git-read-tree: simplify merge loops enormously
Stop trying to haev this stateful thing that keeps track of what it has seen, and use a much simpler "gather all the different stages with the same name together and just merge them in one go" approach. Makes it a lot more understandable, and allows the different merge algorithms to share the basic merge loop.
This commit is contained in:
Linus Torvalds
parent
96cd5429a4
commit
d723c69063
273
read-tree.c
273
read-tree.c
@ -39,27 +39,11 @@ static int same(struct cache_entry *a, struct cache_entry *b)
|
||||
/*
|
||||
* This removes all trivial merges that don't change the tree
|
||||
* and collapses them to state 0.
|
||||
*
|
||||
* _Any_ other merge is left to user policy. That includes "both
|
||||
* created the same file", and "both removed the same file" - which are
|
||||
* trivial, but the user might still want to _note_ it.
|
||||
*/
|
||||
static struct cache_entry *merge_entries(struct cache_entry *a,
|
||||
struct cache_entry *b,
|
||||
struct cache_entry *c)
|
||||
{
|
||||
int len = ce_namelen(a);
|
||||
|
||||
/*
|
||||
* Are they all the same filename? We won't do
|
||||
* any name merging
|
||||
*/
|
||||
if (ce_namelen(b) != len ||
|
||||
ce_namelen(c) != len ||
|
||||
memcmp(a->name, b->name, len) ||
|
||||
memcmp(a->name, c->name, len))
|
||||
return NULL;
|
||||
|
||||
/*
|
||||
* Ok, all three entries describe the same
|
||||
* filename, but maybe the contents or file
|
||||
@ -77,12 +61,14 @@ static struct cache_entry *merge_entries(struct cache_entry *a,
|
||||
* Here "a" is "original", and "b" and "c" are the two
|
||||
* trees we are merging.
|
||||
*/
|
||||
if (same(b,c))
|
||||
return c;
|
||||
if (same(a,b))
|
||||
return c;
|
||||
if (same(a,c))
|
||||
return b;
|
||||
if (a && b && c) {
|
||||
if (same(b,c))
|
||||
return c;
|
||||
if (same(a,b))
|
||||
return c;
|
||||
if (same(a,c))
|
||||
return b;
|
||||
}
|
||||
return NULL;
|
||||
}
|
||||
|
||||
@ -116,88 +102,54 @@ static void reject_merge(struct cache_entry *ce)
|
||||
die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
|
||||
}
|
||||
|
||||
#define CHECK_OLD(ce) if (old && same(old, ce)) { verify_uptodate(old); old = NULL; }
|
||||
|
||||
static void trivially_merge_cache(struct cache_entry **src, int nr)
|
||||
static int merged_entry(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
|
||||
{
|
||||
struct cache_entry **dst = src;
|
||||
struct cache_entry *old = NULL;
|
||||
|
||||
while (nr--) {
|
||||
struct cache_entry *ce, *result;
|
||||
|
||||
ce = *src++;
|
||||
|
||||
/* We throw away original cache entries except for the stat information */
|
||||
if (!ce_stage(ce)) {
|
||||
if (old)
|
||||
reject_merge(old);
|
||||
old = ce;
|
||||
active_nr--;
|
||||
continue;
|
||||
}
|
||||
if (old && !path_matches(old, ce))
|
||||
reject_merge(old);
|
||||
if (nr > 1 && (result = merge_entries(ce, src[0], src[1])) != NULL) {
|
||||
result->ce_flags |= htons(CE_UPDATE);
|
||||
/*
|
||||
* See if we can re-use the old CE directly?
|
||||
* That way we get the uptodate stat info.
|
||||
*
|
||||
* This also removes the UPDATE flag on
|
||||
* a match.
|
||||
*/
|
||||
if (old && same(old, result)) {
|
||||
*result = *old;
|
||||
old = NULL;
|
||||
}
|
||||
CHECK_OLD(ce);
|
||||
CHECK_OLD(src[0]);
|
||||
CHECK_OLD(src[1]);
|
||||
ce = result;
|
||||
ce->ce_flags &= ~htons(CE_STAGEMASK);
|
||||
src += 2;
|
||||
nr -= 2;
|
||||
active_nr -= 2;
|
||||
}
|
||||
|
||||
merge->ce_flags |= htons(CE_UPDATE);
|
||||
if (old) {
|
||||
/*
|
||||
* If we had an old entry that we now effectively
|
||||
* overwrite, make sure it wasn't dirty.
|
||||
* See if we can re-use the old CE directly?
|
||||
* That way we get the uptodate stat info.
|
||||
*
|
||||
* This also removes the UPDATE flag on
|
||||
* a match.
|
||||
*/
|
||||
CHECK_OLD(ce);
|
||||
*dst++ = ce;
|
||||
if (same(old, merge)) {
|
||||
*merge = *old;
|
||||
} else {
|
||||
verify_uptodate(old);
|
||||
}
|
||||
}
|
||||
if (old)
|
||||
reject_merge(old);
|
||||
merge->ce_flags &= ~htons(CE_STAGEMASK);
|
||||
*dst++ = merge;
|
||||
return 1;
|
||||
}
|
||||
|
||||
/*
|
||||
* When we find a "stage2" entry in the two-way merge, that's
|
||||
* the one that will remain. If we have an exact old match,
|
||||
* we don't care whether the file is up-to-date or not, we just
|
||||
* re-use the thing directly.
|
||||
*
|
||||
* If we didn't have an exact match, then we want to make sure
|
||||
* that we've seen a stage1 that matched the old, and that the
|
||||
* old file was up-to-date. Because it will be gone after this
|
||||
* merge..
|
||||
*/
|
||||
static void twoway_check(struct cache_entry *old, int seen_stage1, struct cache_entry *ce)
|
||||
static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **dst)
|
||||
{
|
||||
if (path_matches(old, ce)) {
|
||||
/*
|
||||
* This also removes the UPDATE flag on
|
||||
* a match
|
||||
*/
|
||||
if (same(old, ce)) {
|
||||
*ce = *old;
|
||||
return;
|
||||
}
|
||||
if (!seen_stage1)
|
||||
reject_merge(old);
|
||||
struct cache_entry *old = stages[0];
|
||||
struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
|
||||
struct cache_entry *merge;
|
||||
int count;
|
||||
|
||||
/*
|
||||
* 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
|
||||
* branch", aka "b").
|
||||
*/
|
||||
if (old) {
|
||||
if (!b || !same(old, b))
|
||||
return -1;
|
||||
}
|
||||
verify_uptodate(old);
|
||||
merge = merge_entries(a, b, c);
|
||||
if (merge)
|
||||
return merged_entry(merge, old, dst);
|
||||
if (old)
|
||||
verify_uptodate(old);
|
||||
count = 0;
|
||||
if (a) { *dst++ = a; count++; }
|
||||
if (b) { *dst++ = b; count++; }
|
||||
if (c) { *dst++ = c; count++; }
|
||||
return count;
|
||||
}
|
||||
|
||||
/*
|
||||
@ -208,79 +160,46 @@ static void twoway_check(struct cache_entry *old, int seen_stage1, struct cache_
|
||||
* - if the current entry matches the new tree, we leave it
|
||||
* as-is. Otherwise we require that it be up-to-date.
|
||||
*/
|
||||
static void twoway_merge(struct cache_entry **src, int nr)
|
||||
static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
|
||||
{
|
||||
int seen_stage1 = 0;
|
||||
struct cache_entry *old = NULL;
|
||||
struct cache_entry **dst = src;
|
||||
struct cache_entry *old = src[0];
|
||||
struct cache_entry *a = src[1], *b = src[2];
|
||||
|
||||
while (nr--) {
|
||||
struct cache_entry *ce = *src++;
|
||||
int stage = ce_stage(ce);
|
||||
if (src[3])
|
||||
return -1;
|
||||
|
||||
switch (stage) {
|
||||
case 0:
|
||||
if (old)
|
||||
reject_merge(old);
|
||||
old = ce;
|
||||
seen_stage1 = 0;
|
||||
active_nr--;
|
||||
continue;
|
||||
|
||||
case 1:
|
||||
active_nr--;
|
||||
if (!old)
|
||||
continue;
|
||||
if (!path_matches(old, ce) || !same(old, ce))
|
||||
reject_merge(old);
|
||||
seen_stage1 = 1;
|
||||
continue;
|
||||
|
||||
case 2:
|
||||
ce->ce_flags |= htons(CE_UPDATE);
|
||||
if (old) {
|
||||
twoway_check(old, seen_stage1, ce);
|
||||
old = NULL;
|
||||
}
|
||||
ce->ce_flags &= ~htons(CE_STAGEMASK);
|
||||
*dst++ = ce;
|
||||
continue;
|
||||
}
|
||||
die("impossible two-way stage");
|
||||
}
|
||||
|
||||
/*
|
||||
* Unmatched with a new entry? Make sure it was
|
||||
* at least uptodate in the working directory _and_
|
||||
* the original tree..
|
||||
*/
|
||||
if (old) {
|
||||
if (!seen_stage1)
|
||||
reject_merge(old);
|
||||
verify_uptodate(old);
|
||||
if (!a || !same(old, a))
|
||||
return -1;
|
||||
}
|
||||
if (b)
|
||||
return merged_entry(b, old, dst);
|
||||
if (old)
|
||||
verify_uptodate(old);
|
||||
return 0;
|
||||
}
|
||||
|
||||
static void merge_stat_info(struct cache_entry **src, int nr)
|
||||
/*
|
||||
* One-way merge.
|
||||
*
|
||||
* 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 struct cache_entry null_entry;
|
||||
struct cache_entry **dst = src;
|
||||
struct cache_entry *stat = &null_entry;
|
||||
struct cache_entry *old = src[0];
|
||||
struct cache_entry *a = src[1];
|
||||
|
||||
while (nr--) {
|
||||
struct cache_entry *ce = *src++;
|
||||
if (src[2] || src[3])
|
||||
return -1;
|
||||
|
||||
/* We throw away original cache entries except for the stat information */
|
||||
if (!ce_stage(ce)) {
|
||||
stat = ce;
|
||||
active_nr--;
|
||||
continue;
|
||||
}
|
||||
if (path_matches(ce, stat) && same(ce, stat))
|
||||
*ce = *stat;
|
||||
ce->ce_flags &= ~htons(CE_STAGEMASK);
|
||||
*dst++ = ce;
|
||||
}
|
||||
if (!a)
|
||||
return 0;
|
||||
if (old && same(old, a))
|
||||
*a = *old;
|
||||
a->ce_flags &= ~htons(CE_STAGEMASK);
|
||||
*dst++ = a;
|
||||
return 1;
|
||||
}
|
||||
|
||||
static void check_updates(struct cache_entry **src, int nr)
|
||||
@ -302,6 +221,35 @@ static void check_updates(struct cache_entry **src, int nr)
|
||||
}
|
||||
}
|
||||
|
||||
static void merge_cache(struct cache_entry **src, int nr, int (*fn)(struct cache_entry **, struct cache_entry **))
|
||||
{
|
||||
struct cache_entry **dst = src;
|
||||
|
||||
while (nr) {
|
||||
int entries;
|
||||
struct cache_entry *name, *ce, *stages[4] = { NULL, };
|
||||
|
||||
name = ce = *src;
|
||||
for (;;) {
|
||||
int stage = ce_stage(ce);
|
||||
stages[stage] = ce;
|
||||
ce = *++src;
|
||||
active_nr--;
|
||||
if (!--nr)
|
||||
break;
|
||||
if (!path_matches(ce, name))
|
||||
break;
|
||||
}
|
||||
|
||||
entries = fn(stages, dst);
|
||||
if (entries < 0)
|
||||
reject_merge(name);
|
||||
dst += entries;
|
||||
active_nr += entries;
|
||||
}
|
||||
check_updates(active_cache, active_nr);
|
||||
}
|
||||
|
||||
static char *read_tree_usage = "git-read-tree (<sha> | -m <sha1> [<sha2> [<sha3>]])";
|
||||
|
||||
static struct cache_file cache_file;
|
||||
@ -350,15 +298,14 @@ int main(int argc, char **argv)
|
||||
if (merge) {
|
||||
switch (stage) {
|
||||
case 4: /* Three-way merge */
|
||||
trivially_merge_cache(active_cache, active_nr);
|
||||
check_updates(active_cache, active_nr);
|
||||
merge_cache(active_cache, active_nr, threeway_merge);
|
||||
break;
|
||||
case 3: /* Update from one tree to another */
|
||||
twoway_merge(active_cache, active_nr);
|
||||
merge_cache(active_cache, active_nr, twoway_merge);
|
||||
check_updates(active_cache, active_nr);
|
||||
break;
|
||||
case 2: /* Just read a tree, merge with old cache contents */
|
||||
merge_stat_info(active_cache, active_nr);
|
||||
merge_cache(active_cache, active_nr, oneway_merge);
|
||||
break;
|
||||
default:
|
||||
die("just how do you expect me to merge %d trees?", stage-1);
|
||||
|
||||
Loading…
Reference in New Issue
Block a user