From 0f5921479d9add7c5066e3aed538926b22c28d91 Mon Sep 17 00:00:00 2001
From: Daniel Roe <daniel@roe.dev>
Date: Tue, 25 Aug 2026 19:36:58 +0000
Subject: [PATCH] fix(pr): cut the commit range at the previous tag's date

---
 scripts/update-changelog.ts        | 15 ++++++++++++++-
 test/update-changelog-main.test.ts | 22 ++++++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/scripts/update-changelog.ts b/scripts/update-changelog.ts
index c7415f3..874af8f 100644
--- a/scripts/update-changelog.ts
+++ b/scripts/update-changelog.ts
@@ -249,11 +249,24 @@ function subjectsOnlyOn (ref: string): Set<string> {
   }
 }
 
+/** Committer date of the commit a tag points at, as an ISO 8601 string. */
+function tagDate (ref: string): string | null {
+  try {
+    return execFileSync('git', ['log', '-1', '--format=%cI', ref], { encoding: 'utf8', maxBuffer: MAX_BUFFER }).trim() || null
+  } catch {
+    return null
+  }
+}
+
 function getCommitsSince (tag: Tag | null): Commit[] {
   const range = tag ? `${tag.ref}..HEAD` : 'HEAD'
+  // Merging the base branch into a release branch (or a tag that isn't an
+  // ancestor of HEAD) puts commits older than the tag inside `tag..HEAD`;
+  // they shipped in an earlier release, so cut the range at the tag's date.
+  const since = tag ? tagDate(tag.ref) : null
   const stdout = execFileSync(
     'git',
-    ['log', range, `--pretty=format:%H%x1f%h%x1f%an%x1f%ae%x1f%s%x1f%b%x1e`],
+    ['log', range, ...(since ? ['--since', since] : []), `--pretty=format:%H%x1f%h%x1f%an%x1f%ae%x1f%s%x1f%b%x1e`],
     { encoding: 'utf8', maxBuffer: MAX_BUFFER },
   )
   const commits = stdout
diff --git a/test/update-changelog-main.test.ts b/test/update-changelog-main.test.ts
index 053667a..01e20ea 100644
--- a/test/update-changelog-main.test.ts
+++ b/test/update-changelog-main.test.ts
@@ -51,6 +51,7 @@ const git = {
   tags: [] as string[],
   commits: [] as FakeCommit[],
   revList: [] as string[],
+  divergedSubjects: [] as string[],
   remote: 'git@github.com:owner/repo.git',
   branch: 'main',
 }
@@ -85,6 +86,7 @@ function stubGit () {
     if (sub === 'rev-parse') return args.includes('--abbrev-ref') ? git.branch : HEAD_SHA
     if (sub === 'rev-list') return git.revList.join('\n')
     if (sub === 'log' && args[1] === '-1') return '2024-01-01T00:00:00Z'
+    if (sub === 'log' && args.includes('--pretty=format:%s')) return git.divergedSubjects.join('\n')
     if (sub === 'log') return record(...git.commits)
     throw new Error(`unexpected git call: ${args.join(' ')}`)
   })
@@ -213,6 +215,7 @@ beforeEach(() => {
   git.tags = ['v1.2.3']
   git.commits = [FEAT]
   git.revList = [FEAT.hash]
+  git.divergedSubjects = []
   git.remote = 'git@github.com:owner/repo.git'
   git.branch = 'main'
 
@@ -255,6 +258,25 @@ describe('lockstep main', () => {
     expect(prBody()).toContain('- Ada (@ada)')
   })
 
+  it('omits commits already released on the diverged branch', async () => {
+    const other: FakeCommit = { hash: 'b'.repeat(40), short: 'bbbbbbb', name: 'Bo', email: 'bo@example.com', subject: 'fix: cherry-picked (#8)' }
+    git.commits = [FEAT, other]
+    git.revList = [FEAT.hash, other.hash]
+    api.logins = new Map([['aaaaaaa', 'ada'], ['bbbbbbb', 'bo']])
+    git.divergedSubjects = [other.subject]
+    await main()
+    expect(prBody()).toContain('- add a thing (#7)')
+    expect(prBody()).not.toContain('cherry-picked')
+  })
+
+  it('cuts the commit range at the date of the previous tag', async () => {
+    await main()
+    const calls = execFileSync.mock.calls as Array<[string, string[]]>
+    const args = calls.find(([, args]) => args[0] === 'log' && args[1] === 'refs/tags/v1.2.3..HEAD')![1]
+    expect(args).toContain('--since')
+    expect(args[args.indexOf('--since') + 1]).toBe('2024-01-01T00:00:00Z')
+  })
+
   it('skips when HEAD is the merge of a release PR', async () => {
     api.prsForHead = [{ head: { ref: 'release/v1.2.3' }, merged_at: '2024-01-01T00:00:00Z' }]
     await main()
-- 
2.51.2