Add Rust support to Soong.

Adds support to Soong for building rust modules. This currently only
supports x86_64 device and x86 linux host targets. The functionality
is sufficient to build crosvm.

Bug: 136189233
Test: Test module builds.
Test: crosvm builds.
Change-Id: I6ea04615834a6d673578ab10ea1a2eb04259fe09

rust/proc_macro.go

@@ -0,0 +1,79 @@
+// 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 rust
+
+import (
+	"android/soong/android"
+)
+
+func init() {
+	android.RegisterModuleType("rust_proc_macro", ProcMacroFactory)
+}
+
+type ProcMacroCompilerProperties struct {
+	// path to the source file that is the main entry point of the program (e.g. src/lib.rs)
+	Srcs []string `android:"path,arch_variant"`
+
+	// set name of the procMacro
+	Stem   *string `android:"arch_variant"`
+	Suffix *string `android:"arch_variant"`
+}
+
+type procMacroDecorator struct {
+	*baseCompiler
+
+	Properties           ProcMacroCompilerProperties
+	distFile             android.OptionalPath
+	unstrippedOutputFile android.Path
+}
+
+type procMacroInterface interface {
+}
+
+var _ compiler = (*procMacroDecorator)(nil)
+
+func ProcMacroFactory() android.Module {
+	module, _ := NewProcMacro(android.HostAndDeviceSupported)
+	return module.Init()
+}
+
+func NewProcMacro(hod android.HostOrDeviceSupported) (*Module, *procMacroDecorator) {
+	module := newModule(hod, android.MultilibFirst)
+
+	procMacro := &procMacroDecorator{
+		baseCompiler: NewBaseCompiler("lib", "lib64"),
+	}
+
+	module.compiler = procMacro
+
+	return module, procMacro
+}
+
+func (procMacro *procMacroDecorator) compilerProps() []interface{} {
+	return append(procMacro.baseCompiler.compilerProps(),
+		&procMacro.Properties)
+}
+
+func (procMacro *procMacroDecorator) compile(ctx ModuleContext, flags Flags, deps PathDeps) android.Path {
+	fileName := procMacro.getStem(ctx) + ctx.toolchain().ProcMacroSuffix()
+	outputFile := android.PathForModuleOut(ctx, fileName)
+
+	srcPath := srcPathFromModuleSrcs(ctx, procMacro.Properties.Srcs)
+
+	procMacro.unstrippedOutputFile = outputFile
+
+	TransformSrctoProcMacro(ctx, srcPath, deps, flags, outputFile, deps.linkDirs)
+	return outputFile
+}