oven-sh/bun · error · Error

Unknown wrap kind ${x.wrap_kind}

Error message

Unknown wrap kind ${x.wrap_kind}

What it means

While emitting the JS2Native C++ header, generate-js2native.ts dispatches on each registered call's wrap_kind; today the only implemented kind is "new-function" (emit a JSC::JSFunction::create wrapper). This throw is the exhaustive-match guard: it can only fire if the wrap_kind data structure gains a new value whose emitting branch was never added — i.e. a generator-internal invariant break, not a user configuration error.

Source

Thrown at src/codegen/generate-js2native.ts:238

              type: "rust",
              symbol: x.symbol_target,
              filename: x.filename,
            })});`,
          ),
        "") || "",
        `static ALWAYS_INLINE JSC::JSValue ${x.symbol_generated}(Zig::GlobalObject* globalObject) {`,
        `  return JSC::JSFunction::create(globalObject->vm(), globalObject, ${x.call_length}, ${JSON.stringify(
          x.display_name,
        )}_s, ${symbol({
          type: x.type,
          symbol: x.symbol_target,

          filename: x.filename,
        })}, JSC::ImplementationVisibility::Public);`,
        `}`,
      ].join("\n");
    }
    throw new Error(`Unknown wrap kind ${x.wrap_kind}`);
  });

  return [
    `#pragma once`,
    `#include "root.h"`,
    ...files.map(filename => `#include ${JSON.stringify(filename)}`),
    ...externs,
    "\n" + "namespace JS2NativeGenerated {",
    "using namespace Bun;",
    "using namespace JSC;",
    "using namespace WebCore;" + "\n",
    ...nativeCallStrings,
    ...wrapperCallStrings,
    ...nativeCalls
      .filter(x => x.type === "bind")
      .map(
        x =>
          `extern "C" SYSV_ABI JSC::EncodedJSValue js2native_bindgen_${basename(x.filename.replace(/\.bind\.ts$/, ""))}_${x.symbol}(Zig::GlobalObject*);`,

View on GitHub (pinned to 8c5296ac45)

Solutions

1. Find where the unexpected wrap_kind value is produced (registration at line ~166 or the type at line ~20) and either fix it to "new-function" or implement the new kind
2. Add the matching `if (x.wrap_kind === "...")` branch before the final throw in the emit function
3. Keep the throw as the exhaustiveness guard — do not silence it with a default branch

// exhaustively narrow wrap_kind before emitting
const knownWrapKinds = ["new-function"] as const;
function isKnownWrapKind(k: string): k is (typeof knownWrapKinds)[number] {
  return (knownWrapKinds as readonly string[]).includes(k);
}

When it happens

Trigger: Extending generate-js2native.ts (or its input producers) with a new wrap_kind value while only adding it to the type/registration side, leaving the emit switch at line 215 unhandled.

Common situations: Almost exclusively hit by developers modifying the codegen itself; never by .classes.ts or .bind.ts authors, since no external input can supply a wrap_kind other than "new-function".

Related errors

• Missing output for ${id}
• Expected filename for $${call_type} to have ${ext} extension
• Unknown $rust() file identifier ${JSON.stringify(filename)}.
• Could not find file ${filename} in $${fnName} call
• file did not exist after write: ${outputPath}

AI-assisted analysis of oven-sh/bun@8c5296ac45 (2026-08-16). Data as JSON: /api/errors/7adc3760b26a594f. Report an issue: GitHub.