if offset >= len(src) {
		return end
	}
	if width := bytes.IndexAny(src[offset:], " \n,():;[]+-*"); width > 0 {
		end = start + token.Pos(width)
	}
	return end
}

func ZeroValue(f *ast.File, pkg *types.Package, typ types.Type) ast.Expr {
	// TODO(adonovan): think about generics, and also generic aliases.
	under := aliases.Unalias(typ)
	// Don't call Underlying unconditionally: although it removes