Stamp bundle-size rows with the commit's timestamp, not the day they ran

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01171Lkmug15JzrcN2aMBLMk

.github/scripts/bundle-size-stats-prepare.ts

@@ -200,7 +200,9 @@ export function main() {
     // The last plotted point, as slim rows: [{ bundle, kind, rawBytes, gzipBytes, brotliBytes }].
     previous: readJson<CacheRow[]>(env.LAST) || [],
     threshold: Number(env.MIN_DELTA_PERCENT ?? 1),
-    date: new Date().toISOString().slice(0, 10), // YYYY-MM-DD
+    // The commit's own time rather than the day it was measured, so the merges
+    // of one day keep their order on the chart.
+    date: new Date(env.COMMIT_TIMESTAMP || Date.now()).toISOString(),
     commit: (env.HEAD_SHA || "").slice(0, 12),
     commitMessage: (env.COMMIT_MESSAGE || "").split("\n")[0], // subject line only
     version: readVersion(env.VERSION_PROPS),

.github/scripts/upload-bundle-load-stats.ts

@@ -31,16 +31,20 @@ interface Condition {
 interface CommitStamp {
   sha: string;
   subject: string;
+  /** ISO 8601, in UTC. */
+  timestamp: string;
 }
 
 type LoadTimeRow = Record<string, string | number>;
 
 function buildRows(
   conditions: Condition[],
-  { sha, subject }: CommitStamp,
+  { sha, subject, timestamp }: CommitStamp,
 ): LoadTimeRow[] {
   return conditions.map((condition) => ({
-    Date: new Date().toISOString().slice(0, 10),
+    // The commit's own time rather than the day it was measured, so the merges
+    // of one day keep their order and a backfilled row lands on its commit.
+    Date: timestamp,
     // Truncated the same way the bundle-size table does, so the two join.
     Commit: sha.slice(0, 12),
     // The stats table carries a free-text Description column. Populate it with
@@ -77,6 +81,7 @@ async function main() {
   const rows = buildRows(conditions, {
     sha: process.env.HEAD_SHA || "",
     subject: process.env.COMMIT_MESSAGE || "",
+    timestamp: new Date(process.env.COMMIT_TIMESTAMP || Date.now()).toISOString(),
   });
 
   console.table(rows);

.github/workflows/bundle-size-stats.yml

@@ -134,6 +134,7 @@ jobs:
           # Passed via env (not interpolated into the shell) so the commit
           # message can't inject commands; the script keeps only the subject.
           COMMIT_MESSAGE: ${{ github.event.workflow_run.head_commit.message }}
+          COMMIT_TIMESTAMP: ${{ github.event.workflow_run.head_commit.timestamp }}
         run: bun ./.github/scripts/bundle-size-stats-prepare.ts
       - name: Import sizes (with deltas) into Stats
         id: upload

.github/workflows/test.bundle-load-stats.yml

@@ -120,6 +120,7 @@ jobs:
           # Passed via env (not interpolated into the shell) so the commit
           # message can't inject commands; the script keeps only the subject.
           COMMIT_MESSAGE: ${{ github.event.workflow_run.head_commit.message }}
+          COMMIT_TIMESTAMP: ${{ github.event.workflow_run.head_commit.timestamp }}
           ENG_STATS_URL: ${{ secrets.ENG_STATS_URL }}
           API_KEY: ${{ secrets.ENG_STATS_API_KEY }}
         run: bun .github/scripts/upload-bundle-load-stats.ts