Properly render \n in exceptions with Py3

src/python/pants/base/exception_sink.py

@@ -14,6 +14,7 @@
 from builtins import object, str
 
 import setproctitle
+from future.utils import PY3
 
 from pants.base.build_environment import get_buildroot
 from pants.base.exiter import Exiter
@@ -142,6 +143,9 @@ def reset_exiter(cls, exiter):
     # NB: mutate process-global state!
     sys.excepthook = cls._log_unhandled_exception_and_exit
 
+  # TODO(7080): audit all usages of this function and add Py3 support, e.g. use `sys.stderr.buffer` instead
+  # of sys.stdout. However, we shouldn't need to proactively enforce that the stream is BytesIO, because Py3
+  # should already check when we try to use this.
   @classmethod
   def reset_interactive_output_stream(cls, interactive_output_stream):
     """
@@ -381,4 +385,4 @@ def handle_signal_gracefully(cls, signum, frame):
 # Sets except hook.
 ExceptionSink.reset_exiter(Exiter(exiter=sys.exit))
 # Sets a SIGUSR2 handler.
-ExceptionSink.reset_interactive_output_stream(sys.stderr)
+ExceptionSink.reset_interactive_output_stream(sys.stderr.buffer if PY3 else sys.stderr)

src/python/pants/base/exiter.py

@@ -8,6 +8,8 @@
 import sys
 from builtins import object
 
+from future.utils import PY3
+
 from pants.util.strutil import ensure_binary
 
 
@@ -51,11 +53,11 @@ def exit(self, result=0, msg=None, out=None):
     :param out: The file descriptor to emit `msg` to. (Optional)
     """
     if msg:
-      out = out or sys.stderr
-      # sys.stderr expects bytes in Py2, unicode in Py3
+      out = out or (sys.stderr.buffer if PY3 else sys.stderr)
       msg = ensure_binary(msg)
       try:
-        print(msg, file=out)
+        out.write(msg)
+        out.write(b'\n')
         # TODO: Determine whether this call is a no-op because the stream gets flushed on exit, or
         # if we could lose what we just printed, e.g. if we get interrupted by a signal while
         # exiting and the stream is buffered like stdout.