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[PATCH] Finish making --emu23 equivalent to pure 2-way merge.

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This adds #3ALT rule (and #2ALT rule for symmetry) to the
read-tree 3-way merge logic that collapses paths that are added
only in one branch and not in the other internally.

This makes --emu23 to succeed in the last remaining case where
the pure 2-way merge succeeded and earlier one failed.  Running
diff between t1001 and t1005 test scripts shows that the only
difference between the two is that --emu23 can leave the states
into separate stages so that the user can use usual 3-way merge
resolution techniques to carry forward the local changes when
pure 2-way merge would have refused to run.

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
2005-06-11 02:50:51 -07:00
committed by Linus Torvalds
parent e7f9bc411c
commit 32192e6622
3 changed files with 168 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files

137
read-tree.c
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@ -143,7 +143,72 @@ static int deleted_entry(struct cache_entry *ce, struct cache_entry *old, struct
return 1;
}
static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **dst)
static int causes_df_conflict(struct cache_entry *ce, int stage,
struct cache_entry **dst_,
struct cache_entry **next_,
int tail)
{
/* This is called during the merge operation and walking
* the active_cache[] array is messy, because it is in the
* middle of overlapping copy operation. The invariants
* are:
* (1) active_cache points at the first (zeroth) entry.
* (2) up to dst pointer are resolved entries.
* (3) from the next pointer (head-inclusive) to the tail
* of the active_cache array have the remaining paths
* to be processed. There can be a gap between dst
* and next. Note that next is called "src" in the
* merge_cache() function, and tail is the original
* end of active_cache array when merge_cache() started.
* (4) the path corresponding to *ce is not found in (2)
* or (3). It is in the gap.
*
* active_cache -----......+++++++++++++.
* ^dst ^next ^tail
*/
int i, next, dst;
const char *path = ce->name;
int namelen = ce_namelen(ce);
next = next_ - active_cache;
dst = dst_ - active_cache;
for (i = 0; i < tail; i++) {
int entlen, len;
const char *one, *two;
if (dst <= i && i < next)
continue;
ce = active_cache[i];
if (ce_stage(ce) != stage)
continue;
/* If ce->name is a prefix of path, then path is a file
* that hangs underneath ce->name, which is bad.
* If path is a prefix of ce->name, then it is the
* other way around which also is bad.
*/
entlen = ce_namelen(ce);
if (namelen == entlen)
continue;
if (namelen < entlen) {
len = namelen;
one = path;
two = ce->name;
} else {
len = entlen;
one = ce->name;
two = path;
}
if (memcmp(one, two, len))
continue;
if (two[len] == '/')
return 1;
}
return 0;
}
static int threeway_merge(struct cache_entry *stages[4],
struct cache_entry **dst,
struct cache_entry **next, int tail)
{
struct cache_entry *old = stages[0];
struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
@ -156,6 +221,65 @@ static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **ds
return -1;
return merged_entry_allow_dirty(b, old, dst);
}
/* #2ALT and #3ALT */
if (!a && (!!b != !!c)) {
/*
* The reason we need to worry about directory/file
* conflicts only in #2ALT and #3ALT case is this:
*
* (1) For all other cases that read-tree internally
* resolves a path, we always have such a path in
* *both* stage2 and stage3 when we begin.
* Traditionally, the behaviour has been even
* stricter and we did not resolve a path without
* initially being in all of stage1, 2, and 3.
*
* (2) When read-tree finishes, all resolved paths (i.e.
* the paths that are in stage0) must have come from
* either stage2 or stage3. It is not possible to
* have a stage0 path as a result of a merge if
* neither stage2 nor stage3 had that path.
*
* (3) It is guaranteed that just after reading the
* stages, each stage cannot have directory/file
* conflicts on its own, because they are populated
* by reading hierarchy of a tree. Combined with
* (1) and (2) above, this means that no matter what
* combination of paths we take from stage2 and
* stage3 as a result of a merge, they cannot cause
* a directory/file conflict situation (otherwise
* the "guilty" path would have already had such a
* conflict in the original stage, either stage2
* or stage3). Although its stage2 is synthesized
* by overlaying the current index on top of "our
* head" tree, --emu23 case also has this guarantee,
* by calling add_cache_entry() to create such stage2
* entries.
*
* (4) Only #2ALT and #3ALT lack the guarantee (1).
* They resolve paths that exist only in stage2
* or stage3. The stage2 tree may have a file DF
* while stage3 tree may have a file DF/DF. If
* #2ALT and #3ALT rules happen to apply to both
* of them, we would end up having DF (coming from
* stage2) and DF/DF (from stage3) in the result.
* When we attempt to resolve a path that exists
* only in stage2, we need to make sure there is
* no path that would conflict with it in stage3
* and vice versa.
*/
if (c) { /* #2ALT */
if (!causes_df_conflict(c, 2, dst, next, tail) &&
(!old || same(c, old)))
return merged_entry_allow_dirty(c, old, dst);
}
else { /* #3ALT */
if (!causes_df_conflict(b, 3, dst, next, tail) &&
(!old || same(b, old)))
return merged_entry_allow_dirty(b, old, dst);
}
/* otherwise we will apply the original rule */
}
/*
* If we have an entry in the index cache ("old"), then we want
* to make sure that it matches any entries in stage 2 ("first
@ -186,7 +310,8 @@ static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **ds
* "carry forward" rule, please see <Documentation/git-read-tree.txt>.
*
*/
static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
static int twoway_merge(struct cache_entry **src, struct cache_entry **dst,
struct cache_entry **next, int tail)
{
struct cache_entry *current = src[0];
struct cache_entry *oldtree = src[1], *newtree = src[2];
@ -283,7 +408,8 @@ static void setup_emu23(void)
* The rule is:
* - take the stat information from stage0, take the data from stage1
*/
static int oneway_merge(struct cache_entry **src, struct cache_entry **dst)
static int oneway_merge(struct cache_entry **src, struct cache_entry **dst,
struct cache_entry **next, int tail)
{
struct cache_entry *old = src[0];
struct cache_entry *a = src[1];
@ -324,11 +450,12 @@ static void check_updates(struct cache_entry **src, int nr)
}
}
typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **);
typedef int (*merge_fn_t)(struct cache_entry **, struct cache_entry **, struct cache_entry **, int);
static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
{
struct cache_entry **dst = src;
int tail = nr;
while (nr) {
int entries;
@ -346,7 +473,7 @@ static void merge_cache(struct cache_entry **src, int nr, merge_fn_t fn)
break;
}
entries = fn(stages, dst);
entries = fn(stages, dst, src, tail);
if (entries < 0)
reject_merge(name);
dst += entries;