accept backports from zulip

This patch adds a new Zulip command:
`@triagebot backport <channel> <action> <PR>`

Example:
- `@triagebot backport stable accept 123456`
- `@triagebot backport beta decline 654321`

This can be used to post on GitHub a comment when T-compiler accepts/decline to backport a patch that fixes a regression.

Limitations:
- This command assumes PRs in the `rust-lang/rust` repository
- There is no check on the PR number (in case of mistypes, the comment will go elsewhere)

Author: apiraino

src/zulip.rs

@@ -17,20 +17,47 @@ use crate::utils::pluralize;
 use crate::zulip::api::{MessageApiResponse, Recipient};
 use crate::zulip::client::ZulipClient;
 use crate::zulip::commands::{
-    ChatCommand, LookupCmd, PingGoalsArgs, StreamCommand, WorkqueueCmd, WorkqueueLimit, parse_cli,
+    BackportChannelArgs, BackportVerbArgs, ChatCommand, LookupCmd, PingGoalsArgs, StreamCommand,
+    WorkqueueCmd, WorkqueueLimit, parse_cli,
 };
 use anyhow::{Context as _, format_err};
 use axum::Json;
 use axum::extract::State;
 use axum::extract::rejection::JsonRejection;
 use axum::response::IntoResponse;
+use commands::BackportArgs;
 use itertools::Itertools;
+use octocrab::Octocrab;
 use rust_team_data::v1::{TeamKind, TeamMember};
 use std::cmp::Reverse;
 use std::fmt::Write as _;
 use std::sync::Arc;
 use subtle::ConstantTimeEq;
-use tracing as log;
+use tracing::log;
+
+fn get_text_backport_approved(
+    channel: &BackportChannelArgs,
+    verb: &BackportVerbArgs,
+    zulip_link: &str,
+) -> String {
+    format!("
+{channel:?} backport {verb:?} as per compiler team [on Zulip]({zulip_link}). A backport PR will be authored by the release team at the end of the current development cycle. Backport labels handled by them.
+
+@rustbot label +{channel:?}-accepted")
+}
+
+fn get_text_backport_declined(
+    channel: &BackportChannelArgs,
+    verb: &BackportVerbArgs,
+    zulip_link: &str,
+) -> String {
+    format!(
+        "
+{channel:?} backport {verb:?} as per compiler team [on Zulip]({zulip_link}).
+
+@rustbot label -{channel:?}-nominated"
+    )
+}
 
 #[derive(Debug, serde::Deserialize)]
 pub struct Request {
@@ -296,10 +323,68 @@ async fn handle_command<'a>(
                 .map_err(|e| format_err!("Failed to await at this time: {e:?}")),
             StreamCommand::PingGoals(args) => ping_goals_cmd(ctx, gh_id, message_data, &args).await,
             StreamCommand::DocsUpdate => trigger_docs_update(message_data, &ctx.zulip),
+            StreamCommand::Backport(args) => {
+                accept_decline_backport(message_data, &ctx.octocrab, &ctx.zulip, &args).await
+            }
         }
     }
 }
 
+// TODO: shorter variant of this command (f.e. `backport accept` or even `accept`) that infers everything from the Message payload
+async fn accept_decline_backport(
+    message_data: &Message,
+    octo_client: &Octocrab,
+    zulip_client: &ZulipClient,
+    args_data: &BackportArgs,
+) -> anyhow::Result<Option<String>> {
+    let message = message_data.clone();
+    let args = args_data.clone();
+    let stream_id = message.stream_id.unwrap();
+    let subject = message.subject.unwrap();
+    let octo_client = octo_client.clone();
+
+    // Repository owner and name are hardcoded
+    // This command is only used in this repository
+    let repo_owner = "rust-lang";
+    let repo_name = "rust";
+
+    // TODO: factor out the Zulip "URL encoder" to make it practical to use
+    let zulip_send_req = crate::zulip::MessageApiRequest {
+        recipient: Recipient::Stream {
+            id: stream_id,
+            topic: &subject,
+        },
+        content: "",
+    };
+
+    // NOTE: the Zulip Message API cannot yet pin exactly a single message so the link in the GitHub comment will be to the whole topic
+    // See: https://rust-lang.zulipchat.com/#narrow/channel/122653-zulip/topic/.22near.22.20parameter.20in.20payload.20of.20send.20message.20API
+    let zulip_link = zulip_send_req.url(zulip_client);
+
+    let message_body = match args.verb {
+        BackportVerbArgs::Accept
+        | BackportVerbArgs::Accepted
+        | BackportVerbArgs::Approve
+        | BackportVerbArgs::Approved => {
+            get_text_backport_approved(&args.channel, &args.verb, &zulip_link)
+        }
+        BackportVerbArgs::Decline | BackportVerbArgs::Declined => {
+            get_text_backport_declined(&args.channel, &args.verb, &zulip_link)
+        }
+    };
+
+    let res = octo_client
+        .issues(repo_owner, repo_name)
+        .create_comment(args.pr_num, &message_body)
+        .await
+        .with_context(|| anyhow::anyhow!("unable to post comment on #{}", args.pr_num));
+    if res.is_err() {
+        tracing::error!("failed to post comment: {0:?}", res.err());
+    }
+
+    Ok(Some("".to_string()))
+}
+
 async fn ping_goals_cmd(
     ctx: Arc<Context>,
     gh_id: u64,

src/zulip/commands.rs

@@ -1,5 +1,6 @@
 use crate::db::notifications::Identifier;
 use crate::db::review_prefs::RotationMode;
+use crate::github::PullRequestNumber;
 use clap::{ColorChoice, Parser};
 use std::num::NonZeroU32;
 use std::str::FromStr;
@@ -161,8 +162,10 @@ pub enum StreamCommand {
     Read,
     /// Ping project goal owners.
     PingGoals(PingGoalsArgs),
-    /// Update docs
+    /// Update docs.
     DocsUpdate,
+    /// Accept or decline a backport.
+    Backport(BackportArgs),
 }
 
 #[derive(clap::Parser, Debug, PartialEq, Clone)]
@@ -173,6 +176,34 @@ pub struct PingGoalsArgs {
     pub next_update: String,
 }
 
+/// Backport release channels
+#[derive(Clone, clap::ValueEnum, Debug, PartialEq)]
+pub enum BackportChannelArgs {
+    Beta,
+    Stable,
+}
+
+/// Backport verbs
+#[derive(Clone, clap::ValueEnum, Debug, PartialEq)]
+pub enum BackportVerbArgs {
+    Accept,
+    Accepted,
+    Approve,
+    Approved,
+    Decline,
+    Declined,
+}
+
+#[derive(clap::Parser, Debug, PartialEq, Clone)]
+pub struct BackportArgs {
+    /// Release channel this backport is pointing to. Allowed: "beta" or "stable".
+    pub channel: BackportChannelArgs,
+    /// Accept or decline this backport? Allowed: "accept", "accepted", "approve", "approved", "decline", "declined".
+    pub verb: BackportVerbArgs,
+    /// PR to be backported
+    pub pr_num: PullRequestNumber,
+}
+
 /// Helper function to parse CLI arguments without any colored help or error output.
 pub fn parse_cli<'a, T: Parser, I: Iterator<Item = &'a str>>(input: I) -> anyhow::Result<T> {
     fn allow_title_case(sub: clap::Command) -> clap::Command {
@@ -292,6 +323,26 @@ mod tests {
         assert_eq!(parse_stream(&["await"]), StreamCommand::EndTopic);
     }
 
+    #[test]
+    fn backports_command() {
+        assert_eq!(
+            parse_stream(&["backport", "beta", "accept", "123456"]),
+            StreamCommand::Backport(BackportArgs {
+                channel: BackportChannelArgs::Beta,
+                verb: BackportVerbArgs::Accept,
+                pr_num: 123456
+            })
+        );
+        assert_eq!(
+            parse_stream(&["backport", "stable", "decline", "123456"]),
+            StreamCommand::Backport(BackportArgs {
+                channel: BackportChannelArgs::Stable,
+                verb: BackportVerbArgs::Decline,
+                pr_num: 123456
+            })
+        );
+    }
+
     fn parse_chat(input: &[&str]) -> ChatCommand {
         parse_cli::<ChatCommand, _>(input.into_iter().copied()).unwrap()
     }