Merge #7173 'api/ui: externalize cmdline'

closes #6162

10 files changed, 1153 insertions, 316 deletions

diff --git a/runtime/doc/api.txt b/runtime/doc/api.txt
index 8aead087db..159dd93c5e 100644
--- a/runtime/doc/api.txt
+++ b/runtime/doc/api.txt
@@ -48,7 +48,7 @@ version.api_compatible	API is backwards-compatible with this level
 version.api_prerelease	Declares the current API level as unstable >
 			(version.api_prerelease && fn.since == version.api_level)
 functions		API function signatures
-ui_events		UI event signatures |rpc-remote-ui|
+ui_events		UI event signatures |ui|
 {fn}.since		API level where function {fn} was introduced
 {fn}.deprecated_since	API level where function {fn} was deprecated
 types			Custom handle types defined by Nvim
diff --git a/runtime/doc/msgpack_rpc.txt b/runtime/doc/msgpack_rpc.txt
index 98a74ccfd6..7af6e401da 100644
--- a/runtime/doc/msgpack_rpc.txt
+++ b/runtime/doc/msgpack_rpc.txt
@@ -243,203 +243,4 @@ Even for statically compiled clients it is good practice to avoid hardcoding
 the type codes, because a client may be built against one Nvim version but
 connect to another with different type codes.
 
-==============================================================================
-6. Remote UIs					           *rpc-remote-ui*
-
-GUIs can be implemented as external processes communicating with Nvim over the
-RPC API. The UI model consists of a terminal-like grid with a single,
-monospace font size. Some elements (UI "widgets") can be drawn separately from
-the grid ("externalized").
-
-After connecting to Nvim (usually a spawned, embedded instance) use the
-|nvim_ui_attach| API method to tell Nvim that your program wants to draw the
-Nvim screen on a grid of width × height cells. `options` must be
-a dictionary with these (optional) keys:
-	`rgb`			Controls what color format to use.
-				Set to true (default) to use 24-bit rgb
-				colors.
-				Set to false to use terminal color codes (at
-				most 256 different colors).
-	`ext_popupmenu`		Externalize the popupmenu. |ui-ext-popupmenu|
-	`ext_tabline`		Externalize the tabline. |ui-ext-tabline|
-				Externalized widgets will not be drawn by
-				Nvim; only high-level data will be published
-				in new UI event kinds.
-
-Nvim will then send msgpack-rpc notifications, with the method name "redraw"
-and a single argument, an array of screen updates (described below).  These
-should be processed in order. Preferably the user should only be able to see
-the screen state after all updates in the same "redraw" event are processed
-(not any intermediate state after processing only a part of the array).
-
-Future versions of Nvim may add new update kinds and may append new parameters
-to existing update kinds. Clients must be prepared to ignore such extensions
-to be forward-compatible. |api-contract|
-
-Screen updates are tuples whose first element is the string name of the update
-kind.
-
-["resize", width, height]
-	The grid is resized to `width` and `height` cells.
-
-["clear"]
-	Clear the screen.
-
-["eol_clear"]
-	Clear from the cursor position to the end of the current line.
-
-["cursor_goto", row, col]
-	Move the cursor to position (row, col). Currently, the same cursor is
-	used to define the position for text insertion and the visible cursor.
-	However, only the last cursor position, after processing the entire
-	array in the "redraw" event, is intended to be a visible cursor
-	position.
-
-["update_fg", color]
-["update_bg", color]
-["update_sp", color]
-	Set the default foreground, background and special colors
-	respectively.
-
-["highlight_set", attrs]
-	Set the attributes that the next text put on the screen will have.
-	`attrs` is a dict with the keys below. Any absent key is reset
-	to its default value. Color defaults are set by the `update_fg` etc
-	updates. All boolean keys default to false.
-
-	`foreground`:	foreground color.
-	`background`:	backround color.
-	`special`:	color to use for underline and undercurl, when present.
-	`reverse`:	reverse video. Foreground and background colors are
-			switched.
-	`italic`:	italic text.
-	`bold`:		bold text.
-	`underline`:	underlined text. The line has `special` color.
-	`undercurl`:	undercurled text. The curl has `special` color.
-
-["put", text]
-	The (utf-8 encoded) string `text` is put at the cursor position
-	(and the cursor is advanced), with the highlights as set by the
-	last `highlight_set` update.
-
-["set_scroll_region", top, bot, left, right]
-	Define the scroll region used by `scroll` below.
-
-["scroll", count]
-	Scroll the text in the scroll region. The diagrams below illustrate
-	what will happen, depending on the scroll direction. "=" is used to
-	represent the SR(scroll region) boundaries and "-" the moved rectangles.
-	Note that dst and src share a common region.
-
-	If count is bigger than 0, move a rectangle in the SR up, this can
-	happen while scrolling down.
->
-		+-------------------------+
-		| (clipped above SR)      |            ^
-		|=========================| dst_top    |
-		| dst (still in SR)       |            |
-		+-------------------------+ src_top    |
-		| src (moved up) and dst  |            |
-		|-------------------------| dst_bot    |
-		| src (cleared)           |            |
-		+=========================+ src_bot
-<
-	If count is less than zero, move a rectangle in the SR down, this can
-	happen while scrolling up.
->
-		+=========================+ src_top
-		| src (cleared)           |            |
-		|------------------------ | dst_top    |
-		| src (moved down) and dst|            |
-		+-------------------------+ src_bot    |
-		| dst (still in SR)       |            |
-		|=========================| dst_bot    |
-		| (clipped below SR)      |            v
-		+-------------------------+
-<
-["set_title", title]
-["set_icon", icon]
-	Set the window title, and icon (minimized) window title, respectively.
-	In windowing systems not distinguishing between the two, "set_icon"
-	can be ignored.
-
-["mouse_on"]
-["mouse_off"]
-	Tells the client whether mouse support, as determined by |'mouse'|
-	option, is considered to be active in the current mode. This is mostly
-	useful for a terminal frontend, or other situations where nvim mouse
-	would conflict with other usages of the mouse. It is safe for a client
-	to ignore this and always send mouse events.
-
-["busy_on"]
-["busy_off"]
-	Nvim started or stopped being busy, and possibly not responsible to user
-	input. This could be indicated to the user by hiding the cursor.
-
-["suspend"]
-	|:suspend| command or |Ctrl-Z| mapping is used. A terminal client (or other
-	client where it makes sense) could suspend itself.  Other clients can
-	safely ignore it.
-
-["bell"]
-["visual_bell"]
-	Notify the user with an audible or visual bell, respectively.
-
-["update_menu"]
-	The menu mappings changed.
-
-["mode_info_set", cursor_style_enabled, mode_info]
-`cursor_style_enabled` is a boolean indicating if the UI should set the cursor
-style. `mode_info` is a list of mode property maps. The current mode is given
-by the `mode_idx` field of the `mode_change` event.
-
-Each mode property map may contain these keys:
-	KEY		DESCRIPTION ~
-	`cursor_shape`:	"block", "horizontal", "vertical"
-	`cell_percentage`: Cell % occupied by the cursor.
-	`blinkwait`, `blinkon`, `blinkoff`: See |cursor-blinking|.
-	`hl_id`:	Cursor highlight group.
-	`hl_lm`:	Cursor highlight group if 'langmap' is active.
-	`short_name`:	Mode code name, see 'guicursor'.
-	`name`:		Mode descriptive name.
-	`mouse_shape`:	(To be implemented.)
-
-Some keys are missing in some modes.
-
-["mode_change", mode, mode_idx]
-The mode changed.  The first parameter `mode` is a string representing the
-current mode. `mode_idx` is an index into the array received in the
-`mode_info_set` event. UIs should change the cursor style according to the
-properties specified in the corresponding item. The set of modes reported will
-change in new versions of Nvim, for instance more submodes and temporary
-states might be represented as separate modes.
-
-							*ui-ext-popupmenu*
-["popupmenu_show", items, selected, row, col]
-	When `popupmenu_external` is set to true, nvim will not draw the
-	popupmenu on the grid, instead when the popupmenu is to be displayed
-	this update is sent. `items` is an array of the items to show, the
-	items are themselves arrays of the form [word, kind, menu, info]
-	as defined at |complete-items|, except that `word` is replaced by
-	`abbr` if present.  `selected` is the initially selected item, either a
-	zero-based index into the array of items, or -1 if no item is
-	selected. `row` and `col` is the anchor position, where the first
-	character of the completed word will be.
-
-["popupmenu_select", selected]
-	An item in the currently displayed popupmenu is selected. `selected`
-	is either a zero-based index into the array of items from the last
-	`popupmenu_show` event, or -1 if no item is selected.
-
-["popupmenu_hide"]
-	The popupmenu is hidden.
-
-							*ui-ext-tabline*
-["tabline_update", curtab, tabs]
-	Tabline was updated. UIs should present this data in a custom tabline
-	widget.
-	curtab:	  Current Tabpage
-	tabs:	  List of Dicts [{ "tab": Tabpage, "name": String }, ...]
 
-==============================================================================
- vim:tw=78:ts=8:noet:ft=help:norl:
diff --git a/runtime/doc/ui.txt b/runtime/doc/ui.txt
new file mode 100644
index 0000000000..deac1609c0
--- /dev/null
+++ b/runtime/doc/ui.txt
@@ -0,0 +1,290 @@
+*ui.txt*	Nvim
+
+
+			    NVIM REFERENCE MANUAL
+
+
+Nvim UI protocol							  *ui*
+
+                                      Type |gO| to see the table of contents.
+
+==============================================================================
+Introduction							     *ui-intro*
+
+GUIs can be implemented as external processes communicating with Nvim over the
+RPC API. The UI model consists of a terminal-like grid with a single,
+monospace font size. Some elements (UI "widgets") can be drawn separately from
+the grid ("externalized").
+
+								  *ui-options*
+After connecting to Nvim (usually a spawned, embedded instance) use the
+|nvim_ui_attach| API method to tell Nvim that your program wants to draw the
+Nvim screen grid with a size of width × height cells. `options` must be
+a dictionary with these (optional) keys:
+	`rgb`			Decides the color format.
+				Set true (default) for 24-bit RGB colors.
+				Set false for terminal colors (max of 256).
+							      *ui-ext-options*
+	`ext_popupmenu`		Externalize the popupmenu. |ui-popupmenu|
+	`ext_tabline`		Externalize the tabline. |ui-tabline|
+	`ext_cmdline`		Externalize the cmdline. |ui-cmdline|
+
+Nvim will then send msgpack-rpc notifications, with the method name "redraw"
+and a single argument, an array of screen update events.
+Update events are tuples whose first element is the event name and remaining
+elements the event parameters.
+
+Events must be handled in order. The user should only see the updated screen
+state after all events in the same "redraw" batch are processed (not any
+intermediate state after processing only part of the array).
+
+Nvim sends |ui-global| and |ui-grid| events unconditionally; these suffice to
+implement a terminal-like interface.
+
+Nvim optionally sends screen elements "semantically" as structured events
+instead of raw grid-lines. Then the UI must decide how to present those
+elements itself; Nvim will not draw those elements on the grid. This is
+controlled by the |ui-ext-options|.
+
+Future versions of Nvim may add new update kinds and may append new parameters
+to existing update kinds. Clients must be prepared to ignore such extensions
+to be forward-compatible. |api-contract|
+
+==============================================================================
+Global Events							    *ui-global*
+
+["set_title", title]
+["set_icon", icon]
+	Set the window title, and icon (minimized) window title, respectively.
+	In windowing systems not distinguishing between the two, "set_icon"
+	can be ignored.
+
+["mode_info_set", cursor_style_enabled, mode_info]
+	`cursor_style_enabled` is a boolean indicating if the UI should set
+	the cursor style. `mode_info` is a list of mode property maps. The
+	current mode is given by the `mode_idx` field of the `mode_change`
+	event.
+
+	Each mode property map may contain these keys:
+
+	KEY		DESCRIPTION ~
+	`cursor_shape`:	"block", "horizontal", "vertical"
+	`cell_percentage`: Cell % occupied by the cursor.
+	`blinkwait`, `blinkon`, `blinkoff`: See |cursor-blinking|.
+	`hl_id`:	Cursor highlight group.
+	`hl_lm`:	Cursor highlight group if 'langmap' is active.
+	`short_name`:	Mode code name, see 'guicursor'.
+	`name`:		Mode descriptive name.
+	`mouse_shape`:	(To be implemented.)
+
+	Some keys are missing in some modes.
+
+["mode_change", mode, mode_idx]
+	The mode changed.  The first parameter `mode` is a string representing
+	the current mode. `mode_idx` is an index into the array received in
+	the `mode_info_set` event. UIs should change the cursor style
+	according to the properties specified in the corresponding item. The
+	set of modes reported will change in new versions of Nvim, for
+	instance more submodes and temporary states might be represented as
+	separate modes.
+
+["mouse_on"]
+["mouse_off"]
+	Tells the client whether mouse support, as determined by |'mouse'|
+	option, is considered to be active in the current mode. This is mostly
+	useful for a terminal frontend, or other situations where nvim mouse
+	would conflict with other usages of the mouse. It is safe for a client
+	to ignore this and always send mouse events.
+
+["busy_on"]
+["busy_off"]
+	Nvim started or stopped being busy, and possibly not responsive to
+	user input. This could be indicated to the user by hiding the cursor.
+
+["suspend"]
+	|:suspend| command or |Ctrl-Z| mapping is used. A terminal client (or other
+	client where it makes sense) could suspend itself.  Other clients can
+	safely ignore it.
+
+["update_menu"]
+	The menu mappings changed.
+
+["bell"]
+["visual_bell"]
+	Notify the user with an audible or visual bell, respectively.
+
+==============================================================================
+Grid Events							      *ui-grid*
+
+["resize", width, height]
+	The grid is resized to `width` and `height` cells.
+
+["clear"]
+	Clear the grid.
+
+["eol_clear"]
+	Clear from the cursor position to the end of the current line.
+
+["cursor_goto", row, col]
+	Move the cursor to position (row, col). Currently, the same cursor is
+	used to define the position for text insertion and the visible cursor.
+	However, only the last cursor position, after processing the entire
+	array in the "redraw" event, is intended to be a visible cursor
+	position.
+
+["update_fg", color]
+["update_bg", color]
+["update_sp", color]
+	Set the default foreground, background and special colors
+	respectively.
+
+						      *ui-event-highlight_set*
+["highlight_set", attrs]
+	Set the attributes that the next text put on the grid will have.
+	`attrs` is a dict with the keys below. Any absent key is reset
+	to its default value. Color defaults are set by the `update_fg` etc
+	updates. All boolean keys default to false.
+
+	`foreground`:	foreground color.
+	`background`:	backround color.
+	`special`:	color to use for underline and undercurl, when present.
+	`reverse`:	reverse video. Foreground and background colors are
+			switched.
+	`italic`:	italic text.
+	`bold`:		bold text.
+	`underline`:	underlined text. The line has `special` color.
+	`undercurl`:	undercurled text. The curl has `special` color.
+
+["put", text]
+	The (utf-8 encoded) string `text` is put at the cursor position
+	(and the cursor is advanced), with the highlights as set by the
+	last `highlight_set` update.
+
+["set_scroll_region", top, bot, left, right]
+	Define the scroll region used by `scroll` below.
+
+["scroll", count]
+	Scroll the text in the scroll region. The diagrams below illustrate
+	what will happen, depending on the scroll direction. "=" is used to
+	represent the SR(scroll region) boundaries and "-" the moved rectangles.
+	Note that dst and src share a common region.
+
+	If count is bigger than 0, move a rectangle in the SR up, this can
+	happen while scrolling down.
+>
+		+-------------------------+
+		| (clipped above SR)      |            ^
+		|=========================| dst_top    |
+		| dst (still in SR)       |            |
+		+-------------------------+ src_top    |
+		| src (moved up) and dst  |            |
+		|-------------------------| dst_bot    |
+		| src (cleared)           |            |
+		+=========================+ src_bot
+<
+	If count is less than zero, move a rectangle in the SR down, this can
+	happen while scrolling up.
+>
+		+=========================+ src_top
+		| src (cleared)           |            |
+		|------------------------ | dst_top    |
+		| src (moved down) and dst|            |
+		+-------------------------+ src_bot    |
+		| dst (still in SR)       |            |
+		|=========================| dst_bot    |
+		| (clipped below SR)      |            v
+		+-------------------------+
+<
+==============================================================================
+Popupmenu Events						 *ui-popupmenu*
+
+Only sent if `ext_popupmenu` option is set in |ui-options|
+
+["popupmenu_show", items, selected, row, col]
+	`items` is an array of the items to show, the
+	items are themselves arrays of the form [word, kind, menu, info]
+	as defined at |complete-items|, except that `word` is replaced by
+	`abbr` if present.  `selected` is the initially selected item, either a
+	zero-based index into the array of items, or -1 if no item is
+	selected. `row` and `col` is the anchor position, where the first
+	character of the completed word will be.
+
+["popupmenu_select", selected]
+	An item in the currently displayed popupmenu is selected. `selected`
+	is either a zero-based index into the array of items from the last
+	`popupmenu_show` event, or -1 if no item is selected.
+
+["popupmenu_hide"]
+	The popupmenu is hidden.
+
+==============================================================================
+Tabline Events							   *ui-tabline*
+
+Only sent if `ext_tabline` option is set in |ui-options|
+
+["tabline_update", curtab, tabs]
+	Tabline was updated. UIs should present this data in a custom tabline
+	widget.
+	curtab:	  Current Tabpage
+	tabs:	  List of Dicts [{ "tab": Tabpage, "name": String }, ...]
+
+==============================================================================
+Cmdline Events							   *ui-cmdline*
+
+Only sent if `ext_cmdline` option is set in |ui-options|
+
+["cmdline_show", content, pos, firstc, prompt, indent, level]
+        content: List of [attrs, string]
+	         [[{}, "t"], [attrs, "est"], ...]
+
+	Triggered when the user types in the cmdline.
+	The `content` is the full content that should be displayed in the
+	cmdline, and the `pos` is the position of the cursor that in the
+	cmdline. The content is divided into chunks with different highlight
+	attributes represented as a dict (see |ui-event-highlight_set|).
+
+	`firstc` and `prompt` are text, that if non-empty should be
+	displayed in front of the command line. `firstc` always indicates
+	built-in command lines such as `:` (ex command) and `/` `?` (search),
+	while `prompt` is an |input()| prompt. `indent` tells how many spaces
+	the content should be indented.
+
+	The Nvim command line can be invoked recursively, for instance by
+	typing `<c-r>=` at the command line prompt. The `level` field is used
+	to distinguish different command lines active at the same time. The
+	first invoked command line has level 1, the next recursively-invoked
+	prompt has level 2. A command line invoked from the |cmd-line-window|
+	has a higher level than than the edited command line.
+
+["cmdline_pos", pos, level]
+	Change the cursor position in the cmdline.
+
+["cmdline_special_char", c, shift, level]
+	Display a special char in the cmdline at the cursor position. This is
+	typically used to indicate a pending state, e.g. after |c_CTRL-V|. If
+	`shift` is true the text after the cursor should be shifted, otherwise
+	it should overwrite the char at the cursor.
+
+	Should be hidden at next cmdline_pos.
+
+["cmdline_hide"]
+	Hide the cmdline.
+
+["cmdline_block_show", lines]
+	Show a block of context to the current command line. For example if
+	the user defines a |:function| interactively: >
+	    :function Foo()
+	    :  echo "foo"
+	    :
+<
+	`lines` is a list of lines of highlighted chunks, in the same form as
+	the "cmdline_show" `contents` parameter.
+
+["cmdline_block_append", line]
+	Append a line at the end of the currently shown block.
+
+["cmdline_block_hide"]
+	Hide the block.
+
+==============================================================================
+ vim:tw=78:ts=8:noet:ft=help:norl:
diff --git a/src/nvim/api/private/helpers.c b/src/nvim/api/private/helpers.c
index e736e29e2d..2944925a9c 100644
--- a/src/nvim/api/private/helpers.c
+++ b/src/nvim/api/private/helpers.c
@@ -667,6 +667,22 @@ tabpage_T *find_tab_by_handle(Tabpage tabpage, Error *err)
   return rv;
 }
 
+/// Allocates a String consisting of a single char. Does not support multibyte
+/// characters. The resulting string is also NUL-terminated, to facilitate
+/// interoperating with code using C strings.
+///
+/// @param char the char to convert
+/// @return the resulting String, if the input char was NUL, an
+///         empty String is returned
+String cchar_to_string(char c)
+{
+  char buf[] = { c, NUL };
+  return (String) {
+    .data = xmemdupz(buf, 1),
+    .size = (c != NUL) ? 1 : 0
+  };
+}
+
 /// Copies a C string into a String (binary safe string, characters + length).
 /// The resulting string is also NUL-terminated, to facilitate interoperating
 /// with code using C strings.
@@ -687,6 +703,23 @@ String cstr_to_string(const char *str)
     };
 }
 
+/// Copies buffer to an allocated String.
+/// The resulting string is also NUL-terminated, to facilitate interoperating
+/// with code using C strings.
+///
+/// @param buf the buffer to copy
+/// @param size length of the buffer
+/// @return the resulting String, if the input string was NULL, an
+///         empty String is returned
+String cbuf_to_string(const char *buf, size_t size)
+  FUNC_ATTR_NONNULL_ALL
+{
+  return (String) {
+    .data = xmemdupz(buf, size),
+    .size = size
+  };
+}
+
 /// Creates a String using the given C string. Unlike
 /// cstr_to_string this function DOES NOT copy the C string.
 ///
diff --git a/src/nvim/api/ui_events.in.h b/src/nvim/api/ui_events.in.h
index 1b5d17584f..65357d008a 100644
--- a/src/nvim/api/ui_events.in.h
+++ b/src/nvim/api/ui_events.in.h
@@ -68,4 +68,20 @@ void popupmenu_select(Integer selected)
 void tabline_update(Tabpage current, Array tabs)
   FUNC_API_SINCE(3) FUNC_API_REMOTE_ONLY;
 
+void cmdline_show(Array content, Integer pos, String firstc, String prompt,
+                  Integer indent, Integer level)
+  FUNC_API_SINCE(3) FUNC_API_REMOTE_ONLY;
+void cmdline_pos(Integer pos, Integer level)
+  FUNC_API_SINCE(3) FUNC_API_REMOTE_ONLY;
+void cmdline_special_char(String c, Boolean shift, Integer level)
+  FUNC_API_SINCE(3) FUNC_API_REMOTE_ONLY;
+void cmdline_hide(Integer level)
+  FUNC_API_SINCE(3) FUNC_API_REMOTE_ONLY;
+void cmdline_block_show(Array lines)
+  FUNC_API_SINCE(3) FUNC_API_REMOTE_ONLY;
+void cmdline_block_append(Array lines)
+  FUNC_API_SINCE(3) FUNC_API_REMOTE_ONLY;
+void cmdline_block_hide(void)
+  FUNC_API_SINCE(3) FUNC_API_REMOTE_ONLY;
+
 #endif  // NVIM_API_UI_EVENTS_IN_H
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index ef2f671f36..c7cb51ac29 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -11147,17 +11147,18 @@ void get_user_input(const typval_T *const argvars,
 
   cmd_silent = false;  // Want to see the prompt.
   // Only the part of the message after the last NL is considered as
-  // prompt for the command line.
-  const char *p = strrchr(prompt, '\n');
-  if (p == NULL) {
-    p = prompt;
-  } else {
-    p++;
-    msg_start();
-    msg_clr_eos();
-    msg_puts_attr_len(prompt, p - prompt, echo_attr);
-    msg_didout = false;
-    msg_starthere();
+  // prompt for the command line, unlsess cmdline is externalized
+  const char *p = prompt;
+  if (!ui_is_external(kUICmdline)) {
+    const char *lastnl = strrchr(prompt, '\n');
+    if (lastnl != NULL) {
+      p = lastnl+1;
+      msg_start();
+      msg_clr_eos();
+      msg_puts_attr_len(prompt, p - prompt, echo_attr);
+      msg_didout = false;
+      msg_starthere();
+    }
   }
   cmdline_row = msg_row;
 
@@ -19643,6 +19644,7 @@ void ex_function(exarg_T *eap)
   int todo;
   hashitem_T  *hi;
   int sourcing_lnum_off;
+  bool show_block = false;
 
   /*
    * ":function" without argument: list functions.
@@ -19816,6 +19818,11 @@ void ex_function(exarg_T *eap)
     goto errret_2;
   }
 
+  if (KeyTyped && ui_is_external(kUICmdline)) {
+    show_block = true;
+    ui_ext_cmdline_block_append(0, (const char *)eap->cmd);
+  }
+
   // find extra arguments "range", "dict", "abort" and "closure"
   for (;; ) {
     p = skipwhite(p);
@@ -19868,7 +19875,9 @@ void ex_function(exarg_T *eap)
     if (!eap->skip && did_emsg)
       goto erret;
 
-    msg_putchar('\n');              /* don't overwrite the function name */
+    if (!ui_is_external(kUICmdline)) {
+      msg_putchar('\n');              // don't overwrite the function name
+    }
     cmdline_row = msg_row;
   }
 
@@ -19902,6 +19911,9 @@ void ex_function(exarg_T *eap)
       EMSG(_("E126: Missing :endfunction"));
       goto erret;
     }
+    if (show_block) {
+      ui_ext_cmdline_block_append(indent, (const char *)theline);
+    }
 
     /* Detect line continuation: sourcing_lnum increased more than one. */
     if (sourcing_lnum > sourcing_lnum_off + 1)
@@ -20194,6 +20206,9 @@ ret_free:
   xfree(name);
   did_emsg |= saved_did_emsg;
   need_wait_return |= saved_wait_return;
+  if (show_block) {
+    ui_ext_cmdline_block_leave();
+  }
 }
 
 /// Get a function name, translating "<SID>" and "<SNR>".
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 54e5bcb9ff..e79476ab53 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -67,6 +67,30 @@
 #include "nvim/api/private/helpers.h"
 #include "nvim/highlight_defs.h"
 
+/// Command-line colors: one chunk
+///
+/// Defines a region which has the same highlighting.
+typedef struct {
+  int start;  ///< Colored chunk start.
+  int end;  ///< Colored chunk end (exclusive, > start).
+  int attr;  ///< Highlight attr.
+} CmdlineColorChunk;
+
+/// Command-line colors
+///
+/// Holds data about all colors.
+typedef kvec_t(CmdlineColorChunk) CmdlineColors;
+
+/// Command-line coloring
+///
+/// Holds both what are the colors and what have been colored. Latter is used to
+/// suppress unnecessary calls to coloring callbacks.
+typedef struct {
+  unsigned prompt_id;  ///< ID of the prompt which was colored last.
+  char *cmdbuff;  ///< What exactly was colored last time or NULL.
+  CmdlineColors colors;  ///< Last colors.
+} ColoredCmdline;
+
 /*
  * Variables shared between getcmdline(), redrawcmdline() and others.
  * These need to be saved when using CTRL-R |, that's why they are in a
@@ -91,6 +115,11 @@ struct cmdline_info {
   int input_fn;                 // when TRUE Invoked for input() function
   unsigned prompt_id;  ///< Prompt number, used to disable coloring on errors.
   Callback highlight_callback;  ///< Callback used for coloring user input.
+  ColoredCmdline last_colors;   ///< Last cmdline colors
+  int level;                    // current cmdline level
+  struct cmdline_info *prev_ccline;  ///< pointer to saved cmdline state
+  char special_char;            ///< last putcmdline char (used for redraws)
+  bool special_shift;           ///< shift of last putcmdline char
 };
 /// Last value of prompt_id, incremented when doing new prompt
 static unsigned last_prompt_id = 0;
@@ -143,36 +172,6 @@ typedef struct command_line_state {
   struct cmdline_info save_ccline;
 } CommandLineState;
 
-/// Command-line colors: one chunk
-///
-/// Defines a region which has the same highlighting.
-typedef struct {
-  int start;  ///< Colored chunk start.
-  int end;  ///< Colored chunk end (exclusive, > start).
-  int attr;  ///< Highlight attr.
-} CmdlineColorChunk;
-
-/// Command-line colors
-///
-/// Holds data about all colors.
-typedef kvec_t(CmdlineColorChunk) CmdlineColors;
-
-/// Command-line coloring
-///
-/// Holds both what are the colors and what have been colored. Latter is used to
-/// suppress unnecessary calls to coloring callbacks.
-typedef struct {
-  unsigned prompt_id;  ///< ID of the prompt which was colored last.
-  char *cmdbuff;  ///< What exactly was colored last time or NULL.
-  CmdlineColors colors;  ///< Last colors.
-} ColoredCmdline;
-
-/// Last command-line colors.
-ColoredCmdline last_ccline_colors = {
-  .cmdbuff = NULL,
-  .colors = KV_INITIAL_VALUE
-};
-
 typedef struct cmdline_info CmdlineInfo;
 
 /* The current cmdline_info.  It is initialized in getcmdline() and after that
@@ -185,6 +184,8 @@ static int cmd_showtail;                /* Only show path tail in lists ? */
 
 static int new_cmdpos;          /* position set by set_cmdline_pos() */
 
+static Array cmdline_block;  ///< currently displayed block of context
+
 /*
  * Type used by call_user_expand_func
  */
@@ -239,6 +240,7 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
   }
 
   ccline.prompt_id = last_prompt_id++;
+  ccline.level++;
   ccline.overstrike = false;                // always start in insert mode
   clearpos(&s->match_end);
   s->save_cursor = curwin->w_cursor;        // may be restored later
@@ -258,6 +260,9 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
   ccline.cmdlen = ccline.cmdpos = 0;
   ccline.cmdbuff[0] = NUL;
 
+  ccline.last_colors = (ColoredCmdline){ .cmdbuff = NULL,
+                                         .colors = KV_INITIAL_VALUE };
+
   // autoindent for :insert and :append
   if (s->firstc <= 0) {
     memset(ccline.cmdbuff, ' ', s->indent);
@@ -408,12 +413,19 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
   setmouse();
   ui_cursor_shape();            // may show different cursor shape
   xfree(s->save_p_icm);
+  xfree(ccline.last_colors.cmdbuff);
+  kv_destroy(ccline.last_colors.colors);
 
   {
     char_u *p = ccline.cmdbuff;
 
     // Make ccline empty, getcmdline() may try to use it.
     ccline.cmdbuff = NULL;
+
+    if (ui_is_external(kUICmdline)) {
+      ui_call_cmdline_hide(ccline.level);
+    }
+    ccline.level--;
     return p;
   }
 }
@@ -804,7 +816,9 @@ static int command_line_execute(VimState *state, int key)
       }
 
       if (!cmd_silent) {
-        ui_cursor_goto(msg_row, 0);
+        if (!ui_is_external(kUICmdline)) {
+          ui_cursor_goto(msg_row, 0);
+        }
         ui_flush();
       }
       return 0;
@@ -1134,7 +1148,7 @@ static int command_line_handle_key(CommandLineState *s)
 
       xfree(ccline.cmdbuff);               // no commandline to return
       ccline.cmdbuff = NULL;
-      if (!cmd_silent) {
+      if (!cmd_silent && !ui_is_external(kUICmdline)) {
         if (cmdmsg_rl) {
           msg_col = Columns;
         } else {
@@ -1586,9 +1600,14 @@ static int command_line_handle_key(CommandLineState *s)
     s->do_abbr = false;                   // don't do abbreviation now
     // may need to remove ^ when composing char was typed
     if (enc_utf8 && utf_iscomposing(s->c) && !cmd_silent) {
-      draw_cmdline(ccline.cmdpos, ccline.cmdlen - ccline.cmdpos);
-      msg_putchar(' ');
-      cursorcmd();
+      if (ui_is_external(kUICmdline)) {
+        // TODO(bfredl): why not make unputcmdline also work with true?
+        unputcmdline();
+      } else {
+        draw_cmdline(ccline.cmdpos, ccline.cmdlen - ccline.cmdpos);
+        msg_putchar(' ');
+        cursorcmd();
+      }
     }
     break;
 
@@ -2346,8 +2365,7 @@ enum { MAX_CB_ERRORS = 1 };
 /// Should use built-in command parser or user-specified one. Currently only the
 /// latter is supported.
 ///
-/// @param[in]  colored_ccline  Command-line to color.
-/// @param[out]  ret_ccline_colors  What should be colored. Also holds a cache:
+/// @param[in,out]  colored_ccline  Command-line to color. Also holds a cache:
 ///                                 if ->prompt_id and ->cmdbuff values happen
 ///                                 to be equal to those from colored_cmdline it
 ///                                 will just do nothing, assuming that ->colors
@@ -2357,11 +2375,11 @@ enum { MAX_CB_ERRORS = 1 };
 ///
 /// @return true if draw_cmdline may proceed, false if it does not need anything
 ///         to do.
-static bool color_cmdline(const CmdlineInfo *const colored_ccline,
-                          ColoredCmdline *const ret_ccline_colors)
+static bool color_cmdline(CmdlineInfo *colored_ccline)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
 {
   bool printed_errmsg = false;
+
 #define PRINT_ERRMSG(...) \
   do { \
     msg_putchar('\n'); \
@@ -2370,19 +2388,21 @@ static bool color_cmdline(const CmdlineInfo *const colored_ccline,
   } while (0)
   bool ret = true;
 
+  ColoredCmdline *ccline_colors = &colored_ccline->last_colors;
+
   // Check whether result of the previous call is still valid.
-  if (ret_ccline_colors->prompt_id == colored_ccline->prompt_id
-      && ret_ccline_colors->cmdbuff != NULL
-      && STRCMP(ret_ccline_colors->cmdbuff, colored_ccline->cmdbuff) == 0) {
+  if (ccline_colors->prompt_id == colored_ccline->prompt_id
+      && ccline_colors->cmdbuff != NULL
+      && STRCMP(ccline_colors->cmdbuff, colored_ccline->cmdbuff) == 0) {
     return ret;
   }
 
-  kv_size(ret_ccline_colors->colors) = 0;
+  kv_size(ccline_colors->colors) = 0;
 
   if (colored_ccline->cmdbuff == NULL || *colored_ccline->cmdbuff == NUL) {
     // Nothing to do, exiting.
-    xfree(ret_ccline_colors->cmdbuff);
-    ret_ccline_colors->cmdbuff = NULL;
+    xfree(ccline_colors->cmdbuff);
+    ccline_colors->cmdbuff = NULL;
     return ret;
   }
 
@@ -2395,7 +2415,7 @@ static bool color_cmdline(const CmdlineInfo *const colored_ccline,
 
   static unsigned prev_prompt_id = UINT_MAX;
   static int prev_prompt_errors = 0;
-  Callback color_cb = { .type = kCallbackNone };
+  Callback color_cb = CALLBACK_NONE;
   bool can_free_cb = false;
   TryState tstate;
   Error err = ERROR_INIT;
@@ -2504,7 +2524,7 @@ static bool color_cmdline(const CmdlineInfo *const colored_ccline,
       goto color_cmdline_error;
     }
     if (start != prev_end) {
-      kv_push(ret_ccline_colors->colors, ((CmdlineColorChunk) {
+      kv_push(ccline_colors->colors, ((CmdlineColorChunk) {
         .start = prev_end,
         .end = start,
         .attr = 0,
@@ -2533,14 +2553,14 @@ static bool color_cmdline(const CmdlineInfo *const colored_ccline,
     }
     const int id = syn_name2id((char_u *)group);
     const int attr = (id == 0 ? 0 : syn_id2attr(id));
-    kv_push(ret_ccline_colors->colors, ((CmdlineColorChunk) {
+    kv_push(ccline_colors->colors, ((CmdlineColorChunk) {
       .start = start,
       .end = end,
       .attr = attr,
     }));
   }
   if (prev_end < colored_ccline->cmdlen) {
-    kv_push(ret_ccline_colors->colors, ((CmdlineColorChunk) {
+    kv_push(ccline_colors->colors, ((CmdlineColorChunk) {
       .start = prev_end,
       .end = colored_ccline->cmdlen,
       .attr = 0,
@@ -2552,14 +2572,14 @@ color_cmdline_end:
   if (can_free_cb) {
     callback_free(&color_cb);
   }
-  xfree(ret_ccline_colors->cmdbuff);
+  xfree(ccline_colors->cmdbuff);
   // Note: errors “output” is cached just as well as regular results.
-  ret_ccline_colors->prompt_id = colored_ccline->prompt_id;
+  ccline_colors->prompt_id = colored_ccline->prompt_id;
   if (arg_allocated) {
-    ret_ccline_colors->cmdbuff = (char *)arg.vval.v_string;
+    ccline_colors->cmdbuff = (char *)arg.vval.v_string;
   } else {
-    ret_ccline_colors->cmdbuff = xmemdupz((const char *)colored_ccline->cmdbuff,
-                                          (size_t)colored_ccline->cmdlen);
+    ccline_colors->cmdbuff = xmemdupz((const char *)colored_ccline->cmdbuff,
+                                      (size_t)colored_ccline->cmdlen);
   }
   tv_clear(&tv);
   return ret;
@@ -2572,7 +2592,7 @@ color_cmdline_error:
   (void)printed_errmsg;
 
   prev_prompt_errors++;
-  kv_size(ret_ccline_colors->colors) = 0;
+  kv_size(ccline_colors->colors) = 0;
   redrawcmdline();
   ret = false;
   goto color_cmdline_end;
@@ -2585,7 +2605,13 @@ color_cmdline_error:
  */
 static void draw_cmdline(int start, int len)
 {
-  if (!color_cmdline(&ccline, &last_ccline_colors)) {
+  if (!color_cmdline(&ccline)) {
+    return;
+  }
+
+  if (ui_is_external(kUICmdline)) {
+    ccline.special_char = NUL;
+    ui_ext_cmdline_show(&ccline);
     return;
   }
 
@@ -2687,9 +2713,9 @@ static void draw_cmdline(int start, int len)
     msg_outtrans_len(arshape_buf, newlen);
   } else {
 draw_cmdline_no_arabicshape:
-    if (kv_size(last_ccline_colors.colors)) {
-      for (size_t i = 0; i < kv_size(last_ccline_colors.colors); i++) {
-        CmdlineColorChunk chunk = kv_A(last_ccline_colors.colors, i);
+    if (kv_size(ccline.last_colors.colors)) {
+      for (size_t i = 0; i < kv_size(ccline.last_colors.colors); i++) {
+        CmdlineColorChunk chunk = kv_A(ccline.last_colors.colors, i);
         if (chunk.end <= start) {
           continue;
         }
@@ -2704,6 +2730,107 @@ draw_cmdline_no_arabicshape:
   }
 }
 
+static void ui_ext_cmdline_show(CmdlineInfo *line)
+{
+  Array content = ARRAY_DICT_INIT;
+  if (cmdline_star) {
+    size_t len = 0;
+    for (char_u *p = ccline.cmdbuff; *p; mb_ptr_adv(p)) {
+      len++;
+    }
+    char *buf = xmallocz(len);
+    memset(buf, '*', len);
+    Array item = ARRAY_DICT_INIT;
+    ADD(item, DICTIONARY_OBJ((Dictionary)ARRAY_DICT_INIT));
+    ADD(item, STRING_OBJ(((String) { .data = buf, .size = len })));
+    ADD(content, ARRAY_OBJ(item));
+  } else if (kv_size(line->last_colors.colors)) {
+    for (size_t i = 0; i < kv_size(line->last_colors.colors); i++) {
+      CmdlineColorChunk chunk = kv_A(line->last_colors.colors, i);
+      Array item = ARRAY_DICT_INIT;
+
+      if (chunk.attr) {
+        attrentry_T *aep = syn_cterm_attr2entry(chunk.attr);
+        // TODO(bfredl): this desicion could be delayed by making attr_code a
+        // recognized type
+        HlAttrs rgb_attrs = attrentry2hlattrs(aep, true);
+        ADD(item, DICTIONARY_OBJ(hlattrs2dict(rgb_attrs)));
+      } else {
+        ADD(item, DICTIONARY_OBJ((Dictionary)ARRAY_DICT_INIT));
+      }
+      ADD(item, STRING_OBJ(cbuf_to_string((char *)line->cmdbuff + chunk.start,
+                                          chunk.end-chunk.start)));
+      ADD(content, ARRAY_OBJ(item));
+    }
+  } else {
+    Array item = ARRAY_DICT_INIT;
+    ADD(item, DICTIONARY_OBJ((Dictionary)ARRAY_DICT_INIT));
+    ADD(item, STRING_OBJ(cstr_to_string((char *)(line->cmdbuff))));
+    ADD(content, ARRAY_OBJ(item));
+  }
+  ui_call_cmdline_show(content, line->cmdpos,
+                       cchar_to_string((char)line->cmdfirstc),
+                       cstr_to_string((char *)(line->cmdprompt)),
+                       line->cmdindent,
+                       line->level);
+  if (line->special_char) {
+    ui_call_cmdline_special_char(cchar_to_string((char)(line->special_char)),
+                                 line->special_shift,
+                                 line->level);
+  }
+}
+
+void ui_ext_cmdline_block_append(int indent, const char *line)
+{
+  char *buf = xmallocz(indent + strlen(line));
+  memset(buf, ' ', indent);
+  memcpy(buf+indent, line, strlen(line));
+
+  Array item = ARRAY_DICT_INIT;
+  ADD(item, DICTIONARY_OBJ((Dictionary)ARRAY_DICT_INIT));
+  ADD(item, STRING_OBJ(cstr_as_string(buf)));
+  Array content = ARRAY_DICT_INIT;
+  ADD(content, ARRAY_OBJ(item));
+  ADD(cmdline_block, ARRAY_OBJ(content));
+  if (cmdline_block.size > 1) {
+    ui_call_cmdline_block_append(copy_array(content));
+  } else {
+    ui_call_cmdline_block_show(copy_array(cmdline_block));
+  }
+}
+
+void ui_ext_cmdline_block_leave(void)
+{
+  api_free_array(cmdline_block);
+  ui_call_cmdline_block_hide();
+}
+
+/// Extra redrawing needed for redraw! and on ui_attach
+/// assumes "redrawcmdline()" will already be invoked
+void cmdline_screen_cleared(void)
+{
+  if (!ui_is_external(kUICmdline)) {
+    return;
+  }
+
+  if (cmdline_block.size) {
+    ui_call_cmdline_block_show(copy_array(cmdline_block));
+  }
+
+  int prev_level = ccline.level-1;
+  CmdlineInfo *prev_ccline = ccline.prev_ccline;
+  while (prev_level > 0 && prev_ccline) {
+    if (prev_ccline->level == prev_level) {
+      // don't redraw a cmdline already shown in the cmdline window
+      if (prev_level != cmdwin_level) {
+        ui_ext_cmdline_show(prev_ccline);
+      }
+      prev_level--;
+    }
+    prev_ccline = prev_ccline->prev_ccline;
+  }
+}
+
 /*
  * Put a character on the command line.  Shifts the following text to the
  * right when "shift" is TRUE.  Used for CTRL-V, CTRL-K, etc.
@@ -2711,33 +2838,39 @@ draw_cmdline_no_arabicshape:
  */
 void putcmdline(int c, int shift)
 {
-  if (cmd_silent)
+  if (cmd_silent) {
     return;
-  msg_no_more = TRUE;
-  msg_putchar(c);
-  if (shift)
-    draw_cmdline(ccline.cmdpos, ccline.cmdlen - ccline.cmdpos);
-  msg_no_more = FALSE;
+  }
+  if (!ui_is_external(kUICmdline)) {
+    msg_no_more = true;
+    msg_putchar(c);
+    if (shift) {
+      draw_cmdline(ccline.cmdpos, ccline.cmdlen - ccline.cmdpos);
+    }
+    msg_no_more = false;
+  } else {
+    ccline.special_char = c;
+    ccline.special_shift = shift;
+    ui_call_cmdline_special_char(cchar_to_string((char)(c)), shift,
+                                 ccline.level);
+  }
   cursorcmd();
   ui_cursor_shape();
 }
 
-/*
- * Undo a putcmdline(c, FALSE).
- */
+/// Undo a putcmdline(c, FALSE).
 void unputcmdline(void)
 {
-  if (cmd_silent)
+  if (cmd_silent) {
     return;
-  msg_no_more = TRUE;
-  if (ccline.cmdlen == ccline.cmdpos)
+  }
+  msg_no_more = true;
+  if (ccline.cmdlen == ccline.cmdpos && !ui_is_external(kUICmdline)) {
     msg_putchar(' ');
-  else if (has_mbyte)
-    draw_cmdline(ccline.cmdpos,
-        (*mb_ptr2len)(ccline.cmdbuff + ccline.cmdpos));
-  else
-    draw_cmdline(ccline.cmdpos, 1);
-  msg_no_more = FALSE;
+  } else {
+    draw_cmdline(ccline.cmdpos, mb_ptr2len(ccline.cmdbuff + ccline.cmdpos));
+  }
+  msg_no_more = false;
   cursorcmd();
   ui_cursor_shape();
 }
@@ -2871,9 +3004,6 @@ void put_on_cmdline(char_u *str, int len, int redraw)
     msg_check();
 }
 
-static struct cmdline_info prev_ccline;
-static int prev_ccline_used = FALSE;
-
 /*
  * Save ccline, because obtaining the "=" register may execute "normal :cmd"
  * and overwrite it.  But get_cmdline_str() may need it, thus make it
@@ -2881,15 +3011,12 @@ static int prev_ccline_used = FALSE;
  */
 static void save_cmdline(struct cmdline_info *ccp)
 {
-  if (!prev_ccline_used) {
-    memset(&prev_ccline, 0, sizeof(struct cmdline_info));
-    prev_ccline_used = TRUE;
-  }
-  *ccp = prev_ccline;
-  prev_ccline = ccline;
+  *ccp = ccline;
+  ccline.prev_ccline = ccp;
   ccline.cmdbuff = NULL;
   ccline.cmdprompt = NULL;
   ccline.xpc = NULL;
+  ccline.special_char = NUL;
 }
 
 /*
@@ -2897,8 +3024,7 @@ static void save_cmdline(struct cmdline_info *ccp)
  */
 static void restore_cmdline(struct cmdline_info *ccp)
 {
-  ccline = prev_ccline;
-  prev_ccline = *ccp;
+  ccline = *ccp;
 }
 
 /*
@@ -3066,17 +3192,25 @@ static void redrawcmdprompt(void)
 
   if (cmd_silent)
     return;
-  if (ccline.cmdfirstc != NUL)
+  if (ui_is_external(kUICmdline)) {
+    ui_ext_cmdline_show(&ccline);
+    return;
+  }
+  if (ccline.cmdfirstc != NUL) {
     msg_putchar(ccline.cmdfirstc);
+  }
   if (ccline.cmdprompt != NULL) {
     msg_puts_attr((const char *)ccline.cmdprompt, ccline.cmdattr);
     ccline.cmdindent = msg_col + (msg_row - cmdline_row) * Columns;
-    /* do the reverse of set_cmdspos() */
-    if (ccline.cmdfirstc != NUL)
-      --ccline.cmdindent;
-  } else
-    for (i = ccline.cmdindent; i > 0; --i)
+    // do the reverse of set_cmdspos()
+    if (ccline.cmdfirstc != NUL) {
+      ccline.cmdindent--;
+    }
+  } else {
+    for (i = ccline.cmdindent; i > 0; i--) {
       msg_putchar(' ');
+    }
+  }
 }
 
 /*
@@ -3087,6 +3221,11 @@ void redrawcmd(void)
   if (cmd_silent)
     return;
 
+  if (ui_is_external(kUICmdline)) {
+    draw_cmdline(0, ccline.cmdlen);
+    return;
+  }
+
   /* when 'incsearch' is set there may be no command line while redrawing */
   if (ccline.cmdbuff == NULL) {
     ui_cursor_goto(cmdline_row, 0);
@@ -3130,6 +3269,11 @@ static void cursorcmd(void)
   if (cmd_silent)
     return;
 
+  if (ui_is_external(kUICmdline)) {
+    ui_call_cmdline_pos(ccline.cmdpos, ccline.level);
+    return;
+  }
+
   if (cmdmsg_rl) {
     msg_row = cmdline_row  + (ccline.cmdspos / (int)(Columns - 1));
     msg_col = (int)Columns - (ccline.cmdspos % (int)(Columns - 1)) - 1;
@@ -3147,6 +3291,9 @@ static void cursorcmd(void)
 
 void gotocmdline(int clr)
 {
+  if (ui_is_external(kUICmdline)) {
+    return;
+  }
   msg_start();
   if (cmdmsg_rl)
     msg_col = Columns - 1;
@@ -5204,13 +5351,15 @@ int get_history_idx(int histype)
  */
 static struct cmdline_info *get_ccline_ptr(void)
 {
-  if ((State & CMDLINE) == 0)
+  if ((State & CMDLINE) == 0) {
     return NULL;
-  if (ccline.cmdbuff != NULL)
+  } else if (ccline.cmdbuff != NULL) {
     return &ccline;
-  if (prev_ccline_used && prev_ccline.cmdbuff != NULL)
-    return &prev_ccline;
-  return NULL;
+  } else if (ccline.prev_ccline && ccline.prev_ccline->cmdbuff != NULL) {
+    return ccline.prev_ccline;
+  } else {
+    return NULL;
+  }
 }
 
 /*
@@ -5646,6 +5795,7 @@ static int ex_window(void)
     return K_IGNORE;
   }
   cmdwin_type = get_cmdline_type();
+  cmdwin_level = ccline.level;
 
   // Create empty command-line buffer.
   buf_open_scratch(0, "[Command Line]");
@@ -5698,6 +5848,9 @@ static int ex_window(void)
   curwin->w_cursor.col = ccline.cmdpos;
   changed_line_abv_curs();
   invalidate_botline();
+  if (ui_is_external(kUICmdline)) {
+    ui_call_cmdline_hide(ccline.level);
+  }
   redraw_later(SOME_VALID);
 
   // Save the command line info, can be used recursively.
@@ -5740,6 +5893,7 @@ static int ex_window(void)
   // Restore the command line info.
   restore_cmdline(&save_ccline);
   cmdwin_type = 0;
+  cmdwin_level = 0;
 
   exmode_active = save_exmode;
 
@@ -5974,3 +6128,4 @@ static void set_search_match(pos_T *t)
     coladvance((colnr_T)MAXCOL);
   }
 }
+
diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index 300e506854..0f3e132bc0 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -981,9 +981,10 @@ EXTERN int fill_diff INIT(= '-');
 EXTERN int km_stopsel INIT(= FALSE);
 EXTERN int km_startsel INIT(= FALSE);
 
-EXTERN int cedit_key INIT(= -1);        /* key value of 'cedit' option */
-EXTERN int cmdwin_type INIT(= 0);       /* type of cmdline window or 0 */
-EXTERN int cmdwin_result INIT(= 0);      /* result of cmdline window or 0 */
+EXTERN int cedit_key INIT(= -1);     ///< key value of 'cedit' option
+EXTERN int cmdwin_type INIT(= 0);    ///< type of cmdline window or 0
+EXTERN int cmdwin_result INIT(= 0);  ///< result of cmdline window or 0
+EXTERN int cmdwin_level INIT(= 0);   ///< cmdline recursion level
 
 EXTERN char_u no_lines_msg[] INIT(= N_("--No lines in buffer--"));
 
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 38ecd88ec0..41e900eb4c 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -345,8 +345,9 @@ void update_screen(int type)
   if (need_highlight_changed)
     highlight_changed();
 
-  if (type == CLEAR) {          /* first clear screen */
-    screenclear();              /* will reset clear_cmdline */
+  if (type == CLEAR) {          // first clear screen
+    screenclear();              // will reset clear_cmdline
+    cmdline_screen_cleared();   // clear external cmdline state
     type = NOT_VALID;
   }
 
diff --git a/test/functional/ui/cmdline_spec.lua b/test/functional/ui/cmdline_spec.lua
new file mode 100644
index 0000000000..0f8302b036
--- /dev/null
+++ b/test/functional/ui/cmdline_spec.lua
@@ -0,0 +1,525 @@
+local helpers = require('test.functional.helpers')(after_each)
+local Screen = require('test.functional.ui.screen')
+local clear, feed, eq = helpers.clear, helpers.feed, helpers.eq
+local source = helpers.source
+local ok = helpers.ok
+local command = helpers.command
+
+describe('external cmdline', function()
+  local screen
+  local last_level = 0
+  local cmdline = {}
+  local block = nil
+
+  before_each(function()
+    clear()
+    cmdline, block = {}, nil
+    screen = Screen.new(25, 5)
+    screen:attach({rgb=true, ext_cmdline=true})
+    screen:set_on_event_handler(function(name, data)
+      if name == "cmdline_show" then
+        local content, pos, firstc, prompt, indent, level = unpack(data)
+        ok(level > 0)
+        cmdline[level] = {content=content, pos=pos, firstc=firstc,
+                          prompt=prompt, indent=indent}
+        last_level = level
+      elseif name == "cmdline_hide" then
+        local level = data[1]
+        cmdline[level] = nil
+      elseif name == "cmdline_special_char" then
+        local char, shift, level = unpack(data)
+        cmdline[level].special = {char, shift}
+      elseif name == "cmdline_pos" then
+        local pos, level = unpack(data)
+        cmdline[level].pos = pos
+      elseif name == "cmdline_block_show" then
+        block = data[1]
+      elseif name == "cmdline_block_append" then
+        block[#block+1] = data[1]
+      elseif name == "cmdline_block_hide" then
+        block = nil
+      end
+    end)
+  end)
+
+  after_each(function()
+    screen:detach()
+  end)
+
+  local function expect_cmdline(level, expected)
+    local attr_ids = screen._default_attr_ids
+    local attr_ignore = screen._default_attr_ignore
+    local actual = ''
+    for _, chunk in ipairs(cmdline[level] and cmdline[level].content or {}) do
+      local attrs, text = chunk[1], chunk[2]
+      if screen:_equal_attrs(attrs, {}) then
+        actual = actual..text
+      else
+        local attr_id = screen:_get_attr_id(attr_ids, attr_ignore, attrs)
+        actual =  actual..'{' .. attr_id .. ':' .. text .. '}'
+      end
+    end
+    eq(expected, actual)
+  end
+
+  it('works', function()
+    feed(':')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq(1, last_level)
+      eq({{
+        content = { { {}, "" } },
+        firstc = ":",
+        indent = 0,
+        pos = 0,
+        prompt = ""
+      }}, cmdline)
+    end)
+
+    feed('sign')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "sign" } },
+        firstc = ":",
+        indent = 0,
+        pos = 4,
+        prompt = ""
+      }}, cmdline)
+    end)
+
+    feed('<Left>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "sign" } },
+        firstc = ":",
+        indent = 0,
+        pos = 3,
+        prompt = ""
+      }}, cmdline)
+    end)
+
+    feed('<bs>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "sin" } },
+        firstc = ":",
+        indent = 0,
+        pos = 2,
+        prompt = ""
+      }}, cmdline)
+    end)
+
+    feed('<Esc>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({}, cmdline)
+    end)
+  end)
+
+  it("works with input()", function()
+    feed(':call input("input", "default")<cr>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "default" } },
+        firstc = "",
+        indent = 0,
+        pos = 7,
+        prompt = "input"
+      }}, cmdline)
+    end)
+    feed('<cr>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({}, cmdline)
+    end)
+
+  end)
+
+  it("works with special chars and nested cmdline", function()
+    feed(':xx<c-r>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "xx" } },
+        firstc = ":",
+        indent = 0,
+        pos = 2,
+        prompt = "",
+        special = {'"', true},
+      }}, cmdline)
+    end)
+
+    feed('=')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "xx" } },
+        firstc = ":",
+        indent = 0,
+        pos = 2,
+        prompt = "",
+        special = {'"', true},
+      },{
+        content = { { {}, "" } },
+        firstc = "=",
+        indent = 0,
+        pos = 0,
+        prompt = "",
+      }}, cmdline)
+    end)
+
+    feed('1+2')
+    local expectation = {{
+        content = { { {}, "xx" } },
+        firstc = ":",
+        indent = 0,
+        pos = 2,
+        prompt = "",
+        special = {'"', true},
+      },{
+        content = { { {}, "1+2" } },
+        firstc = "=",
+        indent = 0,
+        pos = 3,
+        prompt = "",
+      }}
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq(expectation, cmdline)
+    end)
+
+    -- erase information, so we check if it is retransmitted
+    cmdline = {}
+    command("redraw!")
+    -- redraw! forgets cursor position. Be OK with that, as UI should indicate
+    -- focus is at external cmdline anyway.
+    screen:expect([[
+                               |
+      ~                        |
+      ~                        |
+      ~                        |
+      ^                         |
+    ]], nil, nil, function()
+      eq(expectation, cmdline)
+    end)
+
+
+    feed('<cr>')
+    screen:expect([[
+                               |
+      ~                        |
+      ~                        |
+      ~                        |
+      ^                         |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "xx3" } },
+        firstc = ":",
+        indent = 0,
+        pos = 3,
+        prompt = "",
+      }}, cmdline)
+    end)
+
+    feed('<esc>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({}, cmdline)
+    end)
+  end)
+
+  it("works with function definitions", function()
+    feed(':function Foo()<cr>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "" } },
+        firstc = ":",
+        indent = 2,
+        pos = 0,
+        prompt = "",
+      }}, cmdline)
+      eq({{{{}, 'function Foo()'}}}, block)
+    end)
+
+    feed('line1<cr>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{{{}, 'function Foo()'}},
+          {{{}, '  line1'}}}, block)
+    end)
+
+    block = {}
+    command("redraw!")
+    screen:expect([[
+                               |
+      ~                        |
+      ~                        |
+      ~                        |
+      ^                         |
+    ]], nil, nil, function()
+      eq({{{{}, 'function Foo()'}},
+          {{{}, '  line1'}}}, block)
+    end)
+
+
+    feed('endfunction<cr>')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq(nil, block)
+    end)
+  end)
+
+  it("works with cmdline window", function()
+    feed(':make')
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "make" } },
+        firstc = ":",
+        indent = 0,
+        pos = 4,
+        prompt = ""
+      }}, cmdline)
+    end)
+
+    feed('<c-f>')
+    screen:expect([[
+                               |
+      [No Name]                |
+      :make^                    |
+      [Command Line]           |
+                               |
+    ]], nil, nil, function()
+      eq({}, cmdline)
+    end)
+
+    -- nested cmdline
+    feed(':yank')
+    screen:expect([[
+                               |
+      [No Name]                |
+      :make^                    |
+      [Command Line]           |
+                               |
+    ]], nil, nil, function()
+      eq({nil, {
+        content = { { {}, "yank" } },
+        firstc = ":",
+        indent = 0,
+        pos = 4,
+        prompt = ""
+      }}, cmdline)
+    end)
+
+    cmdline = {}
+    command("redraw!")
+    screen:expect([[
+                               |
+      [No Name]                |
+      :make                    |
+      [Command Line]           |
+      ^                         |
+    ]], nil, nil, function()
+      eq({nil, {
+        content = { { {}, "yank" } },
+        firstc = ":",
+        indent = 0,
+        pos = 4,
+        prompt = ""
+      }}, cmdline)
+    end)
+
+    feed("<c-c>")
+    screen:expect([[
+                               |
+      [No Name]                |
+      :make^                    |
+      [Command Line]           |
+                               |
+    ]], nil, nil, function()
+      eq({}, cmdline)
+    end)
+
+    feed("<c-c>")
+    screen:expect([[
+                               |
+      [No Name]                |
+      :make^                    |
+      [Command Line]           |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "make" } },
+        firstc = ":",
+        indent = 0,
+        pos = 4,
+        prompt = ""
+      }}, cmdline)
+    end)
+
+    cmdline = {}
+    command("redraw!")
+    screen:expect([[
+                               |
+      ~                        |
+      ~                        |
+      ~                        |
+      ^                         |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "make" } },
+        firstc = ":",
+        indent = 0,
+        pos = 4,
+        prompt = ""
+      }}, cmdline)
+    end)
+  end)
+
+  it('works with inputsecret()', function()
+    feed(":call inputsecret('secret:')<cr>abc123")
+    screen:expect([[
+      ^                         |
+      ~                        |
+      ~                        |
+      ~                        |
+                               |
+    ]], nil, nil, function()
+      eq({{
+        content = { { {}, "******" } },
+        firstc = "",
+        indent = 0,
+        pos = 6,
+        prompt = "secret:"
+      }}, cmdline)
+    end)
+  end)
+
+  it('works with highlighted cmdline', function()
+      source([[
+        highlight RBP1 guibg=Red
+        highlight RBP2 guibg=Yellow
+        highlight RBP3 guibg=Green
+        highlight RBP4 guibg=Blue
+        let g:NUM_LVLS = 4
+        function RainBowParens(cmdline)
+          let ret = []
+          let i = 0
+          let lvl = 0
+          while i < len(a:cmdline)
+            if a:cmdline[i] is# '('
+              call add(ret, [i, i + 1, 'RBP' . ((lvl % g:NUM_LVLS) + 1)])
+              let lvl += 1
+            elseif a:cmdline[i] is# ')'
+              let lvl -= 1
+              call add(ret, [i, i + 1, 'RBP' . ((lvl % g:NUM_LVLS) + 1)])
+            endif
+            let i += 1
+          endwhile
+          return ret
+        endfunction
+        map <f5>  :let x = input({'prompt':'>','highlight':'RainBowParens'})<cr>
+        "map <f5>  :let x = input({'prompt':'>'})<cr>
+      ]])
+      screen:set_default_attr_ids({
+        RBP1={background = Screen.colors.Red},
+        RBP2={background = Screen.colors.Yellow},
+        RBP3={background = Screen.colors.Green},
+        RBP4={background = Screen.colors.Blue},
+        EOB={bold = true, foreground = Screen.colors.Blue1},
+        ERR={foreground = Screen.colors.Grey100, background = Screen.colors.Red},
+        SK={foreground = Screen.colors.Blue},
+        PE={bold = true, foreground = Screen.colors.SeaGreen4}
+      })
+      feed('<f5>(a(b)a)')
+      screen:expect([[
+        ^                         |
+        {EOB:~                        }|
+        {EOB:~                        }|
+        {EOB:~                        }|
+                                 |
+      ]], nil, nil, function()
+        expect_cmdline(1, '{RBP1:(}a{RBP2:(}b{RBP2:)}a{RBP1:)}')
+      end)
+  end)
+end)