Crashes while trying to show tag objects with bad timestamps

["Mantas Mikulėnas" <grawity@gmail.com>]

When messing around with various repositories, I noticed that git 1.8
(currently using 1.8.2.rc0.22.gb3600c3) has problems parsing tag objects
that have invalid timestamps.

Times in tag objects appear to be kept as Unix timestamps, but I didn't
realize this at first, and ran something roughly equivalent to:
  git cat-file -p $tagname | git hash-object -w -t tag --stdin
creating a tag object the "tagger" line containing formatted time
instead of a Unix timestamp.

Git doesn't handle the resulting tag objects nicely at all. For example,
running `git cat-file -p` on the new object outputs a really odd
timestamp "Thu Jun Thu Jan 1 00:16:09 1970 +0016" (I'm guessing it
parses the year as Unix time), and `git show` outright crashes
(backtrace included below.)

I would have expected both commands to print a "tag object corrupt"
message, or maybe even a more specific "bad timestamp in tagger line"...

To reproduce:

printf '%s\n' \
  'object 4b825dc642cb6eb9a060e54bf8d69288fbee4904' 'type tree' \
  'tag test' 'tagger User <user@none> Thu Jun 9 16:44:04 2005 +0000' \
  '' 'Test tag' | git hash-object -w -t tag --stdin | xargs git show


> #0  0x00007f42560bb5f3 in ____strtoull_l_internal () from /usr/lib/libc.so.6
> No symbol table info available.
> #1  0x00000000004b4c81 in pp_user_info (pp=pp@entry=0x7fff3c30f1a0, 
>     what=what@entry=0x50c13b "Tagger", sb=sb@entry=0x7fff3c30f140, 
>     line=0xc267c7 "Jilles Tjoelker <jilles@stack.nl> Thu Jun 9 16:44:04 2005 +0000\n\nTag 1.0rc1.\n\n", encoding=0x507e20 "UTF-8") at pretty.c:431
>         name = {alloc = 24, len = 15, buf = 0xc24690 "Jilles Tjoelker"}
>         mail = {alloc = 24, len = 15, buf = 0xc24750 "jilles@stack.nl"}
>         ident = {
>           name_begin = 0xc267c7 "Jilles Tjoelker <jilles@stack.nl> Thu Jun 9 16:44:04 2005 +0000\n\nTag 1.0rc1.\n\n", 
>           name_end = 0xc267d6 " <jilles@stack.nl> Thu Jun 9 16:44:04 2005 +0000\n\nTag 1.0rc1.\n\n", 
>           mail_begin = 0xc267d8 "jilles@stack.nl> Thu Jun 9 16:44:04 2005 +0000\n\nTag 1.0rc1.\n\n", mail_end = 0xc267e7 "> Thu Jun 9 16:44:04 2005 +0000\n\nTag 1.0rc1.\n\n", 
>           date_begin = 0x0, date_end = 0x0, tz_begin = 0x0, tz_end = 0x0}
>         linelen = <optimized out>
>         line_end = <optimized out>
>         date = <optimized out>
>         mailbuf = 0xc267d8 "jilles@stack.nl> Thu Jun 9 16:44:04 2005 +0000\n\nTag 1.0rc1.\n\n"
>         namebuf = 0xc267c7 "Jilles Tjoelker <jilles@stack.nl> Thu Jun 9 16:44:04 2005 +0000\n\nTag 1.0rc1.\n\n"
>         namelen = 33
>         maillen = 15
>         max_length = 78
>         time = <optimized out>
>         tz = <optimized out>
> #2  0x0000000000439af5 in show_tagger (buf=<optimized out>, len=<optimized out>, 
>     rev=<optimized out>) at builtin/log.c:400
>         pp = {fmt = CMIT_FMT_MEDIUM, abbrev = 0, subject = 0x0, after_subject = 0x0, 
>           preserve_subject = 0, date_mode = DATE_NORMAL, date_mode_explicit = 0, 
>           need_8bit_cte = 0, notes_message = 0x0, reflog_info = 0x0, 
>           output_encoding = 0x0, mailmap = 0x0, color = 0}
>         out = {alloc = 0, len = 0, buf = 0x7a8188 <strbuf_slopbuf> ""}
> #3  show_tag_object (rev=0x7fff3c30f1f0, 
>     sha1=0xc2be44 "\230\211\275\331\365Q\306z\017\071d\331\035\062\247a\347~M8P", <incomplete sequence \303>) at builtin/log.c:427
>         new_offset = 151
>         type = OBJ_TAG
>         buf = 0xc26770 "object ffa28d13e40e03bd367d0219c7eb516be0f180d2\ntype commit\ntag hyperion-1.0rc1\ntagger Jilles Tjoelker <jilles@stack.nl> Thu Jun 9 16:44:04 2005 +0000\n\nTag 1.0rc1.\n\n"
>         size = 165
>         offset = <optimized out>


-- 
Mantas Mikulėnas <grawity@gmail.com>