Create a new mode in soong_ui to generate API only BUILD files

The generated Bazel workspace will only contain api specific targets.
This is feasible since these targets do not have any cross dependencies
with the targets in the bp2build workspace

The advantages of a new mode are
1. Does not pollute bp2build workspace with api targets
2. Does not block api targets with the current allowlist conversion
   mechansims in bp2build
(In the future we might want to combine these two workspaces)

A Soong module type will generate a Bazel target if it implements
ApiProvider interface

Test: m apigen
Test: m nothing

Change-Id: I69c57ca6539f932e0ad554ce84a87fb7936fdba0

bp2build/testing.go

@@ -24,6 +24,8 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/google/blueprint/proptools"
+
 	"android/soong/android"
 	"android/soong/android/allowlists"
 	"android/soong/bazel"
@@ -88,6 +90,22 @@ type Bp2buildTestCase struct {
 }
 
 func RunBp2BuildTestCase(t *testing.T, registerModuleTypes func(ctx android.RegistrationContext), tc Bp2buildTestCase) {
+	bp2buildSetup := func(ctx *android.TestContext) {
+		registerModuleTypes(ctx)
+		ctx.RegisterForBazelConversion()
+	}
+	runBp2BuildTestCaseWithSetup(t, bp2buildSetup, tc)
+}
+
+func RunApiBp2BuildTestCase(t *testing.T, registerModuleTypes func(ctx android.RegistrationContext), tc Bp2buildTestCase) {
+	apiBp2BuildSetup := func(ctx *android.TestContext) {
+		registerModuleTypes(ctx)
+		ctx.RegisterForApiBazelConversion()
+	}
+	runBp2BuildTestCaseWithSetup(t, apiBp2BuildSetup, tc)
+}
+
+func runBp2BuildTestCaseWithSetup(t *testing.T, setup func(ctx *android.TestContext), tc Bp2buildTestCase) {
 	t.Helper()
 	dir := "."
 	filesystem := make(map[string][]byte)
@@ -103,7 +121,7 @@ func RunBp2BuildTestCase(t *testing.T, registerModuleTypes func(ctx android.Regi
 	config := android.TestConfig(buildDir, nil, tc.Blueprint, filesystem)
 	ctx := android.NewTestContext(config)
 
-	registerModuleTypes(ctx)
+	setup(ctx)
 	ctx.RegisterModuleType(tc.ModuleTypeUnderTest, tc.ModuleTypeUnderTestFactory)
 
 	// A default configuration for tests to not have to specify bp2build_available on top level targets.
@@ -118,7 +136,6 @@ func RunBp2BuildTestCase(t *testing.T, registerModuleTypes func(ctx android.Regi
 		})
 	}
 	ctx.RegisterBp2BuildConfig(bp2buildConfig)
-	ctx.RegisterForBazelConversion()
 
 	_, parseErrs := ctx.ParseFileList(dir, toParse)
 	if errored(t, tc, parseErrs) {
@@ -198,6 +215,8 @@ type customProps struct {
 
 	// Prop used to indicate this conversion should be 1 module -> multiple targets
 	One_to_many_prop *bool
+
+	Api *string // File describing the APIs of this module
 }
 
 type customModule struct {
@@ -320,6 +339,7 @@ type customBazelModuleAttributes struct {
 	String_ptr_prop     *string
 	String_list_prop    []string
 	Arch_paths          bazel.LabelListAttribute
+	Api                 bazel.LabelAttribute
 }
 
 func (m *customModule) ConvertWithBp2build(ctx android.TopDownMutatorContext) {
@@ -364,6 +384,23 @@ func (m *customModule) ConvertWithBp2build(ctx android.TopDownMutatorContext) {
 	ctx.CreateBazelTargetModule(props, android.CommonAttributes{Name: m.Name()}, attrs)
 }
 
+var _ android.ApiProvider = (*customModule)(nil)
+
+func (c *customModule) ConvertWithApiBp2build(ctx android.TopDownMutatorContext) {
+	props := bazel.BazelTargetModuleProperties{
+		Rule_class: "custom_api_contribution",
+	}
+	apiAttribute := bazel.MakeLabelAttribute(
+		android.BazelLabelForModuleSrcSingle(ctx, proptools.String(c.props.Api)).Label,
+	)
+	attrs := &customBazelModuleAttributes{
+		Api: *apiAttribute,
+	}
+	ctx.CreateBazelTargetModule(props,
+		android.CommonAttributes{Name: c.Name()},
+		attrs)
+}
+
 // A bp2build mutator that uses load statements and creates a 1:M mapping from
 // module to target.
 func customBp2buildOneToMany(ctx android.TopDownMutatorContext, m *customModule) {