dotnet/runtime · error · Error

Invalid config, resources is not set

Error message

Invalid config, resources is not set

What it means

createRuntime() (loader/run.ts) re-checks at its entry that loaderConfig.resources exists, has coreAssembly, and coreAssembly.length > 0. This is a stricter duplicate of part of validateLoaderConfig() and guards the runtime creation path directly. It throws before doing any work.

Source

Thrown at src/native/libs/Common/JavaScript/loader/run.ts:27

import { getIcuResourceName } from "./icu";
import { loaderConfig, validateLoaderConfig } from "./config";
import { fetchAssembly, fetchIcu, fetchNativeSymbols, fetchPdb, fetchSatelliteAssemblies, fetchVfs, fetchMainWasm, loadDotnetModule, loadJSModule, nativeModulePromiseController, verifyAllAssetsDownloaded, callLibraryInitializerOnRuntimeReady, callLibraryInitializerOnRuntimeConfigLoaded, prefetchAllResources, prefetchJSModuleLinks, resolveAllDownloadsQueued } from "./assets";
import { initPolyfillsLoader } from "./polyfills";
import { validateEngineFeatures } from "./bootstrap";

const runMainPromiseController = createPromiseCompletionSource<number>();

type DownloadMode = "none" | "cacheOnly" | "intoMemory";
let downloadMode: DownloadMode = "none";
let downloadDeferred: PromiseCompletionSource<void> | undefined;
let downloadedIntoMemory = false;
let configInitialized = false;
let modulesAfterConfigLoadedCache: [JsAsset, Promise<any>][] = [];

// many things happen in parallel here, but order matters for performance!
// ideally we want to utilize network and CPU at the same time
export async function createRuntime(downloadOnly: boolean, httpCacheOnly: boolean = false): Promise<any> {
    if (!loaderConfig.resources || !loaderConfig.resources.coreAssembly || !loaderConfig.resources.coreAssembly.length) throw new Error("Invalid config, resources is not set");
    try {
        runtimeState.creatingRuntime = true;

        // Re-entrancy guard: await any in-flight download, skip if already at requested level
        if (downloadOnly) {
            if (downloadDeferred) {
                await downloadDeferred.promise;
            }
            if (downloadMode === "intoMemory" || (httpCacheOnly && downloadMode === "cacheOnly")) {
                return;
            }
            downloadDeferred = createPromiseCompletionSource<void>();
        }

        // Fast path: download() already loaded everything into memory, create() just needs to init
        if (downloadedIntoMemory && !downloadOnly) {
            Module.runtimeKeepalivePush();
            await initializeCoreCLR();

View on GitHub (pinned to 290d5ab72c)

Solutions

1. Ensure resources.coreAssembly is a non-empty array before calling create() — populate from a valid boot config.
2. Republish to regenerate blazor.boot.json / the embedded config.
3. Verify the config file was fetched and parsed (network tab, console) so resources was actually merged.
4. Avoid withConfig() calls that overwrite resources with an object lacking coreAssembly.

Example fix

// before
builder.withConfig({ mainAssemblyName: 'App', resources: {} });
await builder.create(); // throws

// after
builder.withConfig({
  mainAssemblyName: 'App',
  resources: { coreAssembly: [{ name: 'System.Private.CoreLib.dll', hash: '...' }] }
});
await builder.create();

const r = getLoaderConfig().resources;
if (!r?.coreAssembly?.length) {
  throw new Error('Cannot create runtime — resources.coreAssembly is empty. Republish/merge boot config.');
}

function hasRuntimeResources(cfg: any): boolean {
  return Array.isArray(cfg?.resources?.coreAssembly) && cfg.resources.coreAssembly.length > 0;
}

When it happens

Trigger: createRuntime() invoked (via HostBuilder.create/download/runMain/runMainAndExit) while loaderConfig.resources is unset, has no coreAssembly, or coreAssembly is an empty array. Effectively the same condition as error 62, hit one call-frame deeper.

Common situations: Calling create() with a config that has mainAssemblyName but missing/empty resources.coreAssembly; a later withConfig() merge replaced resources; partial boot config due to download/parse failure of blazor.boot.json.

Related errors

• Loader configuration error: 'mainAssemblyName' is required.
• Loader configuration error: 'resources.coreAssembly' is requ
• Failed to invoke 'onRuntimeConfigLoaded' on library initiali
• Unexpected behavior ${asset.behavior} of asset ${asset.name}
• Missing window to the query parameters from

AI-assisted analysis of dotnet/runtime@290d5ab72c (2026-08-06). Data as JSON: /api/errors/677eaf5b86b99733. Report an issue: GitHub.