cc/private/rules_impl/cc_shared_library_impl.bzl

# Copyright 2021 The Bazel Authors. All rights reserved.
#
# 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.

"""Implementation of cc_shared_library"""

load("@bazel_skylib//lib:paths.bzl", "paths")
load("//cc:find_cc_toolchain.bzl", "find_cc_toolchain")
load("//cc/common:cc_common.bzl", "cc_common")
load("//cc/common:cc_helper.bzl", "cc_helper")
load("//cc/common:cc_info.bzl", "CcInfo")
load("//cc/common:cc_shared_library_info.bzl", "CcSharedLibraryInfo")
load("//cc/common:semantics.bzl", "semantics")
load("//cc/private:graph_node_info.bzl", "GraphNodeInfo")
load(":function_providing_rule.bzl", "wrap_starlark_function")

# TODO(#5200): Add export_define to library_to_link and cc_library

# Add this as a tag to any target that can be linked by more than one
# cc_shared_library because it doesn't have static initializers or anything
# else that may cause issues when being linked more than once. This should be
# used sparingly after making sure it's safe to use.
LINKABLE_MORE_THAN_ONCE = "LINKABLE_MORE_THAN_ONCE"

def _programmatic_error(message = ""):
    fail("Your build has triggered a programmatic error in the cc_shared_library rule. " +
         "Please file an issue in https://github.com/bazelbuild/bazel : {}".format(message))

def _sort_linker_inputs(topologically_sorted_labels, label_to_linker_inputs, linker_inputs_count):
    # len(label_to_linker_inputs) might not match the topologically_sorted_labels
    # size. The latter is looking at nodes in the graph but a node may not
    # necessarily contribute any linker_inputs. For example a cc_library with
    # no sources and only deps. Every linker_input.owner must be in
    # topologically_sorted_labels otherwise there is an error in the rule
    # implementation of the target providing that linker_input, e.g. it's
    # missing a CcSharedLibraryHintInfo if it had custom owner names for linker
    # inputs.
    sorted_linker_inputs = []
    for label in topologically_sorted_labels:
        if label not in label_to_linker_inputs:
            # This is ok. It can happen if no linker_inputs
            # were added by a node in the graph.
            continue
        sorted_linker_inputs.extend(label_to_linker_inputs[label])

    if len(sorted_linker_inputs) != linker_inputs_count:
        owners = []
        for sorted_linker_input in sorted_linker_inputs:
            owners.append(str(sorted_linker_input.owner))
        _programmatic_error("{} vs {}".format(",".join(owners), linker_inputs_count))

    return sorted_linker_inputs

# For each target, find out whether it should be linked statically or
# dynamically. The transitive_dynamic_dep_labels parameter is only needed for
# binaries because they link all dynamic_deps (cc_binary|cc_test).
def _separate_static_and_dynamic_link_libraries(
        dynamic_deps,
        deps_graph_nodes,
        can_be_linked_dynamically):
    (
        transitive_dynamic_dep_labels,
        all_dynamic_dep_linker_inputs,
    ) = _build_map_direct_dynamic_dep_to_transitive_dynamic_deps(dynamic_deps)

    node = None
    deps_graph_nodes_to_process = reversed(deps_graph_nodes)
    targets_to_be_linked_statically_map = {}
    targets_to_be_linked_dynamically_set = {}
    seen_labels = {}

    # The cc_shared_library graph is parallel to the cc_library graph.
    # Propagation of linker inputs between cc_libraries happens via the CcInfo
    # provider. Parallel to this we have cc_shared_libraries which may decide
    # different partitions of the cc_library graph.
    #
    # In a previous implementation of cc_shared_library we relied on the
    # topological sort given by flattening
    # cc_info.linking_context.linker_inputs.to_list(), however this was wrong
    # because the dependencies of a shared library (i.e. a pruned node here)
    # influenced the final order.
    #
    # In order to fix this, the pruning below was changed from breadth-first
    # traversal to depth-first traversal. While doing this we also recreate a
    # depset with topological order that takes into account the pruned nodes
    # and which will later be used to order the libraries in the linking
    # command line. This will be in topological order and will respect the
    # order of the deps as listed on the BUILD file as much as possible.
    #
    # Here we say "first_owner" because each node (see GraphNodeInfo) may have
    # more than one linker_input (each potentially with a different owner) but
    # using only the first owner as a key is enough.
    first_owner_to_depset = {}

    # Horrible I know. Perhaps Starlark team gives me a way to prune a tree.
    for _unused in range(2147483647):
        if not len(deps_graph_nodes_to_process):
            break

        node = deps_graph_nodes_to_process[-1]

        must_add_children = False

        # The *_seen variables are used to track a programmatic error and fail
        # if it happens.  Every value in node.owners presumably corresponds to
        # a linker_input in the same exact target. Therefore if we have seen
        # any of the owners already, then we must have also seen all the other
        # owners in the same node. Viceversa when we haven't seen them yet. If
        # both of these values are non-zero after the loop, the most likely
        # reason would be a bug in the implementation. It could potentially be
        # triggered by users if they use owner labels that do not keep most of
        # the ctx.label.package and ctx.label.name which then clash with other
        # target's owners (unlikely). For now though if the error is
        # triggered, it's reasonable to require manual revision by
        # the cc_shared_library implementation owners.
        has_owners_seen = False
        has_owners_not_seen = False
        linked_dynamically = False
        linked_statically = False
        for owner in node.owners:
            # TODO(bazel-team): Do not convert Labels to string to save on
            # garbage string allocations.
            owner_str = str(owner)

            if owner_str in seen_labels:
                has_owners_seen = True
                continue

            has_owners_not_seen = True
            seen_labels[owner_str] = True

            if owner_str in can_be_linked_dynamically:
                targets_to_be_linked_dynamically_set[owner_str] = True
                linked_dynamically = True
            else:
                targets_to_be_linked_statically_map[owner_str] = node.linkable_more_than_once
                must_add_children = True
                linked_statically = True

        if has_owners_seen and has_owners_not_seen:
            _programmatic_error()

        if linked_dynamically and linked_statically:
            error_owners_list = [str(owner) for owner in node.owners]

            # Our granularity is target level. Unless there is a different
            # unsupported custom implementation of this rule it should be
            # impossible for two linker_inputs from the same target to be
            # linked differently, one statically and the other dynamically.
            _programmatic_error(
                message = "Nodes with linker_inputs linked statically and dynamically:" +
                          "\n{}".format("\n".join(error_owners_list)),
            )

        if must_add_children:
            # The order in which we process the children matter. all_children
            # is being used as a stack, we will process first the nodes at the
            # top of the stack (last in the list). The children are the
            # dependencies of the current node, in order to respect the order
            # in which dependencies were listed in the deps attribute in the
            # BUILD file we must reverse the list so that the first one listed
            # in the BUILD file is processed first.
            deps_graph_nodes_to_process.extend(reversed(node.children))
        else:
            if node.owners[0] not in first_owner_to_depset:
                # We have 3 cases in this branch:
                #   1. Node has no children
                #   2. The children have been pruned because the node is linked dynamically
                #   3. Node has children that have been processed
                # For case 3 we add the children's depsets. For case 2 we add the dynamic
                # dep labels for transitive dynamic deps.
                transitive = []
                if str(node.owners[0]) in targets_to_be_linked_statically_map:
                    for child in node.children:
                        transitive.append(first_owner_to_depset[child.owners[0]])
                elif str(node.owners[0]) in transitive_dynamic_dep_labels:
                    transitive.append(transitive_dynamic_dep_labels[str(node.owners[0])])

                first_owner_to_depset[node.owners[0]] = depset(direct = node.owners, transitive = transitive, order = "topological")
            deps_graph_nodes_to_process.pop()

    topologically_sorted_labels = []
    if deps_graph_nodes:
        transitive = []
        for child in deps_graph_nodes:
            transitive.append(first_owner_to_depset[child.owners[0]])
        topologically_sorted_labels = depset(transitive = transitive, order = "topological").to_list()

    return (targets_to_be_linked_statically_map, targets_to_be_linked_dynamically_set, topologically_sorted_labels, all_dynamic_dep_linker_inputs)

def _create_linker_context(linker_inputs):
    return cc_common.create_linking_context(
        linker_inputs = depset(linker_inputs, order = "topological"),
    )

def _merge_cc_shared_library_infos(ctx):
    dynamic_deps = []
    transitive_dynamic_deps = []
    for dep in ctx.attr.dynamic_deps:
        dynamic_dep_entry = struct(
            exports = dep[CcSharedLibraryInfo].exports,
            linker_input = dep[CcSharedLibraryInfo].linker_input,
            link_once_static_libs = dep[CcSharedLibraryInfo].link_once_static_libs,
        )
        dynamic_deps.append(dynamic_dep_entry)
        transitive_dynamic_deps.append(dep[CcSharedLibraryInfo].dynamic_deps)

    return depset(direct = dynamic_deps, transitive = transitive_dynamic_deps, order = "topological")

def _build_exports_map_from_only_dynamic_deps(merged_cc_shared_library_infos_list):
    exports_map = {}
    for entry in merged_cc_shared_library_infos_list:
        exports = entry.exports
        linker_input = entry.linker_input
        for export in exports:
            if export in exports_map:
                fail("Two shared libraries in dependencies export the same symbols. Both " +
                     exports_map[export].libraries[0].dynamic_library.short_path +
                     " and " + linker_input.libraries[0].dynamic_library.short_path +
                     " export " + export)
            exports_map[export] = linker_input
    return exports_map

# The map points from the target that can only be linked once to the
# cc_shared_library target that already links it.
def _build_link_once_static_libs_map(merged_cc_shared_library_infos_list):
    link_once_static_libs_map = {}
    for entry in merged_cc_shared_library_infos_list:
        link_once_static_libs = entry.link_once_static_libs
        linker_input = entry.linker_input
        for static_lib in link_once_static_libs:
            if static_lib in link_once_static_libs_map:
                fail("Two shared libraries in dependencies link the same " +
                     " library statically. Both " + link_once_static_libs_map[static_lib] +
                     " and " + str(linker_input.owner) +
                     " link statically " + static_lib)
            link_once_static_libs_map[static_lib] = str(linker_input.owner)
    return link_once_static_libs_map

def _is_dynamic_only(library_to_link):
    if (library_to_link.static_library == None and
        library_to_link.pic_static_library == None and
        (library_to_link.objects == None or len(library_to_link.objects) == 0) and
        (library_to_link.pic_objects == None or len(library_to_link.pic_objects) == 0)):
        return True
    return False

def _wrap_static_library_with_alwayslink(ctx, feature_configuration, cc_toolchain, linker_input):
    new_libraries_to_link = []
    for old_library_to_link in linker_input.libraries:
        if _is_dynamic_only(old_library_to_link):
            new_libraries_to_link.append(old_library_to_link)
            continue
        new_library_to_link = cc_common.create_library_to_link(
            actions = ctx.actions,
            feature_configuration = feature_configuration,
            cc_toolchain = cc_toolchain,
            static_library = old_library_to_link.static_library,
            objects = old_library_to_link.objects,
            pic_static_library = old_library_to_link.pic_static_library,
            pic_objects = old_library_to_link.pic_objects,
            lto_compilation_context = old_library_to_link._lto_compilation_context,
            pic_lto_compilation_context = old_library_to_link._pic_lto_compilation_context,
            alwayslink = True,
        )
        new_libraries_to_link.append(new_library_to_link)

    return cc_common.create_linker_input(
        owner = linker_input.owner,
        libraries = depset(direct = new_libraries_to_link),
        user_link_flags = linker_input.user_link_flags,
        additional_inputs = depset(direct = linker_input.additional_inputs),
    )

def _check_if_target_under_path(value, pattern):
    if pattern.workspace_name != value.workspace_name:
        return False
    if pattern.name == "__pkg__":
        return pattern.package == value.package
    if pattern.name == "__subpackages__":
        return _same_package_or_above(pattern, value)

    return pattern.package == value.package and pattern.name == value.name

def _check_if_target_should_be_exported_with_filter(target, current_label, exports_filter):
    for export_filter in exports_filter:
        export_filter_label = current_label.relative(export_filter)
        if _check_if_target_under_path(target, export_filter_label):
            return True

    return False

# Checks if the linker_input has code to link statically, i.e. either
# archives or object files, ignores library.dynamic_library.
def _contains_code_to_link(linker_input):
    for library in linker_input.libraries:
        if (library.static_library != None or
            library.pic_static_library != None or
            len(library.objects) or len(library.pic_objects)):
            return True

    return False

def _find_top_level_linker_input_labels(
        deps_graph_nodes,
        linker_inputs_to_be_linked_statically_map,
        targets_to_be_linked_dynamically_set):
    top_level_linker_input_labels_set = {}
    nodes_to_check = list(deps_graph_nodes)

    seen_nodes_set = {}
    for i in range(2147483647):
        if i == len(nodes_to_check):
            break

        node = nodes_to_check[i]
        must_add_children = False
        node_str_owners = []
        for owner in node.owners:
            owner_str = str(owner)
            node_str_owners.append(owner_str)
            if owner_str in linker_inputs_to_be_linked_statically_map:
                must_add_children = True
                for linker_input in linker_inputs_to_be_linked_statically_map[owner_str]:
                    if _contains_code_to_link(linker_input):
                        top_level_linker_input_labels_set[owner_str] = True
                        must_add_children = False
                        break
            elif owner_str not in targets_to_be_linked_dynamically_set:
                # This can happen when there was a target in the graph that exported other libraries'
                # linker_inputs but didn't contribute any linker_input of its own.
                must_add_children = True

        node_key = "".join(node_str_owners)
        if must_add_children and node_key not in seen_nodes_set:
            nodes_to_check.extend(node.children)
            seen_nodes_set[node_key] = True

    return top_level_linker_input_labels_set

def _filter_inputs(
        ctx,
        feature_configuration,
        cc_toolchain,
        deps,
        transitive_exports,
        link_once_static_libs_map):
    curr_link_once_static_libs_set = {}

    deps_root_tree_nodes = []
    dependency_linker_inputs_sets = []
    direct_deps_set = {}
    for dep in deps:
        direct_deps_set[str(dep.label)] = True
        dependency_linker_inputs_sets.append(dep[CcInfo].linking_context.linker_inputs)
        deps_root_tree_nodes.append(dep[GraphNodeInfo])

    dependency_linker_inputs = depset(transitive = dependency_linker_inputs_sets, order = "topological").to_list()

    can_be_linked_dynamically = {}
    for linker_input in dependency_linker_inputs:
        owner = str(linker_input.owner)
        if owner in transitive_exports:
            can_be_linked_dynamically[owner] = True

    # The targets_to_be_linked_statically_map points to whether the target to
    # be linked statically can be linked more than once.
    # Entries in unused_dynamic_linker_inputs will be marked None if they are
    # used
    (
        targets_to_be_linked_statically_map,
        targets_to_be_linked_dynamically_set,
        topologically_sorted_labels,
        unused_dynamic_linker_inputs,
    ) = _separate_static_and_dynamic_link_libraries(
        ctx.attr.dynamic_deps,
        deps_root_tree_nodes,
        can_be_linked_dynamically,
    )

    linker_inputs_to_be_linked_statically_map = {}
    for linker_input in dependency_linker_inputs:
        owner = str(linker_input.owner)
        if owner in targets_to_be_linked_statically_map:
            linker_inputs_to_be_linked_statically_map.setdefault(owner, []).append(linker_input)

    top_level_linker_input_labels_set = _find_top_level_linker_input_labels(
        deps_root_tree_nodes,
        linker_inputs_to_be_linked_statically_map,
        targets_to_be_linked_dynamically_set,
    )

    # We keep track of precompiled_only_dynamic_libraries, so that we can add
    # them to runfiles.
    precompiled_only_dynamic_libraries = []
    exports = {}
    linker_inputs_seen = {}
    linker_inputs_count = 0
    label_to_linker_inputs = {}

    def _add_linker_input_to_dict(owner, linker_input):
        label_to_linker_inputs.setdefault(owner, []).append(linker_input)

    # We use this dictionary to give an error if a target containing only
    # precompiled dynamic libraries is placed directly in roots. If such a
    # precompiled dynamic library is needed it would be because a target in the
    # parallel cc_library graph actually needs it. Therefore the precompiled
    # dynamic library should be made a dependency of that cc_library instead.
    dynamic_only_roots = {}
    linked_statically_but_not_exported = {}
    for linker_input in dependency_linker_inputs:
        stringified_linker_input = cc_helper.stringify_linker_input(linker_input)
        if stringified_linker_input in linker_inputs_seen:
            continue
        linker_inputs_seen[stringified_linker_input] = True
        owner = str(linker_input.owner)
        if owner in targets_to_be_linked_dynamically_set:
            unused_dynamic_linker_inputs[transitive_exports[owner].owner] = None

            # Link the library in this iteration dynamically,
            # transitive_exports contains the artifacts produced by a
            # cc_shared_library
            _add_linker_input_to_dict(linker_input.owner, transitive_exports[owner])
            linker_inputs_count += 1
        elif owner in targets_to_be_linked_statically_map:
            if semantics.is_bazel and not linker_input.libraries:
                # TODO(bazel-team): semantics.should_create_empty_archive() should be
                # cleaned up and return False in every case. cc_libraries shouldn't
                # produce empty archives. For now issue #19920 is only fixed in Bazel.
                continue
            if owner in link_once_static_libs_map:
                # We are building a dictionary that will allow us to give
                # proper errors for libraries that have been linked multiple
                # times elsewhere but haven't been exported. The values in the
                # link_once_static_libs_map dictionary are the
                # cc_shared_library targets. In this iteration we know of at
                # least one target (i.e. owner) which is being linked
                # statically by the cc_shared_library
                # link_once_static_libs_map[owner] but is not being exported
                linked_statically_but_not_exported.setdefault(link_once_static_libs_map[owner], []).append(owner)

            dynamic_only_libraries = []
            static_libraries = []
            for library in linker_input.libraries:
                if _is_dynamic_only(library):
                    dynamic_only_libraries.append(library)
                else:
                    static_libraries.append(library)

            if len(dynamic_only_libraries):
                precompiled_only_dynamic_libraries.extend(dynamic_only_libraries)
                if not len(static_libraries):
                    if owner in direct_deps_set:
                        dynamic_only_roots[owner] = True
                    _add_linker_input_to_dict(linker_input.owner, linker_input)
                    linker_inputs_count += 1
                    continue
            if len(static_libraries) and owner in dynamic_only_roots:
                dynamic_only_roots.pop(owner)

            linker_input_to_be_linked_statically = linker_input
            if owner in top_level_linker_input_labels_set:
                linker_input_to_be_linked_statically = _wrap_static_library_with_alwayslink(
                    ctx,
                    feature_configuration,
                    cc_toolchain,
                    linker_input,
                )
            if _check_if_target_should_be_exported_with_filter(
                linker_input.owner,
                ctx.label,
                ctx.attr.exports_filter,
            ):
                exports[owner] = True

            _add_linker_input_to_dict(linker_input.owner, linker_input_to_be_linked_statically)
            linker_inputs_count += 1

            if not targets_to_be_linked_statically_map[owner]:
                curr_link_once_static_libs_set[owner] = True

    if dynamic_only_roots:
        message = ("Do not place libraries which only contain a " +
                   "precompiled dynamic library in roots. The following " +
                   "libraries only have precompiled dynamic libraries:\n")
        for dynamic_only_root in dynamic_only_roots:
            message += dynamic_only_root + "\n"
        fail(message)

    linker_inputs_count += _add_unused_dynamic_deps(ctx, unused_dynamic_linker_inputs, _add_linker_input_to_dict, topologically_sorted_labels, link_indirect_deps = False)

    linker_inputs = _sort_linker_inputs(
        topologically_sorted_labels,
        label_to_linker_inputs,
        linker_inputs_count,
    )

    _throw_linked_but_not_exported_errors(linked_statically_but_not_exported)
    return (exports, linker_inputs, curr_link_once_static_libs_set.keys(), precompiled_only_dynamic_libraries)

def _throw_linked_but_not_exported_errors(error_libs_dict):
    if not error_libs_dict:
        return

    error_builder = ["The following libraries were linked statically by different cc_shared_libraries but not exported:\n"]
    for cc_shared_library_target, error_libs in error_libs_dict.items():
        error_builder.append("cc_shared_library %s:\n" % str(cc_shared_library_target))
        for error_lib in error_libs:
            error_builder.append("  \"%s\",\n" % str(error_lib))

    error_builder.append("If you are sure that the previous libraries are exported by the cc_shared_libraries because:\n")
    error_builder.append("  1. You have visibility declarations in the source code\n")
    error_builder.append("  2. Or you are passing a visibility script to the linker to export symbols from them\n")
    error_builder.append("then add those libraries to roots or exports_filter for each cc_shared_library.\n")

    fail("".join(error_builder))

def _same_package_or_above(label_a, label_b):
    if label_a.workspace_name != label_b.workspace_name:
        return False
    package_a_tokenized = label_a.package.split("/")
    package_b_tokenized = label_b.package.split("/")
    if len(package_b_tokenized) < len(package_a_tokenized):
        return False

    if package_a_tokenized[0] != "":
        for i in range(len(package_a_tokenized)):
            if package_a_tokenized[i] != package_b_tokenized[i]:
                return False

    return True

def _get_deps(ctx):
    if len(ctx.attr.deps) and len(ctx.attr.roots):
        fail(
            "You are using the attribute 'roots' and 'deps'. 'deps' is the " +
            "new name for the attribute 'roots'. The attribute 'roots' will be" +
            "removed in the future",
            attr = "roots",
        )

    deps = ctx.attr.deps
    if not len(deps):
        deps = ctx.attr.roots

    if len(deps) == 0:
        fail(
            "'cc_shared_library' must have at least one dependency in 'deps' (or 'roots')",
            attr = "deps",
        )

    return deps

def _build_map_direct_dynamic_dep_to_transitive_dynamic_deps(direct_dynamic_deps):
    all_dynamic_dep_linker_inputs = {}
    direct_dynamic_dep_to_transitive_dynamic_deps = {}
    for dep in direct_dynamic_deps:
        owner = dep[CcSharedLibraryInfo].linker_input.owner
        all_dynamic_dep_linker_inputs[owner] = dep[CcSharedLibraryInfo].linker_input
        transitive_dynamic_dep_labels = []
        for dynamic_dep in dep[CcSharedLibraryInfo].dynamic_deps.to_list():
            all_dynamic_dep_linker_inputs[dynamic_dep.linker_input.owner] = dynamic_dep.linker_input
            transitive_dynamic_dep_labels.append(dynamic_dep.linker_input.owner)
        transitive_dynamic_dep_labels_set = depset(transitive_dynamic_dep_labels, order = "topological")
        for export in dep[CcSharedLibraryInfo].exports:
            direct_dynamic_dep_to_transitive_dynamic_deps[export] = transitive_dynamic_dep_labels_set

    return direct_dynamic_dep_to_transitive_dynamic_deps, all_dynamic_dep_linker_inputs

def _add_unused_dynamic_deps(ctx, unused_dynamic_linker_inputs, add_linker_inputs_lambda, topologically_sorted_labels, link_indirect_deps):
    linker_inputs_count = 0
    direct_dynamic_dep_labels = {dep[CcSharedLibraryInfo].linker_input.owner: True for dep in ctx.attr.dynamic_deps}
    topologically_sorted_labels_set = {label: True for label in topologically_sorted_labels}
    for dynamic_linker_input_owner, unused_linker_input in unused_dynamic_linker_inputs.items():
        should_link_input = (unused_linker_input and
                             (link_indirect_deps or dynamic_linker_input_owner in direct_dynamic_dep_labels))
        if should_link_input:
            add_linker_inputs_lambda(
                dynamic_linker_input_owner,
                unused_dynamic_linker_inputs[dynamic_linker_input_owner],
            )
            linker_inputs_count += 1
            if dynamic_linker_input_owner not in topologically_sorted_labels_set:
                topologically_sorted_labels.append(dynamic_linker_input_owner)
    return linker_inputs_count

def _cc_shared_library_impl(ctx):
    if not cc_common.check_experimental_cc_shared_library():
        if len(ctx.attr.static_deps):
            fail(
                "This attribute is a no-op and its usage" +
                " is forbidden after cc_shared_library is no longer experimental. " +
                "Remove it from every cc_shared_library target",
                attr = "static_deps",
            )
        if len(ctx.attr.roots):
            fail(
                "This attribute has been renamed to 'deps'. Simply rename the" +
                " attribute on the target.",
                attr = "roots",
            )

    deps = _get_deps(ctx)

    cc_toolchain = find_cc_toolchain(ctx)
    feature_configuration = cc_common.configure_features(
        ctx = ctx,
        cc_toolchain = cc_toolchain,
        requested_features = ctx.features + ["force_no_whole_archive"],
        unsupported_features = ctx.disabled_features,
    )

    merged_cc_shared_library_infos = _merge_cc_shared_library_infos(ctx)

    # Small performance tweak to avoid flattening merged_cc_shared_library_infos twice:
    merged_cc_shared_library_infos_list = merged_cc_shared_library_infos.to_list()
    exports_map = _build_exports_map_from_only_dynamic_deps(merged_cc_shared_library_infos_list)
    for export in deps:
        # Do not check for overlap between targets matched by the current
        # rule's exports_filter and what is in exports_map. A library in roots
        # will have to be linked in statically into the current rule with 100%
        # guarantee and it will also have to be exported. Therefore, we must
        # check it's not already exported by a different shared library. On the
        # other hand, a library in the transitive closure of the current rule
        # may be matched by the exports_filter but if it's already exported by
        # a dynamic_dep then it won't be linked statically (therefore not give
        # an error either) in the current target. The rule will intentionally
        # not throw an error in these cases.
        if str(export.label) in exports_map:
            fail("Trying to export a library already exported by a different shared library: " +
                 str(export.label))

    link_once_static_libs_map = _build_link_once_static_libs_map(merged_cc_shared_library_infos_list)

    (exports, linker_inputs, curr_link_once_static_libs_set, precompiled_only_dynamic_libraries) = _filter_inputs(
        ctx,
        feature_configuration,
        cc_toolchain,
        deps,
        exports_map,
        link_once_static_libs_map,
    )

    linking_context = _create_linker_context(linker_inputs)

    cc_runtimes_deps = cc_helper.get_cc_runtimes(ctx, True)
    runtimes_linking_contexts = cc_helper.get_linking_contexts_from_deps(cc_runtimes_deps)

    user_link_flags = []
    for user_link_flag in ctx.attr.user_link_flags:
        user_link_flags.append(ctx.expand_location(user_link_flag, targets = ctx.attr.additional_linker_inputs))

    main_output = None
    if ctx.attr.shared_lib_name:
        main_output = ctx.actions.declare_file(ctx.attr.shared_lib_name)

    additional_inputs = []
    additional_outputs = []
    link_variables = {}
    additional_output_groups = {}

    pdb_file = None
    if cc_common.is_enabled(feature_configuration = feature_configuration, feature_name = "generate_pdb_file"):
        if ctx.attr.shared_lib_name:
            pdb_file = ctx.actions.declare_file(paths.replace_extension(ctx.attr.shared_lib_name, ".pdb"))
        else:
            pdb_file = ctx.actions.declare_file(ctx.label.name + ".pdb")
        additional_outputs.append(pdb_file)
        additional_output_groups["pdb_file"] = depset([pdb_file])

    if cc_common.is_enabled(feature_configuration = feature_configuration, feature_name = "targets_windows"):
        object_files = []
        for linker_input in linking_context.linker_inputs.to_list():
            for library in linker_input.libraries:
                if library.pic_static_library != None:
                    if library.pic_objects != None:
                        object_files.extend(library.pic_objects)
                elif library.static_library != None:
                    if library.objects != None:
                        object_files.extend(library.objects)

        generated_def_file = None
        generated_def_file = cc_helper.generate_def_file(
            ctx,
            ctx.file._def_parser,
            object_files,
            ctx.label.name,
            cc_toolchain,
            feature_configuration,
        )
        if generated_def_file != None:
            additional_output_groups["def_file"] = depset([generated_def_file])
        custom_win_def_file = ctx.file.win_def_file
        win_def_file = cc_helper.get_windows_def_file_for_linking(ctx, custom_win_def_file, generated_def_file, feature_configuration)
        link_variables["def_file_path"] = win_def_file.path
        additional_inputs.append(win_def_file)

    additional_inputs.extend(ctx.files.additional_linker_inputs)
    linking_outputs = cc_common.link(
        actions = ctx.actions,
        feature_configuration = feature_configuration,
        cc_toolchain = cc_toolchain,
        linking_contexts = [linking_context] + runtimes_linking_contexts,
        user_link_flags = user_link_flags,
        additional_inputs = additional_inputs,
        name = ctx.label.name,
        output_type = "dynamic_library",
        main_output = main_output,
        variables_extension = link_variables,
        additional_outputs = additional_outputs,
    )

    runfiles_files = []
    if linking_outputs.library_to_link.resolved_symlink_dynamic_library != None:
        runfiles_files.append(linking_outputs.library_to_link.resolved_symlink_dynamic_library)

    # This is different to cc_binary(linkshared=1). Bazel never handles the
    # linking implicitly for a cc_binary(linkshared=1) but it does so for a cc_shared_library,
    # for which it will use the symlink in the solib directory. If we don't add it, a dependent
    # linked against it would fail.
    runfiles_files.append(linking_outputs.library_to_link.dynamic_library)
    runfiles = ctx.runfiles(
        files = runfiles_files,
    )
    for dep in ctx.attr.dynamic_deps:
        runfiles = runfiles.merge(dep[DefaultInfo].data_runfiles)

    precompiled_only_dynamic_libraries_runfiles = []
    for precompiled_dynamic_library in precompiled_only_dynamic_libraries:
        # precompiled_dynamic_library.dynamic_library could be None if the library to link just contains
        # an interface library which is valid if the actual library is obtained from the system.
        if precompiled_dynamic_library.dynamic_library != None:
            precompiled_only_dynamic_libraries_runfiles.append(precompiled_dynamic_library.dynamic_library)

    runfiles = runfiles.merge(ctx.runfiles(files = precompiled_only_dynamic_libraries_runfiles))

    for export in deps:
        exports[str(export.label)] = True

    if not semantics.get_experimental_link_static_libraries_once(ctx):
        curr_link_once_static_libs_set = {}

    library = []
    if linking_outputs.library_to_link.resolved_symlink_dynamic_library != None:
        library.append(linking_outputs.library_to_link.resolved_symlink_dynamic_library)
    else:
        library.append(linking_outputs.library_to_link.dynamic_library)

    interface_library = []
    if linking_outputs.library_to_link.resolved_symlink_interface_library != None:
        interface_library.append(linking_outputs.library_to_link.resolved_symlink_interface_library)
    elif linking_outputs.library_to_link.interface_library != None:
        interface_library.append(linking_outputs.library_to_link.interface_library)
    else:
        interface_library = library

    return [
        DefaultInfo(
            files = depset(library),
            runfiles = runfiles,
        ),
        OutputGroupInfo(
            main_shared_library_output = depset(library),
            interface_library = depset(interface_library),
            **additional_output_groups
        ),
        CcSharedLibraryInfo(
            dynamic_deps = merged_cc_shared_library_infos,
            exports = exports.keys(),
            link_once_static_libs = curr_link_once_static_libs_set,
            linker_input = cc_common.create_linker_input(
                owner = ctx.label,
                libraries = depset([linking_outputs.library_to_link] + precompiled_only_dynamic_libraries),
            ),
        ),
    ]

for_testing_dont_use_check_if_target_under_path = _check_if_target_under_path
merge_cc_shared_library_infos = _merge_cc_shared_library_infos
build_link_once_static_libs_map = _build_link_once_static_libs_map
build_exports_map_from_only_dynamic_deps = _build_exports_map_from_only_dynamic_deps
throw_linked_but_not_exported_errors = _throw_linked_but_not_exported_errors
separate_static_and_dynamic_link_libraries = _separate_static_and_dynamic_link_libraries
sort_linker_inputs = _sort_linker_inputs
add_unused_dynamic_deps = _add_unused_dynamic_deps

cc_shared_library_impl = _cc_shared_library_impl
cc_shared_library_impl_wrapper = wrap_starlark_function(_cc_shared_library_impl)