Declare toolchains in a separate repository

MODULE.bazel

@@ -21,8 +21,8 @@ use_repo(
 
 go_sdk = use_extension("//go:extensions.bzl", "go_sdk")
 go_sdk.download(name = "go_default_sdk", version = "1.18.3")
-use_repo(go_sdk, "go_default_sdk")
-register_toolchains("@go_default_sdk//:all")
+use_repo(go_sdk, "go_default_sdk_toolchains")
+register_toolchains("@go_default_sdk_toolchains//:all")
 
 bazel_dep(name = "gazelle", version = "0.27.0")
 go_deps = use_extension("@gazelle//:extensions.bzl", "go_deps")

go/def.bzl

@@ -41,7 +41,8 @@ load(
 )
 load(
     "//go/private:go_toolchain.bzl",
-    _declare_toolchains = "declare_toolchains",
+    _declare_bazel_toolchains = "declare_bazel_toolchains",
+    _declare_go_toolchains = "declare_go_toolchains",
     _go_toolchain = "go_toolchain",
 )
 load(
@@ -126,7 +127,20 @@ TOOLS_NOGO = [
 # check this to determine compatibility.
 RULES_GO_VERSION = "0.35.0"
 
-declare_toolchains = _declare_toolchains
+def declare_toolchains(host, sdk, builder, sdk_version_setting):
+    host_goos, _, host_goarch = host.partition("_")
+    _declare_go_toolchains(
+        host_goos = host_goos,
+        sdk = sdk,
+        builder = builder,
+    )
+    _declare_bazel_toolchains(
+        host_goos = host_goos,
+        host_goarch = host_goarch,
+        toolchain_prefix = "",
+        sdk_version_setting = sdk_version_setting,
+    )
+
 go_context = _go_context
 go_embed_data = _go_embed_data
 gomock = _gomock

go/private/BUILD.sdk.bazel

@@ -1,7 +1,7 @@
 load("@{rules_go_repo_name}//go/private/rules:binary.bzl", "go_tool_binary")
 load("@{rules_go_repo_name}//go/private/rules:sdk.bzl", "package_list")
-load("@{rules_go_repo_name}//go:def.bzl", "declare_toolchains", "go_sdk")
-load("@bazel_skylib//lib:selects.bzl", "selects")
+load("@{rules_go_repo_name}//go/private:go_toolchain.bzl", "declare_go_toolchains")
+load("@{rules_go_repo_name}//go:def.bzl", "go_sdk")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -59,75 +59,10 @@ package_list(
     root_file = "ROOT",
 )
 
-sdk_version_label = "@{rules_go_repo_name}//go/toolchain:sdk_version"
-
-config_setting(
-    name = "match_all_versions",
-    flag_values = {
-        sdk_version_label: "",
-    },
-    visibility = ["//visibility:private"],
-)
-
-config_setting(
-    name = "match_major_version",
-    flag_values = {
-        sdk_version_label: "{major_version}",
-    },
-    visibility = ["//visibility:private"],
-)
-
-config_setting(
-    name = "match_major_minor_version",
-    flag_values = {
-        sdk_version_label: "{major_version}.{minor_version}",
-    },
-    visibility = ["//visibility:private"],
-)
-
-config_setting(
-    name = "match_patch_version",
-    flag_values = {
-        sdk_version_label: "{major_version}.{minor_version}.{patch_version}",
-    },
-    visibility = ["//visibility:private"],
-)
-
-# If prerelease version is "", this will be the same as ":match_patch_version", but that's fine since we use match_any in config_setting_group.
-config_setting(
-    name = "match_prerelease_version",
-    flag_values = {
-        sdk_version_label: "{major_version}.{minor_version}.{patch_version}{prerelease_suffix}",
-    },
-    visibility = ["//visibility:private"],
-)
-
-config_setting(
-    name = "match_sdk_type",
-    flag_values = {
-        sdk_version_label: "{sdk_type}",
-    },
-    visibility = ["//visibility:private"],
-)
-
-selects.config_setting_group(
-    name = "sdk_version_setting",
-    match_any = [
-        ":match_all_versions",
-        ":match_major_version",
-        ":match_major_minor_version",
-        ":match_patch_version",
-        ":match_prerelease_version",
-        ":match_sdk_type",
-    ],
-    visibility = ["//visibility:private"],
-)
-
-declare_toolchains(
+declare_go_toolchains(
     builder = ":builder",
-    host = "{goos}_{goarch}",
+    host_goos = "{goos}",
     sdk = ":go_sdk",
-    sdk_version_setting = ":sdk_version_setting",
 )
 
 filegroup(

go/private/BUILD.toolchains.bazel

@@ -0,0 +1,77 @@
+load("@{rules_go_repo_name}//go/private:go_toolchain.bzl", "declare_bazel_toolchains")
+load("@bazel_skylib//lib:selects.bzl", "selects")
+
+{version_constants}
+
+package(default_visibility = ["//visibility:public"])
+
+sdk_version_label = "@{rules_go_repo_name}//go/toolchain:sdk_version"
+
+config_setting(
+    name = "match_all_versions",
+    flag_values = {
+        sdk_version_label: "",
+    },
+    visibility = ["//visibility:private"],
+)
+
+config_setting(
+    name = "match_major_version",
+    flag_values = {
+        sdk_version_label: MAJOR_VERSION,
+    },
+    visibility = ["//visibility:private"],
+)
+
+config_setting(
+    name = "match_major_minor_version",
+    flag_values = {
+        sdk_version_label: MAJOR_VERSION + "." + MINOR_VERSION,
+    },
+    visibility = ["//visibility:private"],
+)
+
+config_setting(
+    name = "match_patch_version",
+    flag_values = {
+        sdk_version_label: MAJOR_VERSION + "." + MINOR_VERSION + "." + PATCH_VERSION,
+    },
+    visibility = ["//visibility:private"],
+)
+
+# If prerelease version is "", this will be the same as ":match_patch_version", but that's fine since we use match_any in config_setting_group.
+config_setting(
+    name = "match_prerelease_version",
+    flag_values = {
+        sdk_version_label: MAJOR_VERSION + "." + MINOR_VERSION + "." + PATCH_VERSION + PRERELEASE_SUFFIX,
+    },
+    visibility = ["//visibility:private"],
+)
+
+config_setting(
+    name = "match_sdk_type",
+    flag_values = {
+        sdk_version_label: "{sdk_type}",
+    },
+    visibility = ["//visibility:private"],
+)
+
+selects.config_setting_group(
+    name = "sdk_version_setting",
+    match_any = [
+        ":match_all_versions",
+        ":match_major_version",
+        ":match_major_minor_version",
+        ":match_patch_version",
+        ":match_prerelease_version",
+        ":match_sdk_type",
+    ],
+    visibility = ["//visibility:private"],
+)
+
+declare_bazel_toolchains(
+    host_goos = "{goos}",
+    host_goarch = "{goarch}",
+    toolchain_prefix = "@{sdk_repo}//",
+    sdk_version_setting = ":sdk_version_setting",
+)

go/private/go_toolchain.bzl

@@ -92,11 +92,8 @@ go_toolchain = rule(
     provides = [platform_common.ToolchainInfo],
 )
 
-def declare_toolchains(host, sdk, builder, sdk_version_setting):
-    """Declares go_toolchain and toolchain targets for each platform."""
-
-    # keep in sync with generate_toolchain_names
-    host_goos, _, host_goarch = host.partition("_")
+def declare_go_toolchains(host_goos, sdk, builder):
+    """Declares go_toolchain targets for each platform."""
     for p in PLATFORMS:
         if p.cgo:
             # Don't declare separate toolchains for cgo_on / cgo_off.
@@ -111,17 +108,8 @@ def declare_toolchains(host, sdk, builder, sdk_version_setting):
         if host_goos == "linux":
             cgo_link_flags.append("-Wl,-whole-archive")
 
-        toolchain_name = "go_" + p.name
-        impl_name = toolchain_name + "-impl"
-
-        cgo_constraints = (
-            "@io_bazel_rules_go//go/toolchain:cgo_off",
-            "@io_bazel_rules_go//go/toolchain:cgo_on",
-        )
-        constraints = [c for c in p.constraints if c not in cgo_constraints]
-
         go_toolchain(
-            name = impl_name,
+            name = "go_" + p.name + "-impl",
             goos = p.goos,
             goarch = p.goarch,
             sdk = sdk,
@@ -131,14 +119,31 @@ def declare_toolchains(host, sdk, builder, sdk_version_setting):
             tags = ["manual"],
             visibility = ["//visibility:public"],
         )
+
+def declare_bazel_toolchains(host_goos, host_goarch, toolchain_prefix, sdk_version_setting):
+    """Declares toolchain targets for each platform."""
+    for p in PLATFORMS:
+        if p.cgo:
+            # Don't declare separate toolchains for cgo_on / cgo_off.
+            # This is controlled by the cgo_context_data dependency of
+            # go_context_data, which is configured using constraint_values.
+            continue
+
+        cgo_constraints = (
+            "@io_bazel_rules_go//go/toolchain:cgo_off",
+            "@io_bazel_rules_go//go/toolchain:cgo_on",
+        )
+        constraints = [c for c in p.constraints if c not in cgo_constraints]
+
         native.toolchain(
-            name = toolchain_name,
+            # keep in sync with generate_toolchain_names
+            name = "go_" + p.name,
             toolchain_type = GO_TOOLCHAIN,
             exec_compatible_with = [
                 "@io_bazel_rules_go//go/toolchain:" + host_goos,
                 "@io_bazel_rules_go//go/toolchain:" + host_goarch,
             ],
             target_compatible_with = constraints,
             target_settings = [sdk_version_setting],
-            toolchain = ":" + impl_name,
+            toolchain = toolchain_prefix + ":go_" + p.name + "-impl",
         )