Add a callback to provide external statusline sizes

This is necessary if the statusline is not embedded in tmux, but in a
different external statusline (e.g. the statusline of the window
manager or the kitty statusline).

This was one of the missing pieces to allow embedding the statusline
properly in arbitrary external statuslines.

Fixes #60

autoload/tpipeline.vim

@@ -126,7 +126,10 @@ func tpipeline#initialize()
 	if s:is_nvim
 		let g:tpipeline_fillchar = ""
 
-		if !exists('g:tpipeline_size')
+		if exists('#User#TpipelineSize')
+			call tpipeline#util#set_custom_size()
+			au VimResized * call tpipeline#util#set_custom_size()
+		elseif !exists('g:tpipeline_size')
 			call tpipeline#util#set_size()
 			au VimResized * call tpipeline#util#set_size()
 		endif

autoload/tpipeline/util.vim

@@ -15,6 +15,12 @@ func tpipeline#util#set_size()
 	let g:tpipeline_size = str2nr(systemlist("sh -c 'echo \"\"; tmux display-message -p \"#{window_width}\"'")[-1])
 endfunc
 
+func tpipeline#util#set_custom_size()
+	if exists('#User#TpipelineSize')
+		doautocmd User TpipelineSize
+	endif
+endfunc
+
 func tpipeline#util#check_gui()
 	if (v:event['chan'] && !has('nvim-0.9')) || has('gui_running')
 		call tpipeline#state#restore()

doc/tpipeline-external.txt

@@ -13,6 +13,10 @@ statusline can be embedded in arbitrary external programs. The
 |g:tpipeline_refreshcmd| option already allows running arbitrary commands to
 trigger the update of an external statusline.
 
+The |g:tpipeline_size| option allows to configure the size of the rendered
+statusline, which usually should be set to the numerical size of the external
+statusline, i.e. the number of characters or columns that fit into it.
+
 Depending on the external program, some integration needs to be done on that
 side as well. There exists full documentation for some external programs in
 |tpipeline-external-examples|.

doc/tpipeline.txt

@@ -7,6 +7,7 @@ Introduction					|tpipeline-introduction|
 Tmux Integration				|tpipeline-tmux|
 Configuration					|tpipeline-configure|
 Api						|tpipeline-api|
+Autocommands					|tpipeline-autocommands|
 
 ==============================================================================
 INTRODUCTION						*tpipeline-introduction*
@@ -165,6 +166,14 @@ CONFIGURATION						*tpipeline-configure*
 			set -g pane-border-format '#{pane_title}'
 <
 
+	g:tpipeline_size				*g:tpipeline_size*
+		By default the statusline size is calculated automatically to
+		span the entire tmux window size. With this option you can
+		overwrite a custom statusline size to be used. If the size is
+		not constant and should be recalculated on every statusline
+		evaluation, then the |User_TpipelineSize| autocommand can be
+		used.
+
 ------------------------------------------------------------------------------
 API							*tpipeline-api*
 
@@ -198,5 +207,16 @@ API							*tpipeline-api*
 		Toggles the active state.
 		See also |tpipeline#state#restore()| and |tpipeline#state#reload()|.
 
+------------------------------------------------------------------------------
+AUTOCOMMANDS						*tpipeline-autocommands*
+
+A few |User| |autocommands| are provided to allow extending this
+plugin's functionality. Example usage:
+>
+	autocmd User TpipelineSize let g:tpipeline_size = &co
+<
+							*User_TpipelineSize*
+TpipelineSize		When calculating a custom statusline size. See |g:tpipeline_size|.
+
 ==============================================================================
 	vim:tw=78:sw=4:ts=8:ft=help:norl:noet: