feat(:restart): v:starttime, v:exitreason #39282

Problem:
- The `ZR` feature makes it more obvious that we need some sort of flag so that
  an `ExitPre` / `QuitPre` / `VimLeave` handler can handle restarts differently
  than a normal exit. For example, it's common that users want `:mksession` on
  restart, but perhaps not on a normal exit.
- Nvim has no way to report its "uptime".

Solution:
- Introduce `v:starttime`
- Introduce `v:exitreason`

6 files changed, 76 insertions, 27 deletions

diff --git a/src/nvim/eval/userfunc.c b/src/nvim/eval/userfunc.c
index a16ff39e6f..b22e91864e 100644
--- a/src/nvim/eval/userfunc.c
+++ b/src/nvim/eval/userfunc.c
@@ -3520,7 +3520,7 @@ static void handle_defer_one(funccall_T *funccal)
   ga_clear(&funccal->fc_defer);
 }
 
-/// Called when exiting: call all defer functions.
+/// When exiting: call all ":defer" functions.
 void invoke_all_defer(void)
 {
   for (funccall_T *fc = current_funccal; fc != NULL; fc = fc->fc_caller) {
diff --git a/src/nvim/eval/vars.c b/src/nvim/eval/vars.c
index 4722524872..b2f300e5d1 100644
--- a/src/nvim/eval/vars.c
+++ b/src/nvim/eval/vars.c
@@ -215,6 +215,8 @@ static struct vimvar {
   VV(VV_LUA,              "lua",              VAR_PARTIAL, VV_RO),
   VV(VV_RELNUM,           "relnum",           VAR_NUMBER, VV_RO),
   VV(VV_VIRTNUM,          "virtnum",          VAR_NUMBER, VV_RO),
+  VV(VV_STARTTIME,        "starttime",        VAR_NUMBER, VV_RO),
+  VV(VV_EXITREASON,       "exitreason",       VAR_STRING, VV_RO),
 };
 #undef VV
 
diff --git a/src/nvim/eval_defs.h b/src/nvim/eval_defs.h
index 365bddb00b..7cec3d6167 100644
--- a/src/nvim/eval_defs.h
+++ b/src/nvim/eval_defs.h
@@ -135,4 +135,6 @@ typedef enum {
   VV_LUA,
   VV_RELNUM,
   VV_VIRTNUM,
+  VV_STARTTIME,
+  VV_EXITREASON,
 } VimVarIndex;
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 1a29a61d22..0737e31642 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -4818,10 +4818,15 @@ static void ex_highlight(exarg_T *eap)
 void not_exiting(bool save_exiting)
 {
   exiting = save_exiting;
+  set_vim_var_string(VV_EXITREASON, NULL, -1);
 }
 
 bool before_quit_autocmds(win_T *wp, bool quit_all, bool forceit)
 {
+  // Set v:exitreason if not already set (e.g. by :restart).
+  if (*get_vim_var_str(VV_EXITREASON) == NUL) {
+    set_vim_var_string(VV_EXITREASON, S_LEN("quit"));
+  }
   apply_autocmds(EVENT_QUITPRE, NULL, NULL, false, wp->w_buffer);
 
   // Bail out when autocommands closed the window.
@@ -4830,6 +4835,7 @@ bool before_quit_autocmds(win_T *wp, bool quit_all, bool forceit)
   if (!win_valid(wp)
       || curbuf_locked()
       || (wp->w_buffer->b_nwindows == 1 && wp->w_buffer->b_locked > 0)) {
+    set_vim_var_string(VV_EXITREASON, NULL, -1);
     return true;
   }
 
@@ -4842,6 +4848,7 @@ bool before_quit_autocmds(win_T *wp, bool quit_all, bool forceit)
     if (!win_valid(wp)
         || curbuf_locked()
         || (curbuf->b_nwindows == 1 && curbuf->b_locked > 0)) {
+      set_vim_var_string(VV_EXITREASON, NULL, -1);
       return true;
     }
   }
@@ -4976,15 +4983,10 @@ static void ex_restart(exarg_T *eap)
 
   char **argv = xcalloc((size_t)argc + 3, sizeof(char *));
   size_t i = 0;
-  const char *listen_arg = NULL;
-#ifdef MSWIN
-  // On Windows, don't pass --listen to new server (named pipe can't be reused immediately).
-  // Instead pass the address via RPC, and new server will rebind to it after startup.
-# define HANDLE_LISTEN_ADDR listen_arg = addr; li = next_li; continue
-#else
-# define HANDLE_LISTEN_ADDR listen_arg = addr
-#endif
-  TV_LIST_ITER_CONST(l, li, {
+  const char *listen_arg = NULL;  // --listen arg given by user, if any.
+
+  // Build args to start the new Nvim, based on the current v:argv.
+  for (const listitem_T *li = l->lv_first; li != NULL; li = li->li_next) {
     const char *arg = tv_get_string(TV_LIST_ITEM_TV(li));
     // Drop "-- [files…]". Usually isn't wanted. User can :mksession instead.
     if (i > 0 && strequal(arg, "--")) {
@@ -4992,16 +4994,22 @@ static void ex_restart(exarg_T *eap)
     }
     // Drop "-s <scriptfile>": skip the scriptfile arg too.
     if (i > 0 && strequal(arg, "-s")) {
-      li = TV_LIST_ITEM_NEXT(l, li);
+      li = li->li_next;
       continue;
     }
     // The address after --listen may be in use by the current server.
     if (i > 0 && strequal(arg, "--listen")) {
-      listitem_T *next_li = TV_LIST_ITEM_NEXT(l, li);
+      const listitem_T *next_li = li->li_next;
       if (next_li != NULL) {
         const char *addr = tv_get_string(TV_LIST_ITEM_TV(next_li));
         if (strstr(addr, ":") || strstr(addr, "/") || strstr(addr, "\\")) {
-          HANDLE_LISTEN_ADDR;
+          listen_arg = addr;
+#ifdef MSWIN
+          // On Windows, don't pass --listen to new server (named pipe can't be reused immediately).
+          // Instead pass the address via RPC; new server rebinds after startup.
+          li = next_li;
+          continue;
+#endif
         }
       }
     }
@@ -5019,12 +5027,11 @@ static void ex_restart(exarg_T *eap)
         }
       }
     }
-  });
-#undef HANDLE_LISTEN_ADDR
+  }
 
 #ifdef MSWIN
   // On Windows, --listen is omitted from child argv because the named pipe can't be reused immediately.
-  // Recover the canonical address from the Lua module state (set by the previous rebind_old_addr_after_restart() call),
+  // Recover the canonical address from the Lua module state (set by the previous rebind_after_restart() call),
   // and keep the current listener alive (new server reclaims it).
   char *listen_arg_alloc = NULL;
   if (listen_arg == NULL) {
@@ -5104,8 +5111,7 @@ static void ex_restart(exarg_T *eap)
     result_mem = NULL;
   }
 
-  // Get the new server's initial listen address. On Windows this is the
-  // temporary bootstrap address that UIs should reconnect to first.
+  // Get the new server's initial address. On Windows this is the temporary self-generated address.
   MAXSIZE_TEMP_ARRAY(servername_args, 1);
   ADD_C(servername_args, CSTR_AS_OBJ("servername"));
   Object result = rpc_send_call(channel->id, "nvim_get_vvar", servername_args, &result_mem, &err);
@@ -5116,6 +5122,7 @@ static void ex_restart(exarg_T *eap)
     emsg("restart failed: could not get listen address from new server");
     goto fail_2;
   }
+  // New server's self-generated address.
   char *listen_addr = xmemdupz(result.data.string.data, result.data.string.size);
   arena_mem_free(result_mem);
   result_mem = NULL;
@@ -5126,10 +5133,9 @@ static void ex_restart(exarg_T *eap)
     // then retire the bootstrap address after all UIs have reattached (or timeout).
     MAXSIZE_TEMP_ARRAY(lua_args, 2);
     ADD_C(lua_args,
-          CSTR_AS_OBJ("return require('vim._core.server').rebind_old_addr_after_restart(...)"));
+          CSTR_AS_OBJ("return require('vim._core.server').rebind_after_restart(...)"));
     MAXSIZE_TEMP_ARRAY(handoff_params, 3);
     ADD_C(handoff_params, CSTR_AS_OBJ(listen_arg));
-    ADD_C(handoff_params, CSTR_AS_OBJ(listen_addr));
     ADD_C(handoff_params, INTEGER_OBJ((Integer)ui_active()));
     ADD_C(lua_args, ARRAY_OBJ(handoff_params));
     rpc_send_call(channel->id, "nvim_exec_lua", lua_args, &result_mem, &err);
@@ -5146,6 +5152,8 @@ static void ex_restart(exarg_T *eap)
   ui_flush();
   xfree(listen_addr);
 
+  set_vim_var_string(VV_EXITREASON, S_LEN("restart"));
+
   char *quit_cmd = (eap->do_ecmd_cmd) ? eap->do_ecmd_cmd : "qall";
   char *quit_cmd_copy = NULL;
 
@@ -5154,6 +5162,7 @@ static void ex_restart(exarg_T *eap)
     quit_cmd_copy = concat_str("confirm ", quit_cmd);
     quit_cmd = quit_cmd_copy;
   }
+  // Try to quit.
   nvim_command(cstr_as_string(quit_cmd), &err);
   xfree(quit_cmd_copy);
 
@@ -5165,6 +5174,7 @@ static void ex_restart(exarg_T *eap)
   }
 
 fail_2:
+  set_vim_var_string(VV_EXITREASON, NULL, -1);
   if (ERROR_SET(&err)) {
     emsg(err.msg);
     api_clear_error(&err);
diff --git a/src/nvim/main.c b/src/nvim/main.c
index 62500066e9..08e741b3a7 100644
--- a/src/nvim/main.c
+++ b/src/nvim/main.c
@@ -197,6 +197,7 @@ void early_init(mparm_T *paramp)
   estack_init();
   cmdline_init();
   eval_init();          // init global variables
+  set_vim_var_nr(VV_STARTTIME, (varnumber_T)os_hrtime());
   init_path(argv0 ? argv0 : "nvim");
   init_normal_cmds();   // Init the table of Normal mode commands.
   runtime_init();
@@ -763,7 +764,12 @@ void getout(int exitval)
   set_vim_var_type(VV_EXITING, VAR_NUMBER);
   set_vim_var_nr(VV_EXITING, exitval);
 
-  // Invoked all deferred functions in the function stack.
+  // Set v:exitreason if not already set (e.g. by :restart).
+  if (*get_vim_var_str(VV_EXITREASON) == NUL) {
+    set_vim_var_string(VV_EXITREASON, S_LEN("quit"));
+  }
+
+  // Invoked all ":defer" functions in the function stack.
   invoke_all_defer();
 
   // Optionally print hashtable efficiency.
diff --git a/src/nvim/vvars.lua b/src/nvim/vvars.lua
index 26a62830d1..648e5f1310 100644
--- a/src/nvim/vvars.lua
+++ b/src/nvim/vvars.lua
@@ -268,10 +268,27 @@ M.vars = {
       Exit code, or |v:null| before invoking the |VimLeavePre|
       and |VimLeave| autocmds.  See |:q|, |:x| and |:cquit|.
       Example: >vim
-        :au VimLeave * echo "Exit value is " .. v:exiting
+        :au VimLeave * echo "Exit code is " .. v:exiting
       <
     ]=],
   },
+  exitreason = {
+    type = 'string',
+    desc = [=[
+      Reason for the current exit. Set before |QuitPre|. Reset if
+      exit was canceled.
+
+      Possible values:
+      - ""          Not exiting, or exit was canceled.
+      - "quit"      |:quit|, |:qall|, |:wq|, |ZZ|, |ZQ|, etc.
+      - "restart"   |:restart|, |ZR|.
+
+      Example: >vim
+        autocmd ExitPre * if v:exitreason ==# 'restart' | echomsg 'restarting' | endif
+      <
+      Read-only.
+    ]=],
+  },
   fcs_choice = {
     type = 'string',
     desc = [=[
@@ -301,12 +318,12 @@ M.vars = {
       The reason why the |FileChangedShell| event was triggered.
       Can be used in an autocommand to decide what to do and/or what
       to set v:fcs_choice to.  Possible values:
-        deleted   file no longer exists
-        conflict  file contents, mode or timestamp was
+      - deleted   file no longer exists
+      - conflict  file contents, mode or timestamp was
                   changed and buffer is modified
-        changed   file contents has changed
-        mode      mode of file changed
-        time      only file timestamp changed
+      - changed   file contents has changed
+      - mode      mode of file changed
+      - time      only file timestamp changed
     ]=],
   },
   fname = {
@@ -736,6 +753,18 @@ M.vars = {
       |throw-variables|.
     ]=],
   },
+  starttime = {
+    type = 'integer',
+    desc = [=[
+      Timestamp (monotonic nanoseconds) when the Nvim process
+      started.
+
+      To see the current "uptime": >lua
+        vim.print(('uptime: %d seconds'):format((vim.uv.hrtime() - vim.v.starttime) / 1e9))
+      <
+      Read-only.
+    ]=],
+  },
   statusmsg = {
     type = 'string',
     desc = [=[