path: root/Documentation/technical/trivial-merge.txt
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authorDaniel Barkalow <>2005-09-05 06:05:17 (GMT)
committerJunio C Hamano <>2005-09-11 01:27:41 (GMT)
commit3d89cb4f3f5333d5eb5899352566ad071dbd0d0c (patch)
tree4839378eb41288eaacc91dc12ab9f9e6b8233747 /Documentation/technical/trivial-merge.txt
parentee6566e8d70da682ac4926dd8a67ac821b2c1743 (diff)
[PATCH] Document the trivial merge rules for 3(+more ancestors)-way merges.
Signed-off-by: Daniel Barkalow Signed-off-by: Junio C Hamano <>
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+Trivial merge rules
+This document describes the outcomes of the trivial merge logic in read-tree.
+One-way merge
+This replaces the index with a different tree, keeping the stat info
+for entries that don't change, and allowing -u to make the minimum
+required changes to the working tree to have it match.
+ index tree result
+ -----------------------
+ * (empty) (empty)
+ (empty) tree tree
+ index+ tree tree
+ index+ index index+
+Two-way merge
+Three-way merge
+It is permitted for the index to lack an entry; this does not prevent
+any case from applying.
+If the index exists, it is an error for it not to match either the
+head or (if the merge is trivial) the result.
+If multiple cases apply, the one used is listed first.
+A result of "no merge" means that index is left in stage 0, ancest in
+stage 1, head in stage 2, and remote in stage 3 (if any of these are
+empty, no entry is left for that stage). Otherwise, the given entry is
+left in stage 0, and there are no other entries.
+A result of "no merge" is an error if the index is not empty and not
+*empty* means that the tree must not have a directory-file conflict
+ with the entry.
+For multiple ancestors or remotes, a '+' means that this case applies
+even if only one ancestor or remote fits; normally, all of the
+ancestors or remotes must be the same.
+case ancest head remote result
+1 (empty)+ (empty) (empty) (empty)
+2ALT (empty)+ *empty* remote remote
+2ALT (empty)+ *empty* remote remote
+2 (empty)^ (empty) remote no merge
+3ALT (empty)+ head *empty* head
+3 (empty)^ head (empty) no merge
+4 (empty)^ head remote no merge
+5ALT * head head head
+6 ancest^ (empty) (empty) no merge
+8ALT ancest (empty) ancest (empty)
+7 ancest+ (empty) remote no merge
+9 ancest+ head (empty) no merge
+10ALT ancest ancest (empty) (empty)
+11 ancest+ head remote no merge
+16 anc1/anc2 anc1 anc2 no merge
+13 ancest+ head ancest head
+14 ancest+ ancest remote remote
+14ALT ancest+ ancest remote remote
+Only #2ALT and #3ALT use *empty*, because these are the only cases
+where there can be conflicts that didn't exist before. Note that we
+allow directory-file conflicts between things in different stages
+after the trivial merge.
+A possible alternative for #6 is (empty), which would make it like
+#1. This is not used, due to the likelihood that it arises due to
+moving the file to multiple different locations or moving and deleting
+it in different branches.
+Case #1 is included for completeness, and also in case we decide to
+put on '+' markings; any path that is never mentioned at all isn't
+Note that #16 is when both #13 and #14 apply; in this case, we refuse
+the trivial merge, because we can't tell from this data which is
+right. This is a case of a reverted patch (in some direction, maybe
+multiple times), and the right answer depends on looking at crossings
+of history or common ancestors of the ancestors.
+The status as of Sep 5 is that multiple remotes are not supported \ No newline at end of file