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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. | |
| Entries marked '+' have stat information. Spaces marked '*' don't | |
| affect the result. | |
| index tree result | |
| ----------------------- | |
| * (empty) (empty) | |
| (empty) tree tree | |
| index+ tree tree | |
| index+ index index+ | |
| Two-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 old | |
| or the result. | |
| If multiple cases apply, the one used is listed first. | |
| A result which changes the index is an error if the index is not empty | |
| and not up to date. | |
| Entries marked '+' have stat information. Spaces marked '*' don't | |
| affect the result. | |
| case index old new result | |
| ------------------------------------- | |
| 0/2 (empty) * (empty) (empty) | |
| 1/3 (empty) * new new | |
| 4/5 index+ (empty) (empty) index+ | |
| 6/7 index+ (empty) index index+ | |
| 10 index+ index (empty) (empty) | |
| 14/15 index+ old old index+ | |
| 18/19 index+ old index index+ | |
| 20 index+ index new new | |
| 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, a '+' means that this case applies even if | |
| only one ancestor or remote fits; a '^' means all of the ancestors | |
| must be the same. | |
| case ancest head remote result | |
| ---------------------------------------- | |
| 1 (empty)+ (empty) (empty) (empty) | |
| 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 | |
| 8 ancest^ (empty) ancest no merge | |
| 7 ancest+ (empty) remote no merge | |
| 10 ancest^ ancest (empty) no merge | |
| 9 ancest+ head (empty) no merge | |
| 16 anc1/anc2 anc1 anc2 no merge | |
| 13 ancest+ head ancest head | |
| 14 ancest+ ancest remote remote | |
| 11 ancest+ head remote no merge | |
| 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. | |
| Note that, between #6, #7, #9, and #11, all cases not otherwise | |
| covered are handled in this table. | |
| For #8 and #10, there is alternative behavior, not currently | |
| implemented, where the result is (empty). As currently implemented, | |
| the automatic merge will generally give this effect. | |