python: Provide python rules via CrossResolve. (#316)

This allows rules_python's gazelle plugin to find python rules generated
by rules_proto allowing for a fully gazelle'ified experience working
with protos with Python.

pkg/plugin/grpc/grpc/BUILD.bazel

@@ -14,7 +14,10 @@ go_library(
 
 go_test(
     name = "grpc_test",
-    srcs = ["protoc-gen-grpc-python_test.go"],
+    srcs = [
+        "grpc_test.go",
+        "protoc-gen-grpc-python_test.go",
+    ],
     data = [
         ":protoc",
         ":protoc-gen-grpc-python",

pkg/rule/rules_python/py_library.go

@@ -121,11 +121,25 @@ func (s *PyLibrary) Rule(otherGen ...*rule.Rule) *rule.Rule {
 	return newRule
 }
 
+func pyFilenameToImport(s string) string {
+	if strings.HasSuffix(s, ".py") {
+		return strings.ReplaceAll(s[:len(s)-3], "/", ".")
+	}
+	return s
+}
+
 // Imports implements part of the RuleProvider interface.
 func (s *PyLibrary) Imports(c *config.Config, r *rule.Rule, file *rule.File) []resolve.ImportSpec {
 	if lib, ok := r.PrivateAttr(protoc.ProtoLibraryKey).(protoc.ProtoLibrary); ok {
 		specs := protoc.ProtoLibraryImportSpecsForKind(r.Kind(), lib)
 		specs = maybeStripImportPrefix(specs, lib.StripImportPrefix())
+		from := label.New("", file.Pkg, r.Name())
+		for _, o := range s.Outputs {
+			pyImp := pyFilenameToImport(o)
+			protoc.GlobalResolver().Provide("py", "py", pyImp, from)
+			specs = append(specs, resolve.ImportSpec{Lang: "py", Imp: pyImp})
+		}
+
 		return specs
 	}
 	return nil

pkg/rule/rules_python/py_library_test.go

@@ -1,10 +1,14 @@
 package rules_python
 
 import (
+	"fmt"
+	"path"
 	"testing"
 
 	"github.com/bazelbuild/bazel-gazelle/resolve"
+	"github.com/bazelbuild/bazel-gazelle/rule"
 	"github.com/google/go-cmp/cmp"
+	"github.com/stackb/rules_proto/pkg/protoc"
 )
 
 func TestMaybeStripImportPrefix(t *testing.T) {
@@ -49,3 +53,46 @@ func TestMaybeStripImportPrefix(t *testing.T) {
 		})
 	}
 }
+
+func TestImports(t *testing.T) {
+	kind := "mykind"
+	suffix := "_suffix"
+	pkg := "mypkg"
+	protoName := "test"
+	cases := []struct {
+		Name        string
+		Outputs     []string
+		WantImports []resolve.ImportSpec
+	}{{
+		Name: "Empty",
+		// If for some reason, no python files were output...
+		Outputs: []string{},
+		// Always include the output from the proto_library
+		WantImports: []resolve.ImportSpec{{Lang: kind, Imp: fmt.Sprintf("%s/%s", pkg, protoName)}},
+	}, {
+		Name:    "One output",
+		Outputs: []string{path.Join(pkg, "test_pb2.py")},
+		WantImports: []resolve.ImportSpec{
+			{Lang: kind, Imp: fmt.Sprintf("%s/%s", pkg, protoName)},
+			{Lang: "py", Imp: fmt.Sprintf("%s.%s_pb2", pkg, protoName)},
+		},
+	}}
+
+	for _, c := range cases {
+		t.Run(c.Name, func(t *testing.T) {
+			py := &PyLibrary{
+				KindName:       kind,
+				RuleNameSuffix: suffix,
+				Outputs:        c.Outputs,
+				Resolver:       protoc.ResolveDepsAttr("deps", true),
+			}
+			protoLib := protoc.NewOtherProtoLibrary(&rule.File{}, rule.NewRule("proto_library", protoName+"_proto"), protoc.NewFile(pkg, protoName))
+			r := rule.NewRule(kind, "test"+suffix)
+			r.SetPrivateAttr(protoc.ProtoLibraryKey, protoLib)
+			imps := py.Imports(nil, r, &rule.File{Pkg: pkg})
+			if diff := cmp.Diff(imps, c.WantImports); diff != "" {
+				t.Fatalf("import mismatch: (-got, +want): %s", diff)
+			}
+		})
+	}
+}

rules/private/proto_repository_tools_srcs.bzl

@@ -66,6 +66,9 @@ PROTO_REPOSITORY_TOOLS_SRCS = [
     "@build_stack_rules_proto//pkg/language/protobuf:resolve.go",
     "@build_stack_rules_proto//pkg/plugin/akka/akka_grpc:BUILD.bazel",
     "@build_stack_rules_proto//pkg/plugin/akka/akka_grpc:protoc_gen_akka_grpc.go",
+    "@build_stack_rules_proto//pkg/plugin/bufbuild:BUILD.bazel",
+    "@build_stack_rules_proto//pkg/plugin/bufbuild:connect_es_plugin.go",
+    "@build_stack_rules_proto//pkg/plugin/bufbuild:es_plugin.go",
     "@build_stack_rules_proto//pkg/plugin/builtin:BUILD.bazel",
     "@build_stack_rules_proto//pkg/plugin/builtin:cpp_plugin.go",
     "@build_stack_rules_proto//pkg/plugin/builtin:csharp_plugin.go",
@@ -165,6 +168,7 @@ PROTO_REPOSITORY_TOOLS_SRCS = [
     "@build_stack_rules_proto//pkg/rule/rules_scala:scala_proto_library.go",
     "@build_stack_rules_proto//plugin:BUILD.bazel",
     "@build_stack_rules_proto//plugin/akka/akka-grpc:BUILD.bazel",
+    "@build_stack_rules_proto//plugin/bufbuild:BUILD.bazel",
     "@build_stack_rules_proto//plugin/builtin:BUILD.bazel",
     "@build_stack_rules_proto//plugin/gogo/protobuf:BUILD.bazel",
     "@build_stack_rules_proto//plugin/golang/protobuf:BUILD.bazel",