Add rust_protobuf module.

This adds a new SourceProvider module type to handle protobuf code
generation. See the new test for an example of how to call this.

Bug: 143953733
Test: New soong tests pass.
Test: Replacing genrules in crosvm with rust_protobuf modules.
Change-Id: Ie3117129cde37b8736bc18ee09bf5cde27c01c34
diff --git a/rust/protobuf_test.go b/rust/protobuf_test.go
new file mode 100644
index 0000000..a9dbf39
--- /dev/null
+++ b/rust/protobuf_test.go
@@ -0,0 +1,39 @@
+// Copyright 2020 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"
+	"testing"
+)
+
+func TestRustProtobuf(t *testing.T) {
+	ctx := testRust(t, `
+		rust_protobuf {
+			name: "librust_proto",
+			proto: "buf.proto",
+			crate_name: "rust_proto",
+			source_stem: "buf",
+		}
+	`)
+	// Check that there's a rule to generate the expected output
+	_ = ctx.ModuleForTests("librust_proto", "android_arm64_armv8-a_dylib").Output("buf.rs")
+
+	// Check that libprotobuf is added as a dependency.
+	librust_proto := ctx.ModuleForTests("librust_proto", "android_arm64_armv8-a_dylib").Module().(*Module)
+	if !android.InList("libprotobuf", librust_proto.Properties.AndroidMkDylibs) {
+		t.Errorf("libprotobuf dependency missing for rust_protobuf (dependency missing from AndroidMkDylibs)")
+	}
+}