devops(bots): let a publish-calls pull request go to a branch

.github/actions/publish-calls/calls.d.ts

@@ -88,6 +88,9 @@ export type PullRequest = Text & {
   repo: string;
   /** A new branch for the PR, such as "triage/<issue>/<run id>-<run attempt>". */
   branch: string;
+  /** The branch that the PR goes to. Leave it out for the default branch of the repo. The checkout
+   * of that repo must be on this branch, because the patch is against it. */
+  base?: string;
   /** The title of the commit and of the PR. */
   title: string;
   /** A patch file in $OUTPUT_DIR, against the commit of the checkout of that repo, such as

.github/actions/publish-calls/publish-calls.ts

@@ -83,7 +83,7 @@ const KINDS: Kind[] = ['pull-request', 'push', 'issue', 'comment', 'reply'];
 
 // The keys of each kind. A kind with text takes exactly one of body and bodyFile.
 const SCHEMA: { [K in Kind]: { required: KeysOf<K>[], optional: KeysOf<K>[], text: boolean } } = {
-  'pull-request': { required: ['repo', 'branch', 'title', 'patch'], optional: ['commitBody', 'labels'], text: true },
+  'pull-request': { required: ['repo', 'branch', 'title', 'patch'], optional: ['base', 'commitBody', 'labels'], text: true },
   'push': { required: ['repo', 'pullRequest', 'title', 'patch'], optional: ['commitBody', 'onto'], text: false },
   'issue': { required: ['repo', 'title'], optional: ['labels', 'filedFor'], text: true },
   'comment': { required: ['repo', 'issue'], optional: [], text: true },
@@ -156,7 +156,7 @@ async function publish({ github, context, core }: { github: GitHub, context: Con
           // The branch must be new, so that a mistake cannot push to main or to another branch.
           const cwd = checkoutOf(call.repo, repository);
           const commit = commitPatch({ cwd, patch: call.patch, title: call.title, body: call.commitBody, branch: call.branch, lease: '' });
-          const { data: { default_branch: base } } = await github.rest.repos.get({ owner, repo });
+          const base = call.base ?? (await github.rest.repos.get({ owner, repo })).data.default_branch;
           const { data: pr } = await github.rest.pulls.create({
             owner, repo, head: call.branch, base, title: call.title,
             body: call.body, draft: true,
@@ -315,9 +315,10 @@ function check(key: Key, value: unknown, dir: string): string | number | string[
         throw new Error(`title must be one line of 1 to ${MAX_TITLE} characters`);
       return value.trim();
     }
+    case 'base':
     case 'branch': {
       if (typeof value !== 'string' || !/^[A-Za-z0-9][A-Za-z0-9._/-]{0,199}$/.test(value) || value.includes('..') || value.endsWith('/') || value.endsWith('.lock'))
-        throw new Error(`branch must be a branch name, such as triage/123/456-1, got ${JSON.stringify(value)}`);
+        throw new Error(`${key} must be a branch name, such as triage/123/456-1, got ${JSON.stringify(value)}`);
       return value;
     }
     case 'onto': {

.github/workflows/bots.md

@@ -91,7 +91,7 @@ checks in `publish-calls.ts` are written by hand; keep them in line with `calls.
 
 | Call | Keys | What `publish-calls` does |
 |---|---|---|
-| `pull-request` | `repo`, `branch`, `title`, `patch`, `body` or `bodyFile`, `commitBody`, `labels` | Applies the patch to the checkout with `git apply --index`, rejects a patch that touches `.github/`, commits as the app, pushes to the branch, which must not exist yet, and opens a draft PR on the default branch with the labels that the repo has. |
+| `pull-request` | `repo`, `branch`, `base`, `title`, `patch`, `body` or `bodyFile`, `commitBody`, `labels` | Applies the patch to the checkout with `git apply --index`, rejects a patch that touches `.github/`, commits as the app, pushes to the branch, which must not exist yet, and opens a draft PR on `base`, or on the default branch without it, with the labels that the repo has. |
 | `push` | `repo`, `pullRequest`, `title`, `patch`, `commitBody`, `onto` | Checks that the PR is open and comes from a branch of the repo, and pushes to that branch. With `onto`, the patch is the whole PR against that commit: the PR is replayed on it and the branch is replaced. The push fails when the branch moved since the checkout. |
 | `issue` | `repo`, `title`, `body` or `bodyFile`, `labels`, `filedFor` | Uses an open issue whose text has the `filedFor` URL, or files one with the labels that the repo has. |
 | `comment` | `repo`, `issue`, `body` or `bodyFile` | Posts the text, with `{{pull-request}}` and `{{issue}}` replaced by the URLs of what the calls before it opened, or by a note when they failed. |