go-delve/delve · error

key type not supported %T

Error message

key type not supported %T

What it means

The Starlark mapping wrapper over a Delve variable (mapIndex/Get) only supports string, bool and structVariable (variable) keys; any other Starlark key type (int, tuple, None, etc.) is rejected when evaluating the map index in the debuggee.

Source

Thrown at pkg/terminal/starbind/conv.go:543

func (v mapVariableAsStarlarkValue) Type() string {
	return v.v.Type
}

func (v mapVariableAsStarlarkValue) Get(key starlark.Value) (starlark.Value, bool, error) {
	var keyExpr string
	switch key := key.(type) {
	case starlark.Int:
		keyExpr = key.String()
	case starlark.Float:
		keyExpr = fmt.Sprintf("%g", float64(key))
	case starlark.String:
		keyExpr = fmt.Sprintf("%q", string(key))
	case starlark.Bool:
		keyExpr = fmt.Sprintf("%v", bool(key))
	case structVariableAsStarlarkValue:
		keyExpr = varAddrExpr(key.v)
	default:
		return starlark.None, false, fmt.Errorf("key type not supported %T", key)
	}

	v2 := v.env.autoLoad(fmt.Sprintf("%s[%s]", varAddrExpr(v.v), keyExpr))
	r, err := v.env.variableValueToStarlarkValue(v2, false)
	if err != nil {
		if err.Error() == "key not found" {
			return starlark.None, false, nil
		}
		return starlark.None, false, err
	}
	return r, true, nil
}

func (v mapVariableAsStarlarkValue) Items() []starlark.Tuple {
	r := make([]starlark.Tuple, 0, len(v.v.Children)/2)
	for i := 0; i < len(v.v.Children); i += 2 {
		r = append(r, mapStarlarkTupleAt(v.v, v.env, i))
	}

View on GitHub (pinned to a23773e6c3)

Solutions

1. Use a string key: m["key"] — for integer keys quote them so they are sent as an expression, e.g. m[str(42)] if supported, or use m['%d' % 42] form
2. Index the map directly via the debugger expression instead: env autoLoad of var[expr]
3. Restructure the script to iterate keys via the debugger rather than indexing by native Starlark ints

Example fix

# before
m[42]            # int key not supported
# after
m[str(42)]       # or 'm[42]' evaluated as debugger expression

if not isinstance(key, (str, bool)):
    raise TypeError("map index key must be str or bool, got %s" % type(key))

def is_supported_key(k):
    return isinstance(k, (str, bool)) or hasattr(k, 'v')  # structVariableAsStarlarkValue

try:
    v = m[key]
except Exception as e:
    if "key type not supported" in str(e):
        v = m[str(key)]  # re-index as string expression
    else:
        raise

When it happens

Trigger: `some_map_var[42]` or `some_map_var[(1,2)]` in a Starlark script where the Delve variable is a Go map whose keys must be expressed as an evaluated expression string.

Common situations: Indexing Go maps with numeric literals in scripts; Delve evaluates the index in the target process, so keys must be round-trippable expressions.

Related errors

• can not assign to %T.%q: %v
• can not assign big integer to %T.%q
• can not assign value of type %T to %T.%q
• error setting argument %q to %s: %v
• error setting argument %q: can not convert %s to %s: %s

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/4f59a72c320574bf. Report an issue: GitHub.