Fix git configuration on Windows (#15814)

third_party/git/git_configure.bzl

@@ -1,4 +1,31 @@
-"""Repository rule for Git autoconfiguration."""
+"""Repository rule for Git autoconfiguration.
+
+`git_configure` depends on the following environment variables:
+
+  * `PYTHON_BIN_PATH`: location of python binary.
+"""
+
+_PYTHON_BIN_PATH = "PYTHON_BIN_PATH"
+
+def _fail(msg):
+  """Output failure message when auto configuration fails."""
+  red = "\033[0;31m"
+  no_color = "\033[0m"
+  fail("%sGit Configuration Error:%s %s\n" % (red, no_color, msg))
+
+def _get_python_bin(repository_ctx):
+  """Gets the python bin path."""
+  python_bin = repository_ctx.os.environ.get(_PYTHON_BIN_PATH)
+  if python_bin != None:
+    return python_bin
+  python_bin_path = repository_ctx.which("python")
+  if python_bin_path != None:
+    return str(python_bin_path)
+  _fail("Cannot find python in PATH, please make sure " +
+        "python is installed and add its directory in PATH, or --define " +
+        "%s='/something/else'.\nPATH=%s" % (
+            _PYTHON_BIN_PATH, repository_ctx.os.environ.get("PATH", "")))
+
 
 def _git_conf_impl(repository_ctx):
   repository_ctx.template(
@@ -11,10 +38,18 @@ def _git_conf_impl(repository_ctx):
       Label("@org_tensorflow//tensorflow/tools/git:gen_git_source.py"))
   generated_files_path = repository_ctx.path("gen")
 
-  repository_ctx.execute([
+  result = repository_ctx.execute([
+      _get_python_bin(repository_ctx),
       python_script_path, "--configure", tensorflow_root_path,
       "--gen_root_path", generated_files_path], quiet=False)
 
+  if not result.return_code == 0:
+    _fail(result.stderr)
+
+
 git_configure = repository_rule(
     implementation = _git_conf_impl,
+    environ = [
+        _PYTHON_BIN_PATH,
+    ],
 )