refactor(detach): eliminate nvim__ui_detach #40793

Problem:
`nvim__ui_detach` was added in 85e0559d46 in order to implement
`detach_others` from Lua. Using Lua in this case is doing more harm than
good.

Solution:
Extract `ui_detach_channel`, which also allows it to be used for the
"self detach" path from `ex_detach`.

Bonus: the old MSWIN path always called `os_swap_to_hidden_console()`;
now `ui_detach_channel` only does so for a stdio channel. For the common
stdio TUI this is identical; for a socket UI it's more correct (no
parent console to swap).

runtime/doc/api.txt

@@ -3863,20 +3863,6 @@ nvim_ui_try_resize_grid({grid}, {width}, {height})
       • {width}   (`integer`) The new requested width.
       • {height}  (`integer`) The new requested height.
 
-nvim__ui_detach({chan})                                    *nvim__ui_detach()*
-    WARNING: This feature is experimental/unstable.
-
-    Detaches the UI on channel `chan`.
-
-    Sets the channel's detach flag (so the server doesn't exit on stdio UIs),
-    sends an "error_exit" UI event, and closes the channel.
-
-    Attributes: ~
-        Since: 0.12.0
-
-    Parameters: ~
-      • {chan}  (`integer`) UI channel to disconnect.
-
 
 ==============================================================================
 Win_config Functions                                          *api-win_config*

runtime/doc/gui.txt

@@ -59,11 +59,15 @@ Use cases:
 ------------------------------------------------------------------------------
 Stop or detach the current UI
 
-                                      *:detach* *E5768*
+                                                             *:detach* *E5768*
 :[range]detach
                 Detaches the current UI. Other UIs (if any) remain attached.
-                Fails with |E5768| if no UI is attached.
-                The server (typically `nvim --embed`) continues running as
+                Fails with "E5768" if no UI is attached. If [range] is "%",
+                all UIs _except_ the current UI are detached: >vim
+
+                    :%detach
+
+<                The server (typically `nvim --embed`) continues running as
                 a background process, and you can reattach to it later.
                 Before detaching, you may want to note the server address:
                 >vim

runtime/lua/vim/_core/server.lua

@@ -219,24 +219,4 @@ function M.ex_session_restart(eap, extra)
   end
 end
 
---- Disconnects every UI except `keep_chan`, keeping the server running.
----
---- @param keep_chan integer Channel ID of the UI to preserve.
---- @return integer # Number of UIs detached.
-function M.detach_others(keep_chan)
-  local uicount = #vim.api.nvim_list_uis()
-  for _, ui in ipairs(vim.api.nvim_list_uis()) do
-    if ui.chan and ui.chan ~= keep_chan then
-      vim.api.nvim__ui_detach(ui.chan)
-    end
-  end
-  local n = uicount - #vim.api.nvim_list_uis()
-  if n == 0 then
-    vim.api.nvim_echo({ { 'No other UIs are attached' } }, true, {})
-  else
-    vim.api.nvim_echo({ { ('Detached %d non-current UIs'):format(n) } }, true, {})
-  end
-  return n
-end
-
 return M

runtime/lua/vim/_meta/api.gen.lua

@@ -186,16 +186,6 @@ function vim.api.nvim__set_restart_on_crash(progpath, argv) end
 --- @return table<string,any> # Map of various internal stats.
 function vim.api.nvim__stats() end
 
---- WARNING: This feature is experimental/unstable.
----
---- Detaches the UI on channel `chan`.
----
---- Sets the channel's detach flag (so the server doesn't exit on stdio UIs),
---- sends an "error_exit" UI event, and closes the channel.
----
---- @param chan integer UI channel to disconnect.
-function vim.api.nvim__ui_detach(chan) end
-
 --- WARNING: This feature is experimental/unstable.
 ---
 --- @param str string

src/nvim/api/ui.c

@@ -113,36 +113,68 @@ void remote_ui_disconnect(uint64_t channel_id, Error *err, bool send_error_exit)
   remote_ui_destroy(ui);
 }
 
-/// Detaches the UI on channel `chan`.
-///
-/// Sets the channel's detach flag (so the server doesn't exit on stdio UIs),
-/// sends an "error_exit" UI event, and closes the channel.
+/// Detaches the UI on channel `chan` (server keeps running). Sets `channel.detach`, sends an
+/// "error_exit" UI event, and closes the channel.
 ///
 /// @param chan  UI channel to disconnect.
 /// @param[out] err Error details, if any.
-void nvim__ui_detach(Integer chan, Error *err)
-  FUNC_API_SINCE(14)
+void ui_detach_channel(uint64_t chan, Error *err)
 {
-  Channel *c = find_channel((uint64_t)chan);
+  Channel *c = find_channel(chan);
   VALIDATE(c != NULL, "%s", e_invchan, {
     return;
   });
 #ifdef MSWIN
   bool detach_stdio = c->streamtype == kChannelStreamStdio;
 #endif
+  // Prevent server self-exit on channel-close.
   c->detach = true;
-  remote_ui_disconnect((uint64_t)chan, err, true);
+  // Server-side UI detach. Doesn't close the channel.
+  remote_ui_disconnect(chan, err, true);
   if (ERROR_SET(err)) {
     return;
   }
-  channel_close((uint64_t)chan, kChannelPartAll, NULL);
+  // Server-side channel close.
+  channel_close(chan, kChannelPartAll, NULL);
 #ifdef MSWIN
   if (detach_stdio) {
+    // After UI/channel detach, move this server off the parent's console so it
+    // survives terminal closure and still has working CONIN$/CONOUT$.
     os_swap_to_hidden_console();
   }
 #endif
 }
 
+/// Detaches every UI except `keep_chan` (server keeps running).
+///
+/// @param keep_chan  UI channel to preserve.
+/// @return Number of UIs detached.
+size_t ui_detach_others(uint64_t keep_chan)
+{
+  // Snapshot the channel ids first: ui_detach_channel() mutates connected_uis.
+  kvec_t(uint64_t) chans = KV_INITIAL_VALUE;
+  uint64_t chan;
+  map_foreach_key(&connected_uis, chan, {
+    if (chan != keep_chan) {
+      kv_push(chans, chan);
+    }
+  });
+
+  size_t detached = 0;
+  for (size_t i = 0; i < kv_size(chans); i++) {
+    Error err = ERROR_INIT;
+    ui_detach_channel(kv_A(chans, i), &err);
+    if (ERROR_SET(&err)) {
+      api_clear_error(&err);
+    } else {
+      detached++;
+    }
+  }
+
+  kv_destroy(chans);
+  return detached;
+}
+
 #ifdef EXITFREE
 void remote_ui_free_all_mem(void)
 {

src/nvim/ex_docmd.c

@@ -5964,69 +5964,42 @@ static void ex_tabs(exarg_T *eap)
 /// ":%detach" detaches all UIs _except_ the current UI.
 static void ex_detach(exarg_T *eap)
 {
-  // come on pooky let's burn this mf down
   if (!current_ui) {
     emsg(_(e_noui));
     return;
+  } else if (eap && eap->forceit) {
+    emsg("bang (!) not supported yet");
+    return;
   }
 
   if (eap && eap->addr_count > 0) {
+    // ":%detach" detaches every UI except the current one.
     if (eap->line1 != 1 || eap->line2 != curbuf->b_ml.ml_line_count) {
       emsg(_(e_invrange));
       return;
     }
 
-    typval_T lua_args[] = {
-      { .v_type = VAR_NUMBER, .vval.v_number = (varnumber_T)current_ui },
-      { .v_type = VAR_UNKNOWN },
-    };
-    typval_T rv = TV_INITIAL_VALUE;
-    nlua_call_typval("vim._core.server", "detach_others", lua_args, &rv);
-    ILOG("%%detach current_ui=%" PRIu64 " detached=%zu", current_ui,
-         (rv.v_type == VAR_NUMBER && rv.vval.v_number > 0)
-         ? (size_t)rv.vval.v_number : (size_t)0);
-    tv_clear(&rv);
+    size_t n = ui_detach_others(current_ui);
+    if (n == 0) {
+      msg(_("No other UIs are attached"), 0);
+    } else {
+      smsg(0, _("Detached %d non-current UIs"), (int)n);
+    }
+    ILOG("%%detach current_ui=%" PRIu64 " detached=%zu", current_ui, n);
   } else {
+    // come on pooky let's burn this mf down
+    //
     // 1. Send "error_exit" UI-event (notification only).
     // 2. Perform server-side UI detach.
     // 3. Close server-side channel without self-exit.
-
-    Channel *chan = find_channel(current_ui);
-    if (!chan) {
-      emsg(e_invchan);
+    Error err = ERROR_INIT;
+    ui_detach_channel(current_ui, &err);
+    if (ERROR_SET(&err)) {
+      emsg(err.msg);  // UI disappeared already?
+      api_clear_error(&err);
       return;
     }
-    // Prevent self-exit on channel-close.
-    Error detach_err = ERROR_INIT;
-    nvim__chan_set_detach(chan->id, true, &detach_err);
-    api_clear_error(&detach_err);
-
-    // Server-side UI detach. Doesn't close the channel.
-    Error err2 = ERROR_INIT;
-    remote_ui_disconnect(chan->id, &err2, true);
-    if (ERROR_SET(&err2)) {
-      emsg(err2.msg);  // UI disappeared already?
-      api_clear_error(&err2);
-      return;
-    }
-
-    // Server-side channel close.
-    const char *err = NULL;
-    bool rv = channel_close(chan->id, kChannelPartAll, &err);
-    if (!rv && err) {
-      emsg(err);  // UI disappeared already?
-      return;
-    }
-    // XXX: Can't do this, channel_decref() is async...
-    // assert(!find_channel(chan->id));
-
-#ifdef MSWIN
-    // After UI/channel detach, move this server off the parent's console so it
-    // survives terminal closure and still has working CONIN$/CONOUT$.
-    os_swap_to_hidden_console();
-#endif
-
-    ILOG("detach current_ui=%" PRId64, chan->id);
+    ILOG("detach current_ui=%" PRIu64, current_ui);
   }
 }
 

test/functional/core/main_spec.lua

@@ -193,7 +193,7 @@ describe('vim._core', function()
 
     -- All `vim._core.*` modules are builtin.
     t.eq(
-      { 'detach_others', 'ex_session_restart', 'rebind_after_restart', 'serverlist' },
+      { 'ex_session_restart', 'rebind_after_restart', 'serverlist' },
       n.exec_lua([[local k = vim.tbl_keys(require('vim._core.server')); table.sort(k); return k]])
     )
     local expected = {