patch 9.1.2033: tests: Test_terminal_cwd flaky when using ConPTY

Problem:  tests: Test_terminal_cwd in test_terminal.vim fails flaky
          in the Windows ConPTY terminal.
Solution: In ConPTY, the timeout is extended to 1msec when reading a
          channel associated with a job that is about to finish.  This
          allows Vim to read the last output of a process in a pseudo
          console. Add comments to make the reasoning clear.
          (Muraoka Taro)

Processes that terminate too quickly in the ConPTY terminal cause Vim to
miss their final output.

In my environment, the probability of the "cmd /D /c cd" used in
Test_terminal_cwd occurring is about 1/4.  For a simple statically
linked Hello World, the probability of it occurring is about 3/4.

closes: #19036

Signed-off-by: Muraoka Taro <koron.kaoriya@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/channel.c

@@ -4175,7 +4175,17 @@ channel_handle_events(int only_keep_open)
 	    if (fd == INVALID_FD)
 		continue;
 
-	    int r = channel_wait(channel, fd, 0);
+	    // In normal cases, a timeout of 0 is sufficient.
+	    //
+	    // But, in Windows conpty terminals, the final output of a
+	    // terminated process may be missed.  In this case, in order for
+	    // Vim to read the final output, it is necessary to set the timeout
+	    // to 1 msec or more.  It seems that the final output can be
+	    // received by calling Sleep() once within channel_wait().  Note
+	    // that ch_killing can only be TRUE in conpty terminals, so it has
+	    // no side effects in environments other than conpty.
+	    int r = channel_wait(channel, fd, (channel->ch_killing &&
+			(part == PART_OUT || part == PART_ERR)) ? 1 : 0);
 
 	    if (r == CW_READY)
 		channel_read(channel, part, "channel_handle_events");

src/structs.h

@@ -2716,8 +2716,14 @@ struct channel_S {
 				// reference, the job refers to the channel.
     int		ch_job_killed;	// TRUE when there was a job and it was killed
 				// or we know it died.
-    int		ch_anonymous_pipe;  // ConPTY
-    int		ch_killing;	    // TerminateJobObject() was called
+    int		ch_anonymous_pipe;  // Indicates that anonymous pipes are being
+				    // used for communication in the Windows
+				    // ConPTY terminal.
+    int		ch_killing;	    // Indicates that the job associated with
+				    // the channel is terminating.  It becomes
+				    // TRUE when TerminateJobObject() was
+				    // called or the process associated with
+				    // the job had exited (only ConPTY).
 
     int		ch_refcount;	// reference count
     int		ch_copyID;

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2033,
 /**/
     2032,
 /**/