ci: omit unchanged bundle size scenarios

benchmarks/bundle-size/package.json

@@ -3,7 +3,8 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "build": "node ../../scripts/benchmarks/bundle-size/measure.mjs --skip-package-builds"
+    "build": "node ../../scripts/benchmarks/bundle-size/measure.mjs --skip-package-builds",
+    "test:unit": "node --test ../../scripts/benchmarks/bundle-size/pr-report.test.mjs"
   },
   "nx": {
     "targets": {
@@ -23,6 +24,14 @@
             "target": "build"
           }
         ]
+      },
+      "test:unit": {
+        "inputs": [
+          "default",
+          "^production",
+          "{workspaceRoot}/scripts/benchmarks/bundle-size/pr-report.mjs",
+          "{workspaceRoot}/scripts/benchmarks/bundle-size/pr-report.test.mjs"
+        ]
       }
     }
   },

scripts/benchmarks/bundle-size/pr-report.mjs

@@ -268,10 +268,16 @@ async function main() {
       ? resolveBaselineFromCurrentJson(baselineCurrent)
       : resolveBaselineFromHistory(historyEntries, args.baseSha)
 
+  const metrics = current.metrics || []
   const rows = []
 
-  for (const metric of current.metrics || []) {
+  for (const metric of metrics) {
     const baselineValue = baseline.benchesByName.get(metric.id)
+
+    if (Number.isFinite(baselineValue) && metric.gzipBytes === baselineValue) {
+      continue
+    }
+
     const historySeries = (seriesByScenario.get(metric.id) || []).slice(
       // Reserve one slot for the current metric so the sparkline stays at trendPoints.
       -args.trendPoints + 1,
@@ -290,6 +296,7 @@ async function main() {
       raw: metric.rawBytes,
       brotli: metric.brotliBytes,
       initial: metric.initialGzipBytes,
+      hasBaseline: Number.isFinite(baselineValue),
       deltaCell: formatDelta(metric.gzipBytes, baselineValue),
       trendCell: sparkline(historySeries.slice(-args.trendPoints)),
     })
@@ -299,30 +306,45 @@ async function main() {
   lines.push(args.marker)
   lines.push('## Bundle Size Benchmarks')
   lines.push('')
-  lines.push(`- Commit: \`${formatShortSha(current.sha)}\``)
-  lines.push(
-    `- Measured at: \`${current.measuredAt || current.generatedAt || 'unknown'}\``,
-  )
-  lines.push(`- Baseline source: \`${baseline.source}\``)
-  if (args.dashboardUrl) {
-    lines.push(`- Dashboard: [bundle-size history](${args.dashboardUrl})`)
-  }
-  lines.push('')
-  lines.push(
-    '| Scenario | Current (gzip) | Delta vs baseline | Initial gzip | Raw | Brotli | Trend |',
-  )
-  lines.push('| --- | ---: | ---: | ---: | ---: | ---: | --- |')
 
-  for (const row of rows) {
+  if (metrics.length > 0 && rows.length === 0) {
     lines.push(
-      `| \`${row.id}\` | ${formatBytes(row.current)} | ${row.deltaCell} | ${formatBytes(row.initial)} | ${formatBytes(row.raw)} | ${formatBytes(row.brotli)} | ${row.trendCell} |`,
+      'This pull request does not affect bundle size in any measured scenario.',
     )
-  }
+  } else if (metrics.length === 0) {
+    lines.push('No bundle-size scenarios were measured.')
+  } else {
+    lines.push(`- Commit: \`${formatShortSha(current.sha)}\``)
+    lines.push(
+      `- Measured at: \`${current.measuredAt || current.generatedAt || 'unknown'}\``,
+    )
+    lines.push(`- Baseline source: \`${baseline.source}\``)
+    if (args.dashboardUrl) {
+      lines.push(`- Dashboard: [bundle-size history](${args.dashboardUrl})`)
+    }
+    lines.push('')
+    lines.push(
+      rows.some((row) => !row.hasBaseline)
+        ? 'The following scenarios have bundle-size changes or lack baseline data for comparison:'
+        : 'The following scenarios have bundle-size changes compared with the baseline:',
+    )
+    lines.push('')
+    lines.push(
+      '| Scenario | Current (gzip) | Delta vs baseline | Initial gzip | Raw | Brotli | Trend |',
+    )
+    lines.push('| --- | ---: | ---: | ---: | ---: | ---: | --- |')
 
-  lines.push('')
-  lines.push(
-    '_Current gzip tracks all emitted client JS chunks. Initial gzip tracks only the entry/import graph. Trend sparkline is historical current gzip ending with this PR measurement; lower is better._',
-  )
+    for (const row of rows) {
+      lines.push(
+        `| \`${row.id}\` | ${formatBytes(row.current)} | ${row.deltaCell} | ${formatBytes(row.initial)} | ${formatBytes(row.raw)} | ${formatBytes(row.brotli)} | ${row.trendCell} |`,
+      )
+    }
+
+    lines.push('')
+    lines.push(
+      '_Current gzip tracks all emitted client JS chunks. Initial gzip tracks only the entry/import graph. Trend sparkline is historical current gzip ending with this PR measurement; lower is better._',
+    )
+  }
 
   const markdown = lines.join('\n') + '\n'
   await fsp.mkdir(path.dirname(outputPath), { recursive: true })

scripts/benchmarks/bundle-size/pr-report.test.mjs

@@ -0,0 +1,131 @@
+import assert from 'node:assert/strict'
+import { execFile } from 'node:child_process'
+import { promises as fs } from 'node:fs'
+import os from 'node:os'
+import path from 'node:path'
+import { promisify } from 'node:util'
+import test from 'node:test'
+
+const execFileAsync = promisify(execFile)
+const reportScript = new URL('./pr-report.mjs', import.meta.url)
+
+function metric(id, gzipBytes) {
+  return {
+    id,
+    gzipBytes,
+    rawBytes: gzipBytes * 3,
+    brotliBytes: gzipBytes - 100,
+    initialGzipBytes: gzipBytes - 10,
+  }
+}
+
+async function generateReport({ current, baseline, history, baseSha }) {
+  const fixtureDir = await fs.mkdtemp(
+    path.join(os.tmpdir(), 'bundle-size-pr-report-'),
+  )
+
+  try {
+    const currentPath = path.join(fixtureDir, 'current.json')
+    const outputPath = path.join(fixtureDir, 'report.md')
+    const args = [
+      reportScript.pathname,
+      '--current',
+      currentPath,
+      '--output',
+      outputPath,
+    ]
+
+    await fs.writeFile(currentPath, JSON.stringify(current))
+
+    if (baseline) {
+      const baselinePath = path.join(fixtureDir, 'baseline.json')
+      await fs.writeFile(baselinePath, JSON.stringify(baseline))
+      args.push('--baseline', baselinePath)
+    }
+
+    if (history) {
+      const historyPath = path.join(fixtureDir, 'history.json')
+      await fs.writeFile(historyPath, JSON.stringify(history))
+      args.push('--history', historyPath)
+    }
+
+    if (baseSha) {
+      args.push('--base-sha', baseSha)
+    }
+
+    await execFileAsync(process.execPath, args)
+    return await fs.readFile(outputPath, 'utf8')
+  } finally {
+    await fs.rm(fixtureDir, { recursive: true, force: true })
+  }
+}
+
+function currentJson(metrics) {
+  return {
+    benchmarkName: 'Bundle Size (gzip)',
+    measuredAt: '2026-07-19T09:45:56.787Z',
+    sha: '126aa13f296b1234',
+    metrics,
+  }
+}
+
+test('renders a concise message when no measured scenario changed', async () => {
+  const current = currentJson([metric('react-router.minimal', 1_000)])
+  const report = await generateReport({ current, baseline: current })
+
+  assert.equal(
+    report,
+    '<!-- bundle-size-benchmark -->\n## Bundle Size Benchmarks\n\nThis pull request does not affect bundle size in any measured scenario.\n',
+  )
+})
+
+test('renders only scenarios that changed against the historical baseline', async () => {
+  const current = currentJson([
+    metric('react-router.minimal', 1_000),
+    metric('react-router.full', 1_200),
+  ])
+  const history = {
+    entries: {
+      [current.benchmarkName]: [
+        {
+          commit: { id: 'baseline-sha' },
+          benches: [
+            { name: 'react-router.minimal', value: 1_000 },
+            { name: 'react-router.full', value: 1_100 },
+          ],
+        },
+      ],
+    },
+  }
+  const report = await generateReport({
+    current,
+    history,
+    baseSha: 'baseline-sha',
+  })
+
+  assert.match(
+    report,
+    /The following scenarios have bundle-size changes compared with the baseline:/,
+  )
+  assert.doesNotMatch(report, /`react-router\.minimal`/)
+  assert.match(
+    report,
+    /\| `react-router\.full` \| 1\.17 KiB \| \+100 B \(\+9\.09%\) \|/,
+  )
+})
+
+test('keeps scenarios that do not have baseline data visible', async () => {
+  const current = currentJson([
+    metric('react-router.minimal', 1_000),
+    metric('new-scenario', 900),
+  ])
+  const baseline = currentJson([metric('react-router.minimal', 1_000)])
+  const report = await generateReport({ current, baseline })
+
+  assert.match(
+    report,
+    /The following scenarios have bundle-size changes or lack baseline data for comparison:/,
+  )
+  assert.doesNotMatch(report, /`react-router\.minimal`/)
+  assert.match(report, /\| `new-scenario` \| 900 B \| n\/a \|/)
+})