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.

Low-level (single file) merge

ll_merge

Perform a three-way single-file merge in core. This is a thin wrapper around xdl_merge that takes the path and any merge backend specified in .gitattributes or .git/info/attributes into account. Returns 0 for a clean merge.

The caller:

  1. allocates an mmbuffer_t variable for the result;

  2. allocates and fills variables with the file’s original content and two modified versions (using read_mmfile, for example);

  3. calls ll_merge();

  4. reads the output from result_buf.ptr and result_buf.size;

  5. releases buffers when finished (free(ancestor.ptr); free(ours.ptr); free(theirs.ptr); free(result_buf.ptr);).

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.

The flag parameter is a bitfield:

Everything else

Talk about <merge-recursive.h> and merge_file():

(Daniel, Miklos, Stephan, JC)