Documentation/technical/api-merge.txt

   1 merge API
   2 =========
   3
   4 The merge API helps a program to reconcile two competing sets of
   5 improvements to some files (e.g., unregistered changes from the work
   6 tree versus changes involved in switching to a new branch), reporting
   7 conflicts if found.  The library called through this API is
   8 responsible for a few things.
   9
  10  * determining which trees to merge (recursive ancestor consolidation);
  11
  12  * lining up corresponding files in the trees to be merged (rename
  13    detection, subtree shifting), reporting edge cases like add/add
  14    and rename/rename conflicts to the user;
  15
  16  * performing a three-way merge of corresponding files, taking
  17    path-specific merge drivers (specified in `.gitattributes`)
  18    into account.
  19
  20 Data structures
  21 ---------------
  22
  23 * `mmbuffer_t`, `mmfile_t`
  24
  25 These store data usable for use by the xdiff backend, for writing and
  26 for reading, respectively.  See `xdiff/xdiff.h` for the definitions
  27 and `diff.c` for examples.
  28
  29 * `struct ll_merge_options`
  30
  31 This describes the set of options the calling program wants to affect
  32 the operation of a low-level (single file) merge.  Some options:
  33
  34 `virtual_ancestor`::
  35         Behave as though this were part of a merge between common
  36         ancestors in a recursive merge.
  37         If a helper program is specified by the
  38         `[merge "<driver>"] recursive` configuration, it will
  39         be used (see linkgit:gitattributes[5]).
  40
  41 `variant`::
  42         Resolve local conflicts automatically in favor
  43         of one side or the other (as in 'git merge-file'
  44         `--ours`/`--theirs`/`--union`).  Can be `0`,
  45         `XDL_MERGE_FAVOR_OURS`, `XDL_MERGE_FAVOR_THEIRS`, or
  46         `XDL_MERGE_FAVOR_UNION`.
  47
  48 `renormalize`::
  49         Resmudge and clean the "base", "theirs" and "ours" files
  50         before merging.  Use this when the merge is likely to have
  51         overlapped with a change in smudge/clean or end-of-line
  52         normalization rules.
  53
  54 Low-level (single file) merge
  55 -----------------------------
  56
  57 `ll_merge`::
  58
  59         Perform a three-way single-file merge in core.  This is
  60         a thin wrapper around `xdl_merge` that takes the path and
  61         any merge backend specified in `.gitattributes` or
  62         `.git/info/attributes` into account.  Returns 0 for a
  63         clean merge.
  64
  65 Calling sequence:
  66
  67 * Prepare a `struct ll_merge_options` to record options.
  68   If you have no special requests, skip this and pass `NULL`
  69   as the `opts` parameter to use the default options.
  70
  71 * Allocate an mmbuffer_t variable for the result.
  72
  73 * Allocate and fill variables with the file's original content
  74   and two modified versions (using `read_mmfile`, for example).
  75
  76 * Call `ll_merge()`.
  77
  78 * Read the merged content from `result_buf.ptr` and `result_buf.size`.
  79
  80 * Release buffers when finished.  A simple
  81   `free(ancestor.ptr); free(ours.ptr); free(theirs.ptr);
  82   free(result_buf.ptr);` will do.
  83
  84 If the modifications do not merge cleanly, `ll_merge` will return a
  85 nonzero value and `result_buf` will generally include a description of
  86 the conflict bracketed by markers such as the traditional `<<<<<<<`
  87 and `>>>>>>>`.
  88
  89 The `ancestor_label`, `our_label`, and `their_label` parameters are
  90 used to label the different sides of a conflict if the merge driver
  91 supports this.
  92
  93 Everything else
  94 ---------------
  95
  96 Talk about <merge-recursive.h> and merge_file():
  97
  98  - merge_trees() to merge with rename detection
  99  - merge_recursive() for ancestor consolidation
 100  - try_merge_command() for other strategies
 101  - conflict format
 102  - merge options
 103
 104 (Daniel, Miklos, Stephan, JC)