UTC date in tag target

CHANGELOG.md

@@ -7,6 +7,9 @@ this project uses date-based 'snapshot' version identifiers.
 
 ## [Unreleased]
 
+### Changed
+- Default date in `tag` target is now in UTC
+
 ### Fixed
 - Global `typesetopts` no longer ignored for `luatex` and `lualatex` (issue \#351)
 

l3build-tagging.lua

@@ -62,7 +62,7 @@ local function update_file_tag(file,tagname,tagdate)
 end
 
 function tag(tagnames)
-  local tagdate = options["date"] or os_date("%Y-%m-%d")
+  local tagdate = options["date"] or os_date("!%Y-%m-%d")
   local tagname = nil
   if tagnames then
     tagname = tagnames[1]

l3build.dtx

@@ -594,7 +594,7 @@
 % specified by |tagfiles|; this function updates the `release tag' (or package version)
 % and date.
 % The tag is given as the optional command line argument \meta{tag name} and the date using
-% |--date| (or |-d|). If not given, the date will default to the current date in
+% |--date| (or |-d|). If not given, the date will default to the current UTC date in
 % ISO format (YYYY-MM-DD). If no \meta{tag name} is given, the tag will default to |nil|.
 % Both are passed as arguments to the |update_tag()| function.
 %