Add support for weeks in timespans, change Y to y.

This is initial response to comments made on pull request.  Will look at
--keep-within in a bit.

docs/usage/general/date-time.rst.inc

@@ -12,7 +12,7 @@ Internally, we store and process date and time as UTC.
 
 .. rubric:: TIMESPAN
 
-Some options accept a TIMESPAN parameter, which can be given as a
-number of years (e.g. ``2Y``), months (e.g. ``12m``), days (e.g. ``7d``),
-hours (e.g. ``8H``), minutes (e.g. ``30M``), or seconds (e.g. ``84600s``).
-
+Some options accept a TIMESPAN parameter, which can be given as a number of
+years (e.g. ``2y``), months (e.g. ``12m``), weeks (e.g. ``2w``),
+days (e.g.  ``7d``), hours (e.g. ``8H``), minutes (e.g. ``30M``),
+or seconds (e.g. ``150S``).

src/borg/helpers/parseformat.py

@@ -579,10 +579,10 @@ def validator(text):
 
 
 def relative_time_marker_validator(text: str):
-    time_marker_regex = r"^\d+[YmdHMS]$"
+    time_marker_regex = r"^\d+[ymwdHMS]$"
     match = re.compile(time_marker_regex).search(text)
     if not match:
-        raise argparse.ArgumentTypeError(f"Invalid relative time marker used: {text}, choose from Y, m, d, H, M, S")
+        raise argparse.ArgumentTypeError(f"Invalid relative time marker used: {text}, choose from y, m, w, d, H, M, S")
     else:
         return text
 

src/borg/helpers/time.py

@@ -131,8 +131,10 @@ def calculate_relative_offset(format_string, from_ts, earlier=False):
                 return from_ts + timedelta(days=offset)
             elif unit == "m":
                 return offset_n_months(from_ts, offset)
-            elif unit == "Y":
+            elif unit == "y":
                 return from_ts.replace(year=from_ts.year + offset)
+            elif unit == "w":
+                return from_ts + timedelta(days=offset * 7)
             elif unit == "H":
                 return from_ts + timedelta(seconds=offset * 60 * 60)
             elif unit == "M":