Change to use QueryLanguage | undefined.

extensions/ql-vscode/src/common/query-language.ts

@@ -62,3 +62,9 @@ export const dbSchemeToLanguage: Record<string, QueryLanguage> = {
 export function isQueryLanguage(language: string): language is QueryLanguage {
   return Object.values(QueryLanguage).includes(language as QueryLanguage);
 }
+
+export function tryGetQueryLanguage(
+  language: string,
+): QueryLanguage | undefined {
+  return isQueryLanguage(language) ? language : undefined;
+}

extensions/ql-vscode/src/databases/local-databases-ui.ts

@@ -51,7 +51,7 @@ import {
   createMultiSelectionCommand,
   createSingleSelectionCommand,
 } from "../common/vscode/selection-commands";
-import { QueryLanguage } from "../common/query-language";
+import { QueryLanguage, tryGetQueryLanguage } from "../common/query-language";
 import { LanguageContextStore } from "../language-context-store";
 
 enum SortOrder {
@@ -143,7 +143,9 @@ class DatabaseTreeDataProvider
     if (element === undefined) {
       // Filter items by language
       const displayItems = this.databaseManager.databaseItems.filter((item) => {
-        return this.languageContext.shouldInclude(item.language);
+        return this.languageContext.shouldInclude(
+          tryGetQueryLanguage(item.language),
+        );
       });
 
       // Sort items

extensions/ql-vscode/src/language-context-store.ts

@@ -43,11 +43,7 @@ export class LanguageContextStore extends DisposableObject {
     );
   }
 
-  // This method takes a string to allow it to be used in cases
-  // where the language is not always a known one.
-  // The semantics of such an unknown langauge is that it is
-  // only included if the current language context is "All".
-  public shouldInclude(language: string): boolean {
+  public shouldInclude(language: QueryLanguage | undefined): boolean {
     return this.languageFilter === "All" || this.languageFilter === language;
   }
 }