CI: Track SWC native binary size in PR stats comment (#92938)

### What?

Adds a new "Native Binary" section to the `Stats from current PR`
comment posted by the `generate-pull-request-stats` GitHub Action. The
section reports the size of the SWC native binary
(`packages/next-swc/native/*.node`) built for the PR and the change
relative to the latest value recorded on `canary`.

Example row:

> | Metric | Canary | PR | Change | Trend |
> |:-------|-------:|---:|-------:|:-----:|
> | SWC Binary Size | 113 MB | 121 MB | 🔴 +7.34 MB (+6%) | ▁▃▅▇█ |

### Why?

The `.node` binary is a sizable, user-facing artifact (it ships with
`next`). Today there's no visibility on its size in PRs, so regressions
from Rust/Cargo changes are easy to miss. Surfacing the size (and a diff
vs. canary) in the existing stats comment gives immediate feedback on
any change that affects the binary.

### How?

- **Measurement
(`.github/actions/next-stats-action/src/run/index.js`):** After the
action copies the pre-built native binary into the working dirs, sum the
size of every `*.node` file under the action's `native/` directory and
store it as `General.swcBinarySize` on both the canary and PR stat sets.
- **Canary baseline via KV history
(`.github/actions/next-stats-action/src/add-comment.js`):** The workflow
downloads a single pre-built binary and copies it into both the canary
and PR checkouts, so an in-run diff would always be zero. Instead, for
PR runs we override `mainRepoStats.General.swcBinarySize` with the most
recent `swcBinarySize` from the Vercel KV history (the same store
already used for other canary metrics). Canary runs keep the measured
value, and the existing persistence path (`saveToHistory` / `General`)
writes it back so future PRs see an updated baseline. If no history
exists yet, the Canary column renders `N/A` and no change is shown.
- **Rendering:** New `generateNativeBinarySection` emits a
`<details>`-wrapped section styled like Bundle Sizes / All Metrics,
rendered right after the Bundle Sizes block. It reuses `prettify`,
`formatChange`, and `generateTrendBar` so formatting, thresholds, and
sparklines are consistent with the rest of the comment. A tight
threshold entry (`swcBinarySize: { absoluteMin: 10 KB, percentMin: 0.5%,
percentOnly: 0.05% }`) is added so meaningful movement is flagged while
tiny determinism noise is ignored.
- **Top-line summary:** Because `swcBinarySize` lives on `General`, the
existing `generateChangeSummary` automatically promotes significant
changes into the headline regression/improvement table at the top of the
comment, using the label `SWC Binary Size`.
- **Sharded runs:** The workflow runs two sharded jobs (Webpack and
Turbopack). The binary is bundler-independent, so both shards report the
same value; `aggregate-results.js` merges `General` via `Object.assign`,
which is correct here (last-writer-wins on an identical value).

No workflow changes are required — the existing `pull_request_stats.yml`
already downloads the `next-swc-binary` artifact and copies it into the
action's `native/` directory.

### Verification

Smoke-tested `add-comment.js` locally with `LOCAL_STATS=1` in two
scenarios:

- No KV history configured → Canary column renders `N/A`, PR value
renders, Change is `-`, section still shown.
- Mocked KV history containing prior `swcBinarySize` values → full diff
rendered in both the Native Binary section and the top-level
significance summary, with a sparkline of the last 5 historical entries.

Closes NEXT-

<!-- NEXT_JS_LLM_PR -->

---------

Co-authored-by: Tobias Koppers <sokra@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>

Author: sokra

.github/actions/next-stats-action/src/add-comment.js

@@ -55,6 +55,7 @@ const METRIC_LABELS = {
   buildDurationCachedTurbo: 'Turbo Build Time (cached)',
   // General metrics
   nodeModulesSize: 'node_modules Size',
+  swcBinarySize: 'SWC Binary Size',
 }
 
 // Group configuration for organizing the comment
@@ -209,6 +210,10 @@ const METRIC_THRESHOLDS = {
   // <10KB AND <1%, OR <0.01%
   nodeModulesSize: { absoluteMin: 10240, percentMin: 1, percentOnly: 0.01 },
 
+  // SWC native binary (~tens of MB): deterministic, but smaller baseline
+  // <10KB AND <0.5%, OR <0.05%
+  swcBinarySize: { absoluteMin: 10240, percentMin: 0.5, percentOnly: 0.05 },
+
   // Bundle sizes (KB-MB): deterministic
   // <2KB AND <1%, OR <0.1%
   bytes: { absoluteMin: 2048, percentMin: 1, percentOnly: 0.1 },
@@ -973,6 +978,57 @@ function generateDiffsSection(result) {
   return content
 }
 
+// Find the most recent value for a metric in the KV history.
+function getLatestHistoricalValue(history, metricKey) {
+  if (!history?.entries?.length) return undefined
+  for (let i = history.entries.length - 1; i >= 0; i--) {
+    const val = history.entries[i].metrics?.[metricKey]
+    if (typeof val === 'number') return val
+  }
+  return undefined
+}
+
+// Generate the dedicated Native Binary section shown after Bundle Sizes.
+function generateNativeBinarySection(mainStats, diffStats, history) {
+  const mainGeneral = mainStats?.General || {}
+  const diffGeneral = diffStats?.General || {}
+
+  const mainVal = mainGeneral.swcBinarySize
+  const diffVal = diffGeneral.swcBinarySize
+
+  // Nothing to show if we don't have any measurement
+  if (typeof mainVal !== 'number' && typeof diffVal !== 'number') return ''
+
+  const mainStr = prettify(mainVal, 'bytes')
+  const diffStr = prettify(diffVal, 'bytes')
+  const change = formatChange(mainVal, diffVal, 'bytes', 'swcBinarySize')
+  const histValues = getHistoricalValues(history, 'swcBinarySize')
+  const sparkline = generateTrendBar(histValues)
+
+  const hasTrend = Boolean(sparkline)
+  const header = hasTrend
+    ? `| Metric | Canary | PR | Change | Trend |
+|:-------|-------:|---:|-------:|:-----:|`
+    : `| Metric | Canary | PR | Change |
+|:-------|-------:|---:|-------:|`
+
+  const row = hasTrend
+    ? `| SWC Binary Size | ${mainStr} | ${diffStr} | ${change.text} | ${sparkline} |`
+    : `| SWC Binary Size | ${mainStr} | ${diffStr} | ${change.text} |`
+
+  return `<details>
+<summary><strong>🦀 Native Binary</strong></summary>
+
+Size of the native SWC binary (\`packages/next-swc/native/*.node\`). The Canary column is the most recent value recorded on the canary branch.
+
+${header}
+${row}
+
+</details>
+
+`
+}
+
 function generatePrTarballSection(actionInfo) {
   if (actionInfo.isRelease || !actionInfo.githubHeadSha) return ''
 
@@ -1016,6 +1072,24 @@ module.exports = async function addComment(
     const result = results[i]
     const isLastResult = i === results.length - 1
 
+    // The native SWC binary is shared between the canary and PR checkouts in
+    // a single run (the workflow downloads it once and copies it into both),
+    // so the in-run "canary" value is identical to the PR value. Override the
+    // canary baseline with the last recorded value from KV history so the
+    // diff is meaningful. Canary runs skip this and keep the measured value.
+    if (!actionInfo.isRelease && result.mainRepoStats?.General) {
+      const historicalSwcSize = getLatestHistoricalValue(
+        history,
+        'swcBinarySize'
+      )
+      if (typeof historicalSwcSize === 'number') {
+        result.mainRepoStats.General.swcBinarySize = historicalSwcSize
+      } else {
+        // No history yet — hide the canary value so the table renders N/A
+        delete result.mainRepoStats.General.swcBinarySize
+      }
+    }
+
     // Add summary showing only significant changes (not collapsed)
     if (i === 0) {
       comment += generateChangeSummary(
@@ -1041,6 +1115,13 @@ module.exports = async function addComment(
       comment += `<details>\n<summary><strong>📦 Bundle Sizes</strong></summary>\n\n${bundleSection}</details>\n\n`
     }
 
+    // Add native binary size section (not collapsed, small)
+    comment += generateNativeBinarySection(
+      result.mainRepoStats,
+      result.diffRepoStats,
+      history
+    )
+
     // Add diffs (already collapsed)
     comment += generateDiffsSection(result)
 

.github/actions/next-stats-action/src/run/index.js

@@ -9,6 +9,32 @@ const collectDiffs = require('./collect-diffs')
 const { statsAppDir, diffRepoDir } = require('../constants')
 const { calcStats } = require('../util/stats')
 
+// Location of the native binary that the workflow copies into the action dir.
+// From src/run/index.js → .github/actions/next-stats-action/native
+const nativeBinaryDir = path.join(__dirname, '../../native')
+
+// Sum the size of all *.node files in the action's native/ directory.
+async function getSwcBinarySize() {
+  try {
+    const entries = await fs.readdir(nativeBinaryDir)
+    let total = 0
+    let found = 0
+    for (const entry of entries) {
+      if (!entry.endsWith('.node')) continue
+      const stat = await fs.stat(path.join(nativeBinaryDir, entry))
+      if (stat.isFile()) {
+        total += stat.size
+        found++
+      }
+    }
+    if (found === 0) return null
+    return total
+  } catch (err) {
+    logger(`Unable to measure SWC binary size: ${err.message}`)
+    return null
+  }
+}
+
 // Number of iterations for build benchmarks to get stable median
 const BUILD_BENCHMARK_ITERATIONS = 5
 
@@ -57,6 +83,7 @@ async function runConfigs(
       let curStats = {
         General: {
           nodeModulesSize: null,
+          swcBinarySize: null,
         },
       }
 
@@ -83,6 +110,7 @@ async function runConfigs(
         curStats.General.nodeModulesSize = await getDirSize(
           path.join(statsAppDir, 'node_modules')
         )
+        curStats.General.swcBinarySize = await getSwcBinarySize()
       }
 
       // Run builds for selected bundler(s) and collect stats separately