feat(options): per-buffer 'busy' status #34493

Problem:
Plugins cannot mark a buffer as "busy".

Solution:
- Add a buffer-local 'busy' option.
- Show a busy indicator in the default 'statusline'.

runtime/doc/news.txt

@@ -224,6 +224,7 @@ OPTIONS
 • 'pummaxwidth' sets maximum width for the completion popup menu.
 • 'winborder' "bold" style.
 • |g:clipboard| accepts a string name to force any builtin clipboard tool.
+• 'busy' sets a buffer "busy" status. Indicated in the default statusline.
 
 PERFORMANCE
 
@@ -265,6 +266,7 @@ UI
 • Error messages are more concise:
   • "Error detected while processing:" changed to "Error in:".
   • "Error executing Lua:" changed to "Lua:".
+• 'busy' status is shown in default statusline with symbol ◐
 
 VIMSCRIPT
 

runtime/doc/options.txt

@@ -1217,6 +1217,13 @@ A jump table for the options with a short description can be found at |Q_op|.
 	without saving.  For writing there must be matching |BufWriteCmd|,
 	|FileWriteCmd| or |FileAppendCmd| autocommands.
 
+							*'busy'*
+'busy'			number	(default 0)
+			local to buffer
+	Sets a buffer "busy" status. Indicated in the default statusline.
+	When busy status is larger then 0 busy flag is shown in statusline.
+	The semantics of "busy" are arbitrary, typically decided by the plugin that owns the buffer.
+
 						*'casemap'* *'cmp'*
 'casemap' 'cmp'		string	(default "internal,keepascii")
 			global
@@ -6184,7 +6191,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	an expensive expression can negatively affect render performance.
 
 					*'statusline'* *'stl'* *E540* *E542*
-'statusline' 'stl'	string	(default "%<%f %h%w%m%r %=%{% &showcmdloc == 'statusline' ? '%-10.S ' : '' %}%{% exists('b:keymap_name') ? '<'..b:keymap_name..'> ' : '' %}%{% &ruler ? ( &rulerformat == '' ? '%-14.(%l,%c%V%) %P' : &rulerformat ) : '' %}")
+'statusline' 'stl'	string	(default "%<%f %h%w%m%r %=%{% &showcmdloc == 'statusline' ? '%-10.S ' : '' %}%{% exists('b:keymap_name') ? '<'..b:keymap_name..'> ' : '' %}%{% &busy > 0 ? '◐ ' : '' %}%{% &ruler ? ( &rulerformat == '' ? '%-14.(%l,%c%V%) %P' : &rulerformat ) : '' %}")
 			global or local to window |global-local|
 	Sets the |status-line|.
 

runtime/doc/vim_diff.txt

@@ -404,6 +404,7 @@ Options:
 - 'ttimeout', 'ttimeoutlen' behavior was simplified
 - 'winblend'    pseudo-transparency in floating windows |api-floatwin|
 - 'winhighlight' window-local highlights
+- 'busy' busy status for buffers
 
 Performance:
 - Signs are implemented using Nvim's internal "marktree" (btree) structure.

runtime/lua/vim/_meta/options.lua

@@ -664,6 +664,14 @@ vim.o.bt = vim.o.buftype
 vim.bo.buftype = vim.o.buftype
 vim.bo.bt = vim.bo.buftype
 
+--- Sets a buffer "busy" status. Indicated in the default statusline.
+--- When busy status is larger then 0 busy flag is shown in statusline.
+--- The semantics of "busy" are arbitrary, typically decided by the plugin that owns the buffer.
+---
+--- @type integer
+vim.o.busy = 0
+vim.bo.busy = vim.o.busy
+
 --- Specifies details about changing the case of letters.  It may contain
 --- these words, separated by a comma:
 --- internal	Use internal case mapping functions, the current
@@ -6853,7 +6861,7 @@ vim.wo.stc = vim.wo.statuscolumn
 ---
 ---
 --- @type string
-vim.o.statusline = "%<%f %h%w%m%r %=%{% &showcmdloc == 'statusline' ? '%-10.S ' : '' %}%{% exists('b:keymap_name') ? '<'..b:keymap_name..'> ' : '' %}%{% &ruler ? ( &rulerformat == '' ? '%-14.(%l,%c%V%) %P' : &rulerformat ) : '' %}"
+vim.o.statusline = "%<%f %h%w%m%r %=%{% &showcmdloc == 'statusline' ? '%-10.S ' : '' %}%{% exists('b:keymap_name') ? '<'..b:keymap_name..'> ' : '' %}%{% &busy > 0 ? '◐ ' : '' %}%{% &ruler ? ( &rulerformat == '' ? '%-14.(%l,%c%V%) %P' : &rulerformat ) : '' %}"
 vim.o.stl = vim.o.statusline
 vim.wo.statusline = vim.o.statusline
 vim.wo.stl = vim.wo.statusline