go-delve/delve · error

value not loaded

Error message

value not loaded

What it means

This error comes from variableValueToStarlarkValue in Delve's Starlark scripting bridge. When converting an api.Variable of kind Struct to a Starlark value, a non-empty struct whose Children slice is empty means its fields were never loaded from the debuggee (the variable was evaluated without child loading). Delve refuses to silently expose an empty struct, so it returns 'value not loaded'.

Solutions

1. Re-fetch the variable so children are loaded: use the dlv_command builtin to run a command that fully evaluates the variable, or configure the evaluation to load child values.
2. Increase the load/config settings (MaxLoadValue / MaxVariableRecurse) so struct fields are populated before conversion.
3. Guard scripts: check len(v.Children) == 0 and v.Len != 0 before treating a struct variable as usable, and reload otherwise.

Example fix

// before (script assumes children are present)
val := scope["myStruct"]
print(val.Field)
// after (reload the value via a command that loads children)
cfg := {"MaxVariableRecurse": -1}
dlv_command("print myStruct")  // evaluate with children loaded before scripting access

def is_loaded_struct(v):
    return v.Kind == "struct" and (v.Len == 0 or len(v.Children) > 0)

def is_loaded_struct(v):
    return type(v) == "structVariableAsStarlarkValue" or (hasattr(v, "Len") and (v.Len == 0 or len(v.Children) > 0))

try:
    val = to_starlark(var)
except Exception as e:
    if "value not loaded" in str(e):
        dlv_command("print " + name)  # reload with children
        val = to_starlark(scope[name])
    else:
        raise

When it happens

Trigger: In a Starlark script, accessing a struct-typed variable obtained via an API call that did not load children (e.g. a variable returned with follow-pointers/depth settings that truncated children, or a large struct returned unloaded), then passing it through the conversion used by mapStarlarkTupleAt.

Common situations: Scripts that iterate map values or tuple entries whose struct members were not recursively loaded; using variables fetched with MaxLoadValue settings that skip children; deeply nested structs where only the top level was loaded.

Related errors

• argument of dlv_command is not a string
• argument of read_file was not a string
• can not assign big integer to %T.
• can not assign to %T.
• can not assign value of type %T to %T.

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/2a31e1fa68bcc528. Report an issue: GitHub.

Appendix: source

Thrown at pkg/terminal/starbind/conv.go:250

		return starlark.String(varAddrExpr(&v2)), nil
	}

	return v.env.variableValueToStarlarkValue(&v2, true)
}

func varAddrExpr(v *api.Variable) string {
	return fmt.Sprintf("(*(*%q)(%#x))", v.Type, v.Addr)
}

func (env *Env) variableValueToStarlarkValue(v *api.Variable, top bool) (starlark.Value, error) {
	if !top && v.Addr == 0 && v.Value == "" {
		return starlark.None, nil
	}

	switch v.Kind {
	case reflect.Struct:
		if v.Len != 0 && len(v.Children) == 0 {
			return starlark.None, errors.New("value not loaded")
		}
		return structVariableAsStarlarkValue{v: v, env: env}, nil
	case reflect.Slice, reflect.Array:
		if v.Len != 0 && len(v.Children) == 0 {
			return starlark.None, errors.New("value not loaded")
		}
		return sliceVariableAsStarlarkValue{v: v, env: env}, nil
	case reflect.Map:
		if v.Len != 0 && len(v.Children) == 0 {
			return starlark.None, errors.New("value not loaded")
		}
		return mapVariableAsStarlarkValue{v: v, env: env}, nil
	case reflect.String:
		return starlark.String(v.Value), nil
	case reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Int:
		n, _ := strconv.ParseInt(api.ExtractIntValue(v.Value), 0, 64)
		return starlark.MakeInt64(n), nil
	case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uint, reflect.Uintptr:

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