Check that the set of queries is non-empty at init time

src/config-utils.test.ts

@@ -224,7 +224,9 @@ test("default queries are used", async t => {
         resolveQueriesArgs.push({queries, extraSearchPath});
         return {
           byLanguage: {
-            'javascript': {},
+            'javascript': {
+              'foo.ql': {},
+            },
           },
           noDeclaredLanguage: {},
           multipleDeclaredLanguages: {},
@@ -262,7 +264,11 @@ test("API client used when reading remote config", async t => {
     CodeQL.setCodeQL({
       resolveQueries: async function() {
         return {
-          byLanguage: {},
+          byLanguage: {
+            'javascript': {
+              'foo.ql': {},
+            },
+          },
           noDeclaredLanguage: {},
           multipleDeclaredLanguages: {},
         };

src/config-utils.ts

@@ -577,6 +577,15 @@ async function loadConfig(configFile: string): Promise<Config> {
     });
   }
 
+  // The list of queries should not be empty for any language. If it is then
+  // it is a user configuration error.
+  for (const language of languages) {
+    if (queries[language].length === 0) {
+      throw new Error(`Did not detect any queries to analyze for ${language}. ` +
+          "Please make sure that the default queries are enabled, or you are specifying queries to run.");
+    }
+  }
+
   return {
     languages,
     queries,