improved tty-less progress reporting

Previously when running borg in a systemd service (and similar when piping to a file and co.),
these problems occurred:
- The carriage return both made it so that journald interpreted the output as
  binary, therefore not printing the text, while also not buffering
  correctly, so that log output was only available every once in a while
  in the form [40k blob data]. This can partially be worked around by
  using `journalctl -a` to view the logs, which at least prints the
  text, though only sporadically
- The path was getting truncated to a short length, since the default
  get_terminal_size returns a column width of 80, which isn't relevant
  when printing to e.g. journald

This commit fixes this by introducing a new code path for when stderr is
a tty, which always prints the full paths and never ends with a carriage
return.

Author: infinisil

src/borg/archive.py

@@ -146,7 +146,7 @@ def osize_fmt(self):
     def usize_fmt(self):
         return format_file_size(self.usize, iec=self.iec)
 
-    def show_progress(self, item=None, final=False, stream=None, dt=None):
+    def show_progress(self, item=None, final=False, stream=sys.stderr, dt=None):
         now = time.monotonic()
         if dt is None or now - self.last_progress > dt:
             self.last_progress = now
@@ -160,6 +160,13 @@ def show_progress(self, item=None, final=False, stream=None, dt=None):
                 data.update({"time": time.time(), "type": "archive_progress", "finished": final})
                 msg = json.dumps(data)
                 end = "\n"
+            elif not stream.isatty():
+                if not final:
+                    msg = "{0.osize_fmt} O {0.csize_fmt} C {0.usize_fmt} D {0.nfiles} N ".format(self)
+                    msg += remove_surrogates(item.path) if item else ""
+                else:
+                    msg = ""
+                end = "\n"
             else:
                 columns, lines = get_terminal_size()
                 if not final:
@@ -174,7 +181,7 @@ def show_progress(self, item=None, final=False, stream=None, dt=None):
                 else:
                     msg = " " * columns
                 end = "\r"
-            print(msg, end=end, file=stream or sys.stderr, flush=True)
+            print(msg, end=end, file=stream, flush=True)
 
 
 def is_special(mode):