Allow to download clang and use clang for CPU builds.

Previously we only allowed to download clang when doing GPU builds.

The added skylark files use bazel's autoconf scripts, which were only added in
0.10.0. To provide nice error message for older versions of bazel
(i.e. 'version is less than 0.10' vs 'can't load @bazel_tools/cpp/...'), we
move the bazel version check into WORKSPACE file from workspace.bzl.

PiperOrigin-RevId: 190050798

1 files changed, 27 insertions, 0 deletions

diff --git a/third_party/clang_toolchain/cc_configure_clang.bzl b/third_party/clang_toolchain/cc_configure_clang.bzl
new file mode 100644
index 0000000000..1181110ea9
--- /dev/null
+++ b/third_party/clang_toolchain/cc_configure_clang.bzl
@@ -0,0 +1,27 @@
+""" Downloads clang and configures the crosstool using bazel's autoconf."""
+
+load("@bazel_tools//tools/cpp:cc_configure.bzl", "cc_autoconf_impl")
+load(":download_clang.bzl", "download_clang")
+
+_TF_DOWNLOAD_CLANG = "TF_DOWNLOAD_CLANG"
+_TF_NEED_CUDA = "TF_NEED_CUDA"
+
+def _cc_clang_autoconf(repo_ctx):
+  if repo_ctx.os.environ.get(_TF_DOWNLOAD_CLANG) != "1":
+    return
+  if repo_ctx.os.environ.get(_TF_NEED_CUDA) == "1":
+    # Clang is handled separately for CUDA configs.
+    # See cuda_configure.bzl for more details.
+    return
+
+  download_clang(repo_ctx, out_folder='extra_tools')
+  overriden_tools = {'gcc': 'extra_tools/bin/clang'}
+  cc_autoconf_impl(repo_ctx, overriden_tools)
+
+cc_download_clang_toolchain = repository_rule(
+    environ = [
+        _TF_DOWNLOAD_CLANG,
+        _TF_NEED_CUDA,
+    ],
+    implementation = _cc_clang_autoconf,
+)