go/zodb/zodbtools: Refer to `zodb help tidrange` about how history range should be specified

This syncs to nexedi/zodbtools@f7eff5fe
(*: Refer to `zodb help tidrange` about how history range should be
specified) in zodbtools/py.

go/zodb/str.go

-// Copyright (C) 2017  Nexedi SA and Contributors.
+// Copyright (C) 2017-2019  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -142,6 +142,8 @@ Error:
 //
 // Both <tidmin> and <tidmax> can be empty, in which case defaults 0 and TidMax are used.
 //
+// See `zodb help tidrange` for accepted tidrange syntax.
+//
 // XXX also check tidMin < tidMax here? or allow reverse ranges ?
 func ParseTidRange(s string) (tidMin, tidMax Tid, err error) {
 	s1, s2, err := xstrings.Split2(s, "..")

go/zodb/zodbtools/dump.go

@@ -231,10 +231,11 @@ const dumpSummary = "dump content of a ZODB database"
 
 func dumpUsage(w io.Writer) {
 	fmt.Fprintf(w,
-`Usage: zodb dump [OPTIONS] <storage> [tidmin..tidmax]
+`Usage: zodb dump [OPTIONS] <storage> [<tidrange>]
 Dump content of a ZODB database.
 
 <storage> is an URL (see 'zodb help zurl') of a ZODB-storage.
+<tidrange> is a history range (see 'zodb help tidrange') to dump.
 
 Options:
 

go/zodb/zodbtools/help.go

-// Copyright (C) 2017  Nexedi SA and Contributors.
+// Copyright (C) 2017-2019  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -62,7 +62,40 @@ for example
 	0285cbac258bf266:0000000000000001	- oid 1 at first newest transaction changing it with tid <= 0285cbac258bf266
 `
 
+const helpTidRange =
+`Many zodb commands can be invoked on specific range of database history and
+accept <tidrange> parameter for that. The syntax for <tidrange> is
+
+    tidmin..tidmax
+
+where tidmin and tidmax specify [tidmin, tidmax] range of transactions, ends
+inclusive. Both tidmin and tidmax are optional and default to
+
+    tidmin: 0   (start of database history)
+    tidmax: +∞  (end of database history)
+
+If a tid (tidmin or tidmax) is given, it has to be specified as follows:
+
+    - a 16-digit hex number specifying transaction ID, e.g. 0285cbac258bf266
+
+    TODO (recheck what git does and use dateparser):
+
+    - absolute timestamp,
+    - relative timestamp, e.g. yesterday, 1.week.ago
+
+Example tid ranges:
+
+    ..                                  whole database history
+    000000000000aaaa..                  transactions starting from 000000000000aaaa till latest
+    ..000000000000bbbb                  transactions starting from database beginning till 000000000000bbbb
+    000000000000aaaa..000000000000bbbb  transactions starting from 000000000000aaaa till 000000000000bbbb
+
+In commands <tidrange> is optional - if it is not given at all, it defaults to
+0..+∞, i.e. to whole database history.
+`
+
 var helpTopics = prog.HelpRegistry{
 	{"zurl",     "specifying database URL",   helpZURL},
 	{"xid",      "specifying object address", helpXid},
+	{"tidrange", "specifying history range",  helpTidRange},
 }