rust: rust_proc_macro host snapshot support.

Adds support for capturing rust_proc_macros as part of the host
snapshot. Proc macros target the host and can be thought of as compiler
plugins. Because of this, they don't have vendor image variants and
can't be easily captured as part of the vendor snapshot. Instead we
capture them as part of the host snapshot.

This adds a rust_prebuilt_proc_macro module type.

Bug: 204304380
Test: m HOST_FAKE_SNAPSHOT_ENABLE=true host-fake-snapshot dist
Test: python3 development/vendor_snapshot/update.py --image=host
  --install-dir=vendor/vendor_name/ 31 --local out/dist
Test: Checked Android.bp for rust_prebuilt_proc_macro modules.
Change-Id: I4a8c4d9c41b7ca361b5b97d3f74973918c2a5fe3

rust/prebuilt.go

@@ -22,6 +22,7 @@ func init() {
 	android.RegisterModuleType("rust_prebuilt_library", PrebuiltLibraryFactory)
 	android.RegisterModuleType("rust_prebuilt_dylib", PrebuiltDylibFactory)
 	android.RegisterModuleType("rust_prebuilt_rlib", PrebuiltRlibFactory)
+	android.RegisterModuleType("rust_prebuilt_proc_macro", PrebuiltProcMacroFactory)
 }
 
 type PrebuiltProperties struct {
@@ -38,8 +39,42 @@ type prebuiltLibraryDecorator struct {
 	Properties PrebuiltProperties
 }
 
+type prebuiltProcMacroDecorator struct {
+	android.Prebuilt
+
+	*procMacroDecorator
+	Properties PrebuiltProperties
+}
+
+func PrebuiltProcMacroFactory() android.Module {
+	module, _ := NewPrebuiltProcMacro(android.HostSupportedNoCross)
+	return module.Init()
+}
+
+type rustPrebuilt interface {
+	prebuiltSrcs() []string
+	prebuilt() *android.Prebuilt
+}
+
+func NewPrebuiltProcMacro(hod android.HostOrDeviceSupported) (*Module, *prebuiltProcMacroDecorator) {
+	module, library := NewProcMacro(hod)
+	prebuilt := &prebuiltProcMacroDecorator{
+		procMacroDecorator: library,
+	}
+	module.compiler = prebuilt
+
+	addSrcSupplier(module, prebuilt)
+
+	return module, prebuilt
+}
+
 var _ compiler = (*prebuiltLibraryDecorator)(nil)
 var _ exportedFlagsProducer = (*prebuiltLibraryDecorator)(nil)
+var _ rustPrebuilt = (*prebuiltLibraryDecorator)(nil)
+
+var _ compiler = (*prebuiltProcMacroDecorator)(nil)
+var _ exportedFlagsProducer = (*prebuiltProcMacroDecorator)(nil)
+var _ rustPrebuilt = (*prebuiltProcMacroDecorator)(nil)
 
 func PrebuiltLibraryFactory() android.Module {
 	module, _ := NewPrebuiltLibrary(android.HostAndDeviceSupported)
@@ -56,7 +91,7 @@ func PrebuiltRlibFactory() android.Module {
 	return module.Init()
 }
 
-func addSrcSupplier(module android.PrebuiltInterface, prebuilt *prebuiltLibraryDecorator) {
+func addSrcSupplier(module android.PrebuiltInterface, prebuilt rustPrebuilt) {
 	srcsSupplier := func(_ android.BaseModuleContext, _ android.Module) []string {
 		return prebuilt.prebuiltSrcs()
 	}
@@ -152,3 +187,44 @@ func (prebuilt *prebuiltLibraryDecorator) prebuiltSrcs() []string {
 func (prebuilt *prebuiltLibraryDecorator) prebuilt() *android.Prebuilt {
 	return &prebuilt.Prebuilt
 }
+
+func (prebuilt *prebuiltProcMacroDecorator) prebuiltSrcs() []string {
+	srcs := prebuilt.Properties.Srcs
+	return srcs
+}
+
+func (prebuilt *prebuiltProcMacroDecorator) prebuilt() *android.Prebuilt {
+	return &prebuilt.Prebuilt
+}
+
+func (prebuilt *prebuiltProcMacroDecorator) compilerProps() []interface{} {
+	return append(prebuilt.procMacroDecorator.compilerProps(),
+		&prebuilt.Properties)
+}
+
+func (prebuilt *prebuiltProcMacroDecorator) compile(ctx ModuleContext, flags Flags, deps PathDeps) android.Path {
+	prebuilt.flagExporter.exportLinkDirs(android.PathsForModuleSrc(ctx, prebuilt.Properties.Link_dirs).Strings()...)
+	prebuilt.flagExporter.setProvider(ctx)
+
+	srcPath, paths := srcPathFromModuleSrcs(ctx, prebuilt.prebuiltSrcs())
+	if len(paths) > 0 {
+		ctx.PropertyErrorf("srcs", "prebuilt libraries can only have one entry in srcs (the prebuilt path)")
+	}
+	prebuilt.baseCompiler.unstrippedOutputFile = srcPath
+	return srcPath
+}
+
+func (prebuilt *prebuiltProcMacroDecorator) rustdoc(ctx ModuleContext, flags Flags,
+	deps PathDeps) android.OptionalPath {
+
+	return android.OptionalPath{}
+}
+
+func (prebuilt *prebuiltProcMacroDecorator) compilerDeps(ctx DepsContext, deps Deps) Deps {
+	deps = prebuilt.baseCompiler.compilerDeps(ctx, deps)
+	return deps
+}
+
+func (prebuilt *prebuiltProcMacroDecorator) nativeCoverage() bool {
+	return false
+}