# 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 if target.label.workspace_name == "" or target.label.workspace_name == "com_google_protobuf" ]) 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"], )