Add python_library -> py_library bp2build support

Bug: 196091681
Test: bp2build/python_library_conversion_test.go
Test: build/bazel/ci/mixed_{libc,droid}.sh
Change-Id: Ice87d75533c97fd9c139dc59de09a039e2713a01

python/library.go

@@ -17,11 +17,16 @@ package python
 // This file contains the module types for building Python library.
 
 import (
+	"fmt"
+
 	"android/soong/android"
+	"android/soong/bazel"
+	"github.com/google/blueprint/proptools"
 )
 
 func init() {
 	registerPythonLibraryComponents(android.InitRegistrationContext)
+	android.RegisterBp2BuildMutator("python_library", PythonLibraryBp2Build)
 }
 
 func registerPythonLibraryComponents(ctx android.RegistrationContext) {
@@ -35,8 +40,63 @@ func PythonLibraryHostFactory() android.Module {
 	return module.init()
 }
 
+type bazelPythonLibraryAttributes struct {
+	Srcs         bazel.LabelListAttribute
+	Data         bazel.LabelListAttribute
+	Srcs_version string
+}
+
+func PythonLibraryBp2Build(ctx android.TopDownMutatorContext) {
+	m, ok := ctx.Module().(*Module)
+	if !ok || !m.ConvertWithBp2build(ctx) {
+		return
+	}
+
+	// a Module can be something other than a python_library
+	if ctx.ModuleType() != "python_library" {
+		return
+	}
+
+	// TODO(b/182306917): this doesn't fully handle all nested props versioned
+	// by the python version, which would have been handled by the version split
+	// mutator. This is sufficient for very simple python_library modules under
+	// Bionic.
+	py3Enabled := proptools.BoolDefault(m.properties.Version.Py3.Enabled, true)
+	py2Enabled := proptools.BoolDefault(m.properties.Version.Py2.Enabled, false)
+	var python_version string
+	if py2Enabled && !py3Enabled {
+		python_version = "PY2"
+	} else if !py2Enabled && py3Enabled {
+		python_version = "PY3"
+	} else if !py2Enabled && !py3Enabled {
+		panic(fmt.Errorf(
+			"error for '%s' module: bp2build's python_library converter doesn't understand having "+
+				"neither py2 nor py3 enabled", m.Name()))
+	} else {
+		// do nothing, since python_version defaults to PY2ANDPY3
+	}
+
+	srcs := android.BazelLabelForModuleSrcExcludes(ctx, m.properties.Srcs, m.properties.Exclude_srcs)
+	data := android.BazelLabelForModuleSrc(ctx, m.properties.Data)
+
+	attrs := &bazelPythonLibraryAttributes{
+		Srcs:         bazel.MakeLabelListAttribute(srcs),
+		Data:         bazel.MakeLabelListAttribute(data),
+		Srcs_version: python_version,
+	}
+
+	props := bazel.BazelTargetModuleProperties{
+		// Use the native py_library rule.
+		Rule_class: "py_library",
+	}
+
+	ctx.CreateBazelTargetModule(m.Name(), props, attrs)
+}
+
 func PythonLibraryFactory() android.Module {
 	module := newModule(android.HostAndDeviceSupported, android.MultilibBoth)
 
+	android.InitBazelModule(module)
+
 	return module.init()
 }