[libc][bazel] Create libc_release_library for release configurations. (#130694)

See PR #130327 for background and motivation. This change expands the
libc_support_library and libc_function rules to create filegroups that
allow building a collection of llvm-libc functions together, from
sources, as a part of a single cc_library that can then be used by the
downstream clients.

This change also adds an example use of this macro under
libc/test/BUILD.bazel to confirm that this macro works as expected.

Author: vonosmas

utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl

@@ -64,60 +64,122 @@ def _libc_library(name, copts = [], deps = [], local_defines = [], **kwargs):
         **kwargs
     )
 
+def _libc_library_filegroups(
+        name,
+        is_function,
+        srcs = [],
+        hdrs = [],
+        textual_hdrs = [],
+        deps = [],
+        # We're not using kwargs, but instead explicitly list all possible
+        # arguments that can be passed to libc_support_library or
+        # libc_function macros. This is done to limit the configurability
+        # and ensure the consistent and tightly controlled set of flags
+        # (see libc_common_copts and libc_release_copts above) is used to build
+        # libc code both for tests and for release configuration.
+        target_compatible_with = None,  # @unused
+        weak = False):  # @unused
+    """Internal macro to collect sources and headers required to build a library.
+    """
+
+    # filegroups created from "libc_function" macro has an extra "_fn" in their
+    # name to ensure that no other libc target can depend on libc_function.
+    prefix = name + ("_fn" if is_function else "")
+    native.filegroup(
+        name = prefix + "_srcs",
+        srcs = srcs + hdrs + [dep + "_srcs" for dep in deps],
+    )
+    native.filegroup(
+        name = prefix + "_textual_hdrs",
+        srcs = textual_hdrs + [dep + "_textual_hdrs" for dep in deps],
+    )
+
 # A convenience function which should be used to list all libc support libraries.
 # Any library which does not define a public function should be listed with
 # libc_support_library.
 def libc_support_library(name, **kwargs):
     _libc_library(name = name, **kwargs)
+    _libc_library_filegroups(name = name, is_function = False, **kwargs)
 
 def libc_function(
         name,
-        srcs,
         weak = False,
-        copts = [],
-        local_defines = [],
         **kwargs):
     """Add target for a libc function.
 
-    The libc function is eventually available as a cc_library target by name
-    "name". LLVM libc implementations of libc functions are in C++. So, this
-    rule internally generates a C wrapper for the C++ implementation and adds
-    it to the source list of the cc_library. This way, the C++ implementation
-    and the C wrapper are both available in the cc_library.
+    This macro creates an internal cc_library that can be used to test this
+    function, and creates filegroups required to include this function into
+    a release build of libc.
 
     Args:
       name: Target name. It is normally the name of the function this target is
             for.
-      srcs: The .cpp files which contain the function implementation.
       weak: Make the symbol corresponding to the libc function "weak".
-      copts: The list of options to add to the C++ compilation command.
-      local_defines: The preprocessor defines which will be prepended with -D
-                     and passed to the compile command of this target but not
-                     its deps.
       **kwargs: Other attributes relevant for a cc_library. For example, deps.
     """
 
-    # We compile the code twice, the first target is suffixed with ".__internal__" and contains the
+    # Build "internal" library with a function, the target has ".__internal__" suffix and contains
     # C++ functions in the "LIBC_NAMESPACE" namespace. This allows us to test the function in the
     # presence of another libc.
-    libc_support_library(
+    _libc_library(
         name = libc_internal_target(name),
-        srcs = srcs,
-        copts = copts,
-        local_defines = local_defines,
         **kwargs
     )
 
+    _libc_library_filegroups(name = name, is_function = True, **kwargs)
+
+
+    # TODO(PR #130327): Remove this after downstream uses are migrated to libc_release_library.
     # This second target is the llvm libc C function with default visibility.
     func_attrs = [
         "LLVM_LIBC_FUNCTION_ATTR_" + name + "='LLVM_LIBC_EMPTY, [[gnu::weak]]'",
     ] if weak else []
 
     _libc_library(
         name = name,
-        srcs = srcs,
-        copts = copts + libc_release_copts(),
-        local_defines = local_defines + func_attrs,
+        copts = libc_release_copts(),
+        local_defines = func_attrs,
+        **kwargs
+    )
+
+def libc_release_library(
+        name,
+        libc_functions,
+        weak_symbols = [],
+        **kwargs):
+    """Create the release version of a libc library.
+
+    Args:
+        name: Name of the cc_library target.
+        libc_functions: List of functions to include in the library. They should be
+            created by libc_function macro.
+        weak_symbols: List of function names that should be marked as weak symbols.
+        **kwargs: Other arguments relevant to cc_library.
+    """
+    # Combine all sources into a single filegroup to avoid repeated sources error.
+    native.filegroup(
+        name = name + "_srcs",
+        srcs = [function + "_fn_srcs" for function in libc_functions],
+    )
+
+    native.cc_library(
+        name = name + "_textual_hdr_library",
+        textual_hdrs = [function + "_fn_textual_hdrs" for function in libc_functions],
+    )
+
+    weak_attributes = [
+        "LLVM_LIBC_FUNCTION_ATTR_" + name + "='LLVM_LIBC_EMPTY, [[gnu::weak]]'"
+        for name in weak_symbols
+    ]
+
+    native.cc_library(
+        name = name,
+        srcs = [":" + name + "_srcs"],
+        copts = libc_common_copts() + libc_release_copts(),
+        local_defines = weak_attributes + LIBC_CONFIGURE_OPTIONS,
+        deps = [
+            ":" + name + "_textual_hdr_library",
+        ],
         **kwargs
     )
 

utils/bazel/llvm-project-overlay/libc/test/BUILD.bazel

@@ -2,6 +2,26 @@
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+load("@bazel_skylib//rules:build_test.bzl", "build_test")
+load("//libc:libc_build_rules.bzl", "libc_release_library")
+
 package(default_visibility = ["//visibility:public"])
 
 exports_files(["libc_test_rules.bzl"])
+
+# Smoke test verifying libc_release_library macro functionality.
+libc_release_library(
+    name = "libc_release_test",
+    libc_functions = [
+        "//libc:acosf",
+        "//libc:read",
+    ],
+    weak_symbols = [
+        "read",
+    ],
+)
+
+build_test(
+    name = "libc_release_build_test",
+    targets = [":libc_release_test"],
+)