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, 48 insertions, 0 deletions

diff --git a/tensorflow/version_check.bzl b/tensorflow/version_check.bzl
new file mode 100644
index 0000000000..79e721dab4
--- /dev/null
+++ b/tensorflow/version_check.bzl
@@ -0,0 +1,48 @@
+""" Helpers to check minimum version of bazel."""
+
+def _extract_version_number(bazel_version):
+  """Extracts the semantic version number from a version string
+
+  Args:
+    bazel_version: the version string that begins with the semantic version
+      e.g. "1.2.3rc1 abc1234" where "abc1234" is a commit hash.
+
+  Returns:
+    The semantic version string, like "1.2.3".
+  """
+  for i in range(len(bazel_version)):
+    c = bazel_version[i]
+    if not (c.isdigit() or c == "."):
+      return bazel_version[:i]
+  return bazel_version
+
+# Parse the bazel version string from `native.bazel_version`.
+# e.g.
+# "0.10.0rc1 abc123d" => (0, 10, 0)
+# "0.3.0" => (0, 3, 0)
+def _parse_bazel_version(bazel_version):
+  """Parses a version string into a 3-tuple of ints
+
+  int tuples can be compared directly using binary operators (<, >).
+
+  Args:
+    bazel_version: the Bazel version string
+
+  Returns:
+    An int 3-tuple of a (major, minor, patch) version.
+  """
+
+  version = _extract_version_number(bazel_version)
+  return tuple([int(n) for n in version.split(".")])
+
+def check_bazel_version_at_least(minimum_bazel_version):
+  if "bazel_version" not in dir(native):
+    fail("\nCurrent Bazel version is lower than 0.2.1, expected at least %s\n" % minimum_bazel_version)
+  elif not native.bazel_version:
+    print("\nCurrent Bazel is not a release version, cannot check for compatibility.")
+    print("Make sure that you are running at least Bazel %s.\n" % minimum_bazel_version)
+    return
+
+  if _parse_bazel_version(native.bazel_version) < _parse_bazel_version(minimum_bazel_version):
+    fail("\nCurrent Bazel version is {}, expected at least {}\n".format(
+        native.bazel_version, minimum_bazel_version))