolchains_repo.bzl

@@ -31,6 +31,7 @@ load(
     "WINDOWS_NAME",
 )
 load("//python/private:repo_utils.bzl", "REPO_DEBUG_ENV_VAR", "repo_utils")
+load("//python/private:text_util.bzl", "render")
 
 def get_repository_name(repository_workspace):
     dummy_label = "//:_"
@@ -64,10 +65,15 @@ py_toolchain_suite(
     user_repository_name = "{user_repository_name}_{platform}",
     prefix = "{prefix}{platform}",
     target_compatible_with = {compatible_with},
+    flag_values = {flag_values},
     python_version = "{python_version}",
     set_python_version_constraint = "{set_python_version_constraint}",
 )""".format(
-            compatible_with = meta.compatible_with,
+            compatible_with = render.indent(render.list(meta.compatible_with)).lstrip(),
+            flag_values = render.indent(render.dict(
+                meta.flag_values,
+                key_repr = lambda x: repr(str(x)),  # this is to correctly display labels
+            )).lstrip(),
             platform = platform,
             set_python_version_constraint = set_python_version_constraint,
             user_repository_name = user_repository_name,

python/versions.bzl

@@ -501,6 +501,7 @@ PLATFORMS = {
             "@platforms//os:macos",
             "@platforms//cpu:aarch64",
         ],
+        flag_values = {},
         os_name = MACOS_NAME,
         # Matches the value returned from:
         # repository_ctx.execute(["uname", "-m"]).stdout.strip()
@@ -511,6 +512,9 @@ PLATFORMS = {
             "@platforms//os:linux",
             "@platforms//cpu:aarch64",
         ],
+        flag_values = {
+            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:
@@ -522,6 +526,9 @@ PLATFORMS = {
             "@platforms//os:linux",
             "@platforms//cpu:armv7",
         ],
+        flag_values = {
+            Label("//python/config_settings:py_linux_libc"): "glibc",
+        },
         os_name = LINUX_NAME,
         arch = "armv7",
     ),
@@ -530,6 +537,9 @@ PLATFORMS = {
             "@platforms//os:linux",
             "@platforms//cpu:ppc",
         ],
+        flag_values = {
+            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:
@@ -541,6 +551,9 @@ PLATFORMS = {
             "@platforms//os:linux",
             "@platforms//cpu:riscv64",
         ],
+        flag_values = {
+            Label("//python/config_settings:py_linux_libc"): "glibc",
+        },
         os_name = LINUX_NAME,
         arch = "riscv64",
     ),
@@ -549,6 +562,9 @@ PLATFORMS = {
             "@platforms//os:linux",
             "@platforms//cpu:s390x",
         ],
+        flag_values = {
+            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:
@@ -560,6 +576,7 @@ PLATFORMS = {
             "@platforms//os:macos",
             "@platforms//cpu:x86_64",
         ],
+        flag_values = {},
         os_name = MACOS_NAME,
         arch = "x86_64",
     ),
@@ -568,6 +585,7 @@ PLATFORMS = {
             "@platforms//os:windows",
             "@platforms//cpu:x86_64",
         ],
+        flag_values = {},
         os_name = WINDOWS_NAME,
         arch = "x86_64",
     ),
@@ -576,6 +594,9 @@ PLATFORMS = {
             "@platforms//os:linux",
             "@platforms//cpu:x86_64",
         ],
+        flag_values = {
+            Label("//python/config_settings:py_linux_libc"): "glibc",
+        },
         os_name = LINUX_NAME,
         arch = "x86_64",
     ),