feat(terminal)!: cursor shape and blink (#31562)

When a terminal application running inside the terminal emulator sets
the cursor shape or blink status of the cursor, update the cursor in the
parent terminal to match.

This removes the "virtual cursor" that has been in use by the terminal
emulator since the beginning. The original rationale for using the
virtual cursor was to avoid having to support additional UI methods to
change the cursor color for other (non-TUI) UIs, instead relying on the
TermCursor and TermCursorNC highlight groups.

The TermCursor highlight group is now used in the default 'guicursor'
value, which has a new entry for Terminal mode. However, the
TermCursorNC highlight group is no longer supported: since terminal
windows now use the real cursor, when the window is not focused there is
no cursor displayed in the window at all, so there is nothing to
highlight. Users can still use the StatusLineTermNC highlight group to
differentiate non-focused terminal windows.

BREAKING CHANGE: The TermCursorNC highlight group is no longer supported.

6 files changed, 20 insertions, 6 deletions

diff --git a/runtime/doc/deprecated.txt b/runtime/doc/deprecated.txt
index ab9c0b2ce8..592b6389c4 100644
--- a/runtime/doc/deprecated.txt
+++ b/runtime/doc/deprecated.txt
@@ -38,6 +38,10 @@ DIAGNOSTICS
 - The "cursor_position" parameter of |vim.diagnostic.JumpOpts| is renamed to
   "pos"
 
+HIGHLIGHTS
+• *TermCursorNC*	As of Nvim 0.11, unfocused |terminal| windows no
+			longer have any cursor.
+
 TREESITTER
 • *TSNode:child_containing_descendant()*	Use
   |TSNode:child_with_descendant()| instead; it is identical except that it can
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index 5e70d75cfd..ad0835e80f 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -87,6 +87,11 @@ EVENTS
 • |vim.ui_attach()| callbacks for |ui-messages| `msg_show` events are executed in
   |api-fast| context.
 
+HIGHLIGHTS
+
+• |TermCursorNC| is removed and no longer supported. Unfocused terminals no
+  longer have a cursor.
+
 LSP
 
 • Improved rendering of LSP hover docs. |K-lsp-default|
@@ -281,6 +286,12 @@ TERMINAL
   'scrollback' are not reflown.
 • The |terminal| now supports OSC 8 escape sequences and will display
   hyperlinks in supporting host terminals.
+• The |terminal| now uses the actual cursor, rather than a "virtual" cursor.
+  This means that escape codes sent by applications running in a terminal
+  buffer can change the cursor shape and visibility. However, it also
+  means that the |TermCursorNC| highlight group is no longer supported: an
+  unfocused terminal window will have no cursor at all (so there is nothing to
+  highlight).
 
 TREESITTER
 
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 84f0bfe141..c2ed19f34f 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -2977,7 +2977,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	An |OptionSet| autocmd can be used to set it up to match automatically.
 
 				*'guicursor'* *'gcr'* *E545* *E546* *E548* *E549*
-'guicursor' 'gcr'	string	(default "n-v-c-sm:block,i-ci-ve:ver25,r-cr-o:hor20")
+'guicursor' 'gcr'	string	(default "n-v-c-sm:block,i-ci-ve:ver25,r-cr-o:hor20,t:block-blinkon500-blinkoff500-TermCursor")
 			global
 	Configures the cursor style for each mode. Works in the GUI and many
 	terminals.  See |tui-cursor-shape|.
@@ -3005,6 +3005,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 		ci	Command-line Insert mode
 		cr	Command-line Replace mode
 		sm	showmatch in Insert mode
+		t	Terminal mode
 		a	all modes
 	The argument-list is a dash separated list of these arguments:
 		hor{N}	horizontal bar, {N} percent of the character height
@@ -3021,7 +3022,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 			cursor is not shown.  Times are in msec.  When one of
 			the numbers is zero, there is no blinking. E.g.: >vim
 				set guicursor=n:blinkon0
-<			- Default is "blinkon0" for each mode.
+<
+			Default is "blinkon0" for each mode.
 		{group-name}
 			Highlight group that decides the color and font of the
 			cursor.
diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index c5d3422f62..df4d0f7260 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -5162,8 +5162,6 @@ EndOfBuffer	Filler lines (~) after the end of the buffer.
 		By default, this is highlighted like |hl-NonText|.
 							*hl-TermCursor*
 TermCursor	Cursor in a focused terminal.
-							*hl-TermCursorNC*
-TermCursorNC	Cursor in an unfocused terminal.
 							*hl-ErrorMsg*
 ErrorMsg	Error messages on the command line.
 							*hl-WinSeparator*
diff --git a/runtime/doc/terminal.txt b/runtime/doc/terminal.txt
index 5a1421f430..f9536c2f0c 100644
--- a/runtime/doc/terminal.txt
+++ b/runtime/doc/terminal.txt
@@ -101,7 +101,7 @@ Configuration					*terminal-config*
 
 Options:		'modified', 'scrollback'
 Events:			|TermOpen|, |TermEnter|, |TermLeave|, |TermClose|
-Highlight groups:	|hl-TermCursor|, |hl-TermCursorNC|
+Highlight groups:	|hl-TermCursor|
 
 Terminal sets local defaults for some options, which may differ from your
 global configuration.
diff --git a/runtime/doc/vim_diff.txt b/runtime/doc/vim_diff.txt
index bfef5d5d4a..c93d2b119e 100644
--- a/runtime/doc/vim_diff.txt
+++ b/runtime/doc/vim_diff.txt
@@ -325,7 +325,6 @@ Highlight groups:
 - |hl-MsgSeparator| highlights separator for scrolled messages
 - |hl-Substitute|
 - |hl-TermCursor|
-- |hl-TermCursorNC|
 - |hl-WinSeparator| highlights window separators
 - |hl-Whitespace| highlights 'listchars' whitespace
 - |hl-WinBar| highlights 'winbar'