Show source of missing page links

CHDataManagement/Generator/Results/GenerationResults.swift

@@ -260,6 +260,18 @@ final class GenerationResults: ObservableObject {
         let unused = existingFiles.subtracting(outputFiles)
         update { self.unusedFilesInOutput = unused }
     }
+
+    func sources(forMissingPage page: String) -> [(page: LocalizedItemId, source: String)] {
+        var all = [(page: LocalizedItemId, source: String)]()
+        for (id, results) in cache {
+            guard let sources = results.missingLinkedPages[page]?.sorted() else {
+                continue
+            }
+            let additions = sources.map { (page: id, source: $0) }
+            all.append(contentsOf: additions)
+        }
+        return all
+    }
 }
 
 private extension Dictionary where Value == Set<LocalizedItemId> {