[Bazel] Make LLVM and Clang config headers configurable

utils/bazel/.bazelrc

@@ -58,14 +58,6 @@ build --experimental_cc_shared_library
 # https://github.com/bazelbuild/bazel/commit/03246077f948f2790a83520e7dccc2625650e6df
 build --build_runfile_links=false
 
-###############################################################################
-# Options to select different strategies for linking potential dependent
-# libraries. The default leaves it disabled.
-###############################################################################
-
-build:zlib_external --repo_env=BAZEL_LLVM_ZLIB_STRATEGY=external
-build:zlib_system --repo_env=BAZEL_LLVM_ZLIB_STRATEGY=system
-
 ###############################################################################
 # Options for "generic_clang" builds: these options should generally apply to
 # builds using a Clang-based compiler, and default to the `clang` executable on

utils/bazel/llvm-project-overlay/clang/BUILD.bazel

@@ -2,6 +2,8 @@
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
+load("@bazel_skylib//rules:expand_template.bzl", "expand_template")
 load("@rules_python//python:defs.bzl", "py_binary")
 load(
     "//:vars.bzl",
@@ -13,6 +15,16 @@ load(
 load("//:workspace_root.bzl", "workspace_root")
 load("//llvm:binary_alias.bzl", "binary_alias")
 load("//llvm:cc_plugin_library.bzl", "cc_plugin_library")
+load(
+    "//config:cmakehelpers.bzl",
+    "cmakedefine",
+    "cmakedefine01_off",
+    "cmakedefine01_on",
+    "cmakedefine_sunset",
+    "cmakedefine_unset",
+    "cmakedefine_vset",
+    "cmakedefine_vunset",
+)
 load("//llvm:driver.bzl", "llvm_driver_cc_binary")
 load("//mlir:tblgen.bzl", "gentbl_cc_library", "td_library")
 
@@ -614,6 +626,49 @@ genrule(
     ),
 )
 
+expand_template(
+    name = "config_h",
+    out = "include/clang/Config/config.h",
+    substitutions = (
+        {"${BUG_REPORT_URL}": "https://github.com/llvm/llvm-project/issues/"} |
+        cmakedefine01_on("CLANG_DEFAULT_PIE_ON_LINUX") |
+        {
+            "${CLANG_DEFAULT_LINKER}": "",
+            "${CLANG_DEFAULT_CXX_STDLIB}": "",
+            "${CLANG_DEFAULT_RTLIB}": "",
+            "${CLANG_DEFAULT_UNWINDLIB}": "",
+            "${CLANG_DEFAULT_OBJCOPY}": "objcopy",
+            "${CLANG_DEFAULT_OPENMP_RUNTIME}": "libomp",
+            "${CLANG_SYSTEMZ_DEFAULT_ARCH}": "z10",
+            "${CLANG_INSTALL_LIBDIR_BASENAME}": "lib",
+            "${CLANG_RESOURCE_DIR}": "",
+            "${C_INCLUDE_DIRS}": "",
+        } |
+        cmakedefine_sunset("CLANG_CONFIG_FILE_SYSTEM_DIR") |
+        cmakedefine_sunset("CLANG_CONFIG_FILE_USER_DIR") |
+        {
+            "${DEFAULT_SYSROOT}": "",
+            "${GCC_INSTALL_PREFIX}": "",
+        } |
+        cmakedefine_vunset("CLANG_HAVE_LIBXML") |
+        cmakedefine(
+            "CLANG_HAVE_RLIMITS",
+            disable = "@platforms//os:windows",
+        ) |
+        cmakedefine_vset("CLANG_HAVE_DLFCN_H") |
+        cmakedefine_vset("CLANG_HAVE_DLADDR") |
+        cmakedefine_sunset("HOST_LINK_VERSION") |
+        cmakedefine_unset("ENABLE_LINKER_BUILD_ID") |
+        cmakedefine01_on("ENABLE_X86_RELAX_RELOCATIONS") |
+        cmakedefine01_off("PPC_LINUX_DEFAULT_IEEELONGDOUBLE") |
+        cmakedefine01_off("CLANG_ENABLE_OBJC_REWRITER") |
+        cmakedefine01_on("CLANG_ENABLE_STATIC_ANALYZER") |
+        cmakedefine01_off("CLANG_SPAWN_CC1") |
+        cmakedefine01_off("CLANG_ENABLE_CIR")
+    ),
+    template = "include/clang/Config/config.h.cmake",
+)
+
 cc_library(
     name = "config",
     hdrs = [

utils/bazel/llvm-project-overlay/config/BUILD.bazel

@@ -0,0 +1,177 @@
+# This file is licensed under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+"""Configurable build attributes for the overlay.
+
+To view the configurable build attributes in this file:
+
+    bazel query 'kind(".*_flag", @llvm-project//config:all)'
+"""
+
+load("@bazel_skylib//lib:selects.bzl", "selects")
+load("@bazel_skylib//rules:common_settings.bzl", "bool_flag", "string_flag")
+
+# Common config settings mapping to platform triples.
+#
+# See also: //platform:BUILD.bazel.
+#
+# TODO(aaronmondal): Add triples for more useful configurations as per
+#                   `llvm/include/llvm/TargetParser/Triple.h`.
+
+selects.config_setting_group(
+    name = "aarch64-apple-darwin",
+    match_all = [
+        "@platforms//cpu:aarch64",
+        "@platforms//os:macos",
+    ],
+)
+
+selects.config_setting_group(
+    name = "aarch64-unknown-linux-gnu",
+    match_all = [
+        "@platforms//cpu:aarch64",
+        "@platforms//os:linux",
+    ],
+)
+
+selects.config_setting_group(
+    name = "powerpc64le-unknown-linux-gnu",
+    match_all = [
+        "@platforms//cpu:ppc64le",
+        "@platforms//os:linux",
+    ],
+)
+
+selects.config_setting_group(
+    name = "systemz-unknown-linux_gnu",
+    match_all = [
+        "@platforms//cpu:s390x",
+        "@platforms//os:linux",
+    ],
+)
+
+# TODO(aaronmondal): Split this into `x86_64-pc-windows-gnu` and
+#                    `x86_64-pc-windows-msvc`.
+selects.config_setting_group(
+    name = "x86_64-pc-windows",
+    match_all = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:windows",
+    ],
+)
+
+selects.config_setting_group(
+    name = "x86_64-apple-darwin",
+    match_all = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:macos",
+    ],
+)
+
+selects.config_setting_group(
+    name = "x86_64-unknown-linux-gnu",
+    match_all = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:linux",
+    ],
+)
+
+# Useful helpers.
+
+selects.config_setting_group(
+    name = "posix",
+    match_any = [
+        "@platforms//os:linux",
+        "@platforms//os:macos",
+        "@platforms//os:freebsd",
+    ],
+)
+
+# Configurable build attributes for llvm.
+
+# These map to CMake `option` fields on a best-effort basis. The default maps to
+# CMake's `ON` or `OFF` value.
+[
+    (
+        bool_flag(
+            name = option,
+            build_setting_default = default,
+        ),
+        # Only define the opposite of the default value to reduce target count
+        # and prevent accidental default redeclarations.
+        #
+        # This also acts as a failsafe to prevent drift if a default is flipped
+        # as a changed default triggers straightfoward errors in all places
+        # where no longer existing config_settings need to be adjusted.
+        (
+            config_setting(
+                name = "{}_enabled".format(option),
+                flag_values = {":{}".format(option): "true"},
+            ) if not default else config_setting(
+                name = "{}_disabled".format(option),
+                flag_values = {":{}".format(option): "false"},
+            )
+        ),
+    )
+    for option, default in [
+        ("LLVM_ENABLE_BACKTRACES", True),
+        ("LLVM_ENABLE_CRASH_OVERRIDES", True),
+        ("LLVM_ENABLE_CRASH_DUMPS", False),
+
+        # These deviate slightly from CMake in that we use a boolean rather than
+        # ON/OFF/FORCE_ON since in Bazel ON collapses into FORCE_ON anyways.
+        ("LLVM_ENABLE_ZLIB", True),
+        ("LLVM_ENABLE_ZSTD", True),
+        ("LLVM_HAS_LOGF128", False),
+    ]
+]
+
+# Most builds expect this to be disabled by default but MinGW builds expect it
+# enabled by default. We handle this separately to clarify the intent that the
+# default is ambiguous.
+bool_flag(
+    name = "LLVM_WINDOWS_PREFER_FORWARD_SLASH",
+    build_setting_default = False,
+)
+
+config_setting(
+    name = "LLVM_WINDOWS_PREFER_FORWARD_SLASH_enabled",
+    flag_values = {":LLVM_WINDOWS_PREFER_FORWARD_SLASH": "true"},
+)
+
+config_setting(
+    name = "LLVM_WINDOWS_PREFER_FORWARD_SLASH_disabled",
+    flag_values = {":LLVM_WINDOWS_PREFER_FORWARD_SLASH": "false"},
+)
+
+string_flag(
+    name = "LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING",
+    build_setting_default = "DISABLED",
+    values = [
+        "COVERAGE",
+        "DISABLED",
+    ],
+)
+
+config_setting(
+    name = "LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING_coverage",
+    flag_values = {":LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING": "COVERAGE"},
+)
+
+bool_flag(
+    name = "LLVM_ENABLE_PLUGINS",
+    # TODO(aaronmondal): This should be enabled by default, but that currently
+    #                    breaks @llvm-project//llvm/unittests:analysis_tests.
+    build_setting_default = False,
+)
+
+config_setting(
+    name = "LLVM_ENABLE_PLUGINS_enabled",
+    flag_values = {":LLVM_ENABLE_PLUGINS": "true"},
+)
+
+config_setting(
+    name = "LLVM_ENABLE_PLUGINS_disabled",
+    flag_values = {":LLVM_ENABLE_PLUGINS": "false"},
+)