Add a helper script to run `git bisect` over the Bazel source code

Tests by running Bazel commands in the current working directory.

Change-Id: I0352e206a57e677b1c87e1c842a62ca1d3558bc3

Closes #4729.

Change-Id: Ib44810ebce596e4d40786e087f57e61971e87d25
PiperOrigin-RevId: 187214804

1 files changed, 90 insertions, 0 deletions

diff --git a/scripts/bazel-bisect.sh b/scripts/bazel-bisect.sh
new file mode 100644
index 0000000000..57b8bd23b8
--- /dev/null
+++ b/scripts/bazel-bisect.sh
@@ -0,0 +1,90 @@
+#!/bin/bash
+#
+# Copyright 2018 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+set -eu
+
+USAGE='bazel-bisect.sh GOOD_COMMIT BAD_COMMIT [<bazel arguments>...]'
+DESCRIPTION='
+  Downloads a fresh copy of the Bazel source and runs git bisect from the
+  specified commits, testing by running the given bazel command in the
+  current working directory.'
+
+function usage() {
+  echo "$USAGE" "$DESCRIPTION" >&2
+}
+
+# Configuration params. Export these in your bashrc to set personal defaults.
+
+# The source of Bazel code.
+BAZEL_REPO=${BAZEL_REPO:-https://github.com/bazelbuild/bazel}
+# Where to keep the Bazel repository. If you make changes here, be warned that
+# this script may overwrite or lose them.
+BAZEL_DIR=${BAZEL_DIR:-$HOME/os-bazel-bisect}
+# Bazel to use to build local bazel binaries.
+BAZEL_BINARY=${BAZEL_BINARY:-$(which bazel)}
+
+# Collect the arguments.
+if [ "$#" -lt 3 ]; then
+  usage
+  exit 1
+fi
+
+# Collect the arguments.
+#
+GOOD_COMMIT="$1"
+shift
+BAD_COMMIT="$1"
+shift
+BAZEL_ARGUMENTS="$@"
+
+echo "Bisecting bazel from good $GOOD_COMMIT to bad $BAD_COMMIT: bazel $BAZEL_ARGUMENTS"
+
+# Check out and update Bazel.
+if [ ! -d "$BAZEL_DIR" ]; then
+  git clone "$BAZEL_REPO" "$BAZEL_DIR"
+fi
+# Ensure the repository is up to date.
+(
+  cd "$BAZEL_DIR"
+  git fetch --tags
+  git checkout master
+)
+
+# Run the actual bisect.
+WORKING_DIR="$PWD"
+(
+  BISECT_SCRIPT=/tmp/bisect.sh
+  TMP_BIN=/tmp/bazel.bisect
+
+  cat >$BISECT_SCRIPT <<EOF
+#!/bin/bash
+set -eu
+"$BAZEL_BINARY" build //src:bazel || exit 1
+cp -f bazel-bin/src/bazel $TMP_BIN
+cd "$WORKING_DIR"
+exec "$TMP_BIN" $BAZEL_ARGUMENTS
+EOF
+  chmod +x "$BISECT_SCRIPT"
+  cd "$BAZEL_DIR"
+  git bisect start
+  git bisect good "$GOOD_COMMIT"
+  git bisect bad  "$BAD_COMMIT"
+  result=0
+  git bisect run "$BISECT_SCRIPT" || result=$?
+  git bisect reset
+  exit $result
+)