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
diff --git a/rust/builder.go b/rust/builder.go
new file mode 100644
index 0000000..64e387b
--- /dev/null
+++ b/rust/builder.go
@@ -0,0 +1,132 @@
+// 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 (
+	"strings"
+
+	"github.com/google/blueprint"
+
+	"android/soong/android"
+)
+
+var (
+	_     = pctx.SourcePathVariable("rustcCmd", "${config.RustBin}/rustc")
+	rustc = pctx.AndroidStaticRule("rustc",
+		blueprint.RuleParams{
+			Command: "$rustcCmd " +
+				"-C linker=${config.RustLinker} " +
+				"-C link-args=\"${config.RustLinkerArgs} ${linkFlags}\" " +
+				"-o $out $in ${libFlags} $rustcFlags " +
+				"&& $rustcCmd --emit=dep-info -o $out.d $in ${libFlags} $rustcFlags",
+			CommandDeps: []string{"$rustcCmd"},
+			Depfile:     "$out.d",
+			Deps:        blueprint.DepsGCC, // Rustc deps-info writes out make compatible dep files: https://github.com/rust-lang/rust/issues/7633
+		},
+		"rustcFlags", "linkFlags", "libFlags")
+)
+
+func init() {
+
+}
+
+func TransformSrcToBinary(ctx android.ModuleContext, mainSrc android.Path, deps PathDeps, flags Flags, outputFile android.WritablePath, includeDirs []string) {
+	targetTriple := ctx.(ModuleContext).toolchain().RustTriple()
+
+	transformSrctoCrate(ctx, mainSrc, deps.RLibs, deps.DyLibs, deps.ProcMacros, deps.StaticLibs, deps.SharedLibs, flags, outputFile, "bin", includeDirs, targetTriple)
+}
+
+func TransformSrctoRlib(ctx android.ModuleContext, mainSrc android.Path, deps PathDeps, flags Flags, outputFile android.WritablePath, includeDirs []string) {
+	targetTriple := ctx.(ModuleContext).toolchain().RustTriple()
+
+	transformSrctoCrate(ctx, mainSrc, deps.RLibs, deps.DyLibs, deps.ProcMacros, deps.StaticLibs, deps.SharedLibs, flags, outputFile, "rlib", includeDirs, targetTriple)
+}
+
+func TransformSrctoDylib(ctx android.ModuleContext, mainSrc android.Path, deps PathDeps, flags Flags, outputFile android.WritablePath, includeDirs []string) {
+	targetTriple := ctx.(ModuleContext).toolchain().RustTriple()
+
+	transformSrctoCrate(ctx, mainSrc, deps.RLibs, deps.DyLibs, deps.ProcMacros, deps.StaticLibs, deps.SharedLibs, flags, outputFile, "dylib", includeDirs, targetTriple)
+}
+
+func TransformSrctoProcMacro(ctx android.ModuleContext, mainSrc android.Path, deps PathDeps, flags Flags, outputFile android.WritablePath, includeDirs []string) {
+	// Proc macros are compiler plugins, and thus should target the host compiler
+	targetTriple := ""
+
+	transformSrctoCrate(ctx, mainSrc, deps.RLibs, deps.DyLibs, deps.ProcMacros, deps.StaticLibs, deps.SharedLibs, flags, outputFile, "proc-macro", includeDirs, targetTriple)
+}
+
+func rustLibsToPaths(libs RustLibraries) android.Paths {
+	var paths android.Paths
+	for _, lib := range libs {
+		paths = append(paths, lib.Path)
+	}
+	return paths
+}
+
+func transformSrctoCrate(ctx android.ModuleContext, main android.Path,
+	rlibs, dylibs, proc_macros RustLibraries, static_libs, shared_libs android.Paths, flags Flags, outputFile android.WritablePath, crate_type string, includeDirs []string, targetTriple string) {
+
+	var inputs android.Paths
+	var deps android.Paths
+	var libFlags, rustcFlags []string
+	crate_name := ctx.(ModuleContext).CrateName()
+
+	inputs = append(inputs, main)
+
+	// Collect rustc flags
+	rustcFlags = append(rustcFlags, flags.GlobalFlags...)
+	rustcFlags = append(rustcFlags, flags.RustFlags...)
+	rustcFlags = append(rustcFlags, "--crate-type="+crate_type)
+	rustcFlags = append(rustcFlags, "--crate-name="+crate_name)
+	if targetTriple != "" {
+		rustcFlags = append(rustcFlags, "--target="+targetTriple)
+	}
+
+	// Collect library/crate flags
+	for _, lib := range rlibs {
+		libFlags = append(libFlags, "--extern "+lib.CrateName+"="+lib.Path.String())
+	}
+	for _, lib := range dylibs {
+		libFlags = append(libFlags, "--extern "+lib.CrateName+"="+lib.Path.String())
+	}
+	for _, proc_macro := range proc_macros {
+		libFlags = append(libFlags, "--extern "+proc_macro.CrateName+"="+proc_macro.Path.String())
+	}
+
+	for _, path := range includeDirs {
+		libFlags = append(libFlags, "-L "+path)
+	}
+
+	// Collect dependencies
+	deps = append(deps, rustLibsToPaths(rlibs)...)
+	deps = append(deps, rustLibsToPaths(dylibs)...)
+	deps = append(deps, rustLibsToPaths(proc_macros)...)
+	deps = append(deps, static_libs...)
+	deps = append(deps, shared_libs...)
+
+	ctx.Build(pctx, android.BuildParams{
+		Rule:        rustc,
+		Description: "rustc " + main.Rel(),
+		Output:      outputFile,
+		Inputs:      inputs,
+		Implicits:   deps,
+		Args: map[string]string{
+			"rustcFlags": strings.Join(rustcFlags, " "),
+			"linkFlags":  strings.Join(flags.LinkFlags, " "),
+			"libFlags":   strings.Join(libFlags, " "),
+		},
+	})
+
+}