Make sure the backup option only appears when using sqlite

src/api/admin.rs

 use serde_json::Value;
+use std::process::Command;
 
 use rocket::http::{Cookie, Cookies, SameSite};
 use rocket::request::{self, FlashMessage, Form, FromRequest, Request};
@@ -9,7 +10,7 @@ use rocket_contrib::json::Json;
 use crate::api::{ApiResult, EmptyResult, JsonResult};
 use crate::auth::{decode_admin, encode_jwt, generate_admin_claims, ClientIp};
 use crate::config::ConfigBuilder;
-use crate::db::{models::*, DbConn, backup_database};
+use crate::db::{backup_database, models::*, DbConn};
 use crate::error::Error;
 use crate::mail;
 use crate::CONFIG;
@@ -34,6 +35,10 @@ pub fn routes() -> Vec<Route> {
     ]
 }
 
+lazy_static! {
+    static ref CAN_BACKUP: bool = cfg!(feature = "sqlite") && Command::new("sqlite").arg("-version").status().is_ok();
+}
+
 #[get("/")]
 fn admin_disabled() -> &'static str {
     "The admin panel is disabled, please configure the 'ADMIN_TOKEN' variable to enable it"
@@ -102,6 +107,7 @@ struct AdminTemplateData {
     version: Option<&'static str>,
     users: Vec<Value>,
     config: Value,
+    can_backup: bool,
 }
 
 impl AdminTemplateData {
@@ -111,6 +117,7 @@ impl AdminTemplateData {
             version: VERSION,
             users,
             config: CONFIG.prepare_json(),
+            can_backup: *CAN_BACKUP,
         }
     }
 
@@ -207,7 +214,11 @@ fn delete_config(_token: AdminToken) -> EmptyResult {
 
 #[post("/config/backup_db")]
 fn backup_db(_token: AdminToken) -> EmptyResult {
-    backup_database()
+    if *CAN_BACKUP {
+        backup_database()
+    } else {
+        err!("Can't back up current DB (either it's not SQLite or the 'sqlite' binary is not present)");
+    }
 }
 
 pub struct AdminToken {}

src/static/templates/admin/page.hbs

@@ -157,9 +157,11 @@
 
                     </div>
                 </div>
+
+                {{#if can_backup}}
                 <div class="card bg-light mb-3">
                     <div class="card-header"><button type="button" class="btn btn-link collapsed" data-toggle="collapse"
-                                                     data-target="#g_database">Database</button></div>
+                            data-target="#g_database">Backup Database</button></div>
                     <div id="g_database" class="card-body collapse" data-parent="#config-form">
                         <div class="small mb-3">
                             NOTE: A local installation of sqlite3 is required for this section to work.
@@ -167,6 +169,7 @@
                         <button type="button" class="btn btn-primary" onclick="backupDatabase();">Backup Database</button>
                     </div>
                 </div>
+                {{/if}}
 
                 <button type="submit" class="btn btn-primary">Save</button>
                 <button type="button" class="btn btn-danger float-right" onclick="deleteConf();">Reset defaults</button>