projects / thirdparty / git.git / blame
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|---|---|---|
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1 | Trivial merge rules |
| 2 | =================== | |
| 3 | ||
| 4 | This document describes the outcomes of the trivial merge logic in read-tree. | |
| 5 | ||
| 6 | One-way merge | |
| 7 | ------------- | |
| 8 | ||
| 9 | This replaces the index with a different tree, keeping the stat info | |
| 10 | for entries that don't change, and allowing -u to make the minimum | |
| 11 | required changes to the working tree to have it match. | |
| 12 | ||
| 7061f5c2 DB |
13 | Entries marked '+' have stat information. Spaces marked '*' don't |
| 14 | affect the result. | |
| 15 | ||
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16 | index tree result |
| 17 | ----------------------- | |
| 18 | * (empty) (empty) | |
| 19 | (empty) tree tree | |
| 20 | index+ tree tree | |
| 21 | index+ index index+ | |
| 22 | ||
| 23 | Two-way merge | |
| 24 | ------------- | |
| 25 | ||
| 7061f5c2 DB |
26 | It is permitted for the index to lack an entry; this does not prevent |
| 27 | any case from applying. | |
| 28 | ||
| 29 | If the index exists, it is an error for it not to match either the old | |
| 30 | or the result. | |
| 31 | ||
| 32 | If multiple cases apply, the one used is listed first. | |
| 33 | ||
| 34 | A result which changes the index is an error if the index is not empty | |
| 7560f547 | 35 | and not up to date. |
| 7061f5c2 DB |
36 | |
| 37 | Entries marked '+' have stat information. Spaces marked '*' don't | |
| 38 | affect the result. | |
| 3d89cb4f | 39 | |
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40 | case index old new result |
| 41 | ------------------------------------- | |
| 42 | 0/2 (empty) * (empty) (empty) | |
| 43 | 1/3 (empty) * new new | |
| 44 | 4/5 index+ (empty) (empty) index+ | |
| 45 | 6/7 index+ (empty) index index+ | |
| 46 | 10 index+ index (empty) (empty) | |
| 47 | 14/15 index+ old old index+ | |
| 48 | 18/19 index+ old index index+ | |
| 49 | 20 index+ index new new | |
| 3d89cb4f DB |
50 | |
| 51 | Three-way merge | |
| 52 | --------------- | |
| 53 | ||
| 54 | It is permitted for the index to lack an entry; this does not prevent | |
| 55 | any case from applying. | |
| 56 | ||
| 57 | If the index exists, it is an error for it not to match either the | |
| 58 | head or (if the merge is trivial) the result. | |
| 59 | ||
| 60 | If multiple cases apply, the one used is listed first. | |
| 61 | ||
| 62 | A result of "no merge" means that index is left in stage 0, ancest in | |
| 63 | stage 1, head in stage 2, and remote in stage 3 (if any of these are | |
| 64 | empty, no entry is left for that stage). Otherwise, the given entry is | |
| 65 | left in stage 0, and there are no other entries. | |
| 66 | ||
| 67 | A result of "no merge" is an error if the index is not empty and not | |
| 7560f547 | 68 | up to date. |
| 3d89cb4f DB |
69 | |
| 70 | *empty* means that the tree must not have a directory-file conflict | |
| 71 | with the entry. | |
| 72 | ||
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73 | For multiple ancestors, a '+' means that this case applies even if |
| 74 | only one ancestor or remote fits; a '^' means all of the ancestors | |
| 75 | must be the same. | |
| 3d89cb4f | 76 | |
| 5316c8e9 TA |
77 | case ancest head remote result |
| 78 | ---------------------------------------- | |
| 79 | 1 (empty)+ (empty) (empty) (empty) | |
| 80 | 2ALT (empty)+ *empty* remote remote | |
| 81 | 2 (empty)^ (empty) remote no merge | |
| 82 | 3ALT (empty)+ head *empty* head | |
| 83 | 3 (empty)^ head (empty) no merge | |
| 84 | 4 (empty)^ head remote no merge | |
| 85 | 5ALT * head head head | |
| 86 | 6 ancest+ (empty) (empty) no merge | |
| 87 | 8 ancest^ (empty) ancest no merge | |
| 88 | 7 ancest+ (empty) remote no merge | |
| 89 | 10 ancest^ ancest (empty) no merge | |
| 90 | 9 ancest+ head (empty) no merge | |
| 91 | 16 anc1/anc2 anc1 anc2 no merge | |
| 92 | 13 ancest+ head ancest head | |
| 93 | 14 ancest+ ancest remote remote | |
| 94 | 11 ancest+ head remote no merge | |
| 3d89cb4f DB |
95 | |
| 96 | Only #2ALT and #3ALT use *empty*, because these are the only cases | |
| 97 | where there can be conflicts that didn't exist before. Note that we | |
| 98 | allow directory-file conflicts between things in different stages | |
| 99 | after the trivial merge. | |
| 100 | ||
| 101 | A possible alternative for #6 is (empty), which would make it like | |
| 102 | #1. This is not used, due to the likelihood that it arises due to | |
| 103 | moving the file to multiple different locations or moving and deleting | |
| 104 | it in different branches. | |
| 105 | ||
| 106 | Case #1 is included for completeness, and also in case we decide to | |
| 107 | put on '+' markings; any path that is never mentioned at all isn't | |
| 108 | handled. | |
| 109 | ||
| 110 | Note that #16 is when both #13 and #14 apply; in this case, we refuse | |
| 111 | the trivial merge, because we can't tell from this data which is | |
| 112 | right. This is a case of a reverted patch (in some direction, maybe | |
| 113 | multiple times), and the right answer depends on looking at crossings | |
| 114 | of history or common ancestors of the ancestors. | |
| 115 | ||
| 7061f5c2 DB |
116 | Note that, between #6, #7, #9, and #11, all cases not otherwise |
| 117 | covered are handled in this table. | |
| 118 | ||
| 119 | For #8 and #10, there is alternative behavior, not currently | |
| 120 | implemented, where the result is (empty). As currently implemented, | |
| 121 | the automatic merge will generally give this effect. |