WIP: Make multi-session debugging sort of work

This passes the session id around everywhere and ensures that things
like buffer names are all unique.

We now have the _vimspector_session update to point to the active (or
last accessed tab). This feels fairly natural and mostly seems to work.

NOTE: in vscode there is no "multiple tabs" - they actually add the
subprocesses to the stack trace somehow and when you click on a frame in
that it switches to the session for that process. Each process PC is
visible in the editor. It's kind of confusing.

Things still broken:
 - vimspector_session_windows
 - breakpoints need to be project-wide
 - PC display (how to show "all" PCs, or just show the current one for
   the current tab ?)
 - it would be nice for the tterminal buffers to be visible on all tabs.
   not sure how to do that.

autoload/vimspector/internal/channel.vim

@@ -28,9 +28,8 @@ function! s:_OnServerData( session_id, channel, data ) abort
     return
   endif
 
-  py3 << EOF
-_vimspector_session.OnChannelData( vim.eval( 'a:data' ) )
-EOF
+  py3 _VimspectorSession( vim.eval( 'a:session_id' ) ).OnChannelData(
+        \ vim.eval( 'a:data' ) )
 endfunction
 
 function! s:_OnClose( session_id, channel ) abort
@@ -42,7 +41,7 @@ function! s:_OnClose( session_id, channel ) abort
   echom 'Channel closed'
   redraw
   unlet s:channels[ a:session_id ]
-  py3 _vimspector_session.OnServerExit( 0 )
+  py3 _VimspectorSession( vim.eval( 'a:session_id' ) ).OnServerExit( 0 )
 endfunction
 
 function! vimspector#internal#channel#StartDebugSession(
@@ -99,9 +98,8 @@ function! vimspector#internal#channel#Send( session_id, msg ) abort
 endfunction
 
 function! vimspector#internal#channel#Timeout( session_id, id ) abort
-  py3 << EOF
-_vimspector_session.OnRequestTimeout( vim.eval( 'a:id' ) )
-EOF
+  py3 _VimspectorSession( vim.eval( 'a:session_id' ) ).OnRequestTimeout(
+        \ vim.eval( 'a:id' ) )
 endfunction
 
 function! s:_ChannelExists( session_id ) abort
@@ -149,7 +147,7 @@ function! vimspector#internal#channel#StopDebugSession( session_id ) abort
     call s:_OnServerData( s:channels[ a:session_id ], data )
   endwhile
   if has_key( s:channels, a:session_id )
-    call s:_OnClose( s:channels[ a:session_id ] )
+    call s:_OnClose( a:session_id, s:channels[ a:session_id ] )
   endif
 endfunction
 

autoload/vimspector/internal/job.vim

@@ -29,7 +29,8 @@ function! s:_OnServerData( session_id, channel, data ) abort
     return
   endif
 
-  py3 _vimspector_session.OnChannelData( vim.eval( 'a:data' ) )
+  py3 _VimspectorSession( vim.eval( 'a:session_id' ) ).OnChannelData(
+        \ vim.eval( 'a:data' ) )
 endfunction
 
 function! s:_OnServerError( session_id, channel, data ) abort
@@ -39,7 +40,8 @@ function! s:_OnServerError( session_id, channel, data ) abort
     return
   endif
 
-  py3 _vimspector_session.OnServerStderr( vim.eval( 'a:data' ) )
+  py3 _VimspectorSession( vim.eval( 'a:session_id' ) ).OnServerStderr(
+        \ vim.eval( 'a:data' ) )
 endfunction
 
 
@@ -58,7 +60,8 @@ function! s:_OnExit( session_id, channel, status ) abort
   if has_key( s:jobs, a:session_id )
     unlet s:jobs[ a:session_id ]
   endif
-  py3 _vimspector_session.OnServerExit( vim.eval( 'a:status' ) )
+  py3 _VimspectorSession( vim.eval( 'a:session_id' ) ).OnServerExit(
+        \ vim.eval( 'a:status' ) )
 endfunction
 
 function! s:_OnClose( session_id, channel ) abort

autoload/vimspector/internal/state.vim

@@ -26,11 +26,22 @@ endif
 
 function! vimspector#internal#state#Reset() abort
   try
-    py3 import vim
-    py3 _vimspector_session =  __import__(
-          \ "vimspector",
-          \ fromlist=[ "session_manager" ] ).session_manager.Get().NewSession(
-          \   vim.eval( 's:prefix' ) )
+    py3 <<EOF
+
+import vim
+
+_vimspector_session_man = __import__(
+  "vimspector",
+  fromlist=[ "session_manager" ] ).session_manager.Get()
+
+# Deprecated
+_vimspector_session = _vimspector_session_man.NewSession(
+  vim.eval( 's:prefix' ) )
+
+def _VimspectorSession( session_id ):
+  return _vimspector_session_man.GetSession( int( session_id ) )
+
+EOF
   catch /.*/
     echohl WarningMsg
     echom 'Exception while loading vimspector:' v:exception
@@ -47,6 +58,22 @@ function! vimspector#internal#state#GetAPIPrefix() abort
   return s:prefix
 endfunction
 
+function! vimspector#internal#state#SwitchToSession( id ) abort
+  py3 _vimspector_session = _VimspectorSession( vim.eval( 'a:id' ) )
+endfunction
+
+
+function! vimspector#internal#state#OnTabEnter() abort
+  py3 <<EOF
+session = _vimspector_session_man.SessionForTab(
+  int( vim.eval( 'tabpagenr()' ) ) )
+
+if session is not None:
+  _vimspector_session = session
+EOF
+endfunction
+
+
 " Boilerplate {{{
 let &cpoptions=s:save_cpo
 unlet s:save_cpo