Generate default layout.

    Returns a ``Layout`` instance.

    :param message: Text to be used as prompt.
    :param lexer: Lexer to be used for the highlighting.
    :param is_password: `bool` or `CLIFilter`. When True, display input as '*'.
    :param reserve_space_for_menu: When True, make sure that a minimal height
        is allocated in the terminal, in order to display the completion menu.
    :param get_prompt_tokens: An optional callable that returns the tokens to
        be shown in the menu. (To be used instead of a `message`.)
    :param get_bottom_toolbar_tokens: An optional callable that returns the
        tokens for a toolbar at the bottom.
    :param display_completions_in_columns: `bool` or `CLIFilter`. Display the
        completions in multiple columns.
    :param multiline: `bool` or `CLIFilter`. When True, prefer a layout that is
        more adapted for multiline input. Text after newlines is automatically
        indented, and search/arg input is shown below the input, instead of
        replacing the prompt.

def create_default_layout(app, message='',
                          lexer=None, is_password=False,
                          reserve_space_for_menu=False,
                          get_prompt_tokens=None,
                          get_bottom_toolbar_tokens=None,
                          display_completions_in_columns=False,
                          extra_input_processors=None, multiline=False):
    """
    Generate default layout.

    Returns a ``Layout`` instance.

    :param message: Text to be used as prompt.
    :param lexer: Lexer to be used for the highlighting.
    :param is_password: `bool` or `CLIFilter`. When True, display input as '*'.
    :param reserve_space_for_menu: When True, make sure that a minimal height
        is allocated in the terminal, in order to display the completion menu.
    :param get_prompt_tokens: An optional callable that returns the tokens to
        be shown in the menu. (To be used instead of a `message`.)
    :param get_bottom_toolbar_tokens: An optional callable that returns the
        tokens for a toolbar at the bottom.
    :param display_completions_in_columns: `bool` or `CLIFilter`. Display the
        completions in multiple columns.
    :param multiline: `bool` or `CLIFilter`. When True, prefer a layout that is
        more adapted for multiline input. Text after newlines is automatically
        indented, and search/arg input is shown below the input, instead of
        replacing the prompt.
    """
    assert isinstance(message, text_type)
    assert (get_bottom_toolbar_tokens is None or
            callable(get_bottom_toolbar_tokens))
    assert get_prompt_tokens is None or callable(get_prompt_tokens)
    assert not (message and get_prompt_tokens)

    display_completions_in_columns = to_cli_filter(
        display_completions_in_columns)
    multiline = to_cli_filter(multiline)

    if get_prompt_tokens is None:
        get_prompt_tokens = lambda _: [(Token.Prompt, message)]

    get_prompt_tokens_1, get_prompt_tokens_2 = _split_multiline_prompt(
        get_prompt_tokens)

    # `lexer` is supposed to be a `Lexer` instance. But if a Pygments lexer
    # class is given, turn it into a PygmentsLexer. (Important for
    # backwards-compatibility.)
    try:
        if issubclass(lexer, Lexer):
            lexer = PygmentsLexer(lexer)
    except TypeError:
        # Happens when lexer is `None` or an instance of something else.
        pass

    # Create processors list.
    # (DefaultPrompt should always be at the end.)
    input_processors = [
        ConditionalProcessor(
            # By default, only highlight search when the search
            # input has the focus. (Note that this doesn't mean
            # there is no search: the Vi 'n' binding for instance
            # still allows to jump to the next match in
            # navigation mode.)
            HighlightSearchProcessor(preview_search=Always()),
            HasFocus(SEARCH_BUFFER)),
        HighlightSelectionProcessor(),
        ConditionalProcessor(
            AppendAutoSuggestion(), HasFocus(DEFAULT_BUFFER) & ~IsDone()),
        ConditionalProcessor(PasswordProcessor(), is_password)
    ]

    if extra_input_processors:
        input_processors.extend(extra_input_processors)

    # Show the prompt before the input (using the DefaultPrompt processor.
    # This also replaces it with reverse-i-search and 'arg' when required.
    # (Only for single line mode.)
    input_processors.append(ConditionalProcessor(
        DefaultPrompt(get_prompt_tokens), ~multiline))

    # Create bottom toolbar.
    if get_bottom_toolbar_tokens:
        toolbars = [ConditionalContainer(
            Window(TokenListControl(get_bottom_toolbar_tokens,
                                    default_char=Char(' ', Token.Toolbar)),
                   height=LayoutDimension.exact(1)),
            filter=~IsDone() & RendererHeightIsKnown())]
    else:
        toolbars = []

    def get_height(cli):
        # If there is an autocompletion menu to be shown, make sure that our
        # layout has at least a minimal height in order to display it.
        if reserve_space_for_menu and not cli.is_done:
            return LayoutDimension(min=8)
        else:
            return LayoutDimension()

    def separator():
        return ConditionalContainer(
            content=Window(height=LayoutDimension.exact(1),
                           content=FillControl(u'\u2500',
                                               token=Token.Separator)),
            filter=HasDocumentation(app) & ~IsDone())

    # Create and return Layout instance.
    return HSplit([
        ConditionalContainer(
            Window(
                TokenListControl(get_prompt_tokens_1),
                dont_extend_height=True),
            filter=multiline,
        ),
        VSplit([
            # In multiline mode, the prompt is displayed in a left pane.
            ConditionalContainer(
                Window(
                    TokenListControl(get_prompt_tokens_2),
                    dont_extend_width=True,
                ),
                filter=multiline,
            ),
            # The main input, with completion menus floating on top of it.
            FloatContainer(
                Window(
                    BufferControl(
                        input_processors=input_processors,
                        lexer=lexer,
                        # Enable preview_search, we want to have immediate
                        # feedback in reverse-i-search mode.
                        preview_search=Always(),
                        focus_on_click=True,
                    ),
                    get_height=get_height,
                ),
                [
                    Float(xcursor=True,
                          ycursor=True,
                          content=CompletionsMenu(
                              max_height=16,
                              scroll_offset=1,
                              extra_filter=(HasFocus(DEFAULT_BUFFER) &
                                            ~display_completions_in_columns))),
                    Float(xcursor=True,
                          ycursor=True,
                          content=MultiColumnCompletionsMenu(
                              extra_filter=(HasFocus(DEFAULT_BUFFER) &
                                            display_completions_in_columns),
                              show_meta=Always()))
                ]
            ),
        ]),
        separator(),
        ConditionalContainer(
            content=Window(
                BufferControl(
                    focus_on_click=True,
                    buffer_name=u'clidocs',
                ),
                height=LayoutDimension(max=15)),
            filter=HasDocumentation(app) & ~IsDone(),
        ),
        separator(),
        ValidationToolbar(),
        SystemToolbar(),

        # In multiline mode, we use two toolbars for 'arg' and 'search'.
        ConditionalContainer(ArgToolbar(), multiline),
        ConditionalContainer(SearchToolbar(), multiline),
    ] + toolbars)