Implement rust_aconfig_library

rust_aconfig_library generates src/lib.rs and uses it to build library variants (dylib, rlib-rlib_std, and rlib-dylib_std) as of what `rust_library` produces

Test: go test
Change-Id: I6c4603691d4306c463c2e9521f5c11c30765b1e3

aconfig/rust_aconfig_library.go

@@ -0,0 +1,83 @@
+package aconfig
+
+import (
+	"android/soong/android"
+	"android/soong/rust"
+	"fmt"
+
+	"github.com/google/blueprint"
+)
+
+type rustDeclarationsTagType struct {
+	blueprint.BaseDependencyTag
+}
+
+var rustDeclarationsTag = rustDeclarationsTagType{}
+
+type RustAconfigLibraryProperties struct {
+	// name of the aconfig_declarations module to generate a library for
+	Aconfig_declarations string
+}
+
+type aconfigDecorator struct {
+	*rust.BaseSourceProvider
+
+	Properties RustAconfigLibraryProperties
+}
+
+func NewRustAconfigLibrary(hod android.HostOrDeviceSupported) (*rust.Module, *aconfigDecorator) {
+	aconfig := &aconfigDecorator{
+		BaseSourceProvider: rust.NewSourceProvider(),
+		Properties:         RustAconfigLibraryProperties{},
+	}
+
+	module := rust.NewSourceProviderModule(android.HostAndDeviceSupported, aconfig, false, false)
+	return module, aconfig
+}
+
+// rust_aconfig_library generates aconfig rust code from the provided aconfig declaration. This module type will
+// create library variants that can be used as a crate dependency by adding it to the rlibs, dylibs, and rustlibs
+// properties of other modules.
+func RustAconfigLibraryFactory() android.Module {
+	module, _ := NewRustAconfigLibrary(android.HostAndDeviceSupported)
+	return module.Init()
+}
+
+func (a *aconfigDecorator) SourceProviderProps() []interface{} {
+	return append(a.BaseSourceProvider.SourceProviderProps(), &a.Properties)
+}
+
+func (a *aconfigDecorator) GenerateSource(ctx rust.ModuleContext, deps rust.PathDeps) android.Path {
+	generatedDir := android.PathForModuleGen(ctx)
+	generatedSource := android.PathForModuleGen(ctx, "src", "lib.rs")
+
+	declarationsModules := ctx.GetDirectDepsWithTag(rustDeclarationsTag)
+
+	if len(declarationsModules) != 1 {
+		panic(fmt.Errorf("Exactly one aconfig_declarations property required"))
+	}
+	declarations := ctx.OtherModuleProvider(declarationsModules[0], declarationsProviderKey).(declarationsProviderData)
+
+	ctx.Build(pctx, android.BuildParams{
+		Rule:  rustRule,
+		Input: declarations.IntermediatePath,
+		Outputs: []android.WritablePath{
+			generatedSource,
+		},
+		Description: "rust_aconfig_library",
+		Args: map[string]string{
+			"gendir": generatedDir.String(),
+			// TODO: Add test mode
+			"mode": "production",
+		},
+	})
+	a.BaseSourceProvider.OutputFiles = android.Paths{generatedSource}
+	return generatedSource
+}
+
+func (a *aconfigDecorator) SourceProviderDeps(ctx rust.DepsContext, deps rust.Deps) rust.Deps {
+	deps = a.BaseSourceProvider.SourceProviderDeps(ctx, deps)
+	deps.Rustlibs = append(deps.Rustlibs, "libflags_rust")
+	ctx.AddDependency(ctx.Module(), rustDeclarationsTag, a.Properties.Aconfig_declarations)
+	return deps
+}