Replace go_name_hack with a usage of Label

The Label constructor can be used to transform a label string such as
@io_bazel_rules_go//foo:bar into the canonical label referencing this
target from the repository in which it is called.

For example, `str(Label("@io_bazel_rules_go//foo:bar"))` returns
`"@io_bazel_rules_go//foo:bar"` if rules_go is used as an external
repository from another main workspace, but returns `"//foo:bar"` when
rules_go is the main repository (e.g., when running the tests in the
CI).

This requires raising the minimum version of Bazel from 4.2.0 to 4.2.1
due to bazelbuild/bazel#13890.

.bazelci/presubmit.yml

@@ -2,7 +2,7 @@
 tasks:
   ubuntu1804_bazel400:
     platform: ubuntu1804
-    bazel: 4.2.0 # test minimum supported version of bazel
+    bazel: 4.2.1 # test minimum supported version of bazel
     shell_commands:
       - tests/core/cgo/generate_imported_dylib.sh
     build_targets:

WORKSPACE

@@ -4,7 +4,7 @@ load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 load("@io_bazel_rules_go//go:deps.bzl", "go_register_toolchains", "go_rules_dependencies")
 
-go_rules_dependencies(is_rules_go = True)
+go_rules_dependencies()
 
 go_register_toolchains(version = "1.17")
 

go/private/common.bzl

@@ -199,7 +199,7 @@ def get_versioned_shared_lib_extension(path):
     # something like 1.2.3, or so.1.2, or dylib.1.2, or foo.1.2
     return ""
 
-MINIMUM_BAZEL_VERSION = "4.2.0"
+MINIMUM_BAZEL_VERSION = "4.2.1"
 
 def as_list(v):
     """Returns a list, tuple, or depset as a list."""

go/private/repositories.bzl

@@ -20,7 +20,7 @@ load("//go/private:nogo.bzl", "DEFAULT_NOGO", "go_register_nogo")
 load("//proto:gogo.bzl", "gogo_special_proto")
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
-def go_rules_dependencies(is_rules_go = False):
+def go_rules_dependencies():
     """Declares workspaces the Go rules depend on. Workspaces that use
     rules_go should call this.
 
@@ -285,37 +285,6 @@ def go_rules_dependencies(is_rules_go = False):
         nogo = DEFAULT_NOGO,
     )
 
-    go_name_hack(
-        name = "io_bazel_rules_go_name_hack",
-        is_rules_go = is_rules_go,
-    )
-
 def _maybe(repo_rule, name, **kwargs):
     if name not in native.existing_rules():
         repo_rule(name = name, **kwargs)
-
-def _go_name_hack_impl(ctx):
-    build_content = """\
-load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
-
-bzl_library(
-    name = "def",
-    srcs = ["def.bzl"],
-    visibility = ["//visibility:public"],
-)
-"""
-    ctx.file("BUILD.bazel", build_content)
-    content = "IS_RULES_GO = {}".format(ctx.attr.is_rules_go)
-    ctx.file("def.bzl", content)
-
-go_name_hack = repository_rule(
-    implementation = _go_name_hack_impl,
-    attrs = {
-        "is_rules_go": attr.bool(),
-    },
-    doc = """go_name_hack records whether the main workspace is rules_go.
-
-See documentation for _filter_transition_label in
-go/private/rules/transition.bzl.
-""",
-)

go/private/rules/BUILD.bazel

@@ -119,7 +119,6 @@ bzl_library(
         "@io_bazel_rules_go//go/private:mode",
         "@io_bazel_rules_go//go/private:platforms",
         "@io_bazel_rules_go//go/private:providers",
-        "@io_bazel_rules_go_name_hack//:def",
     ],
 )
 

go/private/rules/transition.bzl

@@ -32,10 +32,6 @@ load(
     "GoLibrary",
     "GoSource",
 )
-load(
-    "@io_bazel_rules_go_name_hack//:def.bzl",
-    "IS_RULES_GO",
-)
 load(
     "@io_bazel_rules_go//go/platform:crosstool.bzl",
     "platform_from_crosstool",
@@ -44,21 +40,16 @@ load(
 def filter_transition_label(label):
     """Transforms transition labels for the current workspace.
 
-    This is a workaround for bazelbuild/bazel#10499. If a transition refers to
-    a build setting in the same workspace, for example
-    @io_bazel_rules_go//go/config:goos, it must use a label without a workspace
-    name if and only if the workspace is the main workspace.
-
-    All Go build settings and transitions are in io_bazel_rules_go. So if
-    io_bazel_rules_go is the main workspace (for development and testing),
-    go_transition must use a label like //go/config:goos. If io_bazel_rules_go
-    is not the main workspace (almost always), go_transition must use a label
-    like @io_bazel_rules_go//go/config:goos.
+    This works around bazelbuild/bazel#10499 by automatically using the correct
+    way to refer to this repository (@io_bazel_rules_go from another workspace,
+    but only repo-relative labels if this repository is the main workspace).
     """
-    if IS_RULES_GO and label.startswith("@io_bazel_rules_go"):
-        return label[len("@io_bazel_rules_go"):]
-    else:
+    if label.startswith("//command_line_option:"):
+        # This is a special label used to refer to Bazel command-line options in
+        # transitions and should not be modified in any way.
         return label
+    else:
+        return str(Label(label))
 
 def go_transition_wrapper(kind, transition_kind, name, **kwargs):
     """Wrapper for rules that may use transitions.