doc/bugs/Git:_changed_behavior_w.r.t._timestamps.mdwn

   1 After some months, I just updated my local ikiwiki sources, and rebuilt
   2 the Hurd web pages, <http://git.savannah.gnu.org/cgit/hurd/web.git/>.
   3
   4 I was confused, having switched to the new automatic (thanks!) --gettime
   5 mechanism, why on some pages the timestamps had changed compared to my
   6 previous use of --getctime and setting files' mtimes (using a script)
   7 according to the last Git commit.  For example:
   8
   9 community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.html
  10
  11 old:
  12
  13     Last edited <span class="date">2008-09-11 18:11:53 UTC</span>
  14     <!-- Created <span class="date">2008-09-11 17:47:08 UTC</span> -->
  15
  16 new:
  17
  18     Last edited <span class="date">2008-09-11 18:12:22 UTC</span>
  19     <!-- Created <span class="date">2008-09-11 17:47:50 UTC</span> -->
  20
  21
  22 I had a look at what git.pm is doing, and began to manually replay /
  23 investigate:
  24
  25     $ git log --pretty=fuller --name-only --relative -- community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
  26     commit 8f1b97bfe45b2f173e3a7d55dee226a9e289a695
  27     Author:     arnebab <arne_bab@web.de>
  28     AuthorDate: Thu Sep 11 20:11:53 2008 +0200
  29     Commit:     arnebab <arne_bab@web.de>
  30     CommitDate: Thu Sep 11 20:11:53 2008 +0200
  31
  32         Added a link to the X.org guide in this wiki.
  33
  34     community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
  35
  36     commit 3ef8b7d80d80572c436c4c60c71879bc74409816
  37     Author:     arnebab <arne_bab@web.de>
  38     AuthorDate: Thu Sep 11 19:47:08 2008 +0200
  39     Commit:     arnebab <arne_bab@web.de>
  40     CommitDate: Thu Sep 11 19:47:08 2008 +0200
  41
  42         Minor update on the enty trying to get X working -> 'watch this place for updates'
  43
  44     community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
  45
  46 OK, these are my old dates.
  47
  48     $ git log --pretty=format:%ci --name-only --relative -- community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
  49     2008-09-11 20:11:53 +0200
  50     community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
  51
  52     2008-09-11 19:47:08 +0200
  53     community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
  54
  55     $ git log --pretty=format:%ct --name-only --relative -- community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
  56     1221156713
  57     community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
  58
  59     1221155228
  60     community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
  61
  62     $ date -d @1221156713
  63     Thu Sep 11 18:11:53 UTC 2008
  64     $ date -d @1221155228
  65     Thu Sep 11 17:47:08 UTC 2008
  66
  67 That's all consistent.
  68
  69
  70 But:
  71
  72     $ perl -le 'use Storable; my $index=Storable::retrieve("indexdb"); use Data::Dumper; print Dumper $index'
  73     [...]
  74                           'community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn' => {
  75                                                                                         'ctime' => '1221155270',
  76                                                                                         'dest' => [
  77                                                                                                     'community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.html'
  78                                                                                                   ],
  79                                                                                         'typedlinks' => {
  80                                                                                                           'tag' => {}
  81                                                                                                         },
  82                                                                                         'mtime' => 1221156742,
  83                                                                                         'depends_simple' => {
  84                                                                                                               'sidebar' => 1
  85                                                                                                             },
  86                                                                                         'links' => [
  87                                                                                                      'community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x/discussion',
  88                                                                                                      'Hurd/DebianXorg'
  89                                                                                                    ],
  90                                                                                         'state' => {
  91     [...]
  92
  93     $ date -d @1221156742
  94     Thu Sep 11 18:12:22 UTC 2008
  95     $ date -d @1221155270
  96     Thu Sep 11 17:47:50 UTC 2008
  97
  98 That's different, and it matches what the new ikiwiki writes into the
  99 HTML file.
 100
 101
 102 Back to Git again, this time without specifying the file:
 103
 104     $ git log --pretty=format:%ct --name-only --relative
 105     [...]
 106     1221255713
 107     1221255655
 108     unsorted/PortingIssues.mdwn
 109
 110     1221156742 [Thu Sep 11 18:12:22 UTC 2008]
 111     1221156713 [Thu Sep 11 18:11:53 UTC 2008]
 112     community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
 113
 114     1221156267
 115     1221156235
 116     index.mdwn
 117
 118     1221156122
 119     1221156091
 120     index.mdwn
 121
 122     1221155942
 123     1221155910
 124     index.mdwn
 125
 126     1221155270 [Thu Sep 11 17:47:50 UTC 2008]
 127     1221155228 [Thu Sep 11 17:47:08 UTC 2008]
 128     community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
 129
 130     1221154986
 131     community/gsoc.mdwn
 132     community/gsoc/project_ideas.mdwn
 133
 134     1221147244
 135     whatsnew.html
 136     [...]
 137
 138 Aha!
 139
 140 ... and some more detail:
 141
 142     $ git log --pretty=fuller --name-only --relative
 143     [...]
 144     commit e4e89e1683012c879012522105a3471a00714613
 145     Author:     Samuel Thibault <samuel.thibault@ens-lyon.org>
 146     AuthorDate: Fri Sep 12 23:40:55 2008 +0200
 147     Commit:     Samuel Thibault <samuel.thibault@ens-lyon.org>
 148     CommitDate: Fri Sep 12 23:40:55 2008 +0200
 149
 150         MSG_NOSIGNAL and IPV6_PKTINFO got fixed
 151
 152     unsorted/PortingIssues.mdwn
 153
 154     commit c389fae98dff86527be62f895ff7272e4ab1932c
 155     Merge: 0339e3e 8f1b97b
 156     Author:     GNU Hurd wiki engine <web-hurd@gnu.org>
 157     AuthorDate: Thu Sep 11 18:12:22 2008 +0000
 158     Commit:     GNU Hurd wiki engine <web-hurd@gnu.org>
 159     CommitDate: Thu Sep 11 18:12:22 2008 +0000
 160
 161         Merge branch 'master' of wiki@192.168.10.50:wiki
 162
 163     commit 8f1b97bfe45b2f173e3a7d55dee226a9e289a695
 164     Author:     arnebab <arne_bab@web.de>
 165     AuthorDate: Thu Sep 11 20:11:53 2008 +0200
 166     Commit:     arnebab <arne_bab@web.de>
 167     CommitDate: Thu Sep 11 20:11:53 2008 +0200
 168
 169         Added a link to the X.org guide in this wiki.
 170
 171     community/weblogs/ArneBab/2008-08-02-gnu_hurd_and_x.mdwn
 172     [...]
 173
 174 So, merges are involved there.
 175
 176 What (the new) ikiwiki code does, is use the timestamp when the merge was
 177 done instead of the timestamp when the commit was done.  Is this
 178 intentional?  Otherwise I could supply a patch.
 179
 180 --[[tschwinge]]
 181
 182 > In order to be nice and fast, the git backend runs git log once
 183 > and records data for all files. Rather than looking at the log for a
 184 > given file. So amoung other things, it does not follow renames.
 185 >
 186 > AFAICS, git log only shows merges modifying files if it was a conflicted
 187 > merge. As the file is then actually modified to resolve the merge
 188 > I think it makes sense to count the merge as the last modification in
 189 > that case. --[[Joey]]
 190
 191 >> That'd be reasonable, but `git log` will also show merges that are not
 192 >> conflicting (as in my case).
 193
 194 >>> Actually when displaying a merge, `git log --stat` only lists files that
 195 >>> were actually modified in a new way as part of the merge resolution.
 196 >>> Ie, if the merge resolution only joins together some of the parent
 197 >>> hunks, the file is not listed as having been modified.
 198 >>>
 199 >>> So, no, ikiwiki's use of git log will not show files modified in
 200 >>> non-conflicting merges.
 201 >>> --[[Joey]]
 202
 203 >> Yet, I'm not totally disagreeing with your choice.  With this `git
 204 >> log` invocation, you're not able to tell from its output whether a
 205 >> conflict was resolved or not.
 206
 207 >> Also, it's a bit like the *should we use the **author timestamp** or
 208 >> **commit timestamp*** discussion.  Your code will always use the
 209 >> latest timestamp.
 210
 211 >> I guess I'll get my head wrapped around that, and it's fine, so this is
 212 >> [[done]].
 213
 214 >> --[[tschwinge]]