cmd/dist: allow builders to control granularity of test/ directory sharding

Even with 10 shards on builders, it still takes about ~2.5 minutes per
shard (and getting slower all the time as the test/ directory grows).
I'm currently experimenting with massively sharding out testing on
Cloud Run (each dist test & normal TestFoo func all running in
parallel), and in such a setup, 2.5 minutes is an eternity. I'd like
to increase that dist test's sharding from 10 to more like 1,000.

Updates golang/go#31834

Change-Id: I8b02989727793b5b5b2013d67e1eb01ef4786e28
Reviewed-on: https://go-review.googlesource.com/c/go/+/175297
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/run.bash b/src/run.bash
index 1acd0194b6..e18540c990 100755
--- a/src/run.bash
+++ b/src/run.bash
@@ -3,6 +3,17 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
+# Environment variables that control run.bash:
+#
+# GO_TEST_SHARDS: number of "dist test" test shards that the
+# $GOROOT/test directory will be sliced up into for parallel
+# execution. Defaults to 1, unless GO_BUILDER_NAME is also specified,
+# in which case it defaults to 10.
+#
+# GO_BUILDER_NAME: the name of the Go builder that's running the tests.
+# Some tests are conditionally enabled or disabled based on the builder
+# name or the builder name being non-empty.
+
 set -e
 
 eval $(go env)