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The merge API helps a program to reconcile two competing sets of improvements to some files (e.g., unregistered changes from the work tree versus changes involved in switching to a new branch), reporting conflicts if found. The library called through this API is responsible for a few things.
-
determining which trees to merge (recursive ancestor consolidation);
-
lining up corresponding files in the trees to be merged (rename detection, subtree shifting), reporting edge cases like add/add and rename/rename conflicts to the user;
-
performing a three-way merge of corresponding files, taking path-specific merge drivers (specified in
.gitattributes
) into account.
Data structures
-
mmbuffer_t
,mmfile_t
These store data usable for use by the xdiff backend, for writing and
for reading, respectively. See xdiff/xdiff.h
for the definitions
and diff.c
for examples.
-
struct ll_merge_options
This describes the set of options the calling program wants to affect the operation of a low-level (single file) merge. Some options:
-
virtual_ancestor
-
Behave as though this were part of a merge between common ancestors in a recursive merge. If a helper program is specified by the
[merge "<driver>"] recursive
configuration, it will be used (see gitattributes[5]). -
variant
-
Resolve local conflicts automatically in favor of one side or the other (as in git merge-file
--ours
/--theirs
/--union
). Can be0
,XDL_MERGE_FAVOR_OURS
,XDL_MERGE_FAVOR_THEIRS
, orXDL_MERGE_FAVOR_UNION
. -
renormalize
-
Resmudge and clean the "base", "theirs" and "ours" files before merging. Use this when the merge is likely to have overlapped with a change in smudge/clean or end-of-line normalization rules.
Low-level (single file) merge
Calling sequence:
-
Prepare a
struct ll_merge_options
to record options. If you have no special requests, skip this and passNULL
as theopts
parameter to use the default options. -
Allocate an mmbuffer_t variable for the result.
-
Allocate and fill variables with the file’s original content and two modified versions (using
read_mmfile
, for example). -
Call
ll_merge()
. -
Read the merged content from
result_buf.ptr
andresult_buf.size
. -
Release buffers when finished. A simple
free(ancestor.ptr); free(ours.ptr); free(theirs.ptr); free(result_buf.ptr);
will do.
If the modifications do not merge cleanly, ll_merge
will return a
nonzero value and result_buf
will generally include a description of
the conflict bracketed by markers such as the traditional <<<<<<<
and >>>>>>>
.
The ancestor_label
, our_label
, and their_label
parameters are
used to label the different sides of a conflict if the merge driver
supports this.