3 files changed, 81 insertions, 0 deletions
diff --git a/third_party/clang_toolchain/BUILD b/third_party/clang_toolchain/BUILD
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/third_party/clang_toolchain/BUILD
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,
+)
diff --git a/third_party/clang_toolchain/download_clang.bzl b/third_party/clang_toolchain/download_clang.bzl
new file mode 100644
index 0000000000..54d383d7d7
--- /dev/null
+++ b/third_party/clang_toolchain/download_clang.bzl
@@ -0,0 +1,54 @@
+""" Helpers to download a recent clang release."""
+
+def _get_platform_folder(os_name):
+  os_name = os_name.lower()
+  if os_name.startswith('windows'):
+    return 'Win'
+  if os_name.startswith('mac os'):
+    return 'Mac'
+  if not os_name.startswith('linux'):
+    fail('Unknown platform')
+  return 'Linux_x64'
+
+def _download_chromium_clang(repo_ctx, platform_folder, package_version, sha256,
+                             out_folder):
+  cds_url = 'https://commondatastorage.googleapis.com/chromium-browser-clang'
+  cds_file = 'clang-%s.tgz' % package_version
+  cds_full_url = '{0}/{1}/{2}'.format(cds_url, platform_folder, cds_file)
+  repo_ctx.download_and_extract(cds_full_url, output=out_folder, sha256=sha256)
+
+def download_clang(repo_ctx, out_folder):
+  """ Download a fresh clang release and put it into out_folder.
+
+  Clang itself will be located in 'out_folder/bin/clang'.
+  We currently download one of the latest releases of clang by the
+  Chromium project (see
+  https://chromium.googlesource.com/chromium/src/+/master/docs/clang.md).
+
+  Args:
+    repo_ctx: An instance of repository_context object.
+    out_folder: A folder to extract the compiler into.
+  """
+  # TODO(ibiryukov): we currently download and extract some extra tools in the
+  # clang release (e.g., sanitizers). We should probably remove the ones
+  # we don't need and document the ones we want provide in addition to clang.
+
+  # Latest CLANG_REVISION and CLANG_SUB_REVISION of the Chromiums's release
+  # can be found in https://chromium.googlesource.com/chromium/src/tools/clang/+/master/scripts/update.py
+  CLANG_REVISION = '321529'
+  CLANG_SUB_REVISION = 2
+
+  package_version = '%s-%s' % (CLANG_REVISION, CLANG_SUB_REVISION)
+
+  checksums = {
+      'Linux_x64':
+          '76d4eb1ad011e3127c4a9de9b9f5d4ac624b5a9395c4d7395c9e0a487b13daf6',
+      'Mac':
+          '4b2a7a65ac1ee892b318c723eec8771f514bb306f346aa8216bb0006f19d87b7',
+      'Win':
+          'eba51bb8f84af41a85903113666bd21c22709010c39c4cb19dc20cf1ed14581b',
+  }
+
+  platform_folder = _get_platform_folder(repo_ctx.os.name)
+  _download_chromium_clang(repo_ctx, platform_folder, package_version,
+                           checksums[platform_folder], out_folder)