pkg/cc_dist_library.bzl - third_party/protobuf - Git at Google

 # Rules for distributable C++ libraries

 load("@rules_cc//cc:action_names.bzl", cc_action_names = "ACTION_NAMES")
 load("@rules_cc//cc:find_cc_toolchain.bzl", "find_cc_toolchain")

 ################################################################################
 # Archive/linking support
 ################################################################################

 def _collect_linker_input_objects(dep_label, cc_info, objs, pic_objs):
     """Accumulate .o and .pic.o files into `objs` and `pic_objs`."""
     link_ctx = cc_info.linking_context
     if link_ctx == None:
         return

     linker_inputs = link_ctx.linker_inputs.to_list()
     for link_input in linker_inputs:
         if link_input.owner != dep_label:
             # This is a transitive dep: skip it.
             continue

         for lib in link_input.libraries:
             objs.extend(lib.objects or [])
             pic_objs.extend(lib.pic_objects or [])

 # Creates an action to build the `output_file` static library (archive)
 # using `object_files`.
 def _create_archive_action(
         ctx,
         feature_configuration,
         cc_toolchain_info,
         output_file,
         object_files):
     # Based on Bazel's src/main/starlark/builtins_bzl/common/cc/cc_import.bzl:

     # Build the command line and add args for all of the input files:
     archiver_variables = cc_common.create_link_variables(
         feature_configuration = feature_configuration,
         cc_toolchain = cc_toolchain_info,
         output_file = output_file.path,
         is_using_linker = False,
     )
     command_line = cc_common.get_memory_inefficient_command_line(
         feature_configuration = feature_configuration,
         action_name = cc_action_names.cpp_link_static_library,
         variables = archiver_variables,
     )
     args = ctx.actions.args()
     args.add_all(command_line)
     args.add_all(object_files)
     args.use_param_file("@%s", use_always = True)

     archiver_path = cc_common.get_tool_for_action(
         feature_configuration = feature_configuration,
         action_name = cc_action_names.cpp_link_static_library,
     )

     env = cc_common.get_environment_variables(
         feature_configuration = feature_configuration,
         action_name = cc_action_names.cpp_link_static_library,
         variables = archiver_variables,
     )

     ctx.actions.run(
         executable = archiver_path,
         arguments = [args],
         env = env,
         inputs = depset(
             direct = object_files,
             transitive = [
                 cc_toolchain_info.all_files,
             ],
         ),
         use_default_shell_env = False,
         outputs = [output_file],
         mnemonic = "CppArchiveDist",
     )

 def _create_dso_link_action(
         ctx,
         feature_configuration,
         cc_toolchain_info,
         object_files,
         pic_object_files):
     compilation_outputs = cc_common.create_compilation_outputs(
         objects = depset(object_files),
         pic_objects = depset(pic_object_files),
     )
     link_output = cc_common.link(
         actions = ctx.actions,
         feature_configuration = feature_configuration,
         cc_toolchain = cc_toolchain_info,
         compilation_outputs = compilation_outputs,
         name = ctx.label.name,
         output_type = "dynamic_library",
         user_link_flags = ctx.attr.linkopts,
     )
     library_to_link = link_output.library_to_link

     outputs = []

     # Note: library_to_link.dynamic_library and interface_library are often
     # symlinks in the solib directory. For DefaultInfo, prefer reporting
     # the resolved artifact paths.
     if library_to_link.resolved_symlink_dynamic_library != None:
         outputs.append(library_to_link.resolved_symlink_dynamic_library)
     elif library_to_link.dynamic_library != None:
         outputs.append(library_to_link.dynamic_library)

     if library_to_link.resolved_symlink_interface_library != None:
         outputs.append(library_to_link.resolved_symlink_interface_library)
     elif library_to_link.interface_library != None:
         outputs.append(library_to_link.interface_library)

     return outputs

 ################################################################################
 # Source file/header support
 ################################################################################

 CcFileList = provider(
     doc = "List of files to be built into a library.",
     fields = {
         # As a rule of thumb, `hdrs` and `textual_hdrs` are the files that
         # would be installed along with a prebuilt library.
         "hdrs": "public header files, including those used by generated code",
         "textual_hdrs": "files which are included but are not self-contained",

         # The `internal_hdrs` are header files which appear in `srcs`.
         # These are only used when compiling the library.
         "internal_hdrs": "internal header files (only used to build .cc files)",
         "srcs": "source files",
     },
 )

 def _flatten_target_files(targets):
     return depset(transitive = [
         target.files
         for target in targets
         # Filter out targets from external workspaces. We also filter out
         # utf8_range since that has a separate CMake build for now.
         if (target.label.workspace_name == "" or
             target.label.workspace_name == "com_google_protobuf") and
            not target.label.package.startswith("third_party/utf8_range")
     ])

 def _get_transitive_sources(targets, attr, deps):
     return depset(targets, transitive = [getattr(dep[CcFileList], attr) for dep in deps if CcFileList in dep])

 def _cc_file_list_aspect_impl(target, ctx):
     # Extract sources from a `cc_library` (or similar):
     if CcInfo not in target:
         return []

     # We're going to reach directly into the attrs on the traversed rule.
     rule_attr = ctx.rule.attr

     # CcInfo is a proxy for what we expect this rule to look like.
     # However, some deps may expose `CcInfo` without having `srcs`,
     # `hdrs`, etc., so we use `getattr` to handle that gracefully.

     internal_hdrs = []
     srcs = []

     # Filter `srcs` so it only contains source files. Headers will go
     # into `internal_headers`.
     for src in _flatten_target_files(getattr(rule_attr, "srcs", [])).to_list():
         if src.extension.lower() in ["c", "cc", "cpp", "cxx"]:
             srcs.append(src)
         else:
             internal_hdrs.append(src)

     return [CcFileList(
         hdrs = _get_transitive_sources(
             _flatten_target_files(getattr(rule_attr, "hdrs", [])).to_list(),
             "hdrs",
             rule_attr.deps,
         ),
         textual_hdrs = _get_transitive_sources(
             _flatten_target_files(getattr(rule_attr, "textual_hdrs", [])).to_list(),
             "textual_hdrs",
             rule_attr.deps,
         ),
         internal_hdrs = _get_transitive_sources(
             internal_hdrs,
             "internal_hdrs",
             rule_attr.deps,
         ),
         srcs = _get_transitive_sources(srcs, "srcs", rule_attr.deps),
     )]

 cc_file_list_aspect = aspect(
     doc = """
 Aspect to provide the list of sources and headers from a rule.

 Output is CcFileList. Example:

   cc_library(
       name = "foo",
       srcs = [
           "foo.cc",
           "foo_internal.h",
       ],
       hdrs = ["foo.h"],
       textual_hdrs = ["foo_inl.inc"],
   )
   # produces:
   # CcFileList(
   #     hdrs = depset([File("foo.h")]),
   #     textual_hdrs = depset([File("foo_inl.inc")]),
   #     internal_hdrs = depset([File("foo_internal.h")]),
   #     srcs = depset([File("foo.cc")]),
   # )
 """,
     required_providers = [CcInfo],
     implementation = _cc_file_list_aspect_impl,
     attr_aspects = ["deps"],
 )

 ################################################################################
 # Rule impl
 ################################################################################

 def _collect_inputs(deps):
     """Collects files from a list of deps.

     This rule collects source files and linker inputs transitively for C++
     deps.

     The return value is a struct with object files (linker inputs),
     partitioned by PIC and non-pic, and the rules' source and header files:

         struct(
             objects = ...,       # non-PIC object files
             pic_objects = ...,   # PIC objects
             cc_file_list = ...,  # a CcFileList
         )

     Args:
       deps: Iterable of immediate deps, which will be treated as roots to
             recurse transitively.
     Returns:
       A struct with linker inputs, source files, and header files.
     """

     objs = []
     pic_objs = []

     # The returned CcFileList will contain depsets of the deps' file lists.
     # These lists hold `depset()`s from each of `deps`.
     srcs = []
     hdrs = []
     internal_hdrs = []
     textual_hdrs = []

     for dep in deps:
         if CcInfo in dep:
             _collect_linker_input_objects(
                 dep.label,
                 dep[CcInfo],
                 objs,
                 pic_objs,
             )

         if CcFileList in dep:
             cfl = dep[CcFileList]
             srcs.append(cfl.srcs)
             hdrs.append(cfl.hdrs)
             internal_hdrs.append(cfl.internal_hdrs)
             textual_hdrs.append(cfl.textual_hdrs)

     return struct(
         objects = objs,
         pic_objects = pic_objs,
         cc_file_list = CcFileList(
             srcs = depset(transitive = srcs),
             hdrs = depset(transitive = hdrs),
             internal_hdrs = depset(transitive = internal_hdrs),
             textual_hdrs = depset(transitive = textual_hdrs),
         ),
     )

 # Given structs a and b returned from _collect_inputs(), returns a copy of a
 # but with all files from b subtracted out.
 def _subtract_files(a, b):
     result_args = {}

     top_level_fields = ["objects", "pic_objects"]
     for field in top_level_fields:
         to_remove = {e: None for e in getattr(b, field)}
         result_args[field] = [e for e in getattr(a, field) if not e in to_remove]

     cc_file_list_args = {}
     file_list_fields = ["srcs", "hdrs", "internal_hdrs", "textual_hdrs"]
     for field in file_list_fields:
         to_remove = {e: None for e in getattr(b.cc_file_list, field).to_list()}
         cc_file_list_args[field] = depset(
             [e for e in getattr(a.cc_file_list, field).to_list() if not e in to_remove],
         )
     result_args["cc_file_list"] = CcFileList(**cc_file_list_args)

     return struct(**result_args)

 # Implementation for cc_dist_library rule.
 def _cc_dist_library_impl(ctx):
     cc_toolchain_info = find_cc_toolchain(ctx)

     feature_configuration = cc_common.configure_features(
         ctx = ctx,
         cc_toolchain = cc_toolchain_info,
     )

     inputs = _subtract_files(_collect_inputs(ctx.attr.deps), _collect_inputs(ctx.attr.dist_deps))

     # For static libraries, build separately with and without pic.

     stemname = "lib" + ctx.label.name
     outputs = []

     if len(inputs.objects) > 0:
         archive_out = ctx.actions.declare_file(stemname + ".a")
         _create_archive_action(
             ctx,
             feature_configuration,
             cc_toolchain_info,
             archive_out,
             inputs.objects,
         )
         outputs.append(archive_out)

     if len(inputs.pic_objects) > 0:
         pic_archive_out = ctx.actions.declare_file(stemname + ".pic.a")
         _create_archive_action(
             ctx,
             feature_configuration,
             cc_toolchain_info,
             pic_archive_out,
             inputs.pic_objects,
         )
         outputs.append(pic_archive_out)

     # For dynamic libraries, use the `cc_common.link` command to ensure
     # everything gets built correctly according to toolchain definitions.
     outputs.extend(_create_dso_link_action(
         ctx,
         feature_configuration,
         cc_toolchain_info,
         inputs.objects,
         inputs.pic_objects,
     ))

     # We could expose the libraries for use from cc rules:
     #
     # linking_context = cc_common.create_linking_context(
     #     linker_inputs = depset([
     #         cc_common.create_linker_input(
     #             owner = ctx.label,
     #             libraries = depset([library_to_link]),
     #         ),
     #     ]),
     # )
     # cc_info = CcInfo(linking_context = linking_context)  # and return this
     #
     # However, if the goal is to force a protobuf dependency to use the
     # DSO, then `cc_import` is a better-supported way to do so.
     #
     # If we wanted to expose CcInfo from this rule (and make it usable as a
     # C++ dependency), then we would probably want to include the static
     # archive and headers as well. exposing headers would probably require
     # an additional aspect to extract CcInfos with just the deps' headers.

     return [
         DefaultInfo(files = depset(outputs)),
         inputs.cc_file_list,
     ]

 cc_dist_library = rule(
     implementation = _cc_dist_library_impl,
     doc = """
 Create libraries suitable for distribution.

 This rule creates static and dynamic libraries from the libraries listed in
 'deps'. The resulting libraries are suitable for distributing all of 'deps'
 in a single logical library, for example, in an installable binary package.
 The result includes all transitive dependencies, excluding those reachable
 from 'dist_deps' or defined in a separate repository (e.g. Abseil).

 The outputs of this rule are a dynamic library and a static library. (If
 the build produces both PIC and non-PIC object files, then there is also a
 second static library.) The example below illustrates additional details.

 This rule is different from Bazel's experimental `shared_cc_library` in two
 ways. First, this rule produces a static archive library in addition to the
 dynamic shared library. Second, this rule is not directly usable as a C++
 dependency (although the outputs could be used, e.g., by `cc_import`).

 Example:

     cc_library(name = "a", srcs = ["a.cc"], hdrs = ["a.h"])
     cc_library(name = "b", srcs = ["b.cc"], hdrs = ["b.h"], deps = [":a"])
     cc_library(name = "c", srcs = ["c.cc"], hdrs = ["c.h"], deps = [":b"])

     # Creates libdist.so and (typically) libdist.pic.a:
     # (This may also produce libdist.a if the build produces non-PIC objects.)
     cc_dist_library(
         name = "dist",
         linkopts = ["-la"],   # libdist.so dynamically links against liba.so.
         deps = [":b", ":c"],  # Output contains a.o, b.o, and c.o.
     )
 """,
     attrs = {
         "deps": attr.label_list(
             doc = ("The list of libraries to be included in the outputs, " +
                    "along with their transitive dependencies."),
             aspects = [cc_file_list_aspect],
         ),
         "dist_deps": attr.label_list(
             doc = ("The list of cc_dist_library dependencies that " +
                    "should be excluded."),
             aspects = [cc_file_list_aspect],
         ),
         "linkopts": attr.string_list(
             doc = ("Add these flags to the C++ linker command when creating " +
                    "the dynamic library."),
         ),
         # C++ toolchain before https://github.com/bazelbuild/bazel/issues/7260:
         "_cc_toolchain": attr.label(
             default = Label("@rules_cc//cc:current_cc_toolchain"),
         ),
     },
     toolchains = [
         # C++ toolchain after https://github.com/bazelbuild/bazel/issues/7260:
         "@bazel_tools//tools/cpp:toolchain_type",
     ],
     fragments = ["cpp"],
 )
	# Rules for distributable C++ libraries

	load("@rules_cc//cc:action_names.bzl", cc_action_names = "ACTION_NAMES")
	load("@rules_cc//cc:find_cc_toolchain.bzl", "find_cc_toolchain")

	################################################################################
	# Archive/linking support
	################################################################################

	def _collect_linker_input_objects(dep_label, cc_info, objs, pic_objs):
	"""Accumulate .o and .pic.o files into `objs` and `pic_objs`."""
	link_ctx = cc_info.linking_context
	if link_ctx == None:
	return

	linker_inputs = link_ctx.linker_inputs.to_list()
	for link_input in linker_inputs:
	if link_input.owner != dep_label:
	# This is a transitive dep: skip it.
	continue

	for lib in link_input.libraries:
	objs.extend(lib.objects or [])
	pic_objs.extend(lib.pic_objects or [])

	# Creates an action to build the `output_file` static library (archive)
	# using `object_files`.
	def _create_archive_action(
	ctx,
	feature_configuration,
	cc_toolchain_info,
	output_file,
	object_files):
	# Based on Bazel's src/main/starlark/builtins_bzl/common/cc/cc_import.bzl:

	# Build the command line and add args for all of the input files:
	archiver_variables = cc_common.create_link_variables(
	feature_configuration = feature_configuration,
	cc_toolchain = cc_toolchain_info,
	output_file = output_file.path,
	is_using_linker = False,
	)
	command_line = cc_common.get_memory_inefficient_command_line(
	feature_configuration = feature_configuration,
	action_name = cc_action_names.cpp_link_static_library,
	variables = archiver_variables,
	)
	args = ctx.actions.args()
	args.add_all(command_line)
	args.add_all(object_files)
	args.use_param_file("@%s", use_always = True)

	archiver_path = cc_common.get_tool_for_action(
	feature_configuration = feature_configuration,
	action_name = cc_action_names.cpp_link_static_library,
	)

	env = cc_common.get_environment_variables(
	feature_configuration = feature_configuration,
	action_name = cc_action_names.cpp_link_static_library,
	variables = archiver_variables,
	)

	ctx.actions.run(
	executable = archiver_path,
	arguments = [args],
	env = env,
	inputs = depset(
	direct = object_files,
	transitive = [
	cc_toolchain_info.all_files,
	],
	),
	use_default_shell_env = False,
	outputs = [output_file],
	mnemonic = "CppArchiveDist",
	)

	def _create_dso_link_action(
	ctx,
	feature_configuration,
	cc_toolchain_info,
	object_files,
	pic_object_files):
	compilation_outputs = cc_common.create_compilation_outputs(
	objects = depset(object_files),
	pic_objects = depset(pic_object_files),
	)
	link_output = cc_common.link(
	actions = ctx.actions,
	feature_configuration = feature_configuration,
	cc_toolchain = cc_toolchain_info,
	compilation_outputs = compilation_outputs,
	name = ctx.label.name,
	output_type = "dynamic_library",
	user_link_flags = ctx.attr.linkopts,
	)
	library_to_link = link_output.library_to_link

	outputs = []

	# Note: library_to_link.dynamic_library and interface_library are often
	# symlinks in the solib directory. For DefaultInfo, prefer reporting
	# the resolved artifact paths.
	if library_to_link.resolved_symlink_dynamic_library != None:
	outputs.append(library_to_link.resolved_symlink_dynamic_library)
	elif library_to_link.dynamic_library != None:
	outputs.append(library_to_link.dynamic_library)

	if library_to_link.resolved_symlink_interface_library != None:
	outputs.append(library_to_link.resolved_symlink_interface_library)
	elif library_to_link.interface_library != None:
	outputs.append(library_to_link.interface_library)

	return outputs

	################################################################################
	# Source file/header support
	################################################################################

	CcFileList = provider(
	doc = "List of files to be built into a library.",
	fields = {
	# As a rule of thumb, `hdrs` and `textual_hdrs` are the files that
	# would be installed along with a prebuilt library.
	"hdrs": "public header files, including those used by generated code",
	"textual_hdrs": "files which are included but are not self-contained",

	# The `internal_hdrs` are header files which appear in `srcs`.
	# These are only used when compiling the library.
	"internal_hdrs": "internal header files (only used to build .cc files)",
	"srcs": "source files",
	},
	)

	def _flatten_target_files(targets):
	return depset(transitive = [
	target.files
	for target in targets
	# Filter out targets from external workspaces. We also filter out
	# utf8_range since that has a separate CMake build for now.
	if (target.label.workspace_name == "" or
	target.label.workspace_name == "com_google_protobuf") and
	not target.label.package.startswith("third_party/utf8_range")
	])

	def _get_transitive_sources(targets, attr, deps):
	return depset(targets, transitive = [getattr(dep[CcFileList], attr) for dep in deps if CcFileList in dep])

	def _cc_file_list_aspect_impl(target, ctx):
	# Extract sources from a `cc_library` (or similar):
	if CcInfo not in target:
	return []

	# We're going to reach directly into the attrs on the traversed rule.
	rule_attr = ctx.rule.attr

	# CcInfo is a proxy for what we expect this rule to look like.
	# However, some deps may expose `CcInfo` without having `srcs`,
	# `hdrs`, etc., so we use `getattr` to handle that gracefully.

	internal_hdrs = []
	srcs = []

	# Filter `srcs` so it only contains source files. Headers will go
	# into `internal_headers`.
	for src in _flatten_target_files(getattr(rule_attr, "srcs", [])).to_list():
	if src.extension.lower() in ["c", "cc", "cpp", "cxx"]:
	srcs.append(src)
	else:
	internal_hdrs.append(src)

	return [CcFileList(
	hdrs = _get_transitive_sources(
	_flatten_target_files(getattr(rule_attr, "hdrs", [])).to_list(),
	"hdrs",
	rule_attr.deps,
	),
	textual_hdrs = _get_transitive_sources(
	_flatten_target_files(getattr(rule_attr, "textual_hdrs", [])).to_list(),
	"textual_hdrs",
	rule_attr.deps,
	),
	internal_hdrs = _get_transitive_sources(
	internal_hdrs,
	"internal_hdrs",
	rule_attr.deps,
	),
	srcs = _get_transitive_sources(srcs, "srcs", rule_attr.deps),
	)]

	cc_file_list_aspect = aspect(
	doc = """
	Aspect to provide the list of sources and headers from a rule.

	Output is CcFileList. Example:

	cc_library(
	name = "foo",
	srcs = [
	"foo.cc",
	"foo_internal.h",
	],
	hdrs = ["foo.h"],
	textual_hdrs = ["foo_inl.inc"],
	)
	# produces:
	# CcFileList(
	# hdrs = depset([File("foo.h")]),
	# textual_hdrs = depset([File("foo_inl.inc")]),
	# internal_hdrs = depset([File("foo_internal.h")]),
	# srcs = depset([File("foo.cc")]),
	# )
	""",
	required_providers = [CcInfo],
	implementation = _cc_file_list_aspect_impl,
	attr_aspects = ["deps"],
	)

	################################################################################
	# Rule impl
	################################################################################

	def _collect_inputs(deps):
	"""Collects files from a list of deps.

	This rule collects source files and linker inputs transitively for C++
	deps.

	The return value is a struct with object files (linker inputs),
	partitioned by PIC and non-pic, and the rules' source and header files:

	struct(
	objects = ..., # non-PIC object files
	pic_objects = ..., # PIC objects
	cc_file_list = ..., # a CcFileList
	)

	Args:
	deps: Iterable of immediate deps, which will be treated as roots to
	recurse transitively.
	Returns:
	A struct with linker inputs, source files, and header files.
	"""

	objs = []
	pic_objs = []

	# The returned CcFileList will contain depsets of the deps' file lists.
	# These lists hold `depset()`s from each of `deps`.
	srcs = []
	hdrs = []
	internal_hdrs = []
	textual_hdrs = []

	for dep in deps:
	if CcInfo in dep:
	_collect_linker_input_objects(
	dep.label,
	dep[CcInfo],
	objs,
	pic_objs,
	)

	if CcFileList in dep:
	cfl = dep[CcFileList]
	srcs.append(cfl.srcs)
	hdrs.append(cfl.hdrs)
	internal_hdrs.append(cfl.internal_hdrs)
	textual_hdrs.append(cfl.textual_hdrs)

	return struct(
	objects = objs,
	pic_objects = pic_objs,
	cc_file_list = CcFileList(
	srcs = depset(transitive = srcs),
	hdrs = depset(transitive = hdrs),
	internal_hdrs = depset(transitive = internal_hdrs),
	textual_hdrs = depset(transitive = textual_hdrs),
	),
	)

	# Given structs a and b returned from _collect_inputs(), returns a copy of a
	# but with all files from b subtracted out.
	def _subtract_files(a, b):
	result_args = {}

	top_level_fields = ["objects", "pic_objects"]
	for field in top_level_fields:
	to_remove = {e: None for e in getattr(b, field)}
	result_args[field] = [e for e in getattr(a, field) if not e in to_remove]

	cc_file_list_args = {}
	file_list_fields = ["srcs", "hdrs", "internal_hdrs", "textual_hdrs"]
	for field in file_list_fields:
	to_remove = {e: None for e in getattr(b.cc_file_list, field).to_list()}
	cc_file_list_args[field] = depset(
	[e for e in getattr(a.cc_file_list, field).to_list() if not e in to_remove],
	)
	result_args["cc_file_list"] = CcFileList(**cc_file_list_args)

	return struct(**result_args)

	# Implementation for cc_dist_library rule.
	def _cc_dist_library_impl(ctx):
	cc_toolchain_info = find_cc_toolchain(ctx)

	feature_configuration = cc_common.configure_features(
	ctx = ctx,
	cc_toolchain = cc_toolchain_info,
	)

	inputs = _subtract_files(_collect_inputs(ctx.attr.deps), _collect_inputs(ctx.attr.dist_deps))

	# For static libraries, build separately with and without pic.

	stemname = "lib" + ctx.label.name
	outputs = []

	if len(inputs.objects) > 0:
	archive_out = ctx.actions.declare_file(stemname + ".a")
	_create_archive_action(
	ctx,
	feature_configuration,
	cc_toolchain_info,
	archive_out,
	inputs.objects,
	)
	outputs.append(archive_out)

	if len(inputs.pic_objects) > 0:
	pic_archive_out = ctx.actions.declare_file(stemname + ".pic.a")
	_create_archive_action(
	ctx,
	feature_configuration,
	cc_toolchain_info,
	pic_archive_out,
	inputs.pic_objects,
	)
	outputs.append(pic_archive_out)

	# For dynamic libraries, use the `cc_common.link` command to ensure
	# everything gets built correctly according to toolchain definitions.
	outputs.extend(_create_dso_link_action(
	ctx,
	feature_configuration,
	cc_toolchain_info,
	inputs.objects,
	inputs.pic_objects,
	))

	# We could expose the libraries for use from cc rules:
	#
	# linking_context = cc_common.create_linking_context(
	# linker_inputs = depset([
	# cc_common.create_linker_input(
	# owner = ctx.label,
	# libraries = depset([library_to_link]),
	# ),
	# ]),
	# )
	# cc_info = CcInfo(linking_context = linking_context) # and return this
	#
	# However, if the goal is to force a protobuf dependency to use the
	# DSO, then `cc_import` is a better-supported way to do so.
	#
	# If we wanted to expose CcInfo from this rule (and make it usable as a
	# C++ dependency), then we would probably want to include the static
	# archive and headers as well. exposing headers would probably require
	# an additional aspect to extract CcInfos with just the deps' headers.

	return [
	DefaultInfo(files = depset(outputs)),
	inputs.cc_file_list,
	]

	cc_dist_library = rule(
	implementation = _cc_dist_library_impl,
	doc = """
	Create libraries suitable for distribution.

	This rule creates static and dynamic libraries from the libraries listed in
	'deps'. The resulting libraries are suitable for distributing all of 'deps'
	in a single logical library, for example, in an installable binary package.
	The result includes all transitive dependencies, excluding those reachable
	from 'dist_deps' or defined in a separate repository (e.g. Abseil).

	The outputs of this rule are a dynamic library and a static library. (If
	the build produces both PIC and non-PIC object files, then there is also a
	second static library.) The example below illustrates additional details.

	This rule is different from Bazel's experimental `shared_cc_library` in two
	ways. First, this rule produces a static archive library in addition to the
	dynamic shared library. Second, this rule is not directly usable as a C++
	dependency (although the outputs could be used, e.g., by `cc_import`).

	Example:

	cc_library(name = "a", srcs = ["a.cc"], hdrs = ["a.h"])
	cc_library(name = "b", srcs = ["b.cc"], hdrs = ["b.h"], deps = [":a"])
	cc_library(name = "c", srcs = ["c.cc"], hdrs = ["c.h"], deps = [":b"])

	# Creates libdist.so and (typically) libdist.pic.a:
	# (This may also produce libdist.a if the build produces non-PIC objects.)
	cc_dist_library(
	name = "dist",
	linkopts = ["-la"], # libdist.so dynamically links against liba.so.
	deps = [":b", ":c"], # Output contains a.o, b.o, and c.o.
	)
	""",
	attrs = {
	"deps": attr.label_list(
	doc = ("The list of libraries to be included in the outputs, " +
	"along with their transitive dependencies."),
	aspects = [cc_file_list_aspect],
	),
	"dist_deps": attr.label_list(
	doc = ("The list of cc_dist_library dependencies that " +
	"should be excluded."),
	aspects = [cc_file_list_aspect],
	),
	"linkopts": attr.string_list(
	doc = ("Add these flags to the C++ linker command when creating " +
	"the dynamic library."),
	),
	# C++ toolchain before https://github.com/bazelbuild/bazel/issues/7260:
	"_cc_toolchain": attr.label(
	default = Label("@rules_cc//cc:current_cc_toolchain"),
	),
	},
	toolchains = [
	# C++ toolchain after https://github.com/bazelbuild/bazel/issues/7260:
	"@bazel_tools//tools/cpp:toolchain_type",
	],
	fragments = ["cpp"],
	)