benchmark: show helpful errors w/o local repo

When running without a local test repository, show a helpful error
message.

Author: ethomson

tests/benchmarks/benchmark_helpers.sh

@@ -21,6 +21,9 @@ else
 	OUTPUT_STYLE="auto"
 fi
 
+HELP_GIT_REMOTE="https://github.com/git/git"
+HELP_LINUX_REMOTE="https://github.com/torvalds/linux"
+
 #
 # parse the arguments to the outer script that's including us; these are arguments that
 # the `benchmark.sh` passes (or that a user could specify when running an individual test)
@@ -384,3 +387,27 @@ gitbench() {
 	hyperfine "${ARGUMENTS[@]}"
 	rm -rf "${SANDBOX_DIR:?}"
 }
+
+# helper script to give useful error messages about configuration
+needs_repo() {
+	REPO="${1}"
+
+	if [ "${REPO}" = "" ]; then
+		echo "usage: needs_repo <repo>" 1>&2
+		exit 1
+	fi
+
+	REPO_UPPER=$(echo "${1}" | tr '[:lower:]' '[:upper:]')
+	REPO_URL=$(eval echo "\${BENCHMARK_${REPO_UPPER}_REPOSITORY}")
+	REPO_REMOTE_URL=$(eval echo "\${HELP_${REPO_UPPER}_REMOTE}")
+
+	if [ "${REPO_URL}" = "" ]; then
+		echo "$0: '${REPO}' repository not configured" 1>&2
+		echo "" 1>&2
+		echo "This benchmark needs an on-disk '${REPO}' repository. First, clone the" 1>&2
+		echo "remote repository ('${REPO_REMOTE_URL}') locally then set," 1>&2
+		echo "the 'BENCHMARK_${REPO_UPPER}_REPOSITORY' environment variable to the path that" 1>&2
+		echo "contains the repository locally, then run this benchmark again." 1>&2
+		exit 1
+	fi
+}

tests/benchmarks/blame__git_cached

@@ -2,6 +2,8 @@
 
 . "$(dirname "$0")/benchmark_helpers.sh"
 
+needs_repo git
+
 gitbench --prepare "clone_repo git && cd git && git reset --hard v2.45.0" \
          --warmup 5 \
          --chdir "git" \

tests/benchmarks/blame__linux_cached

@@ -2,6 +2,8 @@
 
 . "$(dirname "$0")/benchmark_helpers.sh"
 
+needs_repo linux
+
 gitbench --prepare "clone_repo linux && cd linux && git reset --hard v6.9" \
          --warmup 5 \
          --chdir "linux" \