@matheusbsbs / matheus-bagliano / commits / 2b7b788fb3

ll-merge: killing the external merge driver aborts the merge

When an external merge driver dies with a signal, we should not expect that the result left on the filesystem is in any useful state. However, because the current code uses the return value from run_command() and declares any positive value as a sign that the driver successfully left conflicts in the result, and because the return value from run_command() for a subprocess that died upon a signal is positive, we end up treating whatever garbage left on the filesystem as the result the merge driver wanted to leave us. run_command() returns larger than 128 (WTERMSIG(status) + 128, to be exact) when it notices that the subprocess died with a signal, so detect such a case and return LL_MERGE_ERROR from ll_ext_merge(). Signed-off-by: Junio C Hamano <gitster@pobox.com> Reviewed-by: Elijah Newren <newren@gmail.com>

Junio C Hamano committed Jun 22, 2023 at 17:33 UTC 2b7b788fb31a74bcbff4e4c6efc6f3db6c3a49b7

3 files changed +35 -2

Documentation/gitattributes.txt

+4 -1

@@ -1132,7 +1132,10 @@ size (see below).

1132 The merge driver is expected to leave the result of the merge in

1133 the file named with `%A` by overwriting it, and exit with zero

1134 status if it managed to merge them cleanly, or non-zero if there

1135 -were conflicts.

1135 +were conflicts. When the driver crashes (e.g. killed by SEGV),

1136 +it is expected to exit with non-zero status that are higher than

1137 +128, and in such a case, the merge results in a failure (which is

1138 +different from producing a conflict).

1139

1140 The `merge.*.recursive` variable specifies what other merge

1141 driver to use when the merge driver is called for an internal

ll-merge.c

+8 -1

@@ -243,7 +243,14 @@ static enum ll_merge_result ll_ext_merge(const struct ll_merge_driver *fn,

243 unlink_or_warn(temp[i]);

244 strbuf_release(&cmd);

245 strbuf_release(&path_sq);

246 - ret = (status > 0) ? LL_MERGE_CONFLICT : status;

246 +

247 + if (!status)

248 + ret = LL_MERGE_OK;

249 + else if (status <= 128)

250 + ret = LL_MERGE_CONFLICT;

251 + else

252 + /* died due to a signal: WTERMSIG(status) + 128 */

253 + ret = LL_MERGE_ERROR;

254 return ret;

255 }

256

t/t6406-merge-attr.sh

+23

@@ -56,6 +56,12 @@ test_expect_success setup '

56 ) >"$ours+"

57 cat "$ours+" >"$ours"

58 rm -f "$ours+"

59 +

60 + if test -f ./please-abort

61 + then

62 + echo >>./please-abort killing myself

63 + kill -9 $$

64 + fi

65 exit "$exit"

66 EOF

67 chmod +x ./custom-merge

@@ -162,6 +168,23 @@ test_expect_success 'custom merge backend' '

168 rm -f $o $a $b

169 '

170

171 +test_expect_success 'custom merge driver that is killed with a signal' '

172 + test_when_finished "rm -f output please-abort" &&

173 +

174 + git reset --hard anchor &&

175 + git config --replace-all \

176 + merge.custom.driver "./custom-merge %O %A %B 0 %P" &&

177 + git config --replace-all \

178 + merge.custom.name "custom merge driver for testing" &&

179 +

180 + >./please-abort &&

181 + echo "* merge=custom" >.gitattributes &&

182 + test_must_fail git merge main &&

183 + git ls-files -u >output &&

184 + git diff --name-only HEAD >>output &&

185 + test_must_be_empty output

186 +'

187 +

188 test_expect_success 'up-to-date merge without common ancestor' '

189 git init repo1 &&

190 git init repo2 &&