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[PATCH] read-tree --emu23.

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This new flag causes two-way fast forward to internally use the
three-way merge mechanism.  This behaviour is intended to offer
a better fast forward semantics when used in a dirty work tree.

The new test t1005 is parallel to the existing t1001 "pure
2-way" tests, but some parts that are commented out would fail.
These failures are due to three-way merge enforcing too strict
index requirements for cases that could succeed.  This problem
will be addressed by later patches.

Without even changing three-way mechanism, the --emu23 two-way
fast forward already gives the user an easier-to-handle merge
result when a file that "merged head" updates has local
modifications.  This is demonstrated as "case 16" test in t1005.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Junio C Hamano
2005-06-10 18:36:08 -07:00
committed by Linus Torvalds
parent 76bc82ca0e
commit 03efa6d9a4
2 changed files with 393 additions and 4 deletions
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81
read-tree.c
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@ -209,6 +209,58 @@ static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
return deleted_entry(oldtree, current, dst);
}
/*
* Two-way merge emulated with three-way merge.
*
* This treats "read-tree -m H M" by transforming it internally
* into "read-tree -m H I+H M", where I+H is a tree that would
* contain the contents of the current index file, overlayed on
* top of H. Unlike the traditional two-way merge, this leaves
* the stages in the resulting index file and lets the user resolve
* the merge conflicts using standard tools for three-way merge.
*
* This function is just to set-up such an arrangement, and the
* actual merge uses threeway_merge() function.
*/
static void setup_emu23(void)
{
/* stage0 contains I, stage1 H, stage2 M.
* move stage2 to stage3, and create stage2 entries
* by scanning stage0 and stage1 entries.
*/
int i, namelen, size;
struct cache_entry *ce, *stage2;
for (i = 0; i < active_nr; i++) {
ce = active_cache[i];
if (ce_stage(ce) != 2)
continue;
/* hoist them up to stage 3 */
namelen = ce_namelen(ce);
ce->ce_flags = create_ce_flags(namelen, 3);
}
for (i = 0; i < active_nr; i++) {
ce = active_cache[i];
if (ce_stage(ce) > 1)
continue;
namelen = ce_namelen(ce);
size = cache_entry_size(namelen);
stage2 = xmalloc(size);
memcpy(stage2, ce, size);
stage2->ce_flags = create_ce_flags(namelen, 2);
if (add_cache_entry(stage2, ADD_CACHE_OK_TO_ADD) < 0)
die("cannot merge index and our head tree");
/* We are done with this name, so skip to next name */
while (i < active_nr &&
ce_namelen(active_cache[i]) == namelen &&
!memcmp(active_cache[i]->name, ce->name, namelen))
i++;
i--; /* compensate for the loop control */
}
}
/*
* One-way merge.
*
@ -315,7 +367,7 @@ static struct cache_file cache_file;
int main(int argc, char **argv)
{
int i, newfd, merge, reset;
int i, newfd, merge, reset, emu23;
unsigned char sha1[20];
newfd = hold_index_file_for_update(&cache_file, get_index_file());
@ -324,6 +376,7 @@ int main(int argc, char **argv)
merge = 0;
reset = 0;
emu23 = 0;
for (i = 1; i < argc; i++) {
const char *arg = argv[i];
@ -335,7 +388,7 @@ int main(int argc, char **argv)
/* This differs from "-m" in that we'll silently ignore unmerged entries */
if (!strcmp(arg, "--reset")) {
if (stage || merge)
if (stage || merge || emu23)
usage(read_tree_usage);
reset = 1;
merge = 1;
@ -345,7 +398,7 @@ int main(int argc, char **argv)
/* "-m" stands for "merge", meaning we start in stage 1 */
if (!strcmp(arg, "-m")) {
if (stage || merge)
if (stage || merge || emu23)
usage(read_tree_usage);
if (read_cache_unmerged())
die("you need to resolve your current index first");
@ -353,6 +406,17 @@ int main(int argc, char **argv)
merge = 1;
continue;
}
/* "-emu23" uses 3-way merge logic to perform fast-forward */
if (!strcmp(arg, "--emu23")) {
if (stage || merge || emu23)
usage(read_tree_usage);
if (read_cache_unmerged())
die("you need to resolve your current index first");
merge = emu23 = stage = 1;
continue;
}
if (get_sha1(arg, sha1) < 0)
usage(read_tree_usage);
if (stage > 3)
@ -369,9 +433,18 @@ int main(int argc, char **argv)
[2] = twoway_merge,
[3] = threeway_merge,
};
merge_fn_t fn;
if (stage < 2 || stage > 4)
die("just how do you expect me to merge %d trees?", stage-1);
merge_cache(active_cache, active_nr, merge_function[stage-1]);
if (emu23 && stage != 3)
die("--emu23 takes only two trees");
fn = merge_function[stage-1];
if (stage == 3 && emu23) {
setup_emu23();
fn = merge_function[3];
}
merge_cache(active_cache, active_nr, fn);
}
if (write_cache(newfd, active_cache, active_nr) ||
commit_index_file(&cache_file))