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.
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determining which trees to merge (recursive ancestor consolidation);
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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;
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performing a three-way merge of corresponding files, taking path-specific merge drivers (specified in
.gitattributes) into account.
Data structures
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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.
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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:
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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>"] recursiveconfiguration, 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
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ll_merge -
Perform a three-way single-file merge in core. This is a thin wrapper around
xdl_mergethat takes the path and any merge backend specified in.gitattributesor.git/info/attributesinto account. Returns 0 for a clean merge.
Calling sequence:
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Prepare a
struct ll_merge_optionsto record options. If you have no special requests, skip this and passNULLas theoptsparameter to use the default options. -
Allocate an mmbuffer_t variable for the result.
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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.ptrandresult_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.
Everything else
Talk about <merge-recursive.h> and merge_file():
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merge_trees() to merge with rename detection
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merge_recursive() for ancestor consolidation
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try_merge_command() for other strategies
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conflict format
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merge options
(Daniel, Miklos, Stephan, JC)