Cygwin: pty: detect pcon-backed pty for non-Cygwin-spawned children

winsup/cygwin/dtable.cc

@@ -327,7 +327,17 @@ dtable::init_std_file_from_handle (int fd, HANDLE handle)
 	dev.parse (myself->ctty);
       else
 	{
-	  dev.parse (FH_CONSOLE);
+	  /* Check whether the inherited console is actually a pseudo
+	     console bridging a pty.  This happens when our non-Cygwin
+	     parent was itself spawned by a Cygwin process from a pty
+	     (e.g. bash spawning git.exe which then spawns vim).  In
+	     that case, connect to the pty slave instead of treating
+	     the handle as a real console. */
+	  int pcon_minor = cygwin_shared->tty.find_pcon_pty ();
+	  if (pcon_minor >= 0)
+	    dev.parse (FHDEV (DEV_PTYS_MAJOR, pcon_minor));
+	  else
+	    dev.parse (FH_CONSOLE);
 	  CloseHandle (handle);
 	  handle = INVALID_HANDLE_VALUE;
 	}

winsup/cygwin/local_includes/tty.h

@@ -175,6 +175,10 @@ class tty: public tty_min
   void wait_fwd ();
   bool pty_input_state_eq (xfer_dir x) { return pty_input_state == x; }
   bool nat_fg (pid_t pgid);
+  bool has_active_pcon () const
+    { return pcon_activated && switch_to_nat_pipe; }
+  bool has_pcon_and_owner (DWORD pid) const
+    { return pcon_activated && switch_to_nat_pipe && nat_pipe_owner_pid == pid; }
   friend class fhandler_pty_common;
   friend class fhandler_pty_master;
   friend class fhandler_pty_slave;
@@ -193,6 +197,7 @@ class tty_list
   int connect (int);
   void init ();
   tty_min *get_cttyp ();
+  int find_pcon_pty ();
   int attach (int n);
   static void init_session ();
   friend class lock_ttys;

winsup/cygwin/tty.cc

@@ -123,6 +123,43 @@ tty_list::init ()
     }
 }
 
+/* Search for a pty whose pseudo console owns our console.
+   Return tty minor number or -1 if not found.
+   Called from init_std_file_from_handle() for processes started by
+   non-Cygwin parents to detect that inherited console handles are
+   from a pcon-backed pty.
+
+   The cheap precondition (any tty with pcon active in shared memory)
+   short-circuits the common case where no pty has a pseudo console
+   active, avoiding the GetConsoleProcessList() LPC call entirely. */
+int
+tty_list::find_pcon_pty ()
+{
+  DWORD pids[128];
+  DWORD count = 0;
+  bool got_pids = false;
+
+  for (int i = 0; i < NTTYS; i++)
+    {
+      if (!ttys[i].has_active_pcon ())
+	continue;
+
+      /* Fetch the console process list lazily, only on first candidate. */
+      if (!got_pids)
+	{
+	  count = GetConsoleProcessList (pids, 128);
+	  if (!count)
+	    return -1;
+	  got_pids = true;
+	}
+
+      for (DWORD j = 0; j < count; j++)
+	if (ttys[i].has_pcon_and_owner (pids[j]))
+	  return i;
+    }
+  return -1;
+}
+
 /* Search for a free tty and allocate it.
    Return tty number or -1 if error.
  */