metropolis/build/kube-code-generator/defs.bzl - monogon - Gitiles

 #  Copyright 2020 The Monogon Project Authors.
 #
 #  SPDX-License-Identifier: Apache-2.0
 #
 #  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.

 # Bazel rules for generating Kubernetes-style API types using
 # github.com/kubernetes/code-generator.
 #
 # k8s.io/code-gen generators target a peculiar filesystem/package structure for
 # generated code:
 #
 #    example.com/project/apis/goodbye/v1/doc.go          - hand written
 #                                       /types.go        - hand written
 #                                       /zz_generated.go - generated
 #    example.com/project/apis/hello/v1/doc.go            - hand written
 #                                     /types.go          - hand written
 #                                     /zz_generated.go   - generated
 #    example.com/project/generated/clientset/...         - generated
 #    example.com/project/generated/informers/...         - generated
 #    example.com/project/generated/listers/...           - generated
 #
 # This means, that usually the generated files are both colocated directly
 # with the package (for zz_generated.deepcopy.go, generated by deepcopy)
 # and have their own package (for files generated by clientset, informers,
 # listers).
 #
 # Most importantly, however, multiple Go packages (in the above example,
 # goodbye/v1 and hello/v1) are used to in turn generate multiple output Go
 # packages. This proves problematic when generating code for Bazel, as we have
 # to consume the result of code generation from multiple Bazel targets (each
 # representing a different generated Go package).
 #
 # To handle this, we split up the code generation into four main steps. These
 # need to be manually instantiated by any use who wants to consume these rules.
 #
 #  1. Create a rules_go go_path that contains all hand-written API packages.
 #  2. Parse hand written API packages using go_kubernetes_resource_bundle, via
 #     the generated go_path. This prepares outputs (ie., 'runs' generators),
 #     and creates an internal provider (KubeResourceBundle) that contains
 #     informations about generated Go packages.
 #  3. For every output package, create a go_kubernetes_library target,
 #     specifying the bundle from which it's supposed to be created, and which
 #     particular library from that bundle should be used.
 #  4. Next to every go_kubernetes_library, create a go_library with the same
 #     importpath which embeds the go_kubernetes_library. The split between
 #     go_kubernetes_library and go_library is required to let Gazelle know
 #     about the availability of given importpaths at given Bazel targets
 #     (unfortunately, it seems like Gazelle is unable to parse rules that emit
 #     the same providers as go_library does, instead requiring us to use a full
 #     go_library rule instead).
 #
 # Point 3. is somwhat different for the generated deepcopy code, which has to
 # live alongside (in the same importpath) as the hand-written API go_library,
 # and needs to be embedded into that. Special care has to be taken to not cause
 # a cycle (handwritten API -> go_path -> bundle -> kubernetes_library ->
 # go_library) in this case. This is done via a select() which selectively
 # enables the inclusion of the generated deepcopy code within the hand-written
 # API library, only enabling it for the target build, not the preprocessing
 # done by go_kubernetes_resource_bundle.
 #
 # Or, in graphical form:
 #
 #   .------------.   .------------.
 #   | go_library |   | go_library |
 #   |------------|   |------------|
 #   | goodbye/v1 |   | hello/v2   |
 #   '------------'   '------------'
 #        '------. .--------'
 #           .---------.
 #           | go_path |
 #           '---------'
 #                | (preprocessing transition)
 #  .-------------------------------.
 #  | go_kubernetes_resource_bundle |
 #  '-------------------------------'
 #              |   '--------------------------.
 #  .---------------------------.  .--------------------------.
 #  |   go_kubernetes_library   |  |   go_kubernetes_library  |
 #  |---------------------------|  |--------------------------| ... others ...
 #  | clientset/verioned/typed  |  | clientset/verioned/fake  |
 #  '---------------------------'  '--------------------------'
 #              |                               |
 #  .---------------------------.  .--------------------------.
 #  |       go_library          |  |       go_library         |
 #  |---------------------------|  |--------------------------| ... others ...
 #  | clientset/versioned/typed |  | clientset/versioned/fake |
 #  '---------------------------'  '--------------------------'
 #

 load("@io_bazel_rules_go//go:def.bzl", "GoLibrary", "GoPath", "go_context")

 def _preprocessing_transition_impl(settings, attr):
     return {"//metropolis/build/kube-code-generator:preprocessing": "yes"}

 # preprocessing_transition is attached to the incoming go_path in
 # go_kubernetes_resource_bundle, unsets the
 # //metropolis/build/kube-code-generator:embed_deepcopy config setting.
 # This allows go_libraries that make up the handwritten API libraries to only
 # embed the generated deepcopy when they are pulled in for build reasons, not
 # when the graph is being traversed in order to generate the deepcopy itself.
 # This breaks up the cycle that would happen otherwise.
 preprocessing_transition = transition(
     implementation = _preprocessing_transition_impl,
     inputs = [],
     outputs = ["//metropolis/build/kube-code-generator:preprocessing"],
 )

 # KubeResourceBundle is emitted by go_kubernetes_resource_bundle and contains
 # informations about libraries generated by the kubernetes code-generators.
 KubeResourceBundle = provider(
     "Information about the generated Go sources of a k8s.io/code-generator-built library.",
     fields = {
         "libraries": "Map from Go importpath to list of Files that make up this importpath.",
     },
 )

 def _go_kubernetes_library_impl(ctx):
     go = go_context(ctx)
     bundle = ctx.attr.bundle[KubeResourceBundle]
     libraries = bundle.libraries

     found_importpaths = [l.importpath for l in libraries]

     libraries = [l for l in libraries if l.importpath == ctx.attr.importpath]
     if len(libraries) < 1:
         fail("importpath {} not found in bundle (have {})".format(ctx.attr.importpath, ", ".join(found_importpaths)))
     if len(libraries) > 1:
         fail("internal error: multiple libraries with importpath {} found in bundle".format(ctx.attr.importpath))
     library = libraries[0]

     source = go.library_to_source(go, ctx.attr, library, ctx.coverage_instrumented())
     return [library, source, OutputGroupInfo(go_generated_srcs = depset(library.srcs))]

 # go_kubernetes_library picks a single Go library from a kube_resource_bundle
 # and prepares it for being embedded into a go_library.
 go_kubernetes_library = rule(
     implementation = _go_kubernetes_library_impl,
     attrs = {
         "bundle": attr.label(
             mandatory = True,
             providers = [KubeResourceBundle],
             doc = "A go_kubernetes_resource_bundle that contains the result of a kubernetes code-generation run.",
         ),
         "importpath": attr.string(
             mandatory = True,
             doc = "The importpath of the library picked from the bundle, same as the importpath of the go_library that embeds it.",
         ),
         "deps": attr.label_list(
             providers = [GoLibrary],
             doc = "All build dependencies of this library.",
         ),
         "_go_context_data": attr.label(
             default = "@io_bazel_rules_go//:go_context_data",
         ),
     },
     toolchains = ["@io_bazel_rules_go//go:toolchain"],
 )

 # _gotool_run is a helper function which runs an executable under
 # //metropolis/build/gotoolwrap, effectively setting up everything required to
 # use standard Go tooling on the monogon workspace (ie. GOPATH/GOROOT). This is
 # required by generators to run 'go fmt'.
 def _gotool_run(ctx, executable, arguments, **kwargs):
     go = go_context(ctx)
     gopath = ctx.attr.gopath[0][GoPath]

     inputs = [
         gopath.gopath_file,
     ] + kwargs.get("inputs", [])

     tools = [
         executable,
         go.sdk.go,
     ] + go.sdk.tools + kwargs.get("tools", [])

     env = {
         "GOTOOLWRAP_GOPATH": gopath.gopath_file.path,
         "GOTOOLWRAP_GOROOT": go.sdk.root_file.dirname,
     }
     env.update(kwargs.get("env", {}))

     kwargs_ = dict([(k, v) for (k, v) in kwargs.items() if k not in [
         "executable",
         "arguments",
         "inputs",
         "env",
         "tools",
     ]])

     ctx.actions.run(
         executable = ctx.executable._gotoolwrap,
         arguments = [executable.path] + arguments,
         env = env,
         inputs = inputs,
         tools = tools,
         **kwargs_
     )

 # _output_directory returns the relative path into which
 # ctx.action.declare_file writes are rooted. This is used as code-generators
 # require a root path for all outputted files, instead of a list of files to
 # emit.
 def _output_directory(ctx):
     # We combine bin_dir, the BUILDfile path and the target name. This seems
     # wrong. Is there no simpler way to do this?
     buildfile_path = ctx.build_file_path
     parts = buildfile_path.split("/")
     if not parts[-1].startswith("BUILD"):
         fail("internal error: unexpected BUILD file path: {}", parts[-1])
     package_path = "/".join(parts[:-1])
     return "/".join([ctx.bin_dir.path, package_path, ctx.attr.name])

 # _cg returns a 'codegen context', a struct that's used to accumulate the
 # results of code generation. It assumes all output will be rooted in a
 # generated importpath (with more 'shortened' importpaths underneath the root),
 # and collects outputs to pass to the codegen execution action. It also
 # collects a map of importpaths to outputs that make it up.
 def _cg(ctx, importpath):
     output_root = _output_directory(ctx)

     return struct(
         # The 'root' importpath, under which 'shortened' importpaths reside.
         importpath = importpath,
         # The prefix into which all files will be emitted. We use the target
         # name for convenience.
         output_prefix = ctx.attr.name,
         # The full relative path visible to the codegen, pointing to the same
         # directory as output_prefix (just from the point of view of the
         # runtime filesystem, not the ctx.actions filepath declaration API).
         output_root = output_root,
         # The list of outputs that have to be generated by the codegen.
         outputs = [],
         # A map of importpath to list of outputs (from the above list) that
         # make up a generated Go package/library.
         libraries = {},
         ctx = ctx,
     )

 # _declare_library adds a single Go package/library at importpath to the
 # codegen context with the given file paths (rooted in the importpath).
 def _declare_library(cg, importpath, files):
     importpath = cg.importpath + "/" + importpath
     cg.libraries[importpath] = []
     for f in files:
         output = cg.ctx.actions.declare_file("{}/{}/{}".format(
             cg.output_prefix,
             importpath,
             f,
         ))
         cg.outputs.append(output)
         cg.libraries[importpath].append(output)

 # _declare_libraries declares multiple Go package/libraries to the codegen
 # context. The key of the dictionary is the importpath of the library, and the
 # value are the file names of generated outputs.
 def _declare_libraries(cg, libraries):
     for k, v in libraries.items():
         _declare_library(cg, k, v)

 # _codegen_clientset runs the clientset codegenerator.
 def _codegen_clientset(ctx):
     cg = _cg(ctx, ctx.attr.importpath)

     _declare_libraries(cg, {
         "clientset/versioned": ["clientset.go", "doc.go"],
         "clientset/versioned/fake": ["register.go", "clientset_generated.go"],
         "clientset/versioned/scheme": ["register.go", "doc.go"],
     })

     for api, types in ctx.attr.apis.items():
         client_name = api.split("/")[-2]
         _declare_libraries(cg, {
             "clientset/versioned/typed/{}".format(api): [
                 "doc.go",
                 "generated_expansion.go",
                 "{}_client.go".format(client_name),
             ] + [
                 "{}.go".format(t)
                 for t in types
             ],
             "clientset/versioned/typed/{}/fake".format(api): [
                 "doc.go",
                 "fake_{}_client.go".format(client_name),
             ],
         })

     _gotool_run(
         ctx,
         mnemonic = "ClientsetGen",
         executable = ctx.executable._client_gen,
         arguments = [
             "--clientset-name",
             "versioned",
             "--input-base",
             ctx.attr.apipath,
             "--input",
             ",".join(ctx.attr.apis),
             "--output-package",
             cg.importpath + "/clientset",
             "--output-base",
             cg.output_root,
             "--go-header-file",
             ctx.file.boilerplate.path,
         ],
         inputs = [
             ctx.file.boilerplate,
         ],
         outputs = cg.outputs,
     )

     return cg.libraries

 # _codegen_deepcopy runs the deepcopy codegenerator (outputting to the apipath,
 # not the importpath).
 def _codegen_deepcopy(ctx):
     cg = _cg(ctx, ctx.attr.apipath)

     for api, types in ctx.attr.apis.items():
         _declare_libraries(cg, {
             api: ["zz_generated.deepcopy.go"],
         })

     _gotool_run(
         ctx,
         mnemonic = "DeepcopyGen",
         executable = ctx.executable._deepcopy_gen,
         arguments = [
             "--input-dirs",
             ",".join(["{}/{}".format(ctx.attr.apipath, api) for api in ctx.attr.apis]),
             "--go-header-file",
             ctx.file.boilerplate.path,
             "--stderrthreshold",
             "0",
             "-O",
             "zz_generated.deepcopy",
             "--output-base",
             cg.output_root,
             ctx.attr.apipath,
         ],
         inputs = [
             ctx.file.boilerplate,
         ],
         outputs = cg.outputs,
     )
     return cg.libraries

 # _codegen_informer runs the informer codegenerator.
 def _codegen_informer(ctx):
     cg = _cg(ctx, ctx.attr.importpath)

     _declare_libraries(cg, {
         "informers/externalversions": ["factory.go", "generic.go"],
         "informers/externalversions/internalinterfaces": ["factory_interfaces.go"],
     })

     for api, types in ctx.attr.apis.items():
         client_name = api.split("/")[-2]
         _declare_libraries(cg, {
             "informers/externalversions/{}".format(client_name): ["interface.go"],
             "informers/externalversions/{}".format(api): [
                 "interface.go",
             ] + [
                 "{}.go".format(t)
                 for t in types
             ],
         })

     _gotool_run(
         ctx,
         mnemonic = "InformerGen",
         executable = ctx.executable._informer_gen,
         arguments = [
             "--input-dirs",
             ",".join(["{}/{}".format(ctx.attr.apipath, api) for api in ctx.attr.apis]),
             "--versioned-clientset-package",
             "{}/clientset/versioned".format(ctx.attr.importpath),
             "--listers-package",
             "{}/listers".format(ctx.attr.importpath),
             "--output-package",
             "{}/informers".format(ctx.attr.importpath),
             "--output-base",
             cg.output_root,
             "--go-header-file",
             ctx.file.boilerplate.path,
         ],
         inputs = [
             ctx.file.boilerplate,
         ],
         outputs = cg.outputs,
     )

     return cg.libraries

 # _codegen_lister runs the lister codegenerator.
 def _codegen_lister(ctx):
     cg = _cg(ctx, ctx.attr.importpath)

     for api, types in ctx.attr.apis.items():
         client_name = api.split("/")[-2]
         _declare_libraries(cg, {
             "listers/{}".format(api): [
                 "expansion_generated.go",
             ] + [
                 "{}.go".format(t)
                 for t in types
             ],
         })

     _gotool_run(
         ctx,
         mnemonic = "ListerGen",
         executable = ctx.executable._lister_gen,
         arguments = [
             "--input-dirs",
             ",".join(["{}/{}".format(ctx.attr.apipath, api) for api in ctx.attr.apis]),
             "--output-package",
             "{}/listers".format(ctx.attr.importpath),
             "--output-base",
             cg.output_root,
             "--go-header-file",
             ctx.file.boilerplate.path,
             "-v",
             "10",
         ],
         inputs = [
             ctx.file.boilerplate,
         ],
         outputs = cg.outputs,
     )

     return cg.libraries

 # _update_dict_check is a helper function that updates dict a with dict b,
 # ensuring there's no overwritten keys.
 def _update_dict_check(a, b):
     for k in b.keys():
         if k in a:
             fail("internal error: repeat importpath {}", k)
     a.update(b)

 def _go_kubernetes_resource_bundle_impl(ctx):
     go = go_context(ctx)

     all_gens = {}
     _update_dict_check(all_gens, _codegen_clientset(ctx))
     _update_dict_check(all_gens, _codegen_deepcopy(ctx))
     _update_dict_check(all_gens, _codegen_informer(ctx))
     _update_dict_check(all_gens, _codegen_lister(ctx))

     libraries = []
     for importpath, srcs in all_gens.items():
         library = go.new_library(
             go,
             srcs = srcs,
             importpath = importpath,
         )
         libraries.append(library)

     return [KubeResourceBundle(libraries = libraries)]

 # go_kubernetes_resource_bundle runs kubernetes code-generators on a codepath
 # for some requested APIs, and whose output can be made into Go library targets
 # via go_kubernetes_library. This bundle corresponds to a single Kubernetes API
 # resource group.
 go_kubernetes_resource_bundle = rule(
     implementation = _go_kubernetes_resource_bundle_impl,
     attrs = {
         "gopath": attr.label(
             mandatory = True,
             providers = [GoPath],
             cfg = preprocessing_transition,
             doc = "A rules_go go_path that contains all the API libraries for which codegen should be run.",
         ),
         "importpath": attr.string(
             mandatory = True,
             doc = """
                 The root importpath of the generated code (apart from deepcopy
                 codegen). The Bazel target path corresponding to this
                 importpath needs to contain the go_kubernetes_library and
                 go_library targets that allow to actually build against the
                 generated code.
             """,
         ),
         "apipath": attr.string(
             mandatory = True,
             doc = "The root importpath of the APIs for which to generate code.",
         ),
         "apis": attr.string_list_dict(
             mandatory = True,
             doc = """
                 The APIs underneath importpath for which to generated code,
                 eg. foo/v1, mapping into a list of lowercased types generated
                 from each (eg. widget for `type Widget struct`).
             """,
         ),
         "boilerplate": attr.label(
             default = "//metropolis/build/kube-code-generator:boilerplate.go.txt",
             allow_single_file = True,
             doc = "Header that will be used in the generated code.",
         ),
         "_go_context_data": attr.label(
             default = "@io_bazel_rules_go//:go_context_data",
         ),
         "_gotoolwrap": attr.label(
             default = Label("//metropolis/build/gotoolwrap"),
             allow_single_file = True,
             executable = True,
             cfg = "exec",
         ),
         "_deepcopy_gen": attr.label(
             default = Label("@io_k8s_code_generator//cmd/deepcopy-gen"),
             allow_single_file = True,
             executable = True,
             cfg = "exec",
         ),
         "_client_gen": attr.label(
             default = Label("@io_k8s_code_generator//cmd/client-gen"),
             allow_single_file = True,
             executable = True,
             cfg = "exec",
         ),
         "_informer_gen": attr.label(
             default = Label("@io_k8s_code_generator//cmd/informer-gen"),
             allow_single_file = True,
             executable = True,
             cfg = "exec",
         ),
         "_lister_gen": attr.label(
             default = Label("@io_k8s_code_generator//cmd/lister-gen"),
             allow_single_file = True,
             executable = True,
             cfg = "exec",
         ),
         "_allowlist_function_transition": attr.label(
             default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
         ),
     },
     toolchains = ["@io_bazel_rules_go//go:toolchain"],
 )
	# Copyright 2020 The Monogon Project Authors.
	#
	# SPDX-License-Identifier: Apache-2.0
	#
	# 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.

	# Bazel rules for generating Kubernetes-style API types using
	# github.com/kubernetes/code-generator.
	#
	# k8s.io/code-gen generators target a peculiar filesystem/package structure for
	# generated code:
	#
	# example.com/project/apis/goodbye/v1/doc.go - hand written
	# /types.go - hand written
	# /zz_generated.go - generated
	# example.com/project/apis/hello/v1/doc.go - hand written
	# /types.go - hand written
	# /zz_generated.go - generated
	# example.com/project/generated/clientset/... - generated
	# example.com/project/generated/informers/... - generated
	# example.com/project/generated/listers/... - generated
	#
	# This means, that usually the generated files are both colocated directly
	# with the package (for zz_generated.deepcopy.go, generated by deepcopy)
	# and have their own package (for files generated by clientset, informers,
	# listers).
	#
	# Most importantly, however, multiple Go packages (in the above example,
	# goodbye/v1 and hello/v1) are used to in turn generate multiple output Go
	# packages. This proves problematic when generating code for Bazel, as we have
	# to consume the result of code generation from multiple Bazel targets (each
	# representing a different generated Go package).
	#
	# To handle this, we split up the code generation into four main steps. These
	# need to be manually instantiated by any use who wants to consume these rules.
	#
	# 1. Create a rules_go go_path that contains all hand-written API packages.
	# 2. Parse hand written API packages using go_kubernetes_resource_bundle, via
	# the generated go_path. This prepares outputs (ie., 'runs' generators),
	# and creates an internal provider (KubeResourceBundle) that contains
	# informations about generated Go packages.
	# 3. For every output package, create a go_kubernetes_library target,
	# specifying the bundle from which it's supposed to be created, and which
	# particular library from that bundle should be used.
	# 4. Next to every go_kubernetes_library, create a go_library with the same
	# importpath which embeds the go_kubernetes_library. The split between
	# go_kubernetes_library and go_library is required to let Gazelle know
	# about the availability of given importpaths at given Bazel targets
	# (unfortunately, it seems like Gazelle is unable to parse rules that emit
	# the same providers as go_library does, instead requiring us to use a full
	# go_library rule instead).
	#
	# Point 3. is somwhat different for the generated deepcopy code, which has to
	# live alongside (in the same importpath) as the hand-written API go_library,
	# and needs to be embedded into that. Special care has to be taken to not cause
	# a cycle (handwritten API -> go_path -> bundle -> kubernetes_library ->
	# go_library) in this case. This is done via a select() which selectively
	# enables the inclusion of the generated deepcopy code within the hand-written
	# API library, only enabling it for the target build, not the preprocessing
	# done by go_kubernetes_resource_bundle.
	#
	# Or, in graphical form:
	#
	# .------------. .------------.
	# \| go_library \| \| go_library \|
	# \|------------\| \|------------\|
	# \| goodbye/v1 \| \| hello/v2 \|
	# '------------' '------------'
	# '------. .--------'
	# .---------.
	# \| go_path \|
	# '---------'
	# \| (preprocessing transition)
	# .-------------------------------.
	# \| go_kubernetes_resource_bundle \|
	# '-------------------------------'
	# \| '--------------------------.
	# .---------------------------. .--------------------------.
	# \| go_kubernetes_library \| \| go_kubernetes_library \|
	# \|---------------------------\| \|--------------------------\| ... others ...
	# \| clientset/verioned/typed \| \| clientset/verioned/fake \|
	# '---------------------------' '--------------------------'
	# \| \|
	# .---------------------------. .--------------------------.
	# \| go_library \| \| go_library \|
	# \|---------------------------\| \|--------------------------\| ... others ...
	# \| clientset/versioned/typed \| \| clientset/versioned/fake \|
	# '---------------------------' '--------------------------'
	#

	load("@io_bazel_rules_go//go:def.bzl", "GoLibrary", "GoPath", "go_context")

	def _preprocessing_transition_impl(settings, attr):
	return {"//metropolis/build/kube-code-generator:preprocessing": "yes"}

	# preprocessing_transition is attached to the incoming go_path in
	# go_kubernetes_resource_bundle, unsets the
	# //metropolis/build/kube-code-generator:embed_deepcopy config setting.
	# This allows go_libraries that make up the handwritten API libraries to only
	# embed the generated deepcopy when they are pulled in for build reasons, not
	# when the graph is being traversed in order to generate the deepcopy itself.
	# This breaks up the cycle that would happen otherwise.
	preprocessing_transition = transition(
	implementation = _preprocessing_transition_impl,
	inputs = [],
	outputs = ["//metropolis/build/kube-code-generator:preprocessing"],
	)

	# KubeResourceBundle is emitted by go_kubernetes_resource_bundle and contains
	# informations about libraries generated by the kubernetes code-generators.
	KubeResourceBundle = provider(
	"Information about the generated Go sources of a k8s.io/code-generator-built library.",
	fields = {
	"libraries": "Map from Go importpath to list of Files that make up this importpath.",
	},
	)

	def _go_kubernetes_library_impl(ctx):
	go = go_context(ctx)
	bundle = ctx.attr.bundle[KubeResourceBundle]
	libraries = bundle.libraries

	found_importpaths = [l.importpath for l in libraries]

	libraries = [l for l in libraries if l.importpath == ctx.attr.importpath]
	if len(libraries) < 1:
	fail("importpath {} not found in bundle (have {})".format(ctx.attr.importpath, ", ".join(found_importpaths)))
	if len(libraries) > 1:
	fail("internal error: multiple libraries with importpath {} found in bundle".format(ctx.attr.importpath))
	library = libraries[0]

	source = go.library_to_source(go, ctx.attr, library, ctx.coverage_instrumented())
	return [library, source, OutputGroupInfo(go_generated_srcs = depset(library.srcs))]

	# go_kubernetes_library picks a single Go library from a kube_resource_bundle
	# and prepares it for being embedded into a go_library.
	go_kubernetes_library = rule(
	implementation = _go_kubernetes_library_impl,
	attrs = {
	"bundle": attr.label(
	mandatory = True,
	providers = [KubeResourceBundle],
	doc = "A go_kubernetes_resource_bundle that contains the result of a kubernetes code-generation run.",
	),
	"importpath": attr.string(
	mandatory = True,
	doc = "The importpath of the library picked from the bundle, same as the importpath of the go_library that embeds it.",
	),
	"deps": attr.label_list(
	providers = [GoLibrary],
	doc = "All build dependencies of this library.",
	),
	"_go_context_data": attr.label(
	default = "@io_bazel_rules_go//:go_context_data",
	),
	},
	toolchains = ["@io_bazel_rules_go//go:toolchain"],
	)

	# _gotool_run is a helper function which runs an executable under
	# //metropolis/build/gotoolwrap, effectively setting up everything required to
	# use standard Go tooling on the monogon workspace (ie. GOPATH/GOROOT). This is
	# required by generators to run 'go fmt'.
	def _gotool_run(ctx, executable, arguments, **kwargs):
	go = go_context(ctx)
	gopath = ctx.attr.gopath[0][GoPath]

	inputs = [
	gopath.gopath_file,
	] + kwargs.get("inputs", [])

	tools = [
	executable,
	go.sdk.go,
	] + go.sdk.tools + kwargs.get("tools", [])

	env = {
	"GOTOOLWRAP_GOPATH": gopath.gopath_file.path,
	"GOTOOLWRAP_GOROOT": go.sdk.root_file.dirname,
	}
	env.update(kwargs.get("env", {}))

	kwargs_ = dict([(k, v) for (k, v) in kwargs.items() if k not in [
	"executable",
	"arguments",
	"inputs",
	"env",
	"tools",
	]])

	ctx.actions.run(
	executable = ctx.executable._gotoolwrap,
	arguments = [executable.path] + arguments,
	env = env,
	inputs = inputs,
	tools = tools,
	**kwargs_
	)

	# _output_directory returns the relative path into which
	# ctx.action.declare_file writes are rooted. This is used as code-generators
	# require a root path for all outputted files, instead of a list of files to
	# emit.
	def _output_directory(ctx):
	# We combine bin_dir, the BUILDfile path and the target name. This seems
	# wrong. Is there no simpler way to do this?
	buildfile_path = ctx.build_file_path
	parts = buildfile_path.split("/")
	if not parts[-1].startswith("BUILD"):
	fail("internal error: unexpected BUILD file path: {}", parts[-1])
	package_path = "/".join(parts[:-1])
	return "/".join([ctx.bin_dir.path, package_path, ctx.attr.name])

	# _cg returns a 'codegen context', a struct that's used to accumulate the
	# results of code generation. It assumes all output will be rooted in a
	# generated importpath (with more 'shortened' importpaths underneath the root),
	# and collects outputs to pass to the codegen execution action. It also
	# collects a map of importpaths to outputs that make it up.
	def _cg(ctx, importpath):
	output_root = _output_directory(ctx)

	return struct(
	# The 'root' importpath, under which 'shortened' importpaths reside.
	importpath = importpath,
	# The prefix into which all files will be emitted. We use the target
	# name for convenience.
	output_prefix = ctx.attr.name,
	# The full relative path visible to the codegen, pointing to the same
	# directory as output_prefix (just from the point of view of the
	# runtime filesystem, not the ctx.actions filepath declaration API).
	output_root = output_root,
	# The list of outputs that have to be generated by the codegen.
	outputs = [],
	# A map of importpath to list of outputs (from the above list) that
	# make up a generated Go package/library.
	libraries = {},
	ctx = ctx,
	)

	# _declare_library adds a single Go package/library at importpath to the
	# codegen context with the given file paths (rooted in the importpath).
	def _declare_library(cg, importpath, files):
	importpath = cg.importpath + "/" + importpath
	cg.libraries[importpath] = []
	for f in files:
	output = cg.ctx.actions.declare_file("{}/{}/{}".format(
	cg.output_prefix,
	importpath,
	f,
	))
	cg.outputs.append(output)
	cg.libraries[importpath].append(output)

	# _declare_libraries declares multiple Go package/libraries to the codegen
	# context. The key of the dictionary is the importpath of the library, and the
	# value are the file names of generated outputs.
	def _declare_libraries(cg, libraries):
	for k, v in libraries.items():
	_declare_library(cg, k, v)

	# _codegen_clientset runs the clientset codegenerator.
	def _codegen_clientset(ctx):
	cg = _cg(ctx, ctx.attr.importpath)

	_declare_libraries(cg, {
	"clientset/versioned": ["clientset.go", "doc.go"],
	"clientset/versioned/fake": ["register.go", "clientset_generated.go"],
	"clientset/versioned/scheme": ["register.go", "doc.go"],
	})

	for api, types in ctx.attr.apis.items():
	client_name = api.split("/")[-2]
	_declare_libraries(cg, {
	"clientset/versioned/typed/{}".format(api): [
	"doc.go",
	"generated_expansion.go",
	"{}_client.go".format(client_name),
	] + [
	"{}.go".format(t)
	for t in types
	],
	"clientset/versioned/typed/{}/fake".format(api): [
	"doc.go",
	"fake_{}_client.go".format(client_name),
	],
	})

	_gotool_run(
	ctx,
	mnemonic = "ClientsetGen",
	executable = ctx.executable._client_gen,
	arguments = [
	"--clientset-name",
	"versioned",
	"--input-base",
	ctx.attr.apipath,
	"--input",
	",".join(ctx.attr.apis),
	"--output-package",
	cg.importpath + "/clientset",
	"--output-base",
	cg.output_root,
	"--go-header-file",
	ctx.file.boilerplate.path,
	],
	inputs = [
	ctx.file.boilerplate,
	],
	outputs = cg.outputs,
	)

	return cg.libraries

	# _codegen_deepcopy runs the deepcopy codegenerator (outputting to the apipath,
	# not the importpath).
	def _codegen_deepcopy(ctx):
	cg = _cg(ctx, ctx.attr.apipath)

	for api, types in ctx.attr.apis.items():
	_declare_libraries(cg, {
	api: ["zz_generated.deepcopy.go"],
	})

	_gotool_run(
	ctx,
	mnemonic = "DeepcopyGen",
	executable = ctx.executable._deepcopy_gen,
	arguments = [
	"--input-dirs",
	",".join(["{}/{}".format(ctx.attr.apipath, api) for api in ctx.attr.apis]),
	"--go-header-file",
	ctx.file.boilerplate.path,
	"--stderrthreshold",
	"0",
	"-O",
	"zz_generated.deepcopy",
	"--output-base",
	cg.output_root,
	ctx.attr.apipath,
	],
	inputs = [
	ctx.file.boilerplate,
	],
	outputs = cg.outputs,
	)
	return cg.libraries

	# _codegen_informer runs the informer codegenerator.
	def _codegen_informer(ctx):
	cg = _cg(ctx, ctx.attr.importpath)

	_declare_libraries(cg, {
	"informers/externalversions": ["factory.go", "generic.go"],
	"informers/externalversions/internalinterfaces": ["factory_interfaces.go"],
	})

	for api, types in ctx.attr.apis.items():
	client_name = api.split("/")[-2]
	_declare_libraries(cg, {
	"informers/externalversions/{}".format(client_name): ["interface.go"],
	"informers/externalversions/{}".format(api): [
	"interface.go",
	] + [
	"{}.go".format(t)
	for t in types
	],
	})

	_gotool_run(
	ctx,
	mnemonic = "InformerGen",
	executable = ctx.executable._informer_gen,
	arguments = [
	"--input-dirs",
	",".join(["{}/{}".format(ctx.attr.apipath, api) for api in ctx.attr.apis]),
	"--versioned-clientset-package",
	"{}/clientset/versioned".format(ctx.attr.importpath),
	"--listers-package",
	"{}/listers".format(ctx.attr.importpath),
	"--output-package",
	"{}/informers".format(ctx.attr.importpath),
	"--output-base",
	cg.output_root,
	"--go-header-file",
	ctx.file.boilerplate.path,
	],
	inputs = [
	ctx.file.boilerplate,
	],
	outputs = cg.outputs,
	)

	return cg.libraries

	# _codegen_lister runs the lister codegenerator.
	def _codegen_lister(ctx):
	cg = _cg(ctx, ctx.attr.importpath)

	for api, types in ctx.attr.apis.items():
	client_name = api.split("/")[-2]
	_declare_libraries(cg, {
	"listers/{}".format(api): [
	"expansion_generated.go",
	] + [
	"{}.go".format(t)
	for t in types
	],
	})

	_gotool_run(
	ctx,
	mnemonic = "ListerGen",
	executable = ctx.executable._lister_gen,
	arguments = [
	"--input-dirs",
	",".join(["{}/{}".format(ctx.attr.apipath, api) for api in ctx.attr.apis]),
	"--output-package",
	"{}/listers".format(ctx.attr.importpath),
	"--output-base",
	cg.output_root,
	"--go-header-file",
	ctx.file.boilerplate.path,
	"-v",
	"10",
	],
	inputs = [
	ctx.file.boilerplate,
	],
	outputs = cg.outputs,
	)

	return cg.libraries

	# _update_dict_check is a helper function that updates dict a with dict b,
	# ensuring there's no overwritten keys.
	def _update_dict_check(a, b):
	for k in b.keys():
	if k in a:
	fail("internal error: repeat importpath {}", k)
	a.update(b)

	def _go_kubernetes_resource_bundle_impl(ctx):
	go = go_context(ctx)

	all_gens = {}
	_update_dict_check(all_gens, _codegen_clientset(ctx))
	_update_dict_check(all_gens, _codegen_deepcopy(ctx))
	_update_dict_check(all_gens, _codegen_informer(ctx))
	_update_dict_check(all_gens, _codegen_lister(ctx))

	libraries = []
	for importpath, srcs in all_gens.items():
	library = go.new_library(
	go,
	srcs = srcs,
	importpath = importpath,
	)
	libraries.append(library)

	return [KubeResourceBundle(libraries = libraries)]

	# go_kubernetes_resource_bundle runs kubernetes code-generators on a codepath
	# for some requested APIs, and whose output can be made into Go library targets
	# via go_kubernetes_library. This bundle corresponds to a single Kubernetes API
	# resource group.
	go_kubernetes_resource_bundle = rule(
	implementation = _go_kubernetes_resource_bundle_impl,
	attrs = {
	"gopath": attr.label(
	mandatory = True,
	providers = [GoPath],
	cfg = preprocessing_transition,
	doc = "A rules_go go_path that contains all the API libraries for which codegen should be run.",
	),
	"importpath": attr.string(
	mandatory = True,
	doc = """
	The root importpath of the generated code (apart from deepcopy
	codegen). The Bazel target path corresponding to this
	importpath needs to contain the go_kubernetes_library and
	go_library targets that allow to actually build against the
	generated code.
	""",
	),
	"apipath": attr.string(
	mandatory = True,
	doc = "The root importpath of the APIs for which to generate code.",
	),
	"apis": attr.string_list_dict(
	mandatory = True,
	doc = """
	The APIs underneath importpath for which to generated code,
	eg. foo/v1, mapping into a list of lowercased types generated
	from each (eg. widget for `type Widget struct`).
	""",
	),
	"boilerplate": attr.label(
	default = "//metropolis/build/kube-code-generator:boilerplate.go.txt",
	allow_single_file = True,
	doc = "Header that will be used in the generated code.",
	),
	"_go_context_data": attr.label(
	default = "@io_bazel_rules_go//:go_context_data",
	),
	"_gotoolwrap": attr.label(
	default = Label("//metropolis/build/gotoolwrap"),
	allow_single_file = True,
	executable = True,
	cfg = "exec",
	),
	"_deepcopy_gen": attr.label(
	default = Label("@io_k8s_code_generator//cmd/deepcopy-gen"),
	allow_single_file = True,
	executable = True,
	cfg = "exec",
	),
	"_client_gen": attr.label(
	default = Label("@io_k8s_code_generator//cmd/client-gen"),
	allow_single_file = True,
	executable = True,
	cfg = "exec",
	),
	"_informer_gen": attr.label(
	default = Label("@io_k8s_code_generator//cmd/informer-gen"),
	allow_single_file = True,
	executable = True,
	cfg = "exec",
	),
	"_lister_gen": attr.label(
	default = Label("@io_k8s_code_generator//cmd/lister-gen"),
	allow_single_file = True,
	executable = True,
	cfg = "exec",
	),
	"_allowlist_function_transition": attr.label(
	default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
	),
	},
	toolchains = ["@io_bazel_rules_go//go:toolchain"],
	)