go-delve/delve · error

wrong number of arguments

Error message

wrong number of arguments

What it means

The read_file Starlark builtin in Delve's terminal scripting layer accepts exactly one positional argument (the file path). When a Starlark init script calls read_file with zero arguments or more than one, the builtin returns this error, decorated with the Starlark call stack via decorateError. It exists to enforce the documented '(Path)' signature before any file I/O is attempted.

Source

Thrown at pkg/terminal/starbind/starlark.go:107

		argstrs := make([]string, len(args))
		for i := range args {
			a, ok := args[i].(starlark.String)
			if !ok {
				return nil, errors.New("argument of dlv_command is not a string")
			}
			argstrs[i] = string(a)
		}
		err := env.ctx.CallCommand(strings.Join(argstrs, " "))
		if err != nil && strings.Contains(err.Error(), " has exited with status ") {
			return env.interfaceToStarlarkValue(err), nil
		}
		return starlark.None, decorateError(thread, err)
	})
	builtindoc(dlvCommandBuiltinName, "(Command)", "interrupts, continues and steps through the program.")

	env.env[readFileBuiltinName] = starlark.NewBuiltin(readFileBuiltinName, func(thread *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
		if len(args) != 1 {
			return nil, decorateError(thread, errors.New("wrong number of arguments"))
		}
		path, ok := args[0].(starlark.String)
		if !ok {
			return nil, decorateError(thread, errors.New("argument of read_file was not a string"))
		}
		buf, err := os.ReadFile(string(path))
		if err != nil {
			return nil, decorateError(thread, err)
		}
		return starlark.String(string(buf)), nil
	})
	builtindoc(readFileBuiltinName, "(Path)", "reads a file.")

	env.env[appendFileBuiltinName] = starlark.NewBuiltin(appendFileBuiltinName, func(thread *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
		if len(args) != 2 {
			return nil, decorateError(thread, errors.New("wrong number of arguments"))
		}
		path, ok := args[0].(starlark.String)

View on GitHub (pinned to a23773e6c3)

Solutions

1. Call read_file with exactly one string argument: read_file("/path/to/file")
2. If you need to combine multiple paths, build a single string first with the + operator or str() concatenation
3. Run `dlv help` or check the builtins listing (`help()` in the terminal) to confirm the documented signature '(Path)'

Example fix

// before (in .dlv/init Starlark script)
contents = read_file("/tmp/bps.txt", "r")

// after
contents = read_file("/tmp/bps.txt")

// in Starlark before calling
if len(args) != 1:
    fail("read_file requires exactly one path argument")
path = args[0]
if type(path) != "string":
    fail("read_file path must be a string")

def is_str(v):
    return type(v) == "string"

# usage
if is_str(p):
    contents = read_file(p)

When it happens

Trigger: Calling read_file() with no arguments, read_file(a, b) with two or more arguments, or when extra positional arguments are accidentally passed (e.g. leftover arguments from a variable expansion) inside a Starlark init script executed by dlv.

Common situations: Users write ~/.dlv/init scripts or automation scripts that read config/state files; a typo like read_file(path, 0) or refactoring that leaves a second argument behind triggers this. It also appears when porting scripts from Python-style helpers that accept optional arguments.

Related errors

• value not loaded
• not hashable
• cycle in load graph
• argument of dlv_command is not a string
• argument of read_file was not a string

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/42b4353ee25ae8d7. Report an issue: GitHub.