Merge #9829 'startup: remove TUI init special-case'

fixes #7967
fixes #9959

Historically Vim/Nvim does backflips to handle input and show messages
before a UI is available. This logical contradiction was already fixed
for remote UIs (#9024 c236e80cf3df). Fixing it also for the TUI avoids
problems on Windows, simplifies the logic, and avoids races like #9959.

- Move ui_builtin_start() to the same position as embedded_mode
  remote_ui_wait_for_attach().
- If stdin is redirected, save the original `stdin` and replace fd
  0 with tty before calling `ui_builtin_start()`.

3 files changed, 41 insertions, 69 deletions

diff --git a/src/nvim/main.c b/src/nvim/main.c
index ed8788af60..8ff873e127 100644
--- a/src/nvim/main.c
+++ b/src/nvim/main.c
@@ -316,28 +316,9 @@ int main(int argc, char **argv)
   // Set the break level after the terminal is initialized.
   debug_break_level = params.use_debug_break_level;
 
-  //
-  // Read user-input if any TTY is connected.
   // Read ex-commands if invoked with "-es".
-  //
-  bool reading_tty = !headless_mode
-                     && !embedded_mode
-                     && !silent_mode
-                     && (params.input_isatty || params.output_isatty
-                         || params.err_isatty);
-  bool reading_excmds = !params.input_isatty
-                        && silent_mode
-                        && exmode_active == EXMODE_NORMAL;
-  if (reading_tty || reading_excmds) {
-    // One of the startup commands (arguments, sourced scripts or plugins) may
-    // prompt the user, so start reading from a tty now.
-    int fd = STDIN_FILENO;
-    if (!silent_mode
-        && (!params.input_isatty || params.edit_type == EDIT_STDIN)) {
-      // Use stderr or stdout since stdin is being used to read commands.
-      fd = params.err_isatty ? fileno(stderr) : fileno(stdout);
-    }
-    input_start(fd);
+  if (!params.input_isatty && silent_mode && exmode_active == EXMODE_NORMAL) {
+    input_start(STDIN_FILENO);
   }
 
   // open terminals when opening files that start with term://
@@ -366,16 +347,22 @@ int main(int argc, char **argv)
   // startup. This allows an external UI to show messages and prompts from
   // --cmd and buffer loading (e.g. swap files)
   bool early_ui = false;
-  if (embedded_mode && !headless_mode) {
-    TIME_MSG("waiting for embedder to make request");
-    remote_ui_wait_for_attach();
-    TIME_MSG("done waiting for embedder");
+  bool use_remote_ui = (embedded_mode && !headless_mode);
+  bool use_builtin_ui = (!headless_mode && !embedded_mode && !silent_mode);
+  if (use_remote_ui || use_builtin_ui) {
+    TIME_MSG("waiting for UI to make request");
+    if (use_remote_ui) {
+      remote_ui_wait_for_attach();
+    } else {
+      ui_builtin_start();
+    }
+    TIME_MSG("done waiting for UI");
 
     // prepare screen now, so external UIs can display messages
     starting = NO_BUFFERS;
     screenclear();
     early_ui = true;
-    TIME_MSG("initialized screen early for embedder");
+    TIME_MSG("initialized screen early for UI");
   }
 
   // Execute --cmd arguments.
@@ -469,25 +456,12 @@ int main(int argc, char **argv)
     read_stdin();
   }
 
-  if (reading_tty && (need_wait_return || msg_didany)) {
-    // Because there's no UI yet, error messages would have been printed to
-    // stdout.  Before starting we need confirmation that the user has seen the
-    // messages and that is done with a call to wait_return.
-    TIME_MSG("waiting for return");
-    wait_return(true);
-  }
-
-  if (!headless_mode && !embedded_mode && !silent_mode) {
-    input_stop();  // Stop reading input, let the UI take over.
-    ui_builtin_start();
-  }
-
   setmouse();  // may start using the mouse
 
   if (exmode_active || early_ui) {
-    // Don't clear the screen when starting in Ex mode, or when an
-    // embedding UI might have displayed messages
-    must_redraw = CLEAR;
+    // Don't clear the screen when starting in Ex mode, or when a UI might have
+    // displayed messages.
+    redraw_later(VALID);
   } else {
     screenclear();  // clear screen
     TIME_MSG("clearing screen");
diff --git a/src/nvim/tui/input.c b/src/nvim/tui/input.c
index 6d9023bd79..7a725df0a1 100644
--- a/src/nvim/tui/input.c
+++ b/src/nvim/tui/input.c
@@ -48,6 +48,26 @@ void tinput_init(TermInput *input, Loop *loop)
 
   int curflags = termkey_get_canonflags(input->tk);
   termkey_set_canonflags(input->tk, curflags | TERMKEY_CANON_DELBS);
+
+  // If stdin is not a pty, switch to stderr. For cases like:
+  //    echo q | nvim -es
+  //    ls *.md | xargs nvim
+#ifdef WIN32
+  if (!os_isatty(0)) {
+      const HANDLE conin_handle = CreateFile("CONIN$",
+                                             GENERIC_READ | GENERIC_WRITE,
+                                             FILE_SHARE_READ | FILE_SHARE_WRITE,
+                                             (LPSECURITY_ATTRIBUTES)NULL,
+                                             OPEN_EXISTING, 0, (HANDLE)NULL);
+      input->in_fd = _open_osfhandle(conin_handle, _O_RDONLY);
+      assert(input->in_fd != -1);
+  }
+#else
+  if (!os_isatty(0) && os_isatty(2)) {
+    input->in_fd = 2;
+  }
+#endif
+
   // setup input handle
   rstream_init_fd(loop, &input->read_stream, input->in_fd, 0xfff);
   // initialize a timer handle for handling ESC with libtermkey
@@ -435,24 +455,7 @@ static void tinput_read_cb(Stream *stream, RBuffer *buf, size_t count_,
   TermInput *input = data;
 
   if (eof) {
-    if (input->in_fd == 0 && !os_isatty(0) && os_isatty(2)) {
-      // Started reading from stdin which is not a pty but failed. Switch to
-      // stderr since it is a pty.
-      //
-      // This is how we support commands like:
-      //
-      // echo q | nvim -es
-      //
-      // and
-      //
-      // ls *.md | xargs nvim
-      input->in_fd = 2;
-      stream_close(&input->read_stream, NULL, NULL);
-      multiqueue_put(input->loop->fast_events, tinput_restart_reading, 1,
-                     input);
-    } else {
-      loop_schedule(&main_loop, event_create(tinput_done_event, 0));
-    }
+    loop_schedule(&main_loop, event_create(tinput_done_event, 0));
     return;
   }
 
@@ -496,10 +499,3 @@ static void tinput_read_cb(Stream *stream, RBuffer *buf, size_t count_,
   // without wrap around, otherwise it could be misinterpreted.
   rbuffer_reset(input->read_stream.buffer);
 }
-
-static void tinput_restart_reading(void **argv)
-{
-  TermInput *input = argv[0];
-  rstream_init_fd(input->loop, &input->read_stream, input->in_fd, 0xfff);
-  rstream_start(&input->read_stream, tinput_read_cb, input);
-}
diff --git a/test/functional/core/startup_spec.lua b/test/functional/core/startup_spec.lua
index f77af836a6..45bfa93b56 100644
--- a/test/functional/core/startup_spec.lua
+++ b/test/functional/core/startup_spec.lua
@@ -46,7 +46,7 @@ describe('startup', function()
     ]])
   end)
   it('in a TTY: has("ttyin")==1 has("ttyout")==1', function()
-    local screen = Screen.new(25, 3)
+    local screen = Screen.new(25, 4)
     screen:attach()
     if iswin() then
       command([[set shellcmdflag=/s\ /c shellxquote=\"]])
@@ -58,6 +58,7 @@ describe('startup', function()
             ..[[, shellescape(v:progpath))]])
     screen:expect([[
       ^                         |
+      ~                        |
       1 1                      |
                                |
     ]])
@@ -96,7 +97,7 @@ describe('startup', function()
     end)
   end)
   it('input from pipe (implicit) #7679', function()
-    local screen = Screen.new(25, 3)
+    local screen = Screen.new(25, 4)
     screen:attach()
     if iswin() then
       command([[set shellcmdflag=/s\ /c shellxquote=\"]])
@@ -109,6 +110,7 @@ describe('startup', function()
             ..[[, shellescape(v:progpath))]])
     screen:expect([[
       ^foo                      |
+      ~                        |
       0 1                      |
                                |
     ]])