From afca066833c5844e24cfe3b6eb0d1c97d216facf Mon Sep 17 00:00:00 2001
From: syuilo <4439005+syuilo@users.noreply.github.com>
Date: Wed, 15 Jul 2026 21:22:28 +0900
Subject: [PATCH] fix(dev): clarify frontend chunk comparisons

---
 .github/scripts/frontend-js-size.mts      |  8 +++++++-
 .github/scripts/frontend-js-size.test.mts | 22 ++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/.github/scripts/frontend-js-size.mts b/.github/scripts/frontend-js-size.mts
index b4a61e659a..38c6fa07e9 100644
--- a/.github/scripts/frontend-js-size.mts
+++ b/.github/scripts/frontend-js-size.mts
@@ -414,6 +414,12 @@ function compareChunkComparisonRows(a: ReturnType<typeof getChunkComparisonRows>
 		|| a.name.localeCompare(b.name);
 }
 
+function chunkFileDisplay(row: ReturnType<typeof getChunkComparisonRows>[number]) {
+	if (row.beforeFile == null) return row.afterFile ?? '';
+	if (row.afterFile == null || row.beforeFile === row.afterFile) return row.beforeFile;
+	return `${row.beforeFile} → ${row.afterFile}`;
+}
+
 function chunkMarkdownTable(
 	rows: ReturnType<typeof getChunkComparisonRows>,
 	total?: { beforeSize: number; afterSize: number },
@@ -437,7 +443,7 @@ function chunkMarkdownTable(
 	if (hasSummaryRow && rows.length > 0) lines.push('| | | | | |');
 
 	for (const row of rows) {
-		const chunkFile = row.beforeFile ?? row.afterFile ?? '';
+		const chunkFile = chunkFileDisplay(row);
 		if (row.changeType === 'added') {
 			lines.push(`| <details><summary>\`${escapeCell(row.name)}\`</summary> \`${escapeCell(chunkFile)}\` </details> | ${util.formatBytes(row.beforeSize)} | ${util.formatBytes(row.afterSize)} | ${util.calcAndFormatDeltaBytes(row.beforeSize, row.afterSize, 1000)} | $\\color{orange}{\\text{( + )}}$ |`);
 		} else if (row.changeType === 'removed') {
diff --git a/.github/scripts/frontend-js-size.test.mts b/.github/scripts/frontend-js-size.test.mts
index 51b71c075f..3688948e94 100644
--- a/.github/scripts/frontend-js-size.test.mts
+++ b/.github/scripts/frontend-js-size.test.mts
@@ -83,3 +83,25 @@ test('groups generated chunks while preserving full and startup totals', async t
 	assert.match(report, /<summary>`src\/_boot_\.ts`<\/summary>/);
 	assert.match(report, /<summary>`vue`<\/summary>/);
 });
+
+test('fails instead of overwriting duplicate stable chunk keys', async t => {
+	const duplicateVue = fixture('before', 'dist', { entry: 100, generatedA: 10, generatedB: 20, vue: 40, i18n: 50 });
+	duplicateVue.manifest._vueDuplicate = { file: 'scripts/vue-duplicate-before.js', name: 'vue' };
+	duplicateVue.sizes['scripts/vue-duplicate-before.js'] = 60;
+
+	await assert.rejects(
+		runReport(t, duplicateVue, fixture('after', 'esm', { entry: 110, generatedA: 30, generatedB: 40, vue: 45, i18n: 50 })),
+		/Duplicate stable chunk key "named:vue".*vue-before\.js.*vue-duplicate-before\.js/,
+	);
+});
+
+test('shows both filenames for an updated stable chunk', async t => {
+	const report = await runReport(
+		t,
+		fixture('before', 'dist', { entry: 100, generatedA: 10, generatedB: 20, vue: 40, i18n: 50 }),
+		fixture('after', 'esm', { entry: 110, generatedA: 30, generatedB: 40, vue: 45, i18n: 50 }),
+	);
+
+	assert.match(report, /`ja-JP\/entry-before\.js → ja-JP\/entry-after\.js`/);
+	assert.match(report, /`ja-JP\/vue-before\.js → ja-JP\/vue-after\.js`/);
+});