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diff --git a/include/git2/sys/merge.h b/include/git2/sys/merge.h
new file mode 100644
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+++ b/include/git2/sys/merge.h
@@ -0,0 +1,182 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_sys_git_merge_h__
+#define INCLUDE_sys_git_merge_h__
+
+#include "git2/common.h"
+#include "git2/types.h"
+#include "git2/index.h"
+#include "git2/merge.h"
+
+/**
+ * @file git2/sys/merge.h
+ * @brief Git merge driver backend and plugin routines
+ * @defgroup git_merge Git merge driver APIs
+ * @ingroup Git
+ * @{
+ */
+GIT_BEGIN_DECL
+
+typedef struct git_merge_driver git_merge_driver;
+
+/**
+ * Look up a merge driver by name
+ *
+ * @param name The name of the merge driver
+ * @return Pointer to the merge driver object or NULL if not found
+ */
+GIT_EXTERN(git_merge_driver *) git_merge_driver_lookup(const char *name);
+
+#define GIT_MERGE_DRIVER_TEXT   "text"
+#define GIT_MERGE_DRIVER_BINARY "binary"
+#define GIT_MERGE_DRIVER_UNION  "union"
+
+/**
+ * A merge driver source represents the file to be merged
+ */
+typedef struct git_merge_driver_source git_merge_driver_source;
+
+/** Get the repository that the source data is coming from. */
+GIT_EXTERN(git_repository *) git_merge_driver_source_repo(
+	const git_merge_driver_source *src);
+
+/** Gets the ancestor of the file to merge. */
+GIT_EXTERN(const git_index_entry *) git_merge_driver_source_ancestor(
+	const git_merge_driver_source *src);
+
+/** Gets the ours side of the file to merge. */
+GIT_EXTERN(const git_index_entry *) git_merge_driver_source_ours(
+	const git_merge_driver_source *src);
+
+/** Gets the theirs side of the file to merge. */
+GIT_EXTERN(const git_index_entry *) git_merge_driver_source_theirs(
+	const git_merge_driver_source *src);
+
+/** Gets the merge file options that the merge was invoked with */
+GIT_EXTERN(const git_merge_file_options *) git_merge_driver_source_file_options(
+	const git_merge_driver_source *src);
+
+
+/**
+ * Initialize callback on merge driver
+ *
+ * Specified as `driver.initialize`, this is an optional callback invoked
+ * before a merge driver is first used.  It will be called once at most
+ * per library lifetime.
+ *
+ * If non-NULL, the merge driver's `initialize` callback will be invoked
+ * right before the first use of the driver, so you can defer expensive
+ * initialization operations (in case libgit2 is being used in a way that
+ * doesn't need the merge driver).
+ */
+typedef int GIT_CALLBACK(git_merge_driver_init_fn)(git_merge_driver *self);
+
+/**
+ * Shutdown callback on merge driver
+ *
+ * Specified as `driver.shutdown`, this is an optional callback invoked
+ * when the merge driver is unregistered or when libgit2 is shutting down.
+ * It will be called once at most and should release resources as needed.
+ * This may be called even if the `initialize` callback was not made.
+ *
+ * Typically this function will free the `git_merge_driver` object itself.
+ */
+typedef void GIT_CALLBACK(git_merge_driver_shutdown_fn)(git_merge_driver *self);
+
+/**
+ * Callback to perform the merge.
+ *
+ * Specified as `driver.apply`, this is the callback that actually does the
+ * merge.  If it can successfully perform a merge, it should populate
+ * `path_out` with a pointer to the filename to accept, `mode_out` with
+ * the resultant mode, and `merged_out` with the buffer of the merged file
+ * and then return 0.  If the driver returns `GIT_PASSTHROUGH`, then the
+ * default merge driver should instead be run.  It can also return
+ * `GIT_EMERGECONFLICT` if the driver is not able to produce a merge result,
+ * and the file will remain conflicted.  Any other errors will fail and
+ * return to the caller.
+ *
+ * The `filter_name` contains the name of the filter that was invoked, as
+ * specified by the file's attributes.
+ *
+ * The `src` contains the data about the file to be merged.
+ */
+typedef int GIT_CALLBACK(git_merge_driver_apply_fn)(
+	git_merge_driver *self,
+	const char **path_out,
+	uint32_t *mode_out,
+	git_buf *merged_out,
+	const char *filter_name,
+	const git_merge_driver_source *src);
+
+/**
+ * Merge driver structure used to register custom merge drivers.
+ *
+ * To associate extra data with a driver, allocate extra data and put the
+ * `git_merge_driver` struct at the start of your data buffer, then cast
+ * the `self` pointer to your larger structure when your callback is invoked.
+ */
+struct git_merge_driver {
+	/** The `version` should be set to `GIT_MERGE_DRIVER_VERSION`. */
+	unsigned int                 version;
+
+	/** Called when the merge driver is first used for any file. */
+	git_merge_driver_init_fn     initialize;
+
+	/** Called when the merge driver is unregistered from the system. */
+	git_merge_driver_shutdown_fn shutdown;
+
+	/**
+	 * Called to merge the contents of a conflict.  If this function
+	 * returns `GIT_PASSTHROUGH` then the default (`text`) merge driver
+	 * will instead be invoked.  If this function returns
+	 * `GIT_EMERGECONFLICT` then the file will remain conflicted.
+	 */
+	git_merge_driver_apply_fn    apply;
+};
+
+#define GIT_MERGE_DRIVER_VERSION 1
+
+/**
+ * Register a merge driver under a given name.
+ *
+ * As mentioned elsewhere, the initialize callback will not be invoked
+ * immediately.  It is deferred until the driver is used in some way.
+ *
+ * Currently the merge driver registry is not thread safe, so any
+ * registering or deregistering of merge drivers must be done outside of
+ * any possible usage of the drivers (i.e. during application setup or
+ * shutdown).
+ *
+ * @param name The name of this driver to match an attribute.  Attempting
+ * 			to register with an in-use name will return GIT_EEXISTS.
+ * @param driver The merge driver definition.  This pointer will be stored
+ *			as is by libgit2 so it must be a durable allocation (either
+ *			static or on the heap).
+ * @return 0 on successful registry, error code <0 on failure
+ */
+GIT_EXTERN(int) git_merge_driver_register(
+	const char *name, git_merge_driver *driver);
+
+/**
+ * Remove the merge driver with the given name.
+ *
+ * Attempting to remove the builtin libgit2 merge drivers is not permitted
+ * and will return an error.
+ *
+ * Currently the merge driver registry is not thread safe, so any
+ * registering or deregistering of drivers must be done outside of any
+ * possible usage of the drivers (i.e. during application setup or shutdown).
+ *
+ * @param name The name under which the merge driver was registered
+ * @return 0 on success, error code <0 on failure
+ */
+GIT_EXTERN(int) git_merge_driver_unregister(const char *name);
+
+/** @} */
+GIT_END_DECL
+#endif