From 8dab33149a976d2155dbe87addfc56d4d852742e Mon Sep 17 00:00:00 2001
From: Daniel Roe <daniel@roe.dev>
Date: Tue, 25 Aug 2026 19:28:08 +0000
Subject: [PATCH] fix(pr): omit commits already released on a diverged branch

---
 scripts/update-changelog.ts   | 31 ++++++++++++++++++++++++++++++-
 test/update-changelog.test.ts | 26 +++++++++++++++++++++++++-
 2 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/scripts/update-changelog.ts b/scripts/update-changelog.ts
index 288e5d0..c7415f3 100644
--- a/scripts/update-changelog.ts
+++ b/scripts/update-changelog.ts
@@ -222,6 +222,33 @@ function parseCommit (raw: string): Commit | null {
   }
 }
 
+/**
+ * Drop commits whose subject already appears on the other side of a
+ * diverged range. The previous release tag is not always an ancestor of
+ * HEAD (a `4.x` maintenance line tagged after `main` moved on to `5.0`),
+ * so `tag..HEAD` includes everything since the branches diverged, most of
+ * which shipped already as cherry-picks. Subjects are matched exactly:
+ * a cherry-pick keeps its subject but not its hash or patch id.
+ */
+export function dropAlreadyReleased (commits: Commit[], releasedSubjects: Set<string>): Commit[] {
+  if (releasedSubjects.size === 0) return commits
+  return commits.filter(c => !releasedSubjects.has(c.message))
+}
+
+/** Subjects of commits reachable from `ref` but not from HEAD. */
+function subjectsOnlyOn (ref: string): Set<string> {
+  try {
+    const stdout = execFileSync(
+      'git',
+      ['log', `HEAD..${ref}`, '--pretty=format:%s'],
+      { encoding: 'utf8', maxBuffer: MAX_BUFFER },
+    )
+    return new Set(stdout.split('\n').map(s => s.trim()).filter(Boolean))
+  } catch {
+    return new Set()
+  }
+}
+
 function getCommitsSince (tag: Tag | null): Commit[] {
   const range = tag ? `${tag.ref}..HEAD` : 'HEAD'
   const stdout = execFileSync(
@@ -229,12 +256,14 @@ function getCommitsSince (tag: Tag | null): Commit[] {
     ['log', range, `--pretty=format:%H%x1f%h%x1f%an%x1f%ae%x1f%s%x1f%b%x1e`],
     { encoding: 'utf8', maxBuffer: MAX_BUFFER },
   )
-  return stdout
+  const commits = stdout
     .split('\x1e')
     .map(s => s.replace(/^\n/, ''))
     .filter(Boolean)
     .map(parseCommit)
     .filter((c): c is Commit => c !== null)
+
+  return tag ? dropAlreadyReleased(commits, subjectsOnlyOn(tag.ref)) : commits
 }
 
 export function determineBump (commits: Commit[]): BumpLevel {
diff --git a/test/update-changelog.test.ts b/test/update-changelog.test.ts
index 21ba228..931d358 100644
--- a/test/update-changelog.test.ts
+++ b/test/update-changelog.test.ts
@@ -3,7 +3,7 @@ import { tmpdir } from 'node:os'
 import { resolve } from 'node:path'
 import { afterEach, beforeEach, describe, expect, it } from 'vitest'
 
-import { buildBumpFileSet, buildIndependentBody, determineBump, formatChangelog, buildIndependentBumpFileSet, computeIndependentPlan, extractPreamble, truncateBody, incVersion, latestLockstepTag, latestTagForPackage, releaseBranchDrift, isSupersededReleaseBranch, type Commit } from '../scripts/update-changelog.ts'
+import { buildBumpFileSet, buildIndependentBody, determineBump, formatChangelog, buildIndependentBumpFileSet, computeIndependentPlan, extractPreamble, truncateBody, dropAlreadyReleased, incVersion, latestLockstepTag, latestTagForPackage, releaseBranchDrift, isSupersededReleaseBranch, type Commit } from '../scripts/update-changelog.ts'
 import { resolveWorkspaces } from '../scripts/_workspaces.ts'
 
 let tmp: string
@@ -515,6 +515,30 @@ describe('extractPreamble', () => {
   })
 })
 
+describe('dropAlreadyReleased', () => {
+  const commit = (message: string): Commit => ({
+    hash: message,
+    shortHash: message.slice(0, 7),
+    message,
+    type: 'fix',
+    scope: '',
+    description: message,
+    isBreaking: false,
+    author: { name: 'a', email: 'a@b.c' },
+    references: [],
+  })
+
+  it('omits commits whose subject shipped on the diverged branch', () => {
+    const commits = [commit('fix: a (#1)'), commit('fix: b (#2)')]
+    expect(dropAlreadyReleased(commits, new Set(['fix: a (#1)'])).map(c => c.message)).toEqual(['fix: b (#2)'])
+  })
+
+  it('is a no-op without diverged subjects', () => {
+    const commits = [commit('fix: a')]
+    expect(dropAlreadyReleased(commits, new Set())).toBe(commits)
+  })
+})
+
 describe('truncateBody', () => {
   it('leaves bodies within the limit untouched', () => {
     expect(truncateBody('short body')).toBe('short body')
-- 
2.51.2