add is_attached()

osv could be running but not attached to a debuggee instance. This
function allows to differentiate those states.

Author: jbyuki

doc/osv.txt

@@ -164,6 +164,12 @@ is_running()						*osv.is_running()*
     Return: ~
 	True if osv is running.
 
+is_attached()						*osv.is_attached()*
+    Checks whether |osv| is currently attached to a debuggee instance.
+
+    Return: ~
+	True if osv is attached.
+
 print_profiler()					*osv.print_profiler()*
     Prints the last 1000 elapsed times in milliseconds for each profiled sections.
     See |osv.launch()| to enable the profiler.

lua/osv/init.lua

@@ -54,6 +54,8 @@ local client
 
 local debug_hook_conn 
 
+local is_attached = false
+
 local cache = {}
 
 local start_profiler
@@ -311,6 +313,8 @@ function M.prepare_attach(blocking)
 
     M.stop_freeze = false
 
+    is_attached = false
+
   	if not request.terminateDebuggee then
   		vim.schedule(function() M.prepare_attach(false) end)
   	end
@@ -1086,6 +1090,8 @@ function M.prepare_attach(blocking)
         end
       end
 
+      is_attached = true
+
       debug.sethook(function(event, line)
         if lock_debug_loop then return end
 
@@ -1947,6 +1953,8 @@ function M.stop()
 
   M.stop_freeze = false
 
+  is_attached = false
+
 	if exit_autocmd then
 		vim.api.nvim_del_autocmd(exit_autocmd)
 		exit_autocmd = nil
@@ -1958,6 +1966,9 @@ function M.is_running()
 	return nvim_server ~= nil
 end
 
+function M.is_attached()
+	return is_attached
+end
 function M.start_trace()
 	function line_hook(event, line)
 		local surface = 0

src/launch.lua.t2

@@ -58,6 +58,7 @@ function M.prepare_attach(blocking)
   ; implement handlers
   local attach_now = function()
       ; redefine debug traceback
+      ; set is attached
       ; attach to current instance
   end
   if blocking then

src/stop.lua.t2

@@ -54,3 +54,16 @@ function M.is_running()
 	return nvim_server ~= nil
 end
 
+;; script variables
+local is_attached = false
+
+;; reset internal states
+is_attached = false
+
+;; set is attached
+is_attached = true
+
+;; implement
+function M.is_attached()
+	return is_attached
+end