Merge "download_file: download to GERRIT_CACHE_HOME when set" into stable-3.1

Documentation/dev-bazel.txt

diff --git a/Documentation/dev-bazel.txt b/Documentation/dev-bazel.txt
index 782aba0..2a8b7c1 100644
--- a/Documentation/dev-bazel.txt
+++ b/Documentation/dev-bazel.txt
@@ -495,6 +495,10 @@
 * ~/.gerritcodereview/bazel-cache/repository
 * ~/.gerritcodereview/bazel-cache/cas
 
+The `downloaded-artifacts` cache can be relocated by setting the
+`GERRIT_CACHE_HOME` environment variable. The other two can be adjusted with
+`bazel build` options `--repository_cache` and `--disk_cache` respectively.
+
 Currently none of these caches have a maximum size limit. See
 link:https://github.com/bazelbuild/bazel/issues/5139[this bazel issue] for
 details. Users should watch the cache sizes and clean them manually if

tools/download_file.py

diff --git a/tools/download_file.py b/tools/download_file.py
index f86fd3e..936bcef 100755
--- a/tools/download_file.py
+++ b/tools/download_file.py
@@ -17,7 +17,7 @@
 
 import argparse
 from hashlib import sha1
-from os import link, makedirs, path, remove
+from os import environ, link, makedirs, path, remove
 import shutil
 from subprocess import check_call, CalledProcessError
 from sys import stderr
@@ -25,7 +25,10 @@
 from zipfile import ZipFile, BadZipfile, LargeZipFile
 
 GERRIT_HOME = path.expanduser('~/.gerritcodereview')
-CACHE_DIR = path.join(GERRIT_HOME, 'bazel-cache', 'downloaded-artifacts')
+CACHE_DIR = environ.get(
+    'GERRIT_CACHE_HOME',
+    path.join(GERRIT_HOME, 'bazel-cache', 'downloaded-artifacts'))
+
 LOCAL_PROPERTIES = 'local.properties'