Add NO_EXPORTING tag to indicate that a lib doesn't export any

symbols therefore it is safe to link it more than once.

This is useful in some cases, for example,
a static lib has a constructor that needs to be run during loading time of the
shared lib that has it linked into, and this is how the code gets called by the
OS. This static lib might need to be linked as a whole archive dep for multiple
shared libs, otherwise this static lib will be dropped by the linker since
there are no incoming symbol references.

RELNOTES:none
PiperOrigin-RevId: 496497650
Change-Id: I9c13408c051320321fabcb3863d87e76c53b4568

src/main/starlark/builtins_bzl/common/cc/experimental_cc_shared_library.bzl

@@ -33,6 +33,15 @@ cc_common = _builtins.toplevel.cc_common
 # used sparingly after making sure it's safe to use.
 LINKABLE_MORE_THAN_ONCE = "LINKABLE_MORE_THAN_ONCE"
 
+# Add this as a tag to any static lib target that doesn't export any symbols,
+# thus can be statically linked more than once. This is useful in some cases,
+# for example, a static lib has a constructor that needs to be run during
+# loading time of the shared lib that has it linked into, which is how the
+# code gets called by the OS. This static lib might need to be linked as a
+# whole archive dep for multiple shared libs, otherwise this static lib will
+# be dropped by the linker since there are no incoming symbol references.
+NO_EXPORTING = "NO_EXPORTING"
+
 CcSharedLibraryPermissionsInfo = provider(
     "Permissions for a cc shared library.",
     fields = {
@@ -45,6 +54,7 @@ GraphNodeInfo = provider(
         "children": "Other GraphNodeInfo from dependencies of this target",
         "label": "Label of the target visited",
         "linkable_more_than_once": "Linkable into more than a single cc_shared_library",
+        "no_exporting": "The static lib doesn't export any symbols so don't export it",
     },
 )
 CcSharedLibraryInfo = provider(
@@ -532,7 +542,12 @@ def _cc_shared_library_impl(ctx):
     runfiles = runfiles.merge(ctx.runfiles(files = precompiled_only_dynamic_libraries_runfiles))
 
     for export in ctx.attr.roots:
-        exports[str(export.label)] = True
+        export_label = str(export.label)
+        if GraphNodeInfo in export and export[GraphNodeInfo].no_exporting:
+            if export_label in link_once_static_libs:
+                link_once_static_libs.remove(export_label)
+            continue
+        exports[export_label] = True
 
     debug_files = []
     exports_debug_file = ctx.actions.declare_file(ctx.label.name + "_exports.txt")
@@ -595,15 +610,19 @@ def _graph_structure_aspect_impl(target, ctx):
     # TODO(bazel-team): Add flag to Bazel that can toggle the initialization of
     # linkable_more_than_once.
     linkable_more_than_once = False
+    no_exporting = False
     if hasattr(ctx.rule.attr, "tags"):
         for tag in ctx.rule.attr.tags:
             if tag == LINKABLE_MORE_THAN_ONCE:
                 linkable_more_than_once = True
+            elif tag == NO_EXPORTING:
+                no_exporting = True
 
     return [GraphNodeInfo(
         label = ctx.label,
         children = children,
         linkable_more_than_once = linkable_more_than_once,
+        no_exporting = no_exporting,
     )]
 
 def _cc_shared_library_permissions_impl(ctx):

src/main/starlark/tests/builtins_bzl/cc/cc_shared_library/test_cc_shared_library/BUILD.builtin_test

@@ -1,4 +1,14 @@
-load(":starlark_tests.bzl", "additional_inputs_test", "build_failure_test", "debug_files_test", "interface_library_output_group_test", "linking_suffix_test", "paths_test", "runfiles_test")
+load(
+    ":starlark_tests.bzl",
+    "additional_inputs_test",
+    "build_failure_test",
+    "debug_files_test",
+    "interface_library_output_group_test",
+    "linking_suffix_test",
+    "paths_test",
+    "runfiles_test",
+    "no_exporting_static_lib_test",
+)
 
 LINKABLE_MORE_THAN_ONCE = "LINKABLE_MORE_THAN_ONCE"
 
@@ -391,6 +401,51 @@ cc_shared_library_permissions(
     ],
 )
 
+cc_library(
+    name = "static_lib_no_exporting",
+    srcs = [
+        "bar.cc",
+        "bar.h",
+    ],
+    tags = ["NO_EXPORTING"],
+)
+
+cc_library(
+    name = "static_lib_exporting",
+    srcs = [
+        "bar2.cc",
+        "bar2.h",
+    ],
+)
+
+cc_shared_library(
+    name = "lib_with_no_exporting_roots_1",
+    roots = [":static_lib_no_exporting"],
+)
+
+cc_shared_library(
+    name = "lib_with_no_exporting_roots_2",
+    roots = [":static_lib_no_exporting"],
+    dynamic_deps = [":lib_with_no_exporting_roots_3"],
+)
+
+cc_shared_library(
+    name = "lib_with_no_exporting_roots_3",
+    roots = [":static_lib_no_exporting"],
+)
+
+cc_shared_library(
+    name = "lib_with_no_exporting_roots",
+    roots = [
+        ":static_lib_no_exporting",
+        ":static_lib_exporting",
+    ],
+    dynamic_deps = [
+        ":lib_with_no_exporting_roots_1",
+        ":lib_with_no_exporting_roots_2",
+    ],
+)
+
 build_failure_test(
     name = "two_dynamic_deps_same_export_in_so_test",
     message = "Two shared libraries in dependencies export the same symbols",
@@ -439,3 +494,8 @@ build_failure_test(
     }),
     target_under_test = "//src/main/starlark/tests/builtins_bzl/cc/cc_shared_library/test_cc_shared_library/failing_targets:unaccounted_for_libs_so",
 )
+
+no_exporting_static_lib_test(
+    name = "no_exporting_static_lib_test",
+    target_under_test = ":lib_with_no_exporting_roots",
+)

src/main/starlark/tests/builtins_bzl/cc/cc_shared_library/test_cc_shared_library/starlark_tests.bzl

@@ -211,3 +211,21 @@ interface_library_output_group_test = analysistest.make(
         "is_windows": attr.bool(),
     },
 )
+
+def _no_exporting_static_lib_test_impl(ctx):
+    env = analysistest.begin(ctx)
+
+    target_under_test = analysistest.target_under_test(env)
+
+    # There should be only one exported file
+    actual_file = target_under_test[CcSharedLibraryInfo].exports[0]
+
+    # Sometimes "@" is prefixed in some test environments
+    expected = "//src/main/starlark/tests/builtins_bzl/cc/cc_shared_library/test_cc_shared_library:static_lib_exporting"
+    asserts.true(env, actual_file.endswith(expected))
+
+    return analysistest.end(env)
+
+no_exporting_static_lib_test = analysistest.make(
+    _no_exporting_static_lib_test_impl,
+)