1 files changed, 94 insertions, 0 deletions
diff --git a/nixpkgs/lib/fileset/benchmark.sh b/nixpkgs/lib/fileset/benchmark.sh
new file mode 100755
index 000000000000..f72686c4ab3f
--- /dev/null
+++ b/nixpkgs/lib/fileset/benchmark.sh
@@ -0,0 +1,94 @@
+#!/usr/bin/env bash
+
+# Benchmarks lib.fileset
+# Run:
+# [nixpkgs]$ lib/fileset/benchmark.sh HEAD
+
+set -euo pipefail
+shopt -s inherit_errexit dotglob
+
+if (( $# == 0 )); then
+    echo "Usage: $0 HEAD"
+    echo "Benchmarks the current tree against the HEAD commit. Any git ref will work."
+    exit 1
+fi
+compareTo=$1
+
+SCRIPT_FILE=$(readlink -f "${BASH_SOURCE[0]}")
+SCRIPT_DIR=$(dirname "$SCRIPT_FILE")
+
+nixpkgs=$(cd "$SCRIPT_DIR/../.."; pwd)
+
+tmp="$(mktemp -d)"
+clean_up() {
+    rm -rf "$tmp"
+}
+trap clean_up EXIT SIGINT SIGTERM
+work="$tmp/work"
+mkdir "$work"
+cd "$work"
+
+# Create a fairly populated tree
+touch f{0..5}
+mkdir d{0..5}
+mkdir e{0..5}
+touch d{0..5}/f{0..5}
+mkdir -p d{0..5}/d{0..5}
+mkdir -p e{0..5}/e{0..5}
+touch d{0..5}/d{0..5}/f{0..5}
+mkdir -p d{0..5}/d{0..5}/d{0..5}
+mkdir -p e{0..5}/e{0..5}/e{0..5}
+touch d{0..5}/d{0..5}/d{0..5}/f{0..5}
+mkdir -p d{0..5}/d{0..5}/d{0..5}/d{0..5}
+mkdir -p e{0..5}/e{0..5}/e{0..5}/e{0..5}
+touch d{0..5}/d{0..5}/d{0..5}/d{0..5}/f{0..5}
+
+bench() {
+    NIX_PATH=nixpkgs=$1 NIX_SHOW_STATS=1 NIX_SHOW_STATS_PATH=$tmp/stats.json \
+        nix-instantiate --eval --strict --show-trace >/dev/null \
+        --expr '(import <nixpkgs/lib>).fileset.toSource { root = ./.; fileset = ./.; }'
+    cat "$tmp/stats.json"
+}
+
+echo "Running benchmark on index" >&2
+bench "$nixpkgs" > "$tmp/new.json"
+(
+    echo "Checking out $compareTo" >&2
+    git -C "$nixpkgs" worktree add --quiet "$tmp/worktree" "$compareTo"
+    trap 'git -C "$nixpkgs" worktree remove "$tmp/worktree"' EXIT
+    echo "Running benchmark on $compareTo" >&2
+    bench "$tmp/worktree" > "$tmp/old.json"
+)
+
+declare -a stats=(
+    ".envs.elements"
+    ".envs.number"
+    ".gc.totalBytes"
+    ".list.concats"
+    ".list.elements"
+    ".nrFunctionCalls"
+    ".nrLookups"
+    ".nrOpUpdates"
+    ".nrPrimOpCalls"
+    ".nrThunks"
+    ".sets.elements"
+    ".sets.number"
+    ".symbols.number"
+    ".values.number"
+)
+
+different=0
+for stat in "${stats[@]}"; do
+    oldValue=$(jq "$stat" "$tmp/old.json")
+    newValue=$(jq "$stat" "$tmp/new.json")
+    if (( oldValue != newValue )); then
+        percent=$(bc <<< "scale=100; result = 100/$oldValue*$newValue; scale=4; result / 1")
+        if (( oldValue < newValue )); then
+            echo -e "Statistic $stat ($newValue) is \e[0;31m$percent% (+$(( newValue - oldValue )))\e[0m of the old value $oldValue" >&2
+        else
+            echo -e "Statistic $stat ($newValue) is \e[0;32m$percent% (-$(( oldValue - newValue )))\e[0m of the old value $oldValue" >&2
+        fi
+        (( different++ )) || true
+    fi
+done
+echo "$different stats differ between the current tree and $compareTo"