From bf2bb5261cf84958c295dd74e763837e2c021fd8 Mon Sep 17 00:00:00 2001
From: Stephan Renatus <stephan.renatus@gmail.com>
Date: Tue, 23 Jun 2026 12:04:13 +0200
Subject: [PATCH] benchmarks: split off script, emit markdown table

Follow-up to #8811.

Signed-off-by: Stephan Renatus <stephan.renatus@gmail.com>
---
 .github/workflows/benchmarks.yaml | 45 ++-----------------------
 build/bench-comment.sh            | 56 +++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 42 deletions(-)
 create mode 100755 build/bench-comment.sh

diff --git a/.github/workflows/benchmarks.yaml b/.github/workflows/benchmarks.yaml
index 62074e2ff7..4fe2f7c2cc 100644
--- a/.github/workflows/benchmarks.yaml
+++ b/.github/workflows/benchmarks.yaml
@@ -101,53 +101,14 @@ jobs:
           go-version-file: .go-version
       - name: Install tools
         run: cd build/tools && go install tool
-      - name: Run benchmarks
-        env:
-          BEFORE_SHA: ${{ github.event.before }}
-          AFTER_SHA: ${{ github.event.after }}
-          BENCH_PKGS: ${{ needs.check-changes.outputs.bench }}
-        run: |
-          for pkg in $(echo "$BENCH_PKGS" | jq -r '.[]'); do
-            benchlab \
-              -commit "$BEFORE_SHA","$AFTER_SHA" \
-              -pkg "$pkg" \
-              -host local:tags=opa_wasm \
-              -reps 3 \
-              -benchtime 300ms \
-              -run '^$'
-          done
-      - name: Comment on PR with benchmark results
+      - name: Run benchmarks and comment on PR
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           COMMIT_SHA: ${{ github.sha }}
           BEFORE_SHA: ${{ github.event.before }}
           AFTER_SHA: ${{ github.event.after }}
-        run: |
-          PR_NUMBER=$(gh pr list --search "${COMMIT_SHA}" --state merged --json number --jq '.[0].number')
-
-          if [ -z "$PR_NUMBER" ] || [ "$PR_NUMBER" = "null" ]; then
-            echo "Could not find originating PR for commit ${COMMIT_SHA}"
-            exit 0
-          fi
-
-          {
-            echo "<details><summary>Benchmark Comparison (\`${BEFORE_SHA}\` vs \`${AFTER_SHA}\`)</summary>"
-            echo ""
-            echo '```'
-            # Each benchstat file ends with a compact benchmark × host delta table;
-            # extract from that header line onward so the comment stays readable.
-            for f in .benchlab/benchstat.*.txt; do
-              awk '/^benchmark \\ host/{found=1} found{print}' "$f"
-              echo ""
-            done
-            echo '```'
-            echo ""
-            echo "</details>"
-            echo ""
-            echo "_This comment was automatically generated by the benchmarks workflow._"
-          } > body.md
-
-          gh pr comment "${PR_NUMBER}" --body-file body.md
+          BENCH_PKGS: ${{ needs.check-changes.outputs.bench }}
+        run: bash build/bench-comment.sh
 
   notebook:
     permissions:
diff --git a/build/bench-comment.sh b/build/bench-comment.sh
new file mode 100755
index 0000000000..c66be4a9f1
--- /dev/null
+++ b/build/bench-comment.sh
@@ -0,0 +1,56 @@
+#!/usr/bin/env bash
+# Run benchlab comparisons and post (or print) a markdown PR comment.
+#
+# Required env vars:
+#   BEFORE_SHA   base commit
+#   AFTER_SHA    head commit
+#   BENCH_PKGS   JSON array of Go package paths, e.g. '["./topdown","./ast"]'
+#
+# Optional (needed to post a PR comment):
+#   GH_TOKEN     GitHub token with pull-requests:write
+#   COMMIT_SHA   the merge commit SHA used to look up the PR
+set -euo pipefail
+
+: "${BEFORE_SHA:?}"
+: "${AFTER_SHA:?}"
+: "${BENCH_PKGS:?}"
+
+for pkg in $(echo "$BENCH_PKGS" | jq -r '.[]'); do
+  benchlab \
+    -commit "$BEFORE_SHA","$AFTER_SHA" \
+    -pkg "$pkg" \
+    -host local:tags=opa_wasm \
+    -reps 3 \
+    -benchtime 300ms \
+    -run '^$'
+done
+
+body() {
+  echo "<details><summary>Benchmark Comparison (\`${BEFORE_SHA}\` vs \`${AFTER_SHA}\`)</summary>"
+  echo ""
+  for f in .benchlab/benchstat.*.txt; do
+    awk '
+      /^benchmark \\ host/ { found=1; print "| benchmark | delta |"; print "| --- | --- |"; next }
+      found && $2 ~ /^[+-]/ {
+        val = $2; for (i = 3; i <= NF; i++) val = val " " $i
+        print "| " $1 " | " val " |"
+      }
+    ' "$f"
+    echo ""
+  done
+  echo "</details>"
+  echo ""
+  echo "_This comment was automatically generated by the benchmarks workflow._"
+}
+
+if [ -n "${GH_TOKEN:-}" ] && [ -n "${COMMIT_SHA:-}" ]; then
+  PR_NUMBER=$(gh pr list --search "${COMMIT_SHA}" --state merged --json number --jq '.[0].number')
+  if [ -z "$PR_NUMBER" ] || [ "$PR_NUMBER" = "null" ]; then
+    echo "Could not find originating PR for commit ${COMMIT_SHA}"
+    exit 0
+  fi
+  body > body.md
+  gh pr comment "${PR_NUMBER}" --body-file body.md
+else
+  body
+fi