do not write null sha1s to on-disk index

We should never need to write the null sha1 into an index
entry (short of the 1 in 2^160 chance that somebody actually
has content that hashes to it). If we attempt to do so, it
is much more likely that it is a bug, since we use the null
sha1 as a sentinel value to mean "not valid".

The presence of null sha1s in the index (which can come
from, among other things, "update-index --cacheinfo", or by
reading a corrupted tree) can cause problems for later
readers, because they cannot distinguish the literal null
sha1 from its use a sentinel value.  For example, "git
diff-files" on such an entry would make it appear as if it
is stat-dirty, and until recently, the diff code assumed
such an entry meant that we should be diffing a working tree
file rather than a blob.

Ideally, we would stop such entries from entering even our
in-core index. However, we do sometimes legitimately add
entries with null sha1s in order to represent these sentinel
situations; simply forbidding them in add_index_entry breaks
a lot of the existing code. However, we can at least make
sure that our in-core sentinel representation never makes it
to disk.

To be thorough, we will test an attempt to add both a blob
and a submodule entry. In the former case, we might run into
problems anyway because we will be missing the blob object.
But in the latter case, we do not enforce connectivity
across gitlink entries, making this our only point of
enforcement. The current implementation does not care which
type of entry we are seeing, but testing both cases helps
future-proof the test suite in case that changes.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2 files changed
tree: 8ff1aac8da36d559abb9776d767c3973a06858fb
  1. block-sha1/
  2. builtin/
  3. compat/
  4. contrib/
  5. Documentation/
  6. git-gui/
  7. git_remote_helpers/
  8. gitk-git/
  9. gitweb/
  10. mergetools/
  11. perl/
  12. po/
  13. ppc/
  14. t/
  15. templates/
  16. vcs-svn/
  17. xdiff/
  18. .gitattributes
  19. .gitignore
  20. .mailmap
  21. abspath.c
  22. aclocal.m4
  23. advice.c
  24. advice.h
  25. alias.c
  26. alloc.c
  27. archive-tar.c
  28. archive-zip.c
  29. archive.c
  30. archive.h
  31. argv-array.c
  32. argv-array.h
  33. attr.c
  34. attr.h
  35. base85.c
  36. bisect.c
  37. bisect.h
  38. blob.c
  39. blob.h
  40. branch.c
  41. branch.h
  42. builtin.h
  43. bulk-checkin.c
  44. bulk-checkin.h
  45. bundle.c
  46. bundle.h
  47. cache-tree.c
  48. cache-tree.h
  49. cache.h
  50. check-builtins.sh
  51. check-racy.c
  52. check_bindir
  53. color.c
  54. color.h
  55. combine-diff.c
  56. command-list.txt
  57. commit.c
  58. commit.h
  59. config.c
  60. config.mak.in
  61. configure.ac
  62. connect.c
  63. connected.c
  64. connected.h
  65. convert.c
  66. convert.h
  67. copy.c
  68. COPYING
  69. credential-cache--daemon.c
  70. credential-cache.c
  71. credential-store.c
  72. credential.c
  73. credential.h
  74. csum-file.c
  75. csum-file.h
  76. ctype.c
  77. daemon.c
  78. date.c
  79. decorate.c
  80. decorate.h
  81. delta.h
  82. diff-delta.c
  83. diff-lib.c
  84. diff-no-index.c
  85. diff.c
  86. diff.h
  87. diffcore-break.c
  88. diffcore-delta.c
  89. diffcore-order.c
  90. diffcore-pickaxe.c
  91. diffcore-rename.c
  92. diffcore.h
  93. dir.c
  94. dir.h
  95. editor.c
  96. entry.c
  97. environment.c
  98. exec_cmd.c
  99. exec_cmd.h
  100. fast-import.c
  101. fetch-pack.h
  102. fixup-builtins
  103. fmt-merge-msg.h
  104. fsck.c
  105. fsck.h
  106. generate-cmdlist.sh
  107. gettext.c
  108. gettext.h
  109. git-add--interactive.perl
  110. git-am.sh
  111. git-archimport.perl
  112. git-bisect.sh
  113. git-compat-util.h
  114. git-cvsexportcommit.perl
  115. git-cvsimport.perl
  116. git-cvsserver.perl
  117. git-difftool--helper.sh
  118. git-difftool.perl
  119. git-filter-branch.sh
  120. git-instaweb.sh
  121. git-lost-found.sh
  122. git-merge-octopus.sh
  123. git-merge-one-file.sh
  124. git-merge-resolve.sh
  125. git-mergetool--lib.sh
  126. git-mergetool.sh
  127. git-parse-remote.sh
  128. git-pull.sh
  129. git-quiltimport.sh
  130. git-rebase--am.sh
  131. git-rebase--interactive.sh
  132. git-rebase--merge.sh
  133. git-rebase.sh
  134. git-relink.perl
  135. git-remote-testgit.py
  136. git-repack.sh
  137. git-request-pull.sh
  138. git-send-email.perl
  139. git-sh-i18n.sh
  140. git-sh-setup.sh
  141. git-stash.sh
  142. git-submodule.sh
  143. git-svn.perl
  144. GIT-VERSION-GEN
  145. git-web--browse.sh
  146. git.c
  147. git.spec.in
  148. gpg-interface.c
  149. gpg-interface.h
  150. graph.c
  151. graph.h
  152. grep.c
  153. grep.h
  154. hash.c
  155. hash.h
  156. help.c
  157. help.h
  158. hex.c
  159. http-backend.c
  160. http-fetch.c
  161. http-push.c
  162. http-walker.c
  163. http.c
  164. http.h
  165. ident.c
  166. imap-send.c
  167. INSTALL
  168. kwset.c
  169. kwset.h
  170. levenshtein.c
  171. levenshtein.h
  172. LGPL-2.1
  173. list-objects.c
  174. list-objects.h
  175. ll-merge.c
  176. ll-merge.h
  177. lockfile.c
  178. log-tree.c
  179. log-tree.h
  180. mailmap.c
  181. mailmap.h
  182. Makefile
  183. match-trees.c
  184. merge-file.c
  185. merge-file.h
  186. merge-recursive.c
  187. merge-recursive.h
  188. name-hash.c
  189. notes-cache.c
  190. notes-cache.h
  191. notes-merge.c
  192. notes-merge.h
  193. notes.c
  194. notes.h
  195. object.c
  196. object.h
  197. pack-check.c
  198. pack-refs.c
  199. pack-refs.h
  200. pack-revindex.c
  201. pack-revindex.h
  202. pack-write.c
  203. pack.h
  204. pager.c
  205. parse-options-cb.c
  206. parse-options.c
  207. parse-options.h
  208. patch-delta.c
  209. patch-ids.c
  210. patch-ids.h
  211. path.c
  212. pkt-line.c
  213. pkt-line.h
  214. preload-index.c
  215. pretty.c
  216. progress.c
  217. progress.h
  218. prompt.c
  219. prompt.h
  220. quote.c
  221. quote.h
  222. reachable.c
  223. reachable.h
  224. read-cache.c
  225. README
  226. reflog-walk.c
  227. reflog-walk.h
  228. refs.c
  229. refs.h
  230. remote-curl.c
  231. remote.c
  232. remote.h
  233. replace_object.c
  234. rerere.c
  235. rerere.h
  236. resolve-undo.c
  237. resolve-undo.h
  238. revision.c
  239. revision.h
  240. run-command.c
  241. run-command.h
  242. send-pack.h
  243. sequencer.c
  244. sequencer.h
  245. server-info.c
  246. setup.c
  247. sh-i18n--envsubst.c
  248. sha1-array.c
  249. sha1-array.h
  250. sha1-lookup.c
  251. sha1-lookup.h
  252. sha1_file.c
  253. sha1_name.c
  254. shallow.c
  255. shell.c
  256. shortlog.h
  257. show-index.c
  258. sideband.c
  259. sideband.h
  260. sigchain.c
  261. sigchain.h
  262. strbuf.c
  263. strbuf.h
  264. streaming.c
  265. streaming.h
  266. string-list.c
  267. string-list.h
  268. submodule.c
  269. submodule.h
  270. symlinks.c
  271. tag.c
  272. tag.h
  273. tar.h
  274. test-chmtime.c
  275. test-credential.c
  276. test-ctype.c
  277. test-date.c
  278. test-delta.c
  279. test-dump-cache-tree.c
  280. test-genrandom.c
  281. test-index-version.c
  282. test-line-buffer.c
  283. test-match-trees.c
  284. test-mktemp.c
  285. test-obj-pool.c
  286. test-parse-options.c
  287. test-path-utils.c
  288. test-run-command.c
  289. test-scrap-cache-tree.c
  290. test-sha1.c
  291. test-sha1.sh
  292. test-sigchain.c
  293. test-string-pool.c
  294. test-subprocess.c
  295. test-svn-fe.c
  296. test-treap.c
  297. thread-utils.c
  298. thread-utils.h
  299. trace.c
  300. transport-helper.c
  301. transport.c
  302. transport.h
  303. tree-diff.c
  304. tree-walk.c
  305. tree-walk.h
  306. tree.c
  307. tree.h
  308. unimplemented.sh
  309. unix-socket.c
  310. unix-socket.h
  311. unpack-trees.c
  312. unpack-trees.h
  313. upload-pack.c
  314. url.c
  315. url.h
  316. usage.c
  317. userdiff.c
  318. userdiff.h
  319. utf8.c
  320. utf8.h
  321. walker.c
  322. walker.h
  323. wrap-for-bin.sh
  324. wrapper.c
  325. write_or_die.c
  326. ws.c
  327. wt-status.c
  328. wt-status.h
  329. xdiff-interface.c
  330. xdiff-interface.h
  331. zlib.c