[Bug 272120] touch(1) -r modifies file's birthtime

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=272120

            Bug ID: 272120
           Summary: touch(1) -r modifies file's birthtime
           Product: Base System
           Version: 13.2-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: bin
          Assignee: bugs@FreeBSD.org
          Reporter: danfe@FreeBSD.org

touch(1) goes beyond what would one expect and what is documented in the
manpage:

  -m      Change the modification time of the file.  The access time of
          the file is not changed unless the -a flag is also specified.

  -r      Use the access and modifications times from the specified file
          instead of the current time of day.

I'm seeing this on both UFS and ZFS:

$ cp -ai /some/real/file somefile
$ stat -x somefile | tail -4
Access: Sun Aug 11 22:06:44 2019
Modify: Sun Aug 11 22:06:48 2019        <-- created, written, closed
Change: Wed Jun 21 10:30:56 2023
 Birth: Sun Aug 11 22:06:48 2019        <-- it's an old file

$ echo blah >> somefile
$ stat -x somefile | tail -4
Access: Sun Aug 11 22:06:44 2019
Modify: Wed Jun 21 10:31:21 2023        <-- we've just modified it
Change: Wed Jun 21 10:31:21 2023
 Birth: Sun Aug 11 22:06:48 2019        <-- remains the same (correct)

$ touch -m -r /.rnd somefile            <-- /.rnd is from 2014
$ stat -x somefile | tail -4
Access: Sun Aug 11 22:06:44 2019
Modify: Mon Jan 13 17:19:43 2014        <-- this is fine (expected)
Change: Wed Jun 21 10:31:42 2023
 Birth: Mon Jan 13 17:19:43 2014        <-- WTF?!

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