What causes "unexpected input type: %s" in vitessio/vitess?

Fully qualify the interface: use ' . '

unexpected input type: %s

Error message

unexpected input type: %s

What it means

Returned by the asthelpergen tool when it encounters an AST node input type it has no generator case for; indicates the tool needs a new case added for that type.

Source

Thrown at go/tools/asthelpergen/asthelpergen.go:320

		newPathGen(pName, ifaceName),
		newVisitGen(pName, ifaceName),
		newRewriterGen(pName, ifaceName),
		newCOWGen(pName, nt),
	)

	it, err := generator.GenerateCode()
	if err != nil {
		return nil, err
	}

	return it, nil
}

// findTypeObject finds the types.Object for the given interface from the given scopes.
func findTypeObject(interfaceToFind string, scopes map[string]*types.Scope) (types.Object, error) {
	pos := strings.LastIndexByte(interfaceToFind, '.')
	if pos < 0 {
		return nil, fmt.Errorf("unexpected input type: %s", interfaceToFind)
	}

	pkgname := interfaceToFind[:pos]
	typename := interfaceToFind[pos+1:]

	scope := scopes[pkgname]
	if scope == nil {
		return nil, fmt.Errorf("no scope found for type '%s'", interfaceToFind)
	}

	tt := scope.Lookup(typename)
	if tt == nil {
		return nil, fmt.Errorf("no type called '%s' found in '%s'", typename, pkgname)
	}
	return tt, nil
}

var _ generatorSPI = (*astHelperGen)(nil)

View on GitHub (pinned to 01a25a7d17)

Solutions

Fully qualify the interface: use '<full import path>.<TypeName>'
Check how the interface string is constructed in your Options/generator registration
Add a validation that input contains a dot before calling findTypeObject

Example fix

// before
Interfaces: []string{"SQLNode"}
// after
Interfaces: []string{"vitess.io/vitess/go/vt/sqlparser.SQLNode"}

Defensive patterns

Strategy: validation

Validate before calling

func validateInterfaceName(s string) error {
    if !strings.Contains(s, ".") {
        return fmt.Errorf("interface %q must be fully qualified as pkgpath.Type", s)
    }
    return nil
}

Type guard

func isQualifiedName(s string) bool {
    return strings.LastIndexByte(s, '.') >= 0
}

Prevention

Always list interfaces as '<full import path>.<TypeName>' in Options
Validate Options at startup/PreRun before generation
Build names programmatically from pkg path + type name instead of hand-writing strings

When it happens

Trigger: Calling GenerateASTHelpers with Options.Visitable interfaces (or the generator's interface list) containing a bare type name like "SQLNode" instead of "vitess.io/vitess/go/vt/sqlparser.SQLNode".

Common situations: Hand-editing the Options interface list; registering a new helper generator and forgetting to fully qualify the interface name.

Related errors

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/575eab709cda969a. Report an issue: GitHub.