FR: Allow disabling or customizing proto rule generation

[meowcakes]

Currently this always generates the following rules when a proto_library rule is present:

java_proto_library(
    name = "my_java_proto",
    deps = [":my_proto"],
)

java_library(
    name = "my_java_library",
    visibility = ["//:__subpackages__"],
    exports = [":my_java_proto"],
)

It would be nice if this could be disabled by config or customizable so that it is compatible with other rules, e.g. https://rules-proto-grpc.com/en/latest/lang/java.html#java-proto-library

[illicitonion]

Thanks for filing the issue - I'd be happy to review a PR that did either or both of the following:

1. Added a new directive, # gazelle:java_generate_proto, like # gazelle:go_generate_proto, which allowed disabling the java_proto_library generation
2. Added a new directive # gazelle:java_proto_ruleset which accepted values rules_java and rules_proto_grpc and conditionally generated either target as you'd expect.

To do so, roughly we'd need to:

1. Create a new directive and register it here:

   rules_jvm/java/gazelle/configure.go

   Line 51 in d99cc64

   func (jc *Configurer) KnownDirectives() []string {

   and parse it into the config object here:

   rules_jvm/java/gazelle/configure.go

   Line 71 in d99cc64

   func (jc *Configurer) Configure(c *config.Config, rel string, f *rule.File) {

2. Sniff the config out of cfg here and conditional-ise the codegen:

   rules_jvm/java/gazelle/generate.go

   Lines 74 to 104 in d99cc64

   	jplName := strings.TrimSuffix(protoRuleName, "_proto") + "_java_proto"
   	jglName := strings.TrimSuffix(protoRuleName, "_proto") + "_java_grpc"
   	jlName := strings.TrimSuffix(protoRuleName, "_proto") + "_java_library"
   	rjpl := rule.NewRule("java_proto_library", jplName)
   	rjpl.SetAttr("deps", []string{":" + protoRuleName})
   	res.Gen = append(res.Gen, rjpl)
   	res.Imports = append(res.Imports, types.ResolveInput{})
   	if protoPackage.HasServices {
   	r := rule.NewRule("java_grpc_library", jglName)
   	r.SetAttr("srcs", []string{":" + protoRuleName})
   	r.SetAttr("deps", []string{":" + jplName})
   	res.Gen = append(res.Gen, r)
   	res.Imports = append(res.Imports, types.ResolveInput{})
   	}
   	rjl := rule.NewRule("java_library", jlName)
   	rjl.SetAttr("visibility", []string{"//:__subpackages__"})
   	var exports []string
   	if protoPackage.HasServices {
   	exports = append(exports, ":"+jglName)
   	}
   	rjl.SetAttr("exports", append(exports, ":"+jplName))
   	packageName := types.NewPackageName(protoPackage.Options["java_package"])
   	log.Debug().Str("pkg", packageName.Name).Msg("adding the proto import statement")
   	rjl.SetPrivateAttr(packagesKey, []types.ResolvableJavaPackage{*types.NewResolvableJavaPackage(packageName, false, false)})
   	res.Gen = append(res.Gen, rjl)
   	res.Imports = append(res.Imports, types.ResolveInput{
   	PackageNames: sorted_set.NewSortedSetFn([]types.PackageName{packageName}, types.PackageNameLess),
   	})