ci/github-script/commits: allow reason for not cherry-picking (#433387)

ci/github-script/check-cherry-picks.md

@@ -1,10 +0,0 @@
-This report is automatically generated by the `PR / Check / cherry-pick` CI workflow.
-
-Some of the commits in this PR require the author's and reviewer's attention.
-
-Please follow the [backporting guidelines](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md#how-to-backport-pull-requests) and cherry-pick with the `-x` flag.
-This requires changes to the unstable `master` and `staging` branches first, before backporting them.
-
-Occasionally, it is not possible to cherry-pick exactly the same patch.
-This most frequently happens when resolving merge conflicts or when updating minor versions of packages which have already advanced to the next major on unstable.
-If you need to merge this PR despite the warnings, please [dismiss](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/dismissing-a-pull-request-review) this review shortly before merging.

ci/github-script/commits.js

@@ -23,21 +23,35 @@ module.exports = async function ({ github, context, core, dry }) {
         pull_number
 
     async function extract({ sha, commit }) {
+      const noCherryPick = Array.from(
+        commit.message.matchAll(/^Not-cherry-picked-because: (.*)$/g)
+      ).at(0)
+
+      if (noCherryPick)
+        return {
+          sha,
+          commit,
+          severity: 'important',
+          message: `${sha} is not a cherry-pick, because: ${noCherryPick[1]}. Please review this commit manually.`,
+          type: 'no-cherry-pick',
+        }
+
       // Using the last line with "cherry" + hash, because a chained backport
       // can result in multiple of those lines. Only the last one counts.
-      const match = Array.from(
+      const cherry = Array.from(
         commit.message.matchAll(/cherry.*([0-9a-f]{40})/g),
       ).at(-1)
 
-      if (!match)
+      if (!cherry)
         return {
           sha,
           commit,
           severity: 'warning',
           message: `Couldn't locate original commit hash in message of ${sha}.`,
+          type: 'no-commit-hash',
         }
 
-      const original_sha = match[1]
+      const original_sha = cherry[1]
 
       let branches
       try {
@@ -121,6 +135,7 @@ module.exports = async function ({ github, context, core, dry }) {
         colored_diff,
         severity: 'warning',
         message: `Difference between ${sha} and original ${original_sha} may warrant inspection.`,
+        type: 'diff',
       }
     }
 
@@ -202,10 +217,29 @@ module.exports = async function ({ github, context, core, dry }) {
     if (results.some(({ severity }) => severity == 'error'))
       process.exitCode = 1
 
-    core.summary.addRaw(
-      await readFile(join(__dirname, 'check-cherry-picks.md'), 'utf-8'),
-      true,
-    )
+    core.summary.addRaw('This report is automatically generated by the `PR / Check / cherry-pick` CI workflow.', true)
+    core.summary.addEOL()
+    core.summary.addRaw("Some of the commits in this PR require the author's and reviewer's attention.", true)
+    core.summary.addEOL()
+
+    if (results.some(({ type }) => type === 'no-commit-hash')) {
+      core.summary.addRaw('Please follow the [backporting guidelines](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md#how-to-backport-pull-requests) and cherry-pick with the `-x` flag.', true)
+      core.summary.addRaw('This requires changes to the unstable `master` and `staging` branches first, before backporting them.', true)
+      core.summary.addEOL()
+      core.summary.addRaw('Occasionally, commits are not cherry-picked at all, for example when updating minor versions of packages which have already advanced to the next major on unstable.', true)
+      core.summary.addRaw('These commits can optionally be marked with a `Not-cherry-picked-because: <reason>` footer.', true)
+      core.summary.addEOL()
+    }
+
+    if (results.some(({ type }) => type === 'diff')) {
+      core.summary.addRaw('Sometimes it is not possible to cherry-pick exactly the same patch.', true)
+      core.summary.addRaw('This most frequently happens when resolving merge conflicts.', true)
+      core.summary.addRaw('The range-diff will help to review the resolution of conflicts.', true)
+      core.summary.addEOL()
+    }
+
+    core.summary.addRaw('If you need to merge this PR despite the warnings, please [dismiss](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/dismissing-a-pull-request-review) this review shortly before merging.', true)
+
     results.forEach(({ severity, message, diff }) => {
       if (severity == 'info') return
 
@@ -222,7 +256,7 @@ module.exports = async function ({ github, context, core, dry }) {
       // Whether this is intended or just an implementation detail is unclear.
       core.summary.addRaw('<blockquote>')
       core.summary.addRaw(
-        `\n\n[!${severity == 'warning' ? 'WARNING' : 'CAUTION'}]`,
+        `\n\n[!${({ important: 'IMPORTANT', warning: 'WARNING', error: 'CAUTION' })[severity]}]`,
         true,
       )
       core.summary.addRaw(`${message}`, true)