go_compat_repo: alias constraint values and settings to bazel_tools or platforms

go/platform/list.bzl

@@ -59,14 +59,14 @@ def declare_config_settings():
     native.config_setting(
         name = "ios",
         constraint_values = [
-            "@bazel_tools//platforms:ios",
+            "@io_bazel_rules_go_compat//platforms:ios",
         ],
     )
     for goarch in ("arm", "arm64", "386", "amd64"):
         native.config_setting(
             name = "ios_" + goarch,
             constraint_values = [
-                "@bazel_tools//platforms:ios",
+                "@io_bazel_rules_go_compat//platforms:ios",
                 "@io_bazel_rules_go//go/toolchain:" + goarch,
             ],
         )

go/private/compat/BUILD.platforms.v23.bzl

@@ -0,0 +1,25 @@
+[alias(
+    name = name,
+    actual = "@bazel_tools//platforms:{}".format(name),
+    visibility = ["//visibility:public"],
+) for name in [
+    # OS constraint_values
+    "android",
+    "freebsd",
+    "ios",
+    "linux",
+    "osx",
+    "windows",
+
+    # Arch constraint_values
+    "aarch64",
+    "arm",
+    "ppc",
+    "s390x",
+    "x86_32",
+    "x86_64",
+
+    # constraint_settings
+    "os",
+    "cpu",
+]]

go/private/compat/BUILD.platforms.v28.bzl

@@ -0,0 +1,27 @@
+[alias(
+    name = name,
+    actual = "@platforms//os:{}".format(name),
+    visibility = ["//visibility:public"],
+) for name in (
+    "android",
+    "freebsd",
+    "ios",
+    "linux",
+    "os",
+    "osx",
+    "windows",
+)]
+
+[alias(
+    name = name,
+    actual = "@platforms//cpu:{}".format(name),
+    visibility = ["//visibility:public"],
+) for name in (
+    "aarch64",
+    "arm",
+    "cpu",
+    "ppc",
+    "s390x",
+    "x86_32",
+    "x86_64",
+)]

go/private/compat/compat_repo.bzl

@@ -26,30 +26,58 @@
 
 load("@io_bazel_rules_go//go/private:skylib/lib/versions.bzl", "versions")
 
+def _choose(version_impls):
+    """Picks the newest implementation supported by the current version of
+    Bazel from a sequence of version / implementation pairs.
+
+    Args:
+        version_impls: sequence of pairs. The first element of each pair is a
+            parsed semantic version tuple (for example, (1, 2, 3)). The
+            second element is a value that may be returned. The sequence must be
+            sorted by version.
+
+    Returns: the value from the sequence corresponding to the maximum version
+        that is less than the Bazel version. If the Bazel version is not set
+        (in a development build), the last value is returned. If no Bazel
+        version is supported, the first value is returned, and we hope for
+        the best.
+    """
+    if not native.bazel_version:
+        # bazel_version is None in development builds, so we can't do a
+        # version comparison. Use the newest version of the compat file.
+        return version_impls[-1][1]
+    bazel_version = versions.parse(native.bazel_version)
+    newest_supported_impl = version_impls[0][1]
+    for v, impl in version_impls[1:]:
+        if bazel_version < v:
+            break
+        newest_supported_impl = impl
+    return newest_supported_impl
+
 def _go_rules_compat_impl(ctx):
     ctx.file("BUILD.bazel")
-    ctx.symlink(ctx.attr.impl, "compat.bzl")
+    ctx.template("compat.bzl", ctx.attr.impl)
+    ctx.template("platforms/BUILD.bazel", ctx.attr.platforms_build_file)
 
 _go_rules_compat = repository_rule(
     implementation = _go_rules_compat_impl,
     attrs = {
         "impl": attr.label(),
+        "platforms_build_file": attr.label(),
     },
 )
 
 def go_rules_compat(**kwargs):
-    impls = [23, 25]  # keep sorted
-    if not native.bazel_version:
-        # bazel_version is None in development builds, so we can't do a
-        # version comparison. Use the newest version of the compat file.
-        impl = impls[-1]
-    else:
-        bazel_version = versions.parse(native.bazel_version)
-        impl = impls[0]
-        for iv in impls[1:]:
-            next_version = (0, iv, 0)
-            if bazel_version < next_version:
-                break
-            impl = iv
-    impl_label = "@io_bazel_rules_go//go/private:compat/v{}.bzl".format(impl)
-    _go_rules_compat(impl = impl_label, **kwargs)
+    bzl_impl_labels = (
+        ((0, 23, 0), "@io_bazel_rules_go//go/private:compat/v23.bzl"),
+        ((0, 25, 0), "@io_bazel_rules_go//go/private:compat/v25.bzl"),
+    )
+    platforms_build_labels = (
+        ((0, 23, 0), "@io_bazel_rules_go//go/private:compat/BUILD.platforms.v23.bzl"),
+        ((0, 28, 0), "@io_bazel_rules_go//go/private:compat/BUILD.platforms.v28.bzl"),
+    )
+    _go_rules_compat(
+        impl = _choose(bzl_impl_labels),
+        platforms_build_file = _choose(platforms_build_labels),
+        **kwargs
+    )

go/private/platforms.bzl

@@ -17,20 +17,20 @@
 # constraint_values, platforms, and toolchains.
 
 BAZEL_GOOS_CONSTRAINTS = {
-    "android": "@bazel_tools//platforms:android",
-    "darwin": "@bazel_tools//platforms:osx",
-    "freebsd": "@bazel_tools//platforms:freebsd",
-    "linux": "@bazel_tools//platforms:linux",
-    "windows": "@bazel_tools//platforms:windows",
+    "android": "@io_bazel_rules_go_compat//platforms:android",
+    "darwin": "@io_bazel_rules_go_compat//platforms:osx",
+    "freebsd": "@io_bazel_rules_go_compat//platforms:freebsd",
+    "linux": "@io_bazel_rules_go_compat//platforms:linux",
+    "windows": "@io_bazel_rules_go_compat//platforms:windows",
 }
 
 BAZEL_GOARCH_CONSTRAINTS = {
-    "386": "@bazel_tools//platforms:x86_32",
-    "amd64": "@bazel_tools//platforms:x86_64",
-    "arm": "@bazel_tools//platforms:arm",
-    "arm64": "@bazel_tools//platforms:aarch64",
-    "ppc64le": "@bazel_tools//platforms:ppc",
-    "s390x": "@bazel_tools//platforms:s390x",
+    "386": "@io_bazel_rules_go_compat//platforms:x86_32",
+    "amd64": "@io_bazel_rules_go_compat//platforms:x86_64",
+    "arm": "@io_bazel_rules_go_compat//platforms:arm",
+    "arm64": "@io_bazel_rules_go_compat//platforms:aarch64",
+    "ppc64le": "@io_bazel_rules_go_compat//platforms:ppc",
+    "s390x": "@io_bazel_rules_go_compat//platforms:s390x",
 }
 
 GOOS_GOARCH = (
@@ -159,7 +159,7 @@ def _generate_platforms():
 
     for goarch in ("arm", "arm64", "386", "amd64"):
         constraints = [
-            "@bazel_tools//platforms:ios",
+            "@io_bazel_rules_go_compat//platforms:ios",
             GOARCH_CONSTRAINTS[goarch],
         ]
         platforms.append(struct(

go/private/repositories.bzl

@@ -47,6 +47,20 @@ def go_rules_dependencies():
         name = "io_bazel_rules_go_compat",
     )
 
+    # Repository of standard constraint settings and values.
+    # Bazel declares this automatically after 0.28.0, but it's better to
+    # define an explicit version.
+    _maybe(
+        http_archive,
+        name = "platforms",
+        strip_prefix = "platforms-441afe1bfdadd6236988e9cac159df6b5a9f5a98",
+        urls = [
+            "https://mirror.bazel.build/github.com/bazelbuild/platforms/archive/441afe1bfdadd6236988e9cac159df6b5a9f5a98.zip",
+            "https://github.com/bazelbuild/platforms/archive/441afe1bfdadd6236988e9cac159df6b5a9f5a98.zip",
+        ],
+        sha256 = "a07fe5e75964361885db725039c2ba673f0ee0313d971ae4f50c9b18cd28b0b5",
+    )
+
     # Needed by rules_go implementation and tests.
     # We can't call bazel_skylib_workspace from here. At the moment, it's only
     # used to register unittest toolchains, which rules_go does not need.

go/toolchain/toolchains.bzl

@@ -40,8 +40,9 @@ def declare_constraints():
 
     Each constraint_value corresponds to a valid goos or goarch.
     The goos and goarch values belong to the constraint_settings
-    @bazel_tools//platforms:os and @bazel_tools//platforms:cpu, respectively.
-    To avoid redundancy, if there is an equivalent value in @bazel_tools,
+    @platforms//os:os and @platforms//cpu:cpu, respectively (which are
+    aliased through @io_bazel_rules_go_compat//platforms for compatibility).
+    To avoid redundancy, if there is an equivalent value in @platforms,
     we define an alias here instead of another constraint_value.
 
     Each platform defined here selects a goos and goarch constraint value.
@@ -53,7 +54,7 @@ def declare_constraints():
         if constraint.startswith("@io_bazel_rules_go//go/toolchain:"):
             native.constraint_value(
                 name = goos,
-                constraint_setting = "@bazel_tools//platforms:os",
+                constraint_setting = "@io_bazel_rules_go_compat//platforms:os",
             )
         else:
             native.alias(
@@ -65,7 +66,7 @@ def declare_constraints():
         if constraint.startswith("@io_bazel_rules_go//go/toolchain:"):
             native.constraint_value(
                 name = goarch,
-                constraint_setting = "@bazel_tools//platforms:cpu",
+                constraint_setting = "@io_bazel_rules_go_compat//platforms:cpu",
             )
         else:
             native.alias(

tests/core/cross/ios_select_test.go

@@ -37,7 +37,7 @@ go_library(
 
 config_setting(
     name = "is_osx",
-    constraint_values = ["@bazel_tools//platforms:osx"],
+    constraint_values = ["@io_bazel_rules_go_compat//platforms:osx"],
 )
 
 go_library(