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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)
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/*
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* This removes all trivial merges that don't change the tree
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* and collapses them to state 0.
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*
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* _Any_ other merge is left to user policy. That includes "both
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* created the same file", and "both removed the same file" - which are
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* trivial, but the user might still want to _note_ it.
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*/
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static struct cache_entry *merge_entries(struct cache_entry *a,
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struct cache_entry *b,
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struct cache_entry *c)
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{
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int len = ce_namelen(a);
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/*
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* Are they all the same filename? We won't do
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* any name merging
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*/
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if (ce_namelen(b) != len ||
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ce_namelen(c) != len ||
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memcmp(a->name, b->name, len) ||
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memcmp(a->name, c->name, len))
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return NULL;
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/*
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* Ok, all three entries describe the same
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* filename, but maybe the contents or file
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@ -77,12 +61,14 @@ static struct cache_entry *merge_entries(struct cache_entry *a,
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* Here "a" is "original", and "b" and "c" are the two
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* trees we are merging.
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*/
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if (same(b,c))
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return c;
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if (same(a,b))
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return c;
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if (same(a,c))
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return b;
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if (a && b && c) {
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if (same(b,c))
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return c;
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if (same(a,b))
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return c;
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if (same(a,c))
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return b;
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}
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return NULL;
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}
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@ -116,88 +102,54 @@ static void reject_merge(struct cache_entry *ce)
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die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
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}
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#define CHECK_OLD(ce) if (old && same(old, ce)) { verify_uptodate(old); old = NULL; }
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static void trivially_merge_cache(struct cache_entry **src, int nr)
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static int merged_entry(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst)
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{
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struct cache_entry **dst = src;
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struct cache_entry *old = NULL;
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while (nr--) {
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struct cache_entry *ce, *result;
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ce = *src++;
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/* We throw away original cache entries except for the stat information */
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if (!ce_stage(ce)) {
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if (old)
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reject_merge(old);
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old = ce;
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active_nr--;
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continue;
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}
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if (old && !path_matches(old, ce))
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reject_merge(old);
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if (nr > 1 && (result = merge_entries(ce, src[0], src[1])) != NULL) {
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result->ce_flags |= htons(CE_UPDATE);
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/*
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* See if we can re-use the old CE directly?
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* That way we get the uptodate stat info.
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*
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* This also removes the UPDATE flag on
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* a match.
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*/
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if (old && same(old, result)) {
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*result = *old;
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old = NULL;
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}
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CHECK_OLD(ce);
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CHECK_OLD(src[0]);
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CHECK_OLD(src[1]);
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ce = result;
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ce->ce_flags &= ~htons(CE_STAGEMASK);
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src += 2;
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nr -= 2;
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active_nr -= 2;
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}
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merge->ce_flags |= htons(CE_UPDATE);
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if (old) {
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/*
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* If we had an old entry that we now effectively
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* overwrite, make sure it wasn't dirty.
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* See if we can re-use the old CE directly?
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* That way we get the uptodate stat info.
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*
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* This also removes the UPDATE flag on
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* a match.
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*/
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CHECK_OLD(ce);
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*dst++ = ce;
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if (same(old, merge)) {
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*merge = *old;
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} else {
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verify_uptodate(old);
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}
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}
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if (old)
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reject_merge(old);
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merge->ce_flags &= ~htons(CE_STAGEMASK);
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*dst++ = merge;
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return 1;
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}
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/*
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* When we find a "stage2" entry in the two-way merge, that's
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* the one that will remain. If we have an exact old match,
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* we don't care whether the file is up-to-date or not, we just
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* re-use the thing directly.
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*
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* If we didn't have an exact match, then we want to make sure
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* that we've seen a stage1 that matched the old, and that the
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* old file was up-to-date. Because it will be gone after this
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* merge..
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*/
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static void twoway_check(struct cache_entry *old, int seen_stage1, struct cache_entry *ce)
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static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **dst)
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{
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if (path_matches(old, ce)) {
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/*
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* This also removes the UPDATE flag on
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* a match
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*/
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if (same(old, ce)) {
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*ce = *old;
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return;
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}
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if (!seen_stage1)
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reject_merge(old);
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struct cache_entry *old = stages[0];
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struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3];
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struct cache_entry *merge;
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int count;
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/*
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* If we have an entry in the index cache ("old"), then we want
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* to make sure that it matches any entries in stage 2 ("first
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* branch", aka "b").
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*/
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if (old) {
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if (!b || !same(old, b))
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return -1;
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}
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verify_uptodate(old);
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merge = merge_entries(a, b, c);
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if (merge)
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return merged_entry(merge, old, dst);
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if (old)
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verify_uptodate(old);
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count = 0;
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if (a) { *dst++ = a; count++; }
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if (b) { *dst++ = b; count++; }
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if (c) { *dst++ = c; count++; }
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return count;
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}
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/*
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@ -208,79 +160,46 @@ static void twoway_check(struct cache_entry *old, int seen_stage1, struct cache_
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* - if the current entry matches the new tree, we leave it
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* as-is. Otherwise we require that it be up-to-date.
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*/
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static void twoway_merge(struct cache_entry **src, int nr)
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static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
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{
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int seen_stage1 = 0;
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struct cache_entry *old = NULL;
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struct cache_entry **dst = src;
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struct cache_entry *old = src[0];
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struct cache_entry *a = src[1], *b = src[2];
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while (nr--) {
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struct cache_entry *ce = *src++;
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int stage = ce_stage(ce);
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if (src[3])
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return -1;
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switch (stage) {
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case 0:
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if (old)
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reject_merge(old);
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old = ce;
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seen_stage1 = 0;
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active_nr--;
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continue;
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case 1:
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active_nr--;
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if (!old)
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continue;
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if (!path_matches(old, ce) || !same(old, ce))
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reject_merge(old);
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seen_stage1 = 1;
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continue;
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case 2:
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ce->ce_flags |= htons(CE_UPDATE);
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if (old) {
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twoway_check(old, seen_stage1, ce);
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old = NULL;
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}
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ce->ce_flags &= ~htons(CE_STAGEMASK);
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*dst++ = ce;
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continue;
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}
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die("impossible two-way stage");
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}
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/*
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* Unmatched with a new entry? Make sure it was
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* at least uptodate in the working directory _and_
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* the original tree..
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*/
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if (old) {
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if (!seen_stage1)
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reject_merge(old);
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verify_uptodate(old);
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if (!a || !same(old, a))
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return -1;
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}
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if (b)
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return merged_entry(b, old, dst);
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if (old)
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verify_uptodate(old);
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return 0;
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}
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static void merge_stat_info(struct cache_entry **src, int nr)
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/*
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* One-way merge.
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*
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* The rule is:
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* - take the stat information from stage0, take the data from stage1
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*/
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static int oneway_merge(struct cache_entry **src, struct cache_entry **dst)
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{
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static struct cache_entry null_entry;
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struct cache_entry **dst = src;
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struct cache_entry *stat = &null_entry;
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struct cache_entry *old = src[0];
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struct cache_entry *a = src[1];
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while (nr--) {
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struct cache_entry *ce = *src++;
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if (src[2] || src[3])
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return -1;
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/* We throw away original cache entries except for the stat information */
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if (!ce_stage(ce)) {
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stat = ce;
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active_nr--;
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continue;
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}
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if (path_matches(ce, stat) && same(ce, stat))
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*ce = *stat;
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ce->ce_flags &= ~htons(CE_STAGEMASK);
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*dst++ = ce;
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}
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if (!a)
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return 0;
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if (old && same(old, a))
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*a = *old;
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a->ce_flags &= ~htons(CE_STAGEMASK);
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*dst++ = a;
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return 1;
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}
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static void check_updates(struct cache_entry **src, int nr)
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@ -302,6 +221,35 @@ static void check_updates(struct cache_entry **src, int nr)
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}
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}
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static void merge_cache(struct cache_entry **src, int nr, int (*fn)(struct cache_entry **, struct cache_entry **))
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{
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struct cache_entry **dst = src;
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while (nr) {
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int entries;
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struct cache_entry *name, *ce, *stages[4] = { NULL, };
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name = ce = *src;
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for (;;) {
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int stage = ce_stage(ce);
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stages[stage] = ce;
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ce = *++src;
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active_nr--;
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if (!--nr)
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break;
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if (!path_matches(ce, name))
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break;
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}
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entries = fn(stages, dst);
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if (entries < 0)
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reject_merge(name);
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dst += entries;
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active_nr += entries;
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}
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check_updates(active_cache, active_nr);
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}
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static char *read_tree_usage = "git-read-tree (<sha> | -m <sha1> [<sha2> [<sha3>]])";
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static struct cache_file cache_file;
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@ -350,15 +298,14 @@ int main(int argc, char **argv)
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if (merge) {
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switch (stage) {
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case 4: /* Three-way merge */
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trivially_merge_cache(active_cache, active_nr);
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check_updates(active_cache, active_nr);
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merge_cache(active_cache, active_nr, threeway_merge);
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break;
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case 3: /* Update from one tree to another */
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twoway_merge(active_cache, active_nr);
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merge_cache(active_cache, active_nr, twoway_merge);
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check_updates(active_cache, active_nr);
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break;
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case 2: /* Just read a tree, merge with old cache contents */
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merge_stat_info(active_cache, active_nr);
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merge_cache(active_cache, active_nr, oneway_merge);
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break;
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default:
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die("just how do you expect me to merge %d trees?", stage-1);
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