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diff --git a/Documentation/technical/trivial-merge.txt b/Documentation/technical/trivial-merge.txt new file mode 100644 index 0000000..b3a9915 --- /dev/null +++ b/Documentation/technical/trivial-merge.txt @@ -0,0 +1,92 @@ +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 +up-to-date. + +*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 +handled. + +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
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