Fix crash when searching fails

Tusker/Screens/Search/SearchResultsViewController.swift

@@ -36,6 +36,7 @@ class SearchResultsViewController: EnhancedTableViewController {
     var dataSource: UITableViewDiffableDataSource<Section, Item>!
 
     private var activityIndicator: UIActivityIndicatorView!
+    private var errorLabel: UILabel!
     
     /// Types of results to search for. `nil` means all results will be included.
     var resultTypes: [SearchResultType]? = nil
@@ -61,6 +62,22 @@ class SearchResultsViewController: EnhancedTableViewController {
     override func viewDidLoad() {
         super.viewDidLoad()
         
+        errorLabel = UILabel()
+        errorLabel.translatesAutoresizingMaskIntoConstraints = false
+        errorLabel.font = .preferredFont(forTextStyle: .callout)
+        errorLabel.textColor = .secondaryLabel
+        errorLabel.numberOfLines = 0
+        errorLabel.textAlignment = .center
+        errorLabel.setContentHuggingPriority(.defaultLow, for: .horizontal)
+        tableView.addSubview(errorLabel)
+        NSLayoutConstraint.activate([
+            errorLabel.centerYAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerYAnchor),
+            errorLabel.centerXAnchor.constraint(equalTo: tableView.centerXAnchor),
+            errorLabel.leadingAnchor.constraint(equalToSystemSpacingAfter: tableView.leadingAnchor, multiplier: 1),
+            tableView.trailingAnchor.constraint(equalToSystemSpacingAfter: errorLabel.trailingAnchor, multiplier: 1),
+        ])
+
+
         tableView.register(UINib(nibName: "AccountTableViewCell", bundle: .main), forCellReuseIdentifier: accountCell)
         tableView.register(UINib(nibName: "TimelineStatusTableViewCell", bundle: .main), forCellReuseIdentifier: statusCell)
         tableView.register(UINib(nibName: "HashtagTableViewCell", bundle: .main), forCellReuseIdentifier: hashtagCell)
@@ -131,19 +148,30 @@ class SearchResultsViewController: EnhancedTableViewController {
 
         activityIndicator.isHidden = false
         activityIndicator.startAnimating()
+        errorLabel.isHidden = true
 
-        let resultTypes = self.resultTypes
         let request = Client.search(query: query, types: resultTypes, resolve: true, limit: 10)
         mastodonController.run(request) { (response) in
-            guard case let .success(results, _) = response else { fatalError() }
+            switch response {
-
+            case let .success(results, _):
+                guard self.currentQuery == query else { return }
                 DispatchQueue.main.async {
                     self.activityIndicator.isHidden = true
                     self.activityIndicator.stopAnimating()
                 }
+                self.showSearchResults(results)
+            case let .failure(error):
+                DispatchQueue.main.async {
+                    self.activityIndicator.isHidden = true
+                    self.activityIndicator.stopAnimating()
 
-            guard self.currentQuery == query else { return }
+                    self.showSearchError(error)
+                }
+            }
+        }
+    }
     
+    private func showSearchResults(_ results: SearchResults) {
         let oldSnapshot = self.dataSource.snapshot()
         var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
         
@@ -162,6 +190,7 @@ class SearchResultsViewController: EnhancedTableViewController {
                 }
             }
             
+            let resultTypes = self.resultTypes
             if !results.accounts.isEmpty && (resultTypes == nil || resultTypes!.contains(.accounts)) {
                 snapshot.appendSections([.accounts])
                 snapshot.appendItems(results.accounts.map { .account($0.id) }, toSection: .accounts)
@@ -178,10 +207,18 @@ class SearchResultsViewController: EnhancedTableViewController {
             }
         }, completion: {
             DispatchQueue.main.async {
+                self.errorLabel.isHidden = true
                 self.dataSource.apply(snapshot)
             }
         })
     }
+    
+    private func showSearchError(_ error: Client.Error) {
+        let snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
+        dataSource.apply(snapshot)
+        
+        errorLabel.isHidden = false
+        errorLabel.text = error.localizedDescription
     }
     
     // MARK: - Table view delegate