feat: Don't allow the merging of PRs when they don't have a clean state [WIP]

src/bors/comment.rs

@@ -276,6 +276,12 @@ Hint: Remove **{keyword}** from this PR's title when it is ready for review.
     ))
 }
 
+pub fn approve_non_clean_pr() -> Comment {
+    Comment::new(
+        r":clipboard: Looks like this PR is not ready to be merged, ignoring approval.".to_string(),
+    )
+}
+
 pub fn approve_blocking_labels_present(blocking_labels: &[&str]) -> Comment {
     let labels = blocking_labels
         .iter()

src/bors/handlers/review.rs

@@ -4,8 +4,9 @@ use crate::bors::RepositoryState;
 use crate::bors::command::RollupMode;
 use crate::bors::command::{Approver, CommandPrefix};
 use crate::bors::comment::{
-    approve_blocking_labels_present, approve_non_open_pr_comment, approve_wip_title,
-    approved_comment, delegate_comment, delegate_try_builds_comment, unapprove_non_open_pr_comment,
+    approve_blocking_labels_present, approve_non_clean_pr, approve_non_open_pr_comment,
+    approve_wip_title, approved_comment, delegate_comment, delegate_try_builds_comment,
+    unapprove_non_open_pr_comment,
 };
 use crate::bors::handlers::labels::handle_label_trigger;
 use crate::bors::handlers::workflow::{AutoBuildCancelReason, maybe_cancel_auto_build};
@@ -20,6 +21,7 @@ use crate::github::LabelTrigger;
 use crate::github::{GithubUser, PullRequestNumber};
 use crate::permissions::PermissionType;
 use crate::{BorsContext, PgDbClient};
+use octocrab::models::pulls::MergeableState;
 
 /// Approve a pull request.
 /// A pull request can only be approved by a user of sufficient authority.
@@ -81,6 +83,10 @@ async fn check_pr_approval_validity(
         return Ok(Some(approve_non_open_pr_comment()));
     }
 
+    if matches!(pr.github.mergeable_state, MergeableState::Dirty) {
+        return Ok(Some(approve_non_clean_pr()));
+    }
+
     // Check WIP title
     let title = pr.github.title.to_lowercase();
     if let Some(wip_kw) = WIP_KEYWORDS.iter().find(|kw| title.contains(*kw)) {
@@ -1214,6 +1220,20 @@ mod tests {
         .await;
     }
 
+    #[sqlx::test]
+    async fn approve_dirty_pr(pool: sqlx::PgPool) {
+        run_test(pool, async |tester: &mut BorsTester| {
+            tester.edit_pr((), |pr| pr.dirty_pull_request()).await?;
+            tester.post_comment("@bors r+").await?;
+            insta::assert_snapshot!(tester.get_next_comment_text(()).await?, @r"
+            :clipboard: Looks like this PR is not ready to be merged, ignoring approval.
+            ");
+            tester.get_pr_copy(()).await.expect_unapproved();
+            Ok(())
+        })
+        .await;
+    }
+
     #[sqlx::test]
     async fn approve_closed_pr(pool: sqlx::PgPool) {
         run_test(pool, async |tester: &mut BorsTester| {

src/tests/mocks/pull_request.rs

@@ -206,6 +206,10 @@ impl PullRequest {
         self.status = PullRequestStatus::Draft;
     }
 
+    pub fn dirty_pull_request(&mut self) {
+        self.mergeable_state = MergeableState::Dirty;
+    }
+
     pub fn add_comment_to_history(&mut self, comment: Comment) {
         self.comment_history.push(comment);
     }