Use cc_toolchain_* for clang shipped with Swift toolchain

MODULE.bazel

@@ -19,6 +19,7 @@ use_repo(
     non_module_deps,
     "build_bazel_rules_swift_index_import",
     "build_bazel_rules_swift_local_config",
+    "build_bazel_rules_swift_cc_toolchain",
     "com_github_apple_swift_log",
     "com_github_apple_swift_nio",
     "com_github_apple_swift_nio_extras",
@@ -33,3 +34,5 @@ use_repo(apple_cc_configure, "local_config_apple_cc")
 
 # Dev dependencies
 bazel_dep(name = "stardoc", version = "0.5.3", dev_dependency = True, repo_name = "io_bazel_stardoc")
+
+register_toolchains("@build_bazel_rules_swift_cc_toolchain//:all")

swift/internal/linking.bzl

@@ -107,7 +107,7 @@ into the binary. Possible values are:
             # Do not add references; temporary attribute for C++ toolchain
             # Starlark migration.
             "_cc_toolchain": attr.label(
-                default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
+                default = Label("@build_bazel_rules_swift_local_config//:current_swift_cc_toolchain"),
             ),
             # A late-bound attribute denoting the value of the `--custom_malloc`
             # command line flag (or None if the flag is not provided).

swift/internal/swift_autoconfiguration.bzl

@@ -24,6 +24,7 @@ should be loaded here. Do not load anything else, even common libraries like
 Skylib.
 """
 
+load("@bazel_tools//tools/cpp:unix_cc_configure.bzl", "configure_unix_toolchain")
 load(
     "@build_bazel_rules_swift//swift/internal:feature_names.bzl",
     "SWIFT_FEATURE_CODEVIEW_DEBUG_INFO",
@@ -241,6 +242,7 @@ def _create_linux_toolchain(repository_ctx):
     if not path_to_swiftc:
         fail("No 'swiftc' executable found in $PATH")
 
+    toolchain_root = path_to_swiftc.dirname
     root = path_to_swiftc.dirname.dirname
     feature_values = _compute_feature_values(repository_ctx, path_to_swiftc)
     version_file = _write_swift_version(repository_ctx, path_to_swiftc)
@@ -255,13 +257,105 @@ def _create_linux_toolchain(repository_ctx):
     repository_ctx.file(
         "BUILD",
         """
+load("@bazel_tools//tools/cpp:unix_cc_toolchain_config.bzl", "cc_toolchain_config")
 load(
     "@build_bazel_rules_swift//swift/internal:swift_toolchain.bzl",
     "swift_toolchain",
 )
 
 package(default_visibility = ["//visibility:public"])
 
+cc_toolchain_config(
+    name = "swift_cc_toolchain_config",
+    cpu = "{cpu}",
+    compiler = "clang",
+    toolchain_identifier = "swift-cc-local",
+    host_system_name = "local",
+    target_system_name = "local",
+    target_libc = "local",
+    abi_version = "local",
+    abi_libc_version = "local",
+    cxx_builtin_include_directories = [],
+    tool_paths = {{
+        "ar": "{toolchain_root}/llvm-ar",
+        "ld": "{toolchain_root}/lld",
+        "llvm-cov": "{toolchain_root}/bin/llvm-cov",
+        "llvm-profdata": "{toolchain_root}/bin/llvm-profdata",
+        "cpp": "{toolchain_root}/clang-cpp",
+        "gcc": "{toolchain_root}/clang",
+        "dwp": "/usr/bin/dwp",
+        "gcov": "/usr/bin/gcov",
+        "nm": "/usr/bin/nm",
+        "objcopy": "/usr/bin/objcopy",
+        "objdump": "/usr/bin/objdump",
+        "strip": "/usr/bin/strip",
+    }},
+    compile_flags = [
+        "-fstack-protector",
+        "-Wall",
+        "-Wthread-safety",
+        "-Wself-assign",
+        "-Wunused-but-set-parameter",
+        "-Wno-free-nonheap-object",
+        "-fcolor-diagnostics",
+        "-fno-omit-frame-pointer",
+    ],
+    opt_compile_flags = [
+        "-g0",
+        "-O2",
+        "-D_FORTIFY_SOURCE=1",
+        "-DNDEBUG",
+        "-ffunction-sections",
+        "-fdata-sections",
+    ],
+    dbg_compile_flags = ["-g"],
+    cxx_flags = ["-std=c++0x"],
+    link_flags = [
+        "-Wl,-no-as-needed",
+        "-Wl,-z,relro,-z,now",
+        "-B/usr/local",
+    ],
+    link_libs = [
+        "-lstdc++",
+        "-lm",
+    ],
+    opt_link_flags = ["-Wl,--gc-sections"],
+    unfiltered_compile_flags = [
+        "-fno-canonical-system-headers",
+        "-Wno-builtin-macro-redefined",
+        "-D__DATE__=redacted",
+        "-D__TIMESTAMP__=redacted",
+        "-D__TIME__=redacted",
+    ],
+    coverage_compile_flags = ["--coverage"],
+    coverage_link_flags = ["--coverage"],
+    supports_start_end_lib = False,
+)
+
+filegroup(
+    name = "empty"
+)
+
+cc_toolchain(
+    name = "swift_cc_toolchain",
+    toolchain_identifier = "swift-cc-toolchain",
+    toolchain_config = ":swift_cc_toolchain_config",
+    all_files = ":empty",
+    compiler_files = ":empty",
+    dwp_files = ":empty",
+    linker_files = ":empty",
+    objcopy_files = ":empty",
+    strip_files = ":empty",
+    supports_param_files = 0,
+)
+
+cc_toolchain_suite(
+    name = "current_swift_cc_toolchain",
+    toolchains = {{
+        "k8": ":swift_cc_toolchain",
+    }}
+)
+
 swift_toolchain(
     name = "toolchain",
     arch = "{cpu}",
@@ -277,6 +371,7 @@ swift_toolchain(
                 for feature in feature_values
             ]),
             root = root,
+            toolchain_root = toolchain_root,
             version_file = version_file,
         ),
     )
@@ -392,6 +487,20 @@ swift_toolchain(
         ),
     )
 
+def _swift_cc_toolchain_impl(repository_ctx):
+    cpu = _normalized_linux_cpu(repository_ctx.os.arch)
+    path_to_swiftc = repository_ctx.which("swiftc")
+    if not path_to_swiftc:
+        fail("No 'swiftc' executable found in $PATH")
+
+    root = path_to_swiftc.dirname.dirname
+
+swift_cc_toolchain = repository_rule(
+    environ = ["PATH"],
+    implementation = _swift_cc_toolchain_impl,
+    local = True,
+)
+
 def _swift_autoconfiguration_impl(repository_ctx):
     # TODO(allevato): This is expedient and fragile. Use the
     # platforms/toolchains APIs instead to define proper toolchains, and make it

swift/internal/swift_import.bzl

@@ -172,7 +172,7 @@ The `.swiftmodule` file provided to Swift targets that depend on this target.
                 mandatory = False,
             ),
             "_cc_toolchain": attr.label(
-                default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
+                default = Label("@build_bazel_rules_swift_local_config//:current_swift_cc_toolchain"),
                 doc = """\
 The C++ toolchain from which linking flags and other tools needed by the Swift
 toolchain (such as `clang`) will be retrieved.

swift/internal/swift_toolchain.bzl

@@ -272,11 +272,6 @@ def _swift_toolchain_impl(ctx):
     toolchain_root = ctx.attr.root
     cc_toolchain = find_cpp_toolchain(ctx)
 
-    if cc_toolchain.compiler != "clang":
-        fail("Swift requires the configured CC toolchain to be LLVM (clang). " +
-             "Either use the locally installed LLVM by setting `CC=clang` in your environment " +
-             "before invoking Bazel, or configure a Bazel LLVM CC toolchain.")
-
     if ctx.attr.os == "windows":
         swift_linkopts_cc_info = _swift_windows_linkopts_cc_info(
             ctx.attr.arch,
@@ -437,7 +432,7 @@ configuration options that are applied to targets on a per-package basis.
                 allow_single_file = True,
             ),
             "_cc_toolchain": attr.label(
-                default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
+                default = Label("@build_bazel_rules_swift_local_config//:current_swift_cc_toolchain"),
                 doc = """\
 The C++ toolchain from which other tools needed by the Swift toolchain (such as
 `clang` and `ar`) will be retrieved.

swift/internal/xcode_swift_toolchain.bzl

@@ -779,7 +779,7 @@ configuration options that are applied to targets on a per-package basis.
                 providers = [[SwiftPackageConfigurationInfo]],
             ),
             "_cc_toolchain": attr.label(
-                default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
+                default = Label("@build_bazel_rules_swift_local_config//:current_swift_cc_toolchain"),
                 doc = """\
 The C++ toolchain from which linking flags and other tools needed by the Swift
 toolchain (such as `clang`) will be retrieved.

swift/repositories.bzl

@@ -18,6 +18,7 @@ load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 load(
     "@build_bazel_rules_swift//swift/internal:swift_autoconfiguration.bzl",
     "swift_autoconfiguration",
+    "swift_cc_toolchain",
 )
 
 def _maybe(repo_rule, name, **kwargs):