Add support for --@io_bazel_rules_go//go/toolchain:sdk_version flag.

go/private/BUILD.sdk.bazel

@@ -1,6 +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")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -58,10 +59,60 @@ 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: "",
+    },
+)
+
+config_setting(
+    name = "match_major_version",
+    flag_values = {
+        sdk_version_label: "{major_version}",
+    },
+)
+
+config_setting(
+    name = "match_major_minor_version",
+    flag_values = {
+        sdk_version_label: "{major_version}.{minor_version}",
+    },
+)
+
+config_setting(
+    name = "match_patch_version",
+    flag_values = {
+        sdk_version_label: "{major_version}.{minor_version}.{patch_version}",
+    },
+)
+
+# 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}",
+    },
+)
+
+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",
+    ],
+)
+
 declare_toolchains(
     builder = ":builder",
     host = "{goos}_{goarch}",
     sdk = ":go_sdk",
+    sdk_version_setting = ":sdk_version_setting",
 )
 
 filegroup(

go/private/go_toolchain.bzl

@@ -92,7 +92,7 @@ go_toolchain = rule(
     provides = [platform_common.ToolchainInfo],
 )
 
-def declare_toolchains(host, sdk, builder):
+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
@@ -139,5 +139,6 @@ def declare_toolchains(host, sdk, builder):
                 "@io_bazel_rules_go//go/toolchain:" + host_goarch,
             ],
             target_compatible_with = constraints,
+            target_settings = [sdk_version_setting],
             toolchain = ":" + impl_name,
         )

go/private/sdk.bzl

@@ -30,7 +30,8 @@ MIN_SUPPORTED_VERSION = (1, 14, 0)
 def _go_host_sdk_impl(ctx):
     goroot = _detect_host_sdk(ctx)
     platform = _detect_sdk_platform(ctx, goroot)
-    _sdk_build_file(ctx, platform)
+    version = _detect_sdk_version(ctx, goroot)
+    _sdk_build_file(ctx, platform, version)
     _local_sdk(ctx, goroot)
 
 _go_host_sdk = repository_rule(
@@ -53,7 +54,6 @@ def _go_download_sdk_impl(ctx):
             fail("goos set but goarch not set")
         goos, goarch = ctx.attr.goos, ctx.attr.goarch
     platform = goos + "_" + goarch
-    _sdk_build_file(ctx, platform)
 
     version = ctx.attr.version
     sdks = ctx.attr.sdks
@@ -100,6 +100,9 @@ def _go_download_sdk_impl(ctx):
     filename, sha256 = sdks[platform]
     _remote_sdk(ctx, [url.format(filename) for url in ctx.attr.urls], ctx.attr.strip_prefix, sha256)
 
+    detected_version = _detect_sdk_version(ctx, ".")
+    _sdk_build_file(ctx, platform, detected_version)
+
     if not ctx.attr.sdks and not ctx.attr.version:
         # Returning this makes Bazel print a message that 'version' must be
         # specified for a reproducible build.
@@ -134,7 +137,8 @@ def go_download_sdk(name, register_toolchains = True, **kwargs):
 def _go_local_sdk_impl(ctx):
     goroot = ctx.attr.path
     platform = _detect_sdk_platform(ctx, goroot)
-    _sdk_build_file(ctx, platform)
+    version = _detect_sdk_version(ctx, goroot)
+    _sdk_build_file(ctx, platform, version)
     _local_sdk(ctx, goroot)
 
 _go_local_sdk = repository_rule(
@@ -164,7 +168,8 @@ def _go_wrap_sdk_impl(ctx):
         root_file = Label(ctx.attr.root_files[platform])
     goroot = str(ctx.path(root_file).dirname)
     platform = _detect_sdk_platform(ctx, goroot)
-    _sdk_build_file(ctx, platform)
+    version = _detect_sdk_version(ctx, goroot)
+    _sdk_build_file(ctx, platform, version)
     _local_sdk(ctx, goroot)
 
 _go_wrap_sdk = repository_rule(
@@ -226,9 +231,16 @@ def _local_sdk(ctx, path):
     for entry in ["src", "pkg", "bin", "lib"]:
         ctx.symlink(path + "/" + entry, entry)
 
-def _sdk_build_file(ctx, platform):
+def _sdk_build_file(ctx, platform, version):
     ctx.file("ROOT")
     goos, _, goarch = platform.partition("_")
+
+    pv = _parse_version(version)
+    if pv == None or len(pv) < 3:
+        fail("error parsing sdk version: " + version)
+    major, minor, patch = pv[0], pv[1], pv[2]
+    prerelease = pv[3] if len(pv) > 3 else ""
+
     ctx.template(
         "BUILD.bazel",
         Label("//go/private:BUILD.sdk.bazel"),
@@ -238,6 +250,10 @@ def _sdk_build_file(ctx, platform):
             "{goarch}": goarch,
             "{exe}": ".exe" if goos == "windows" else "",
             "{rules_go_repo_name}": "io_bazel_rules_go",
+            "{major_version}": str(major),
+            "{minor_version}": str(minor),
+            "{patch_version}": str(patch),
+            "{prerelease_suffix}": prerelease,
         },
     )
 
@@ -321,6 +337,16 @@ def _detect_sdk_platform(ctx, goroot):
         fail("Could not detect SDK platform: found multiple platforms %s in %s" % (platforms, path))
     return platforms[0]
 
+def _detect_sdk_version(ctx, goroot):
+    path = goroot + "/VERSION"
+    version_contents = ctx.read(path)
+
+    # VERSION file has version prefixed by go, eg. go1.18.3
+    version = version_contents[2:]
+    if _parse_version(version) == None:
+        fail("Could not parse SDK version from version file (%s): %s" % (path, version_contents))
+    return version
+
 def _parse_versions_json(data):
     """Parses version metadata returned by golang.org.
 

go/toolchain/BUILD.bazel

@@ -1,4 +1,5 @@
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
+load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
 load(
     ":toolchains.bzl",
     "declare_constraints",
@@ -8,6 +9,11 @@ package(default_visibility = ["//visibility:public"])
 
 declare_constraints()
 
+string_flag(
+    name = "sdk_version",
+    build_setting_default = "",
+)
+
 filegroup(
     name = "all_rules",
     srcs = glob(["*.bzl"]),

go/toolchains.rst

@@ -67,6 +67,16 @@ SDKs are specific to a host platform (e.g., ``linux_amd64``) and a version of
 Go. They may target all platforms that Go supports. The Go SDK is naturally
 cross compiling.
 
+By default, all ``go_binary``, ``go_test``, etc. rules will use the first declared
+Go SDK. If you would like to build a target using a specific Go SDK version, first
+ensure that you have declared a Go SDK of that version using one of the above rules
+(`go_download_sdk`_, `go_host_sdk`_, `go_local_sdk`_, `go_wrap_sdk`_). Then you
+can specify the sdk version to build with when running a ``bazel build`` by passing
+the flag ``--@io_bazel_rules_go//go/toolchain:sdk_version="version"`` where
+``"version"`` is the SDK version you would like to build with, eg. ``"1.18.3"``.
+The SDK version can omit the patch, or include a prerelease part, eg. ``"1"``,
+``"1.18"``, ``"1.18.0"``, and ``"1.19.0beta1"`` are all valid values for ``sdk_version``.
+
 The toolchain
 ~~~~~~~~~~~~~
 

tests/bcr/bcr.patch

@@ -33,7 +33,7 @@ index 9a364815..2eb6349d 100644
 
  def _go_toolchain_impl(ctx):
      sdk = ctx.attr.sdk[GoSDK]
-@@ -115,8 +115,8 @@ def declare_toolchains(host, sdk, builder):
+@@ -115,8 +115,8 @@ def declare_toolchains(host, sdk, builder, sdk_version_setting):
          impl_name = toolchain_name + "-impl"
 
          cgo_constraints = (
@@ -44,7 +44,7 @@ index 9a364815..2eb6349d 100644
          )
          constraints = [c for c in p.constraints if c not in cgo_constraints]
 
-@@ -135,8 +135,8 @@ def declare_toolchains(host, sdk, builder):
+@@ -135,8 +135,8 @@ def declare_toolchains(host, sdk, builder, sdk_version_setting):
              name = toolchain_name,
              toolchain_type = GO_TOOLCHAIN,
              exec_compatible_with = [
@@ -54,7 +54,7 @@ index 9a364815..2eb6349d 100644
 +                "@rules_go//go/toolchain:" + host_goarch,
              ],
              target_compatible_with = constraints,
-             toolchain = ":" + impl_name,
+             target_settings = [sdk_version_setting],
 diff --git a/go/private/nogo.bzl b/go/private/nogo.bzl
 index 1d3491bb..efb4594f 100644
 --- a/go/private/nogo.bzl
@@ -128,15 +128,15 @@ diff --git a/go/private/sdk.bzl b/go/private/sdk.bzl
 index ee53cb0b..768b174d 100644
 --- a/go/private/sdk.bzl
 +++ b/go/private/sdk.bzl
-@@ -237,7 +237,7 @@ def _sdk_build_file(ctx, platform):
+@@ -249,7 +249,7 @@ def _sdk_build_file(ctx, platform, version):
              "{goos}": goos,
              "{goarch}": goarch,
              "{exe}": ".exe" if goos == "windows" else "",
 -            "{rules_go_repo_name}": "io_bazel_rules_go",
 +            "{rules_go_repo_name}": "rules_go",
-         },
-     )
-
+             "{major_version}": str(major),
+             "{minor_version}": str(minor),
+             "{patch_version}": str(patch),
 diff --git a/go/toolchain/toolchains.bzl b/go/toolchain/toolchains.bzl
 index b4e070cf..6a342da7 100644
 --- a/go/toolchain/toolchains.bzl

tests/core/go_download_sdk/go_download_sdk_test.go

@@ -55,7 +55,8 @@ func Test(t *testing.T) {
 
 func Test(t *testing.T) {
 	for _, test := range []struct {
-		desc, rule, wantVersion string
+		desc, rule       string
+		optToWantVersion map[string]string
 	}{
 		{
 			desc: "version",
@@ -68,7 +69,7 @@ go_download_sdk(
 )
 
 `,
-			wantVersion: "go1.16",
+			optToWantVersion: map[string]string{"": "go1.16"},
 		}, {
 			desc: "custom_archives",
 			rule: `
@@ -84,7 +85,33 @@ go_download_sdk(
     },
 )
 `,
-			wantVersion: "go1.16",
+			optToWantVersion: map[string]string{"": "go1.16"},
+		},
+		{
+			desc: "multiple_sdks",
+			rule: `
+load("@io_bazel_rules_go//go:deps.bzl", "go_download_sdk")
+
+go_download_sdk(
+    name = "go_sdk",
+    version = "1.16",
+)
+go_download_sdk(
+    name = "go_sdk_1_17",
+    version = "1.17",
+)
+go_download_sdk(
+    name = "go_sdk_1_17_1",
+    version = "1.17.1",
+)
+`,
+			optToWantVersion: map[string]string{
+				"": "go1.16",
+				"--@io_bazel_rules_go//go/toolchain:sdk_version=1":   "go1.16",
+				"--@io_bazel_rules_go//go/toolchain:sdk_version=1.17":   "go1.17",
+				"--@io_bazel_rules_go//go/toolchain:sdk_version=1.17.0": "go1.17",
+				"--@io_bazel_rules_go//go/toolchain:sdk_version=1.17.1": "go1.17.1",
+			},
 		},
 	} {
 		t.Run(test.desc, func(t *testing.T) {
@@ -115,8 +142,18 @@ go_register_toolchains()
 				}
 			}()
 
-			if err := bazel_testing.RunBazel("test", "//:version_test", "--test_arg=-version="+test.wantVersion); err != nil {
-				t.Fatal(err)
+			for opt, wantVersion := range test.optToWantVersion {
+				args := []string{
+					"test",
+					"//:version_test",
+					"--test_arg=-version=" + wantVersion,
+				}
+				if opt != "" {
+					args = append(args, opt)
+				}
+				if err := bazel_testing.RunBazel(args...); err != nil {
+					t.Fatal(err)
+				}
 			}
 		})
 	}