refactor(exit): pass error message to preserve_exit() (#22097)

Problem:
1. Some calls to preserve_exit() don't put a message in IObuff, so the
   IObuff printed by preserve_exit() contains unrelated information.
2. If a TUI client runs out of memory or receives a deadly signal, the
   error message is shown on alternate screen and cannot be easily seen
   because the TUI exits alternate screen soon afterwards.

Solution:
Pass error message to preserve_exit() and exit alternate screen before
printing it.

Note that this doesn't fix the problem that server error messages cannot
be easily seen on exit. This is tracked in #21608 and #21843.

src/nvim/event/rstream.c

@@ -155,7 +155,7 @@ static void fread_idle_cb(uv_idle_t *handle)
   uintmax_t fpos_intmax = stream->fpos;
   if (fpos_intmax > INT64_MAX) {
     ELOG("stream offset overflow");
-    preserve_exit();
+    preserve_exit("stream offset overflow");
   }
 
   // Synchronous read

src/nvim/lua/executor.c

@@ -211,9 +211,7 @@ static int nlua_luv_cfpcall(lua_State *lstate, int nargs, int nresult, int flags
   if (status) {
     if (status == LUA_ERRMEM && !(flags & LUVF_CALLBACK_NOEXIT)) {
       // consider out of memory errors unrecoverable, just like xmalloc()
-      os_errmsg(e_outofmem);
-      os_errmsg("\n");
-      preserve_exit();
+      preserve_exit(e_outofmem);
     }
     const char *error = lua_tostring(lstate, -1);
 

src/nvim/main.c

@@ -790,10 +790,10 @@ void getout(int exitval)
   os_exit(exitval);
 }
 
-/// Preserve files, print contents of `IObuff`, and exit 1.
+/// Preserve files, print contents of `errmsg`, and exit 1.
 ///
 /// May be called from deadly_signal().
-void preserve_exit(void)
+void preserve_exit(const char *errmsg)
   FUNC_ATTR_NORETURN
 {
   // 'true' when we are sure to exit, e.g., after a deadly signal
@@ -812,12 +812,15 @@ void preserve_exit(void)
   // Ignore SIGHUP while we are already exiting. #9274
   signal_reject_deadly();
 
+  if (ui_client_channel_id) {
+    // For TUI: exit alternate screen so that the error messages can be seen.
+    ui_client_stop();
+  }
+  os_errmsg(errmsg);
+  os_errmsg("\n");
   if (ui_client_channel_id) {
     os_exit(1);
   }
-
-  os_errmsg(IObuff);
-  os_errmsg("\n");
   ui_flush();
 
   ml_close_notmod();                // close all not-modified buffers

src/nvim/memory.c

@@ -121,9 +121,7 @@ void *xmalloc(size_t size)
 {
   void *ret = try_malloc(size);
   if (!ret) {
-    os_errmsg(e_outofmem);
-    os_errmsg("\n");
-    preserve_exit();
+    preserve_exit(e_outofmem);
   }
   return ret;
 }
@@ -152,9 +150,7 @@ void *xcalloc(size_t count, size_t size)
     try_to_free_memory();
     ret = calloc(allocated_count, allocated_size);
     if (!ret) {
-      os_errmsg(e_outofmem);
-      os_errmsg("\n");
-      preserve_exit();
+      preserve_exit(e_outofmem);
     }
   }
   return ret;
@@ -174,9 +170,7 @@ void *xrealloc(void *ptr, size_t size)
     try_to_free_memory();
     ret = realloc(ptr, allocated_size);
     if (!ret) {
-      os_errmsg(e_outofmem);
-      os_errmsg("\n");
-      preserve_exit();
+      preserve_exit(e_outofmem);
     }
   }
   return ret;
@@ -194,8 +188,7 @@ void *xmallocz(size_t size)
 {
   size_t total_size = size + 1;
   if (total_size < size) {
-    os_errmsg(_("Vim: Data too large to fit into virtual memory space\n"));
-    preserve_exit();
+    preserve_exit(_("Vim: Data too large to fit into virtual memory space\n"));
   }
 
   void *ret = xmalloc(total_size);

src/nvim/os/input.c

@@ -550,8 +550,7 @@ static void read_error_exit(void)
   if (silent_mode) {  // Normal way to exit for "nvim -es".
     getout(0);
   }
-  STRCPY(IObuff, _("Vim: Error reading input, exiting...\n"));
-  preserve_exit();
+  preserve_exit(_("Vim: Error reading input, exiting...\n"));
 }
 
 static bool pending_events(MultiQueue *events)

src/nvim/os/signal.c

@@ -172,11 +172,10 @@ static void deadly_signal(int signum)
 
   ILOG("got signal %d (%s)", signum, signal_name(signum));
 
-  snprintf(IObuff, sizeof(IObuff), "Vim: Caught deadly signal '%s'\r\n",
-           signal_name(signum));
+  snprintf(IObuff, IOSIZE, "Vim: Caught deadly signal '%s'\r\n", signal_name(signum));
 
   // Preserve files and exit.
-  preserve_exit();
+  preserve_exit(IObuff);
 }
 
 static void on_signal(SignalWatcher *handle, int signum, void *data)

src/nvim/tui/tui.c

@@ -458,9 +458,6 @@ static void tui_terminal_stop(TUIData *tui)
 
 void tui_stop(TUIData *tui)
 {
-  if (tui->stopped) {
-    return;
-  }
   tui_terminal_stop(tui);
   stream_set_blocking(tui->input.in_fd, true);   // normalize stream (#2598)
   tinput_destroy(&tui->input);
@@ -470,7 +467,7 @@ void tui_stop(TUIData *tui)
 }
 
 /// Returns true if UI `ui` is stopped.
-static bool tui_is_stopped(TUIData *tui)
+bool tui_is_stopped(TUIData *tui)
 {
   return tui->stopped;
 }

src/nvim/ui_client.c

@@ -122,7 +122,9 @@ void ui_client_run(bool remote_ui)
 
 void ui_client_stop(void)
 {
-  tui_stop(tui);
+  if (!tui_is_stopped(tui)) {
+    tui_stop(tui);
+  }
 }
 
 void ui_client_set_size(int width, int height)