Add bazel to the PATH in setup.py (#9590)

Co-authored-by: Mehrdad <noreply@github.com>

python/setup.py

@@ -1,6 +1,7 @@
 import argparse
 import glob
 import io
+import logging
 import os
 import re
 import shutil
@@ -16,6 +17,8 @@ import urllib.error
 import urllib.parse
 import urllib.request
 
+logger = logging.getLogger(__name__)
+
 # Ideally, we could include these files by putting them in a
 # MANIFEST.in or using the package_data argument to setup, but the
 # MANIFEST.in gets applied at the very beginning when setup.py runs
@@ -23,6 +26,7 @@ import urllib.request
 # manually.
 
 SUPPORTED_PYTHONS = [(3, 5), (3, 6), (3, 7), (3, 8)]
+SUPPORTED_BAZEL = (3, 2, 0)
 
 ROOT_DIR = os.path.dirname(__file__)
 BUILD_JAVA = os.getenv("RAY_INSTALL_JAVA") == "1"
@@ -129,6 +133,28 @@ def is_invalid_windows_platform():
     return platform == "msys" or (platform == "win32" and ver and "GCC" in ver)
 
 
+# Calls Bazel in PATH, falling back to the standard user installatation path
+# (~/.bazel/bin/bazel) if it isn't found.
+def bazel_invoke(invoker, cmdline, *args, **kwargs):
+    home = os.path.expanduser("~")
+    candidates = ["bazel"]
+    if sys.platform == "win32":
+        mingw_dir = os.getenv("MINGW_DIR")
+        if mingw_dir:
+            candidates.append(mingw_dir + "/bin/bazel.exe")
+    else:
+        candidates.append(os.path.join(home, ".bazel", "bin", "bazel"))
+    result = None
+    for i, cmd in enumerate(candidates):
+        try:
+            result = invoker([cmd] + cmdline, *args, **kwargs)
+            break
+        except IOError:
+            if i >= len(candidates) - 1:
+                raise
+    return result
+
+
 def download(url):
     try:
         result = urllib.request.urlopen(url).read()
@@ -221,12 +247,19 @@ def build(build_python, build_java):
             ] + pip_packages,
             env=dict(os.environ, CC="gcc"))
 
-    bazel = os.getenv("BAZEL_EXECUTABLE", "bazel")
+    version_info = bazel_invoke(subprocess.check_output, ["--version"])
+    bazel_version_str = version_info.rstrip().decode("utf-8").split(" ", 1)[1]
+    bazel_version = tuple(map(int, bazel_version_str.split(".")))
+    if bazel_version <= SUPPORTED_BAZEL:
+        logger.warning("Expected Bazel version {} but found {}",
+                       bazel_version, SUPPORTED_BAZEL)
+
     bazel_targets = []
     bazel_targets += ["//:ray_pkg"] if build_python else []
     bazel_targets += ["//java:ray_java_pkg"] if build_java else []
-    return subprocess.check_call(
-        [bazel, "build", "--verbose_failures", "--"] + bazel_targets,
+    return bazel_invoke(
+        subprocess.check_call,
+        ["build", "--verbose_failures", "--"] + bazel_targets,
         env=bazel_env)
 
 
@@ -318,7 +351,8 @@ def pip_run(build_ext):
 
 def api_main(program, *args):
     parser = argparse.ArgumentParser()
-    parser.add_argument("command", type=str, choices=["build", "help"])
+    choices = ["build", "bazel_version", "help"]
+    parser.add_argument("command", type=str, choices=choices)
     parser.add_argument(
         "-l",
         "--language",
@@ -341,6 +375,8 @@ def api_main(program, *args):
             else:
                 raise ValueError("invalid language: {!r}".format(lang))
         result = build(**kwargs)
+    elif parsed_args.command == "bazel_version":
+        print(".".join(map(str, SUPPORTED_BAZEL)))
     elif parsed_args.command == "help":
         parser.print_help()
     else: