docs-update: Switch to using a separate repo for creating the commits.

src/github.rs

@@ -1499,6 +1499,23 @@ impl Repository {
         issue.pull_request = Some(PullRequestDetails {});
         Ok(issue)
     }
+
+    /// Synchronize a branch (in a forked repository) by pulling in its upstream contents.
+    pub async fn merge_upstream(&self, client: &GithubClient, branch: &str) -> anyhow::Result<()> {
+        let url = format!("{}/merge-upstream", self.url());
+        client
+            ._send_req(client.post(&url).json(&serde_json::json!({
+                "branch": branch,
+            })))
+            .await
+            .with_context(|| {
+                format!(
+                    "{} failed to merge upstream branch {branch}",
+                    self.full_name
+                )
+            })?;
+        Ok(())
+    }
 }
 
 pub struct Query<'a> {

src/handlers/docs_update.rs

@@ -9,6 +9,11 @@ use reqwest::Client;
 use std::fmt::Write;
 use std::str::FromStr;
 
+/// This is the repository where the commits will be created.
+const WORK_REPO: &str = "rustbot/rust";
+/// This is the repository where the PR will be created.
+const DEST_REPO: &str = "rust-lang/rust";
+/// This is the branch in `WORK_REPO` to create the commits.
 const BRANCH_NAME: &str = "docs-update";
 
 const SUBMODULES: &[&str] = &[
@@ -56,16 +61,19 @@ pub async fn handle_job() -> Result<()> {
 
 async fn docs_update() -> Result<()> {
     let gh = GithubClient::new_with_default_token(Client::new());
-    let repo = gh.repository("rust-lang/rust").await?;
+    let work_repo = gh.repository(WORK_REPO).await?;
+    work_repo
+        .merge_upstream(&gh, &work_repo.default_branch)
+        .await?;
 
-    let updates = get_submodule_updates(&gh, &repo).await?;
+    let updates = get_submodule_updates(&gh, &work_repo).await?;
     if updates.is_empty() {
         tracing::trace!("no updates this week?");
         return Ok(());
     }
 
-    create_commit(&gh, &repo, &updates).await?;
-    create_pr(&gh, &repo, &updates).await?;
+    create_commit(&gh, &work_repo, &updates).await?;
+    create_pr(&gh, &updates).await?;
     Ok(())
 }
 
@@ -176,14 +184,17 @@ async fn create_commit(
     Ok(())
 }
 
-async fn create_pr(gh: &GithubClient, rust_repo: &Repository, updates: &[Update]) -> Result<()> {
+async fn create_pr(gh: &GithubClient, updates: &[Update]) -> Result<()> {
+    let dest_repo = gh.repository(DEST_REPO).await?;
     let mut body = String::new();
     for update in updates {
         write!(body, "{}\n", update.pr_body).unwrap();
     }
 
-    let pr = rust_repo
-        .new_pr(gh, TITLE, BRANCH_NAME, &rust_repo.default_branch, &body)
+    let username = WORK_REPO.split('/').next().unwrap();
+    let head = format!("{username}:{BRANCH_NAME}");
+    let pr = dest_repo
+        .new_pr(gh, TITLE, &head, &dest_repo.default_branch, &body)
         .await?;
     tracing::debug!("created PR {}", pr.html_url);
     Ok(())