Fix module, import, export, and call errors

Separate decoding, validation, linking, and invocation. The first boundary that fails tells you where to look next.

Decode or validation failure

Separate validation from execution:

wago validate fib.wasm

Common causes are malformed bytes, a disabled proposal, a module built for a different WebAssembly feature profile, or a feature unavailable on the selected platform. Wago enables its supported Core 3 feature set by default.

Select Core 2 compatibility when the producer or deployment requires that narrower profile:

wago run --core 2 --invoke fib fib.wasm 20

Do not use feature flags to force malformed Wasm through.

Missing import

wago module imports fib.wasm
wago module capabilities fib.wasm

An unresolved import means the module needs another plugin scope, an uninstalled plugin, an application host function, or a corrected name and signature.

For a local project:

wago init --run
wago add github.com/wago-org/wasi
wago plugin list

For the Go API:

imports := wago.NewImports()
imports.HostFunc("host", "log", logFunc)

instance, err := runtime.Instantiate(ctx, module, wago.WithImports(imports))

Missing export

Command modules normally export _start. Select a library function explicitly:

wago run --invoke missing fib.wasm 20

A source-language function name does not necessarily survive compilation as a Wasm export.

Rejected arguments

Wago follows the Wasm signature. This fails before guest code because nope is not an i32:

wago run --invoke fib fib.wasm nope

Use a value that matches the signature:

wago run --invoke fib fib.wasm 30:i32

In Go, match the declared signature with slot helpers (wago.I32, wago.I64, wago.F32, wago.F64). The typed API can also report a type mismatch before running the guest:

out, err := inst.InvokeValues(ctx, "add", wago.ValueI32(20), wago.ValueI32(22))

A Go embedder never starts the program

The CLI chooses an export for you. Runtime.Instantiate only runs a WebAssembly start section if one exists; it does not select _start, main, or _initialize. Invoke the entry point the guest toolchain documents. TinyGo reactor guests in the embedding tutorial export _initialize, which must run once per instance before your own exports.

A guest that uses WASI also needs those imports. A successful Compile checks the module, but it does not install a WASI provider or grant filesystem access.

A raw result changes after another call

Invoke, InvokeContext, and WasmFunc.Invoke return instance-owned result slots. Copy a result slice before the next invocation if you need to keep it. InvokeValues returns an independently owned typed slice, but is deprecated in favor of the raw APIs for normal invocation; use it deliberately when its typed checks or Runtime invoke hooks are needed.