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builtin-commit: use reduce_heads() only when appropriate

Since commit 6bb6b034 (builtin-commit: use commit_tree(), 2008-09-10), builtin-commit performs a reduce_heads() unconditionally. However, it's not always needed, and in some cases even harmful. reduce_heads() is not needed for the initial commit or for an "ordinary" commit, because they don't have any or have only one parent, respectively. reduce_heads() must be avoided when 'git commit' is run after a 'git merge --no-ff --no-commit', otherwise it will turn the non-fast-forward merge into fast-forward. For the same reason, reduce_heads() must be avoided when amending such a merge commit. To resolve this issue, 'git merge' will write info about whether fast-forward is allowed or not to $GIT_DIR/MERGE_MODE. Based on this info, 'git commit' will only perform reduce_heads() when it's committing a merge and fast-forward is enabled. Also add test cases to ensure that non-fast-forward merges are committed and amended properly. Signed-off-by: Miklos Vajna <vmiklos@frugalware.org> Signed-off-by: SZEDER Gábor <szeder@ira.uka.de> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Miklos Vajna committed Oct 3, 2008 at 14:04 UTC cf10f9fdd5e673a163847f0e931ce9731507e03b

4 files changed +41 -2

branch.c

@@ -168,5 +168,6 @@ void remove_branch_state(void)

168 unlink(git_path("MERGE_HEAD"));

169 unlink(git_path("MERGE_RR"));

170 unlink(git_path("MERGE_MSG"));

171 + unlink(git_path("MERGE_MODE"));

172 unlink(git_path("SQUASH_MSG"));

173 }

builtin-commit.c

+14 -2

@@ -937,6 +937,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)

937 unsigned char commit_sha1[20];

938 struct ref_lock *ref_lock;

939 struct commit_list *parents = NULL, **pptr = &parents;

940 + struct stat statbuf;

941 + int allow_fast_forward = 1;

942

943 git_config(git_commit_config, NULL);

944

@@ -951,6 +953,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)

953 return 1;

954 }

955

956 + strbuf_init(&sb, 0);

957 /* Determine parents */

958 if (initial_commit) {

959 reflog_msg = "commit (initial)";

@@ -984,14 +987,22 @@ int cmd_commit(int argc, const char **argv, const char *prefix)

987 }

988 fclose(fp);

989 strbuf_release(&m);

990 + if (!stat(git_path("MERGE_MODE"), &statbuf)) {

991 + if (strbuf_read_file(&sb, git_path("MERGE_MODE"), 0) < 0)

992 + die("could not read MERGE_MODE: %s",

993 + strerror(errno));

994 + if (!strcmp(sb.buf, "no-ff"))

995 + allow_fast_forward = 0;

996 + }

997 + if (allow_fast_forward)

998 + parents = reduce_heads(parents);

999 } else {

1000 reflog_msg = "commit";

1001 pptr = &commit_list_insert(lookup_commit(head_sha1), pptr)->next;

1002 }

991 - parents = reduce_heads(parents);

1003

1004 /* Finally, get the commit message */

994 - strbuf_init(&sb, 0);

1005 + strbuf_reset(&sb);

1006 if (strbuf_read_file(&sb, git_path(commit_editmsg), 0) < 0) {

1007 rollback_index_files();

1008 die("could not read commit message");

@@ -1040,6 +1051,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)

1051

1052 unlink(git_path("MERGE_HEAD"));

1053 unlink(git_path("MERGE_MSG"));

1054 + unlink(git_path("MERGE_MODE"));

1055 unlink(git_path("SQUASH_MSG"));

1056

1057 if (commit_index_files())

builtin-merge.c

+10

@@ -180,6 +180,7 @@ static void drop_save(void)

180 {

181 unlink(git_path("MERGE_HEAD"));

182 unlink(git_path("MERGE_MSG"));

183 + unlink(git_path("MERGE_MODE"));

184 }

185

186 static void save_state(void)

@@ -1210,6 +1211,15 @@ int cmd_merge(int argc, const char **argv, const char *prefix)

1211 merge_msg.len)

1212 die("Could not write to %s", git_path("MERGE_MSG"));

1213 close(fd);

1214 + fd = open(git_path("MERGE_MODE"), O_WRONLY | O_CREAT | O_TRUNC, 0666);

1215 + if (fd < 0)

1216 + die("Could open %s for writing", git_path("MERGE_MODE"));

1217 + strbuf_reset(&buf);

1218 + if (!allow_fast_forward)

1219 + strbuf_addf(&buf, "no-ff");

1220 + if (write_in_full(fd, buf.buf, buf.len) != buf.len)

1221 + die("Could not write to %s", git_path("MERGE_MODE"));

1222 + close(fd);

1223 }

1224

1225 if (merge_was_ok) {

t/t7600-merge.sh

+16

@@ -511,4 +511,20 @@ test_expect_success 'in-index merge' '

511

512 test_debug 'gitk --all'

513

514 +test_expect_success 'merge --no-ff --no-commit && commit' '

515 + git reset --hard c0 &&

516 + git merge --no-ff --no-commit c1 &&

517 + EDITOR=: git commit &&

518 + verify_parents $c0 $c1

519 +'

520 +

521 +test_debug 'gitk --all'

522 +

523 +test_expect_success 'amending no-ff merge commit' '

524 + EDITOR=: git commit --amend &&

525 + verify_parents $c0 $c1

526 +'

527 +

528 +test_debug 'gitk --all'

529 +

530 test_done