remove tool constraints

toolchain/templates/toolchain.bazel

@@ -1,29 +1,11 @@
 load("@local_config_platform//:constraints.bzl", "HOST_CONSTRAINTS")
 load("@rules_cc//cc:defs.bzl", "cc_toolchain")
 load("@toolchains_arm_gnu//toolchain:config.bzl", "cc_arm_gnu_toolchain_config")
+load("@toolchains_arm_gnu//toolchain:toolchain.bzl", "host_from")
 load("@toolchains_arm_gnu//toolchain:transitions.bzl", "toolchain_transition_library")
 
 HOSTS = %hosts%
 
-def _normalize(x):
-    mapping = {
-        "osx": "macos",
-        "darwin": "macos",
-        "aarch64": "arm64",
-    }
-    return mapping.get(x, default=x)
-
-
-def _host_os_cpu():
-    host_constraints = HOST_CONSTRAINTS
-    if "os" not in host_constraints:
-        host_constraints = reversed(host_constraints)
-
-    return struct(
-        os = _normalize(Label(host_constraints[0]).name),
-        cpu = _normalize(Label(host_constraints[1]).name),
-    )
-
 def _toolchain_variants(name, additional_link_libraries, target_compatible_with):
     """
     List of toolchain variants to create.
@@ -118,11 +100,8 @@ def %toolchain_name%_toolchain(
         ],
     )
 
-    host = _host_os_cpu()
-
     for host_repo, exec_compatible_with in HOSTS.items():
-        os, cpu = [Label(x).name for x in exec_compatible_with]
-        if _normalize(os) == host.os and _normalize(cpu) == host.cpu:
+        if host_repo == "%toolchain_name%_{}".format(host_from(HOST_CONSTRAINTS)):
             native.alias(
                 name = name,
                 actual =  ":{}_{}".format(name, host_repo),

toolchain/templates/top.BUILD

@@ -4,35 +4,30 @@ repository, i.e., the targets defined here appear in the workspace as
 "@arm_none_eabi//:*" for arm-none-eabi toolchains.
 """
 
-load("@toolchains_arm_gnu//toolchain:toolchain.bzl", "hosts", "tools")
 load("@bazel_skylib//rules:native_binary.bzl", "native_binary")
+load("@local_config_platform//:constraints.bzl", "HOST_CONSTRAINTS")
+load(
+    "@toolchains_arm_gnu//toolchain:toolchain.bzl",
+    "host_from",
+    "hosts",
+    "tools",
+)
 
 package(default_visibility = ["//visibility:public"])
 
-TOOLS = tools + ["bin"]
-
-[
-    config_setting(
-        name = host,
-        constraint_values = constraint_values,
-    )
-    for host, constraint_values in hosts["%toolchain_prefix%"].items()
-]
+TOOLS = tools
+host = host_from(HOST_CONSTRAINTS)
 
 [
     native_binary(
         name = tool,
-        src = select({
-            host: "@%toolchain_name%_{}//:{}".format(host, tool)
-            for host in hosts["%toolchain_prefix%"].keys()
-        }),
+        src = "@%toolchain_name%_{}//:{}".format(host, tool),
         out = tool,
-        target_compatible_with = select({
-            host: constraint_values
-            for host, constraint_values in hosts["%toolchain_prefix%"].items()
-        } | {
-            "//conditions:default": ["@platforms//:incompatible"],
-        }),
+        target_compatible_with = (
+            []
+            if host in hosts["%toolchain_prefix%"].keys() else
+            ["@platforms//:incompatible"]
+        ),
     )
     for tool in TOOLS
 ]

toolchain/toolchain.bzl

@@ -70,6 +70,28 @@ hosts = {
     },
 }
 
+def host_from(host_constraints):
+    if "os" != Label(host_constraints[0]).package:
+        host_constraints = reversed(host_constraints)
+
+    mapping = {
+        "osx": "darwin",
+        "macos": "darwin",
+        "x86_64": "amd64",
+        "aarch64": "arm64",
+    }
+
+    normalize = lambda x: mapping.get(x, default = x)
+
+    os, cpu = [normalize(Label(x).name) for x in host_constraints]
+
+    if os == "darwin":
+        return "darwin_x86_64" if cpu == "amd64" else "darwin_arm64"
+    elif os == "linux":
+        return "linux_x86_64" if cpu == "amd64" else "linux_aarch64"
+    else:
+        return "windows_x86_64"
+
 def _arm_gnu_toolchain(
         name,
         toolchain = "",