Add Darwin+Arm64 toolchain support

This just sets up the toolchain and allows Darwin+Arm64 to be specified
as a HostCross target. These variants will not be exported to Make, or
be installed on a Soong-only build. A future CL will add support for
universal binaries using these variants.

This config is a bit stranger than the regular 64/32 multilib, as it's
two primary 64-bit configs. And on a Darwin/X86 machine, the Arm64
versions are HostCross (doesn't work on the current machines), while a
Darwin/Arm64 machine, either version works (if Rosetta is installed).

Bug: 203607969
Change-Id: Iacaed77d267773672da027cd74917e33fb1c1e94
diff --git a/rust/config/darwin_host.go b/rust/config/darwin_host.go
new file mode 100644
index 0000000..03bea82
--- /dev/null
+++ b/rust/config/darwin_host.go
@@ -0,0 +1,129 @@
+// Copyright 2019 The Android Open Source Project
+//
+// 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 config
+
+import (
+	"strings"
+
+	"android/soong/android"
+)
+
+var (
+	DarwinRustFlags     = []string{}
+	DarwinRustLinkFlags = []string{
+		"-B${cc_config.MacToolPath}",
+	}
+	darwinArm64Rustflags = []string{}
+	darwinArm64Linkflags = []string{}
+	darwinX8664Rustflags = []string{}
+	darwinX8664Linkflags = []string{}
+)
+
+func init() {
+	registerToolchainFactory(android.Darwin, android.Arm64, darwinArm64ToolchainFactory)
+	registerToolchainFactory(android.Darwin, android.X86_64, darwinX8664ToolchainFactory)
+
+	pctx.StaticVariable("DarwinToolchainRustFlags", strings.Join(DarwinRustFlags, " "))
+	pctx.StaticVariable("DarwinToolchainLinkFlags", strings.Join(DarwinRustLinkFlags, " "))
+
+	pctx.StaticVariable("DarwinToolchainArm64RustFlags", strings.Join(darwinArm64Rustflags, " "))
+	pctx.StaticVariable("DarwinToolchainArm64LinkFlags", strings.Join(darwinArm64Linkflags, " "))
+	pctx.StaticVariable("DarwinToolchainX8664RustFlags", strings.Join(darwinX8664Rustflags, " "))
+	pctx.StaticVariable("DarwinToolchainX8664LinkFlags", strings.Join(darwinX8664Linkflags, " "))
+
+}
+
+type toolchainDarwin struct {
+	toolchain64Bit
+	toolchainRustFlags string
+	toolchainLinkFlags string
+}
+
+type toolchainDarwinArm64 struct {
+	toolchainDarwin
+}
+
+type toolchainDarwinX8664 struct {
+	toolchainDarwin
+}
+
+func (toolchainDarwinArm64) Supported() bool {
+	return true
+}
+
+func (toolchainDarwinX8664) Supported() bool {
+	return true
+}
+
+func (toolchainDarwin) Bionic() bool {
+	return false
+}
+
+func (t *toolchainDarwinArm64) Name() string {
+	return "arm64"
+}
+
+func (t *toolchainDarwinX8664) Name() string {
+	return "x86_64"
+}
+
+func (t *toolchainDarwinArm64) RustTriple() string {
+	return "aarch64-apple-darwin"
+}
+
+func (t *toolchainDarwinX8664) RustTriple() string {
+	return "x86_64-apple-darwin"
+}
+
+func (t *toolchainDarwin) SharedLibSuffix() string {
+	return ".dylib"
+}
+
+func (t *toolchainDarwin) DylibSuffix() string {
+	return ".rustlib.dylib"
+}
+
+func (t *toolchainDarwin) ProcMacroSuffix() string {
+	return ".dylib"
+}
+
+func (t *toolchainDarwinArm64) ToolchainLinkFlags() string {
+	// Prepend the lld flags from cc_config so we stay in sync with cc
+	return "${cc_config.DarwinLldflags} ${config.DarwinToolchainLinkFlags} ${config.DarwinToolchainArm64LinkFlags}"
+}
+
+func (t *toolchainDarwinArm64) ToolchainRustFlags() string {
+	return "${config.DarwinToolchainRustFlags} ${config.DarwinToolchainArm64RustFlags}"
+}
+
+func (t *toolchainDarwinX8664) ToolchainLinkFlags() string {
+	// Prepend the lld flags from cc_config so we stay in sync with cc
+	return "${cc_config.DarwinLldflags} ${config.DarwinToolchainLinkFlags} ${config.DarwinToolchainX8664LinkFlags}"
+}
+
+func (t *toolchainDarwinX8664) ToolchainRustFlags() string {
+	return "${config.DarwinToolchainRustFlags} ${config.DarwinToolchainX8664RustFlags}"
+}
+
+func darwinArm64ToolchainFactory(arch android.Arch) Toolchain {
+	return toolchainDarwinArm64Singleton
+}
+
+func darwinX8664ToolchainFactory(arch android.Arch) Toolchain {
+	return toolchainDarwinX8664Singleton
+}
+
+var toolchainDarwinArm64Singleton Toolchain = &toolchainDarwinArm64{}
+var toolchainDarwinX8664Singleton Toolchain = &toolchainDarwinX8664{}