feat(bazel): Add rule for generating .swagger.json files

examples/examplepb/BUILD.bazel

@@ -1,5 +1,6 @@
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
 load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
+load("@grpc_ecosystem_grpc_gateway//protoc-gen-swagger:protoc-gen-swagger.bzl", "protoc_gen_swagger")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -49,3 +50,18 @@ go_library(
     embed = [":examplepb_go_proto"],
     importpath = "github.com/grpc-ecosystem/grpc-gateway/examples/examplepb",
 )
+
+protoc_gen_swagger(
+    name = "expamplepb_protoc_gen_swagger",
+    proto_service = "a_bit_of_everything.proto",
+    deps = [
+        "//examples/sub:sub_proto",
+        "//examples/sub2:sub2_proto",
+        "//protoc-gen-swagger/options:options_proto",
+        "@com_github_googleapis_googleapis//google/api:api_proto",
+        "@com_google_protobuf//:duration_proto",
+        "@com_google_protobuf//:empty_proto",
+        "@com_google_protobuf//:timestamp_proto",
+        "@com_google_protobuf//:wrappers_proto",
+    ],
+)

protoc-gen-swagger/BUILD.bazel

@@ -19,6 +19,7 @@ go_library(
 go_binary(
     name = "protoc-gen-swagger",
     embed = [":go_default_library"],
+    visibility = ["//visibility:public"]
 )
 
 go_test(

protoc-gen-swagger/protoc-gen-swagger.bzl

@@ -0,0 +1,79 @@
+def _collect_includes(srcs):
+  includes = ["."]
+  for src in srcs:
+    include = src.dirname
+    if include and not include in includes:
+      includes += [include]
+
+  return includes
+
+def _run_proto_gen_swagger(proto_service, transitive_proto_srcs, actions, protoc, protoc_gen_swagger):
+  swagger_file = actions.declare_file(
+    "%s.swagger.json" % proto_service.basename[:-len(".proto")],
+    sibling = proto_service,
+  )
+
+  args = actions.args()
+  args.add("--plugin=%s" % protoc_gen_swagger.path)
+  args.add("--swagger_out=logtostderr=true:%s" % swagger_file.dirname)
+  args.add("-Iexternal/com_google_protobuf/src")
+  args.add("-Iexternal/grpc_ecosystem_grpc_gateway/third_party/googleapis/")
+  args.add(["-I%s" % include for include in _collect_includes(transitive_proto_srcs)])
+  args.add(proto_service.basename)
+
+  actions.run(
+    executable = protoc,
+    inputs = transitive_proto_srcs + [protoc_gen_swagger],
+    outputs = [swagger_file],
+    arguments = [args],
+  )
+
+  return swagger_file
+
+def _proto_gen_swagger_impl(ctx):
+  transitive_proto_srcs = depset([ctx.file.proto_service] + ctx.files._googleapis + ctx.files._well_known_protos)
+  for dep in ctx.attr.deps:
+    transitive_proto_srcs = depset(transitive=[transitive_proto_srcs, dep.proto.transitive_sources])
+
+  return struct(
+    files=depset([
+      _run_proto_gen_swagger(
+        ctx.file.proto_service,
+        transitive_proto_srcs.to_list(),
+        ctx.actions,
+        ctx.executable._protoc,
+        ctx.executable._protoc_gen_swagger
+      )
+    ])
+  )
+
+protoc_gen_swagger = rule(
+    implementation = _proto_gen_swagger_impl,
+    attrs = {
+      "proto_service": attr.label(
+       mandatory=True,
+        allow_single_file = True,
+      ),
+      "deps": attr.label_list(
+        allow_rules = ["proto_library"]
+      ),
+      "_protoc": attr.label(
+        default = "@com_google_protobuf//:protoc",
+        executable = True,
+        cfg = "host"
+      ),
+      "_well_known_protos": attr.label(
+        default = "@com_google_protobuf//:well_known_protos",
+        allow_files = True,
+      ),
+      "_protoc_gen_swagger": attr.label(
+        default = Label("@grpc_ecosystem_grpc_gateway//protoc-gen-swagger:protoc-gen-swagger"),
+        executable = True,
+        cfg = "host"
+      ),
+      "_googleapis": attr.label(
+        default = Label("@grpc_ecosystem_grpc_gateway//third_party/googleapis:googleapis"),
+        allow_files = True,
+      )
+    },
+)

third_party/googleapis/BUILD.bazel

@@ -0,0 +1,6 @@
+package(default_visibility = ["//visibility:public"])
+
+filegroup(
+    name = "googleapis",
+    srcs = glob(["**/*.proto"])
+)