Add install_symlink soong module type

This can be used to install symlinks to arbitrary locations/targets
on the device. Used to replace a make-built symlink.

Bug: 205632228
Test: built and ran the emulator observed the /system/bin/hwservicemanager symlink is still there
Change-Id: I6df922c8d919e6d56fa79702815a89c98f4d65ed

etc/install_symlink.go

@@ -0,0 +1,92 @@
+// Copyright 2023 Google Inc. 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 etc
+
+import (
+	"android/soong/android"
+	"path/filepath"
+	"strings"
+)
+
+func init() {
+	RegisterInstallSymlinkBuildComponents(android.InitRegistrationContext)
+}
+
+func RegisterInstallSymlinkBuildComponents(ctx android.RegistrationContext) {
+	ctx.RegisterModuleType("install_symlink", InstallSymlinkFactory)
+}
+
+// install_symlink can be used to install an symlink with an arbitrary target to an arbitrary path
+// on the device.
+func InstallSymlinkFactory() android.Module {
+	module := &InstallSymlink{}
+	module.AddProperties(&module.properties)
+	android.InitAndroidMultiTargetsArchModule(module, android.DeviceSupported, android.MultilibCommon)
+	return module
+}
+
+type InstallSymlinkProperties struct {
+	// Where to install this symlink, relative to the partition it's installed on.
+	// Which partition it's installed on can be controlled by the vendor, system_ext, ramdisk, etc.
+	// properties.
+	Installed_location string
+	// The target of the symlink, aka where the symlink points.
+	Symlink_target string
+}
+
+type InstallSymlink struct {
+	android.ModuleBase
+	properties InstallSymlinkProperties
+
+	output        android.Path
+	installedPath android.InstallPath
+}
+
+func (m *InstallSymlink) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	if filepath.Clean(m.properties.Symlink_target) != m.properties.Symlink_target {
+		ctx.PropertyErrorf("symlink_target", "Should be a clean filepath")
+		return
+	}
+	if filepath.Clean(m.properties.Installed_location) != m.properties.Installed_location {
+		ctx.PropertyErrorf("installed_location", "Should be a clean filepath")
+		return
+	}
+	if strings.HasPrefix(m.properties.Installed_location, "../") || strings.HasPrefix(m.properties.Installed_location, "/") {
+		ctx.PropertyErrorf("installed_location", "Should not start with / or ../")
+		return
+	}
+
+	out := android.PathForModuleOut(ctx, "out.txt")
+	android.WriteFileRuleVerbatim(ctx, out, "")
+	m.output = out
+
+	name := filepath.Base(m.properties.Installed_location)
+	installDir := android.PathForModuleInstall(ctx, filepath.Dir(m.properties.Installed_location))
+	m.installedPath = ctx.InstallAbsoluteSymlink(installDir, name, m.properties.Symlink_target)
+}
+
+func (m *InstallSymlink) AndroidMkEntries() []android.AndroidMkEntries {
+	return []android.AndroidMkEntries{{
+		Class: "FAKE",
+		// Need at least one output file in order for this to take effect.
+		OutputFile: android.OptionalPathForPath(m.output),
+		Include:    "$(BUILD_PHONY_PACKAGE)",
+		ExtraEntries: []android.AndroidMkExtraEntriesFunc{
+			func(ctx android.AndroidMkExtraEntriesContext, entries *android.AndroidMkEntries) {
+				entries.AddStrings("LOCAL_SOONG_INSTALL_SYMLINKS", m.installedPath.String())
+			},
+		},
+	}}
+}