Only run C++ build and test if C++ code has changed

Author: Scott Schneider

cpp/build-and-test.sh

@@ -1,15 +1,21 @@
 #!/bin/bash
 
 TARGETS="benchmark_driver benchmark_driver_stats ooo_adversary data_benchmark test dynamic_benchmark"
-FQDN_IMAGE="swag-builder-cpp"
+IMAGE="swag-builder-cpp"
 CWD="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
 
+# only proceed if this directory is in the latest commit
+if [ $(./can-skip.sh .) ]; then
+    echo "Skipping build and test for C++ code."
+    exit 0
+fi
+
 # build the docker image if not present
-[ ! -z $(docker images -q ${FQDN_IMAGE}) ]  || make -C ${CWD} builder-image
+[ ! -z $(docker images -q ${IMAGE}) ]  || make -C ${CWD} builder-image
 
 docker run -it \
        --user $(id -u):$(id -g) \
        -v ${CWD}:/stage \
-       ${FQDN_IMAGE} \
+       ${IMAGE} \
        bash -c "cd /stage; make ${TARGETS} && make zip && ./bin/test"
 

cpp/can-skip.sh

@@ -0,0 +1,26 @@
+#!/bin/bash
+
+# Determines if we can skip build and test based on the provided paths we care
+# about. If the provided paths DO NOT appear in the latest commits, then we can
+# skip build and test. We exit with 0 to indicate we can skip tests and 1 if 
+# we need to run tests. Based on:
+#     https://fant.io/p/circleci-early-exit/
+set -e
+
+PATHS_TO_SEARCH="$*"
+
+# an empty path trivially means we can skip build and tests
+if [ -z "$PATHS_TO_SEARCH" ]; then
+    exit 0
+fi
+
+LATEST_COMMIT=$(git rev-parse HEAD)
+LATEST_COMMIT_IN_PATH=$(git log -1 --format=format:%H --full-diff $PATHS_TO_SEARCH)
+
+# if the given path is not in the latest commit, then we can skip build and tests
+if [ $LATEST_COMMIT != $LATEST_COMMIT_IN_PATH ]; then
+    exit 0
+fi
+
+# we need to run the tests
+exit 1