Add work queue tracking in triagebot DB

src/db.rs

@@ -335,4 +335,5 @@ CREATE table review_prefs (
 CREATE EXTENSION intarray;
 CREATE UNIQUE INDEX review_prefs_user_id ON review_prefs(user_id);
  ",
+    "ALTER TABLE review_prefs ADD COLUMN max_assigned_prs INTEGER DEFAULT NULL;",
 ];

src/lib.rs

@@ -132,17 +132,26 @@ pub struct ReviewPrefs {
     pub username: String,
     pub user_id: i64,
     pub assigned_prs: Vec<i32>,
+    pub max_assigned_prs: Option<i32>,
 }
 
 impl ReviewPrefs {
     fn to_string(&self) -> String {
+        let capacity = if self.max_assigned_prs.is_some() {
+            format!("{}", self.max_assigned_prs.expect("This can't fail"))
+        } else {
+            String::from("Not set (i.e. unlimited)")
+        };
         let prs = self
             .assigned_prs
             .iter()
             .map(|pr| format!("#{}", pr))
             .collect::<Vec<String>>()
             .join(", ");
-        format!("Username: {}\nAssigned PRs: {}", self.username, prs)
+        format!(
+            "Username: {}\nAssigned PRs: {}\nReview capacity: {}",
+            self.username, prs, capacity
+        )
     }
 }
 
@@ -153,6 +162,7 @@ impl From<tokio_postgres::row::Row> for ReviewPrefs {
             username: row.get("username"),
             user_id: row.get("user_id"),
             assigned_prs: row.get("assigned_prs"),
+            max_assigned_prs: row.get("max_assigned_prs"),
         }
     }
 }