Add merge-bots configuration per branch protection

Instead of just assuming that when bors (homu) is enabled for a repository, all its repositories will be automatically managed by it, this PR adds an opt-in mechanism to use bors/homu for specific branch protections.

Author: Kobzol

docs/toml-schema.md

@@ -352,4 +352,12 @@ required-approvals = 1
 # can push/merge to the branch.
 # (optional)
 allowed-merge-teams = ["awesome-team"]
+# Determines the merge queue bot(s) that manage pushes to this branch.
+# When a bot manages the queue, some other options, like
+# `required-approvals` and `pr-required` options are not valid.
+#
+# Currently, only the "homu" option is supported.
+# When "homu" is used, "bors" has to be in the `bots` array.
+# (optional)
+merge-bots = ["homu"]
 ```

src/schema.rs

@@ -787,6 +787,12 @@ pub(crate) enum RepoPermission {
     Admin,
 }
 
+#[derive(serde_derive::Deserialize, Debug, PartialEq, Eq)]
+#[serde(rename_all = "kebab-case")]
+pub(crate) enum MergeBot {
+    Homu,
+}
+
 #[derive(serde_derive::Deserialize, Debug)]
 #[serde(deny_unknown_fields, rename_all = "kebab-case")]
 pub(crate) struct BranchProtection {
@@ -801,4 +807,6 @@ pub(crate) struct BranchProtection {
     pub pr_required: bool,
     #[serde(default)]
     pub allowed_merge_teams: Vec<String>,
+    #[serde(default)]
+    pub merge_bots: Vec<MergeBot>,
 }

src/validate.rs

@@ -1,6 +1,8 @@
 use crate::data::Data;
 use crate::github::GitHubApi;
-use crate::schema::{Bot, Email, Permissions, Team, TeamKind, TeamPeople, ZulipGroupMember};
+use crate::schema::{
+    Bot, Email, MergeBot, Permissions, Team, TeamKind, TeamPeople, ZulipGroupMember,
+};
 use crate::zulip::ZulipApi;
 use anyhow::{bail, Error};
 use log::{error, warn};
@@ -824,7 +826,8 @@ fn validate_branch_protections(data: &Data, errors: &mut Vec<String>) {
     let github_teams = data.github_teams();
 
     wrapper(data.repos(), errors, |repo, _| {
-        let bors_used = repo.bots.iter().any(|b| matches!(b, Bot::Bors));
+        let homu_configured = repo.bots.iter().any(|b| matches!(b, Bot::Bors));
+
         for protection in &repo.branch_protections {
             for team in &protection.allowed_merge_teams {
                 let key = (repo.org.clone(), team.clone());
@@ -858,19 +861,24 @@ but that team does not seem to exist"#,
                 }
             }
 
-            if bors_used {
-                if protection.required_approvals.is_some() {
+            let managed_by_homu = protection.merge_bots.contains(&MergeBot::Homu);
+            if managed_by_homu {
+                if !homu_configured {
                     bail!(
-                        r#"repo '{}' uses bors and its branch protection for {} uses the `required-approvals` attribute;
-please remove the attribute when using bors"#,
+                        r#"repo '{}' uses homu to manage a branch protection for '{}', but homu is not enabled. Add "bors" to the `bots` array"#,
                         repo.name,
                         protection.pattern,
                     );
                 }
-                if !protection.allowed_merge_teams.is_empty() {
+                if protection.required_approvals.is_some()
+                    || protection.dismiss_stale_review
+                    || !protection.pr_required
+                    || !protection.allowed_merge_teams.is_empty()
+                {
                     bail!(
-                        r#"repo '{}' uses bors and its branch protection for {} uses the `allowed-merge-teams` attribute;
-please remove the attribute when using bors"#,
+                        r#"repo '{}' uses the homu merge bot, but its branch protection for {} uses invalid
+attributes (`required-approvals`, `dismiss-stale-review`, `pr-required` or `allowed-merge-teams`).
+Please remove the attributes when using bors"#,
                         repo.name,
                         protection.pattern,
                     );