webpack/webpack · error · Error

unknown type: ${globalType.valtype}

Error message

unknown type: ${globalType.valtype}

What it means

The sync WebAssembly generator rewrites every imported global into a mutable local with a default zero-initializer. createDefaultInitForGlobal only knows how to synthesize that initializer for numeric value types whose valtype starts with 'i' (i32/i64) or 'f' (f32/f64). A global whose valtype is a reference type (externref/funcref/anyref) or a SIMD vector (v128) has no numeric default, so the rewrite aborts. This only fires under experiments.syncWebAssembly; the async path does not rewrite globals this way.

Source

Thrown at lib/wasm-sync/WebAssemblyGenerator.js:163

/**
 * Creates an init instruction for a global type
 * @param {t.GlobalType} globalType the global type
 * @returns {t.Instruction} init expression
 */
const createDefaultInitForGlobal = (globalType) => {
	if (globalType.valtype[0] === "i") {
		// create NumberLiteral global initializer
		return t.objectInstruction("const", globalType.valtype, [
			t.numberLiteralFromRaw(66)
		]);
	} else if (globalType.valtype[0] === "f") {
		// create FloatLiteral global initializer
		return t.objectInstruction("const", globalType.valtype, [
			t.floatLiteral(66, false, false, "66")
		]);
	}
	throw new Error(`unknown type: ${globalType.valtype}`);
};

/**
 * Rewrite the import globals:
 * - removes the ModuleImport instruction
 * - injects at the same offset a mutable global of the same type
 *
 * Since the imported globals are before the other global declarations, our
 * indices will be preserved.
 *
 * Note that globals will become mutable.
 * @param {object} state transformation state
 * @param {AST} state.ast Module's ast
 * @param {t.Instruction[]} state.additionalInitCode list of addition instructions for the init function
 * @returns {ArrayBufferTransform} transform
 */
const rewriteImportedGlobals = (state) => (bin) => {
	const additionalInitCode = state.additionalInitCode;

View on GitHub (pinned to 318421ea8a)

Solutions

1. Switch experiments.syncWebAssembly to experiments.asyncWebAssembly; the async generator does not rewrite imported globals and accepts reference/SIMD types.
2. Rebuild the wasm module without the offending imported global (disable reference-types/SIMD in the toolchain, e.g. rustc -C target-feature=-reference-types,-simd128, or define the global inside the module instead of importing it).
3. Filter the offending .wasm out of the sync-wasm pipeline (different module.rules test) and load it through a side channel that does not require global rewriting.

Example fix

// before
module.exports = {
  experiments: { syncWebAssembly: true }
};

// after
module.exports = {
  experiments: { asyncWebAssembly: true }
};

// Pre-build: decode the wasm and reject modules whose imported globals
// use a non-numeric valtype before webpack's sync generator trips on them.
const { decode } = require('@webassemblyjs/wasm-parser');
const t = require('@webassemblyjs/ast');

function assertNoUnsupportedImportedGlobals(wasmBuffer) {
  const ast = decode(wasmBuffer, { ignoreCodeSection: true, ignoreDataSection: true });
  t.traverse(ast, {
    ModuleImport({ node }) {
      if (t.isGlobalType(node.descr)) {
        const v = node.descr.valtype;
        if (v[0] !== 'i' && v[0] !== 'f') {
          throw new Error(`Unsupported imported global type ${v} in ${node.module}:${node.name}; rebuild without reference-types/SIMD globals or use asyncWebAssembly.`);
        }
      }
    }
  });
}
// assertNoUnsupportedImportedGlobals(fs.readFileSync('./module.wasm'));

/** @param {string} valtype wasm global value type
 * @returns {boolean} true when createDefaultInitForGlobal can handle it */
function isNumericValtype(valtype) {
  return valtype[0] === 'i' || valtype[0] === 'f';
}

When it happens

Trigger: Bundling a .wasm module that imports a global of a non-numeric type (v128, externref, funcref) while experiments.syncWebAssembly is enabled. The generator's rewriteImportedGlobals transform calls createDefaultInitForGlobal for each imported global during WebAssemblyGenerator.generate.

Common situations: Using the deprecated experiments.syncWebAssembly experiment with a modern wasm module that uses reference-types or SIMD globals; upgrading a Rust/AssemblyScript toolchain that started emitting reference-type globals; switching a build from asyncWebAssembly to syncWebAssembly and hitting a module the async path tolerated.

Related errors

• Universal wasm loading type is only supported by asynchronou
• optimization.usedExports can't be used with cacheUnaffected
• WebAssemblyParser input must be a Buffer
• Source phase imports require valid WebAssembly modules. Inva
• WebAssemblyParser input must be a Buffer

AI-assisted analysis of webpack/webpack@318421ea8a (2026-08-03). Data as JSON: /data/errors/7db677aa341e4af4.json. Report an issue: GitHub.