toolchains: remove default value from cgo and darwin constraints

.bazelci/presubmit.yml

@@ -171,7 +171,6 @@ platforms:
     - "-//tests/core/coverage:coverage_test_test"
     - "-//tests/core/coverage:cross_cover_test_test"
     - "-//tests/core/cross:cross_test"
-    - "-//tests/core/cross:ios_select_test"
     - "-//tests/core/go_binary:go_default_test"
     - "-//tests/core/go_path:go_path"
     - "-//tests/core/go_path:go_path_test"
@@ -341,7 +340,6 @@ platforms:
     - "-//tests/core/coverage:coverage_test_test"
     - "-//tests/core/coverage:cross_cover_test_test"
     - "-//tests/core/cross:cross_test"
-    - "-//tests/core/cross:ios_select_test"
     - "-//tests/core/go_binary:go_default_test"
     - "-//tests/core/go_binary:stamp_test"
     - "-//tests/core/go_path:go_path"

go/platform/list.bzl

@@ -28,38 +28,45 @@ GOARCH = _GOARCH
 RACE_GOOS_GOARCH = _RACE_GOOS_GOARCH
 MSAN_GOOS_GOARCH = _MSAN_GOOS_GOARCH
 
-def _os_constraint(goos):
-    if goos == "darwin":
-        return "@io_bazel_rules_go//go/toolchain:is_darwin"
-    else:
-        return "@io_bazel_rules_go//go/toolchain:" + goos
-
-def _arch_constraint(goarch):
-    return "@io_bazel_rules_go//go/toolchain:" + goarch
-
 def declare_config_settings():
     """Generates config_setting targets for each goos, goarch, and valid
     goos_goarch pair. These targets may be used in select expressions.
     Each target refers to a corresponding constraint_value in //go/toolchain.
-
-    Note that the "darwin" targets are true when building for either
-    macOS or iOS.
     """
     for goos in GOOS:
         native.config_setting(
             name = goos,
-            constraint_values = [_os_constraint(goos)],
+            constraint_values = ["@io_bazel_rules_go//go/toolchain:" + goos],
         )
     for goarch in GOARCH:
         native.config_setting(
             name = goarch,
-            constraint_values = [_arch_constraint(goarch)],
+            constraint_values = ["@io_bazel_rules_go//go/toolchain:" + goarch],
         )
     for goos, goarch in GOOS_GOARCH:
         native.config_setting(
             name = goos + "_" + goarch,
             constraint_values = [
-                _os_constraint(goos),
-                _arch_constraint(goarch),
+                "@io_bazel_rules_go//go/toolchain:" + goos,
+                "@io_bazel_rules_go//go/toolchain:" + goarch,
             ],
         )
+
+    # Additional settings for ios. Unfortunately, we cannot have a "darwin"
+    # setting that covers both operating systems, so "darwin" here means macOS.
+    # The "darwin" build tag will be true for both during execution; this only
+    # matters when evaluating select expressions.
+    native.config_setting(
+        name = "ios",
+        constraint_values = [
+            "@bazel_tools//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//go/toolchain:" + goarch,
+            ]
+        )

go/private/compat/compat_repo.bzl

@@ -27,13 +27,6 @@
 load("@io_bazel_rules_go//go/private:skylib/lib/versions.bzl", "versions")
 
 def _go_rules_compat_impl(ctx):
-    darwin_tpl_path = ctx.path(Label("@io_bazel_rules_go//go/private:compat/darwin.bzl.tpl"))
-    if "mac" in ctx.os.name:
-        default_darwin_constraint_value = "@io_bazel_rules_go//go/toolchain:is_darwin"
-    else:
-        default_darwin_constraint_value = "@io_bazel_rules_go//go/toolchain:not_darwin"
-    ctx.template("darwin.bzl", darwin_tpl_path, {"{default_darwin_constraint_value}": default_darwin_constraint_value})
-
     ctx.file("BUILD.bazel")
     ctx.symlink(ctx.attr.impl, "compat.bzl")
 

go/private/go_toolchain.bzl

@@ -112,6 +112,17 @@ def declare_toolchains(host, sdk, builder):
 
         cgo_context_data = "@io_bazel_rules_go//:cgo_context_data" if p.cgo else None
 
+        constraints = p.constraints
+        if p.goos != host_goos or p.goarch != host_goarch:
+            # When cross-compiling, don't require cgo_off.
+            # It won't be set on a custom platform outside of //go/toolchain.
+            constraints = [c for c in constraints if c != "@io_bazel_rules_go//go/toolchain:cgo_off"]
+        else:
+            # When compiling for the host platform, don't require cgo_on.
+            # It won't be set on @bazel_tools//platforms:target_platform,
+            # which is probably the target.
+            constraints = [c for c in constraints if c != "@io_bazel_rules_go//go/toolchain:cgo_on"]
+
         go_toolchain(
             name = impl_name,
             goos = p.goos,
@@ -131,6 +142,6 @@ def declare_toolchains(host, sdk, builder):
                 "@io_bazel_rules_go//go/toolchain:" + host_goos,
                 "@io_bazel_rules_go//go/toolchain:" + host_goarch,
             ],
-            target_compatible_with = p.constraints,
+            target_compatible_with = constraints,
             toolchain = ":" + impl_name,
         )

go/private/platforms.bzl

@@ -141,7 +141,6 @@ def _generate_platforms():
             GOOS_CONSTRAINTS[goos],
             GOARCH_CONSTRAINTS[goarch],
         ]
-        constraints.append("@io_bazel_rules_go//go/toolchain:" + ("is_darwin" if goos == "darwin" else "not_darwin"))
         platforms.append(struct(
             name = goos + "_" + goarch,
             goos = goos,
@@ -162,22 +161,19 @@ def _generate_platforms():
         constraints = [
             "@bazel_tools//platforms:ios",
             GOARCH_CONSTRAINTS[goarch],
-            "@io_bazel_rules_go//go/toolchain:is_darwin",
-            "@io_bazel_rules_go//go/toolchain:cgo_off",
         ]
         platforms.append(struct(
             name = "ios_" + goarch,
             goos = "darwin",
             goarch = goarch,
-            constraints = constraints,
+            constraints = constraints + ["@io_bazel_rules_go//go/toolchain:cgo_off"],
             cgo = False,
         ))
-        constraints[-1] = "@io_bazel_rules_go//go/toolchain:cgo_on"
         platforms.append(struct(
             name = "ios_" + goarch + "_cgo",
             goos = "darwin",
             goarch = goarch,
-            constraints = constraints,
+            constraints = constraints + ["@io_bazel_rules_go//go/toolchain:cgo_on"],
             cgo = True,
         ))
 

go/toolchain/toolchains.bzl

@@ -28,10 +28,6 @@ load(
     "GOOS_CONSTRAINTS",
     "PLATFORMS",
 )
-load(
-    "@io_bazel_rules_go_compat//:darwin.bzl",
-    "DEFAULT_DARWIN_CONSTRAINT_VALUE",
-)
 
 # These symbols should be loaded from sdk.bzl or deps.bzl instead of here..
 DEFAULT_VERSION = _DEFAULT_VERSION
@@ -48,10 +44,6 @@ def declare_constraints():
     To avoid redundancy, if there is an equivalent value in @bazel_tools,
     we define an alias here instead of another constraint_value.
 
-    There is a special constraint_setting for Darwin, "darwin_constraint".
-    The value is "is_darwin" when the target is macOS or iOS and "not_darwin"
-    otherwise.
-
     Each platform defined here selects a goos and goarch constraint value.
     These platforms may be used with --platforms for cross-compilation,
     though users may create their own platforms (and
@@ -81,24 +73,8 @@ def declare_constraints():
                 actual = constraint,
             )
 
-    native.constraint_setting(
-        name = "darwin_constraint",
-        default_constraint_value = DEFAULT_DARWIN_CONSTRAINT_VALUE,
-    )
-
-    native.constraint_value(
-        name = "is_darwin",
-        constraint_setting = ":darwin_constraint",
-    )
-
-    native.constraint_value(
-        name = "not_darwin",
-        constraint_setting = ":darwin_constraint",
-    )
-
     native.constraint_setting(
         name = "cgo_constraint",
-        default_constraint_value = ":cgo_on",
     )
 
     native.constraint_value(

tests/core/cross/BUILD.bazel

@@ -51,35 +51,9 @@ go_test(
     deps = ["//go/tools/bazel:go_default_library"],
 )
 
-bazel_test(
+go_bazel_test(
     name = "ios_select_test",
-    args = ["--platforms=@io_bazel_rules_go//go/toolchain:ios_amd64"],
-    command = "build",
-    targets = [":ios_lib"],
-)
-
-go_library(
-    name = "use_ios_lib",
-    importpath = "github.com/bazelbuild/rules_go/tests/core/cross/use_ios_lib",
-    deps = select({
-        ":is_osx": [":ios_lib"],
-        "//conditions:default": [],
-    }),
-)
-
-config_setting(
-    name = "is_osx",
-    constraint_values = ["@bazel_tools//platforms:osx"],
-)
-
-go_library(
-    name = "ios_lib",
-    srcs = select({
-        "@io_bazel_rules_go//go/platform:darwin": ["ios_good.go"],
-        "//conditions:default": ["ios_bad.go"],
-    }),
-    importpath = "github.com/bazelbuild/rules_go/tests/core/cross/ios_lib",
-    tags = ["manual"],
+    srcs = ["ios_select_test.go"],
 )
 
 go_bazel_test(

tests/core/cross/ios_select_test.go

@@ -0,0 +1,66 @@
+// Copyright 2019 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ios_select_test
+
+import (
+	"testing"
+
+	"github.com/bazelbuild/rules_go/go/tools/bazel_testing"
+)
+
+func TestMain(m *testing.M) {
+	bazel_testing.TestMain(m, bazel_testing.Args{
+		Main: `
+-- BUILD.bazel --
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "use_ios_lib",
+    importpath = "github.com/bazelbuild/rules_go/tests/core/cross/use_ios_lib",
+    deps = select({
+        ":is_osx": [":ios_lib"],
+        "//conditions:default": [],
+    }),
+)
+
+config_setting(
+    name = "is_osx",
+    constraint_values = ["@bazel_tools//platforms:osx"],
+)
+
+go_library(
+    name = "ios_lib",
+    srcs = select({
+        "@io_bazel_rules_go//go/platform:darwin": ["ios_good.go"],
+        "@io_bazel_rules_go//go/platform:ios": ["ios_good.go"],
+        "//conditions:default": ["ios_bad.go"],
+    }),
+    importpath = "github.com/bazelbuild/rules_go/tests/core/cross/ios_lib",
+)
+
+-- ios_good.go --
+package ios_lib
+
+-- ios_bad.go --
+donotbuild
+`,
+	})
+}
+
+func Test(t *testing.T) {
+	if err := bazel_testing.RunBazel("build", "--platforms=@io_bazel_rules_go//go/toolchain:ios_amd64", ":ios_lib"); err != nil {
+		t.Fatal(err)
+	}
+}