Add Rust fuzzing support.

Add a rust_fuzz module which builds a libfuzzer binary that enabes
asan+sancov. This relies on the libfuzzer-sys crate.

Bug: 147140513
Test: Local rust_fuzz example builds, fuzzes with asan+sancov.
Change-Id: I57db3b8d25869791824ccfab768d13b0bb9d42fa

rust/fuzz_test.go

@@ -0,0 +1,66 @@
+// 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 (
+	"strings"
+	"testing"
+
+	"android/soong/android"
+)
+
+func TestRustFuzz(t *testing.T) {
+	ctx := testRust(t, `
+			rust_library {
+				name: "libtest_fuzzing",
+				crate_name: "test_fuzzing",
+				srcs: ["foo.rs"],
+			}
+			rust_fuzz {
+				name: "fuzz_libtest",
+				srcs: ["foo.rs"],
+				rustlibs: ["libtest_fuzzing"],
+			}
+	`)
+
+	// Check that appropriate dependencies are added and that the rustlib linkage is correct.
+	fuzz_libtest_mod := ctx.ModuleForTests("fuzz_libtest", "android_arm64_armv8-a_fuzzer").Module().(*Module)
+	if !android.InList("libclang_rt.asan-aarch64-android", fuzz_libtest_mod.Properties.AndroidMkSharedLibs) {
+		t.Errorf("libclang_rt.asan-aarch64-android shared library dependency missing for rust_fuzz module.")
+	}
+	if !android.InList("liblibfuzzer_sys.rlib-std", fuzz_libtest_mod.Properties.AndroidMkRlibs) {
+		t.Errorf("liblibfuzzer_sys rlib library dependency missing for rust_fuzz module. %#v", fuzz_libtest_mod.Properties.AndroidMkRlibs)
+	}
+	if !android.InList("libtest_fuzzing.rlib-std", fuzz_libtest_mod.Properties.AndroidMkRlibs) {
+		t.Errorf("rustlibs not linked as rlib for rust_fuzz module.")
+	}
+
+	// Check that compiler flags are set appropriately .
+	fuzz_libtest := ctx.ModuleForTests("fuzz_libtest", "android_arm64_armv8-a_fuzzer").Output("fuzz_libtest")
+	if !strings.Contains(fuzz_libtest.Args["rustcFlags"], "-Z sanitizer=address") ||
+		!strings.Contains(fuzz_libtest.Args["rustcFlags"], "-C passes='sancov'") ||
+		!strings.Contains(fuzz_libtest.Args["rustcFlags"], "--cfg fuzzing") {
+		t.Errorf("rust_fuzz module does not contain the expected flags (sancov, cfg fuzzing, address sanitizer).")
+
+	}
+
+	// Check that dependencies have 'fuzzer' variants produced for them as well.
+	libtest_fuzzer := ctx.ModuleForTests("libtest_fuzzing", "android_arm64_armv8-a_rlib_rlib-std_fuzzer").Output("libtest_fuzzing.rlib")
+	if !strings.Contains(libtest_fuzzer.Args["rustcFlags"], "-Z sanitizer=address") ||
+		!strings.Contains(libtest_fuzzer.Args["rustcFlags"], "-C passes='sancov'") ||
+		!strings.Contains(libtest_fuzzer.Args["rustcFlags"], "--cfg fuzzing") {
+		t.Errorf("rust_fuzz dependent library does not contain the expected flags (sancov, cfg fuzzing, address sanitizer).")
+	}
+}