Implement bp2build for the `package` module

* We are interested mostly in the conversion the `default_applicable_licenses`
  attribute, as `default_visibility` cannot be handled until every module's
  `visibility` is handled.
* Several referenced license modules had to be manually enabled for
  conversion, and likewise a few trivial Android.bp containing only
  package and license modules.
* As Bazel allows only a single `package` rule, the package rules in a
  manually converted BUILD.bazel files were removed (in
  external/protobuf and prebuilts/clang/host/linux-x86 trees).
* The converted package rule is emitted before the `load` statements per
  Bazel documentation.

Bug: 190817312
Test: treehugger
Change-Id: If8bf6fee1580177de3bb402923615bcd48923ed2
diff --git a/bp2build/Android.bp b/bp2build/Android.bp
index a3f618e..7c9af1a 100644
--- a/bp2build/Android.bp
+++ b/bp2build/Android.bp
@@ -67,6 +67,7 @@
         "license_kind_conversion_test.go",
         "linker_config_conversion_test.go",
         "ndk_headers_conversion_test.go",
+        "package_conversion_test.go",
         "performance_test.go",
         "prebuilt_etc_conversion_test.go",
         "python_binary_conversion_test.go",
diff --git a/bp2build/build_conversion.go b/bp2build/build_conversion.go
index 49b9144..ee162b2 100644
--- a/bp2build/build_conversion.go
+++ b/bp2build/build_conversion.go
@@ -64,7 +64,16 @@
 // BazelTargets is a typedef for a slice of BazelTarget objects.
 type BazelTargets []BazelTarget
 
-// sort a list of BazelTargets in-place by name
+func (targets BazelTargets) packageRule() *BazelTarget {
+	for _, target := range targets {
+		if target.ruleClass == "package" {
+			return &target
+		}
+	}
+	return nil
+}
+
+// sort a list of BazelTargets in-place, by name, and by generated/handcrafted types.
 func (targets BazelTargets) sort() {
 	sort.Slice(targets, func(i, j int) bool {
 		return targets[i].name < targets[j].name
@@ -77,7 +86,9 @@
 func (targets BazelTargets) String() string {
 	var res string
 	for i, target := range targets {
-		res += target.content
+		if target.ruleClass != "package" {
+			res += target.content
+		}
 		if i != len(targets)-1 {
 			res += "\n\n"
 		}
diff --git a/bp2build/conversion.go b/bp2build/conversion.go
index 731b17e..b6190c6 100644
--- a/bp2build/conversion.go
+++ b/bp2build/conversion.go
@@ -96,10 +96,14 @@
 # This file was automatically generated by bp2build for the Bazel migration project.
 # Feel free to edit or test it, but do *not* check it into your version control system.
 `
-
-			// Hardcode the default visibility.
-			content += "package(default_visibility = [\"//visibility:public\"])\n"
 			content += targets.LoadStatements()
+			content += "\n\n"
+			// Get package rule from the handcrafted BUILD file, otherwise emit the default one.
+			prText := "package(default_visibility = [\"//visibility:public\"])\n"
+			if pr := targets.packageRule(); pr != nil {
+				prText = pr.content
+			}
+			content += prText
 		} else if mode == QueryView {
 			content = soongModuleLoad
 		}
@@ -160,7 +164,7 @@
 		// internal to Soong only, and these fields do not have PkgPath.
 		return true
 	}
-	// fields with tag `blueprint:"mutated"` are exported to enable modification in mutators, etc
+	// fields with tag `blueprint:"mutated"` are exported to enable modification in mutators, etc.
 	// but cannot be set in a .bp file
 	if proptools.HasTag(field, "blueprint", "mutated") {
 		return true
diff --git a/bp2build/package_conversion_test.go b/bp2build/package_conversion_test.go
new file mode 100644
index 0000000..3704b2d
--- /dev/null
+++ b/bp2build/package_conversion_test.go
@@ -0,0 +1,85 @@
+// Copyright 2022 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 bp2build
+
+import (
+	"android/soong/android"
+	"android/soong/genrule"
+	"testing"
+)
+
+func registerDependentModules(ctx android.RegistrationContext) {
+	ctx.RegisterModuleType("license", android.LicenseFactory)
+	ctx.RegisterModuleType("genrule", genrule.GenRuleFactory)
+}
+
+func TestPackage(t *testing.T) {
+	tests := []struct {
+		description string
+		modules     string
+		expected    []ExpectedRuleTarget
+	}{
+		{
+			description: "with default applicable licenses",
+			modules: `
+license {
+  name: "my_license",
+  visibility: [":__subpackages__"],
+  license_kinds: ["SPDX-license-identifier-Apache-2.0"],
+  license_text: ["NOTICE"],
+}
+
+package {
+  default_applicable_licenses: ["my_license"],
+}
+`,
+			expected: []ExpectedRuleTarget{
+				{
+					"package",
+					"",
+					AttrNameToString{
+						"default_applicable_licenses": `[":my_license"]`,
+						"default_visibility":          `["//visibility:public"]`,
+					},
+					android.HostAndDeviceDefault,
+				},
+				{
+					"android_license",
+					"my_license",
+					AttrNameToString{
+						"license_kinds": `["SPDX-license-identifier-Apache-2.0"]`,
+						"license_text":  `"NOTICE"`,
+						"visibility":    `[":__subpackages__"]`,
+					},
+					android.HostAndDeviceDefault,
+				},
+			},
+		},
+	}
+	for _, test := range tests {
+		expected := make([]string, 0, len(test.expected))
+		for _, e := range test.expected {
+			expected = append(expected, e.String())
+		}
+		RunBp2BuildTestCase(t, registerDependentModules,
+			Bp2buildTestCase{
+				Description:                test.description,
+				ModuleTypeUnderTest:        "package",
+				ModuleTypeUnderTestFactory: android.PackageFactory,
+				Blueprint:                  test.modules,
+				ExpectedBazelTargets:       expected,
+			})
+	}
+}