Surface module properties as Bazel BUILD target attributes in the Bazel overlay

This patchset changes bazel_overlay to generate soong_module as a macro,
instead of a rule, and generate module properties in the BUILD files as
kwargs to the soong_module macro.

Here's a sample of the new BUILD files with module properties:

bionic/libdl/BUILD.bazel:
https://paste.googleplex.com/6484466996346880?raw

art/build/apex/BUILD.bazel:
https://paste.googleplex.com/5461276001042432?raw

bionic/apex/BUILD.bazel:
https://paste.googleplex.com/4932795173437440?raw

soong_module is now a macro that conditionally expands to underlying
soong_<module type> rules with statically defined attributes. In this
CL, we are starting with a hardcoded filegroup rule definition to
demonstrate the conditional rule loading within the soong_module macro.
If the module_type matches an existing Bazel rule, soong_module forwards
the entire **kwargs into the rule, which Bazel typechecks.

Non-filegroup module types will be expanded into generic_soong_module,
but with the kwargs dropped.

This approach allows us to:

1) Programmtically generate soong_<module type> rules for all module
types available in Soong, together with the statically defined attribute
types in `attrs`.
2) Incrementally migrate and test individual module types from
generic_soong_module to their module rule shims.
3) Swap out the module rule shims to the actual Bazel rules (e.g
cc_library, java_library) and perform attribute manipulation in Starlark
itself.

Example of querying against the 'srcs' attribute in soong_filegroup:

```
$ bazel cquery 'kind(soong_filegroup, //...)' | wc -l
590

$ bazel cquery --output=build 'attr(srcs, "linker.cpp",
kind(soong_filegroup, //bionic/...))'
INFO: Analyzed 3907 targets (0 packages loaded, 0 targets configured).
INFO: Found 3907 targets...
/usr/local/google/home/jingwen/aosp/out/soong/bazel_overlay/bionic/linker/BUILD.bazel:4144:13
soong_filegroup(
  name = "linker_sources",
  generator_name = "linker_sources",
  generator_function = "soong_module",
  generator_location = "bionic/linker/BUILD.bazel:4144:13",
  srcs = ["dlfcn.cpp", "linker.cpp", "linker_block_allocator.cpp",
"linker_dlwarning.cpp", "linker_cfi.cpp", "linker_config.cpp",
"linker_debug.cpp", "linker_gdb_support.cpp", "linker_globals.cpp",
"linker_libc_support.c", "linker_libcxx_support.cpp",
"linker_namespaces.cpp", "linker_logger.cpp",
"linker_mapped_file_fragment.cpp", "linker_phdr.cpp",
"linker_relocate.cpp", "linker_sdk_versions.cpp", "linker_soinfo.cpp",
"linker_tls.cpp", "linker_utils.cpp", "rt.cpp"],
  deps = [],
)
/usr/local/google/home/jingwen/aosp/out/soong/bazel_overlay/soong_module.bzl:32:23
in <toplevel>
```

This CL is known to be lacking the following features, and will be looked at in follow up CLs:

1) Pretty printing reflect.Interface properties, like arch, multilib and
dists.
2) Generating module Bazel rule shims for all module types, instead of
hardcoding them like `soong_filegroup`.

Bug: 162720644
Test: bazel_overlay_test.go (soong build test)
Test: m bazel_overlay && cd out/soong/bazel_overlay && bazel cquery //...
Signed-off-by: Jingwen Chen <jingwen@google.com>
Change-Id: Ic1e448887eb540ed15a55bc4090cf75a4d832d41
diff --git a/cmd/soong_build/bazel_overlay_test.go b/cmd/soong_build/bazel_overlay_test.go
new file mode 100644
index 0000000..67599c0
--- /dev/null
+++ b/cmd/soong_build/bazel_overlay_test.go
@@ -0,0 +1,255 @@
+// Copyright 2020 Google Inc. All rights reserved.
+//
+// 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 main
+
+import (
+	"android/soong/android"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+var buildDir string
+
+func setUp() {
+	var err error
+	buildDir, err = ioutil.TempDir("", "bazel_overlay_test")
+	if err != nil {
+		panic(err)
+	}
+}
+
+func tearDown() {
+	os.RemoveAll(buildDir)
+}
+
+func TestMain(m *testing.M) {
+	run := func() int {
+		setUp()
+		defer tearDown()
+
+		return m.Run()
+	}
+
+	os.Exit(run())
+}
+
+type customModule struct {
+	android.ModuleBase
+}
+
+func (m *customModule) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	// nothing for now.
+}
+
+func customModuleFactory() android.Module {
+	module := &customModule{}
+	android.InitAndroidModule(module)
+	return module
+}
+
+func TestGenerateBazelOverlayFromBlueprint(t *testing.T) {
+	testCases := []struct {
+		bp                  string
+		expectedBazelTarget string
+	}{
+		{
+			bp: `custom {
+	name: "foo",
+}
+		`,
+			expectedBazelTarget: `soong_module(
+    name = "foo",
+    module_name = "foo",
+    module_type = "custom",
+    module_variant = "",
+    deps = [
+    ],
+)`,
+		},
+		{
+			bp: `custom {
+	name: "foo",
+	ramdisk: true,
+}
+		`,
+			expectedBazelTarget: `soong_module(
+    name = "foo",
+    module_name = "foo",
+    module_type = "custom",
+    module_variant = "",
+    deps = [
+    ],
+    ramdisk = True,
+)`,
+		},
+		{
+			bp: `custom {
+	name: "foo",
+	owner: "a_string_with\"quotes\"_and_\\backslashes\\\\",
+}
+		`,
+			expectedBazelTarget: `soong_module(
+    name = "foo",
+    module_name = "foo",
+    module_type = "custom",
+    module_variant = "",
+    deps = [
+    ],
+    owner = "a_string_with\"quotes\"_and_\\backslashes\\\\",
+)`,
+		},
+		{
+			bp: `custom {
+	name: "foo",
+	required: ["bar"],
+}
+		`,
+			expectedBazelTarget: `soong_module(
+    name = "foo",
+    module_name = "foo",
+    module_type = "custom",
+    module_variant = "",
+    deps = [
+    ],
+    required = [
+        "bar",
+    ],
+)`,
+		},
+		{
+			bp: `custom {
+	name: "foo",
+	target_required: ["qux", "bazqux"],
+}
+		`,
+			expectedBazelTarget: `soong_module(
+    name = "foo",
+    module_name = "foo",
+    module_type = "custom",
+    module_variant = "",
+    deps = [
+    ],
+    target_required = [
+        "qux",
+        "bazqux",
+    ],
+)`,
+		},
+		{
+			bp: `custom {
+	name: "foo",
+	dist: {
+		targets: ["goal_foo"],
+		tag: ".foo",
+	},
+	dists: [
+		{
+			targets: ["goal_bar"],
+			tag: ".bar",
+		},
+	],
+}
+		`,
+			expectedBazelTarget: `soong_module(
+    name = "foo",
+    module_name = "foo",
+    module_type = "custom",
+    module_variant = "",
+    deps = [
+    ],
+    dist = {
+        "tag": ".foo",
+        "targets": [
+            "goal_foo",
+        ],
+    },
+    dists = [
+        {
+            "tag": ".bar",
+            "targets": [
+                "goal_bar",
+            ],
+        },
+    ],
+)`,
+		},
+		{
+			bp: `custom {
+	name: "foo",
+	required: ["bar"],
+	target_required: ["qux", "bazqux"],
+	ramdisk: true,
+	owner: "custom_owner",
+	dists: [
+		{
+			tag: ".tag",
+			targets: ["my_goal"],
+		},
+	],
+}
+		`,
+			expectedBazelTarget: `soong_module(
+    name = "foo",
+    module_name = "foo",
+    module_type = "custom",
+    module_variant = "",
+    deps = [
+    ],
+    dists = [
+        {
+            "tag": ".tag",
+            "targets": [
+                "my_goal",
+            ],
+        },
+    ],
+    owner = "custom_owner",
+    ramdisk = True,
+    required = [
+        "bar",
+    ],
+    target_required = [
+        "qux",
+        "bazqux",
+    ],
+)`,
+		},
+	}
+
+	for _, testCase := range testCases {
+		config := android.TestConfig(buildDir, nil, testCase.bp, nil)
+		ctx := android.NewTestContext()
+		ctx.RegisterModuleType("custom", customModuleFactory)
+		ctx.Register(config)
+
+		_, errs := ctx.ParseFileList(".", []string{"Android.bp"})
+		android.FailIfErrored(t, errs)
+		_, errs = ctx.PrepareBuildActions(config)
+		android.FailIfErrored(t, errs)
+
+		module := ctx.ModuleForTests("foo", "").Module().(*customModule)
+		blueprintCtx := ctx.Context.Context
+
+		actualBazelTarget := generateSoongModuleTarget(blueprintCtx, module)
+		if actualBazelTarget != testCase.expectedBazelTarget {
+			t.Errorf(
+				"Expected generated Bazel target to be '%s', got '%s'",
+				testCase.expectedBazelTarget,
+				actualBazelTarget,
+			)
+		}
+	}
+}