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/library_test.go

@@ -0,0 +1,61 @@
+// 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"
+	"testing"
+)
+
+// Test that variants are being generated correctly, and that crate-types are correct.
+func TestLibraryVariants(t *testing.T) {
+
+	ctx := testRust(t, `
+		rust_library_host {
+			name: "libfoo",
+			srcs: ["foo.rs"],
+			crate_name: "foo",
+		}`)
+
+	// Test both variants are being built.
+	libfooRlib := ctx.ModuleForTests("libfoo", "linux_glibc_x86_64_rlib").Output("libfoo.rlib")
+	libfooDylib := ctx.ModuleForTests("libfoo", "linux_glibc_x86_64_dylib").Output("libfoo.so")
+
+	// Test crate type for rlib is correct.
+	if !strings.Contains(libfooRlib.Args["rustcFlags"], "crate-type=rlib") {
+		t.Errorf("missing crate-type for libfoo rlib, rustcFlags: %#v", libfooRlib.Args["rustcFlags"])
+	}
+
+	// Test crate type for dylib is correct.
+	if !strings.Contains(libfooDylib.Args["rustcFlags"], "crate-type=dylib") {
+		t.Errorf("missing crate-type for libfoo dylib, rustcFlags: %#v", libfooDylib.Args["rustcFlags"])
+	}
+}
+
+// Test that dylibs are not statically linking the standard library.
+func TestDylibPreferDynamic(t *testing.T) {
+	ctx := testRust(t, `
+		rust_library_host_dylib {
+			name: "libfoo",
+			srcs: ["foo.rs"],
+			crate_name: "foo",
+		}`)
+
+	libfooDylib := ctx.ModuleForTests("libfoo", "linux_glibc_x86_64_dylib").Output("libfoo.so")
+
+	if !strings.Contains(libfooDylib.Args["rustcFlags"], "prefer-dynamic") {
+		t.Errorf("missing prefer-dynamic flag for libfoo dylib, rustcFlags: %#v", libfooDylib.Args["rustcFlags"])
+	}
+}