Check existing reviewers in a case-insensitive manner

src/bors/handlers/review.rs

@@ -674,6 +674,23 @@ approved = ["+approved"]
         .await;
     }
 
+    #[sqlx::test]
+    async fn approve_with_known_reviewer_different_case(pool: sqlx::PgPool) {
+        run_test(pool, async |ctx: &mut BorsTester| {
+            ctx.post_comment("@bors r=DEFAULT-USER").await?;
+            insta::assert_snapshot!(
+                ctx.get_next_comment_text(()).await?,
+                @"
+            :pushpin: Commit pr-1-sha has been approved by `DEFAULT-USER`
+
+            It is now in the [queue](https://bors-test.com/queue/borstest) for this repository.
+            "
+            );
+            Ok(())
+        })
+        .await;
+    }
+
     #[sqlx::test]
     async fn insufficient_permission_approve(pool: sqlx::PgPool) {
         run_test(pool, async |ctx: &mut BorsTester| {

src/permissions.rs

@@ -36,7 +36,10 @@ impl UserPermissions {
     ) -> Self {
         Self {
             review_users,
-            review_usernames,
+            review_usernames: review_usernames
+                .into_iter()
+                .map(|username| username.to_lowercase())
+                .collect(),
             try_users,
         }
     }
@@ -48,8 +51,10 @@ impl UserPermissions {
         }
     }
 
+    /// Checks if the given username is a valid reviewer.
+    /// The usernames are checked in a case-insensitive manner.
     pub fn has_reviewer(&self, username: &str) -> bool {
-        self.review_usernames.contains(username)
+        self.review_usernames.contains(&username.to_lowercase())
     }
 }