nvim: plugin: Add a simple session management plugin

nvim/.config/nvim/plugin/session.vim

@@ -0,0 +1,66 @@
+" Session management which does exactly what we want. No Telescope non-sense.
+" Saves session with a fixed name to a fixed path. We do not allow creating
+" sessions in non Git repositories. Automatically loads a session if one is
+" available for the current directory. Exposes SessionSave command for creating
+" a session.
+
+let g:session_in_pager_mode = 0
+let g:session_loaded        = 0
+
+function! s:SessionFile()
+  let session_name = join(split(getcwd(), '/'), '\%') . ".vim"
+  let session_path = expand('~/.vim/session/')
+  let session_file = session_path . '\%'. session_name
+  return session_file
+endfunction
+
+function! s:SessionCreate()
+  if (fugitive#Head() == '')
+    echo "Will not create session in a non Git repository"
+    return
+  endif
+
+  let session_file = s:SessionFile()
+  silent execute ':mksession! ' . session_file
+endfunction
+
+function! s:SessionLoad()
+  " Do not load session if
+  " - neovim is started with arguments
+  " - neovim is opened outside a git repository
+  " - neovim is in pager mode and is getting input from STDIN
+  if (argc(-1) > 0 || fugitive#Head() == '' || g:session_in_pager_mode == 1)
+    return
+  endif
+
+  let session_file = s:SessionFile()
+  if (!empty(glob(session_file)))
+    silent execute ':source' . session_file
+    " We noticed a case where session was loaded, so argc() had to be 0
+    " but after session load, argc() returned 1. Use a global variable to
+    " track if session was loaded. The save path will check this and save
+    " only if a session was loaded in the first place.
+    let g:session_loaded = 1
+  endif
+endfunction
+
+function! s:SessionSave()
+  " Do not save a session which was not loaded in the first place.
+  if (g:session_loaded == 1)
+    let session_file = s:SessionFile()
+    silent execute ':mksession! ' . session_file
+  endif
+endfunction
+
+augroup Session
+  autocmd!
+  autocmd VimEnter * nested call s:SessionLoad()
+  autocmd VimLeavePre * call s:SessionSave()
+augroup END
+
+augroup StdIn
+  autocmd!
+  autocmd StdinReadPre * let g:session_in_pager_mode = 1
+augroup END
+
+command SessionSave :call s:SessionCreate()