thodg/libgit2

diff --git a/include/git2/merge.h b/include/git2/merge.h
index cfec32f..38e3408 100644
--- a/include/git2/merge.h
+++ b/include/git2/merge.h
@@ -23,6 +23,43 @@
 GIT_BEGIN_DECL
 
 /**
+ * The file inputs to `git_merge_file`.  Callers should populate the
+ * `git_merge_file_input` structure with descriptions of the files in
+ * each side of the conflict for use in producing the merge file.
+ */
+typedef struct {
+	unsigned int version;
+
+	/** Pointer to the contents of the file. */
+	const char *ptr;
+
+	/** Size of the contents pointed to in `ptr`. */
+	size_t size;
+
+	/** File name of the conflicted file, or `NULL` to not merge the path. */
+	const char *path;
+
+	/** File mode of the conflicted file, or `0` to not merge the mode. */
+	unsigned int mode;
+} git_merge_file_input;
+
+#define GIT_MERGE_FILE_INPUT_VERSION 1
+#define GIT_MERGE_FILE_INPUT_INIT {GIT_MERGE_FILE_INPUT_VERSION}
+
+/**
+ * Initializes a `git_merge_file_input` with default values. Equivalent to
+ * creating an instance with GIT_MERGE_FILE_INPUT_INIT.
+ *
+ * @param opts the `git_merge_file_input` instance to initialize.
+ * @param version the version of the struct; you should pass
+ *        `GIT_MERGE_FILE_INPUT_VERSION` here.
+ * @return Zero on success; -1 on failure.
+ */
+GIT_EXTERN(int) git_merge_file_init_input(
+	git_merge_file_input *opts,
+	int version);
+
+/**
  * Flags for `git_merge_tree` options.  A combination of these flags can be
  * passed in via the `flags` value in the `git_merge_tree_opts`.
  */
@@ -71,6 +108,86 @@ typedef enum {
 	GIT_MERGE_FILE_FAVOR_UNION = 3,
 } git_merge_file_favor_t;
 
+typedef enum {
+	/* Defaults */
+	GIT_MERGE_FILE_DEFAULT = 0,
+
+	/* Create standard conflicted merge files */
+	GIT_MERGE_FILE_STYLE_MERGE = (1 << 0),
+
+	/* Create diff3-style files */
+	GIT_MERGE_FILE_STYLE_DIFF3 = (1 << 1),
+
+	/* Condense non-alphanumeric regions for simplified diff file */
+	GIT_MERGE_FILE_SIMPLIFY_ALNUM = (1 << 2),
+} git_merge_file_flags_t;
+
+typedef struct {
+	unsigned int version;
+
+	/**
+	 * Label for the ancestor file side of the conflict which will be prepended
+	 * to labels in diff3-format merge files.
+	 */
+	const char *ancestor_label;
+
+	/**
+	 * Label for our file side of the conflict which will be prepended
+	 * to labels in merge files.
+	 */
+	const char *our_label;
+
+	/**
+	 * Label for their file side of the conflict which will be prepended
+	 * to labels in merge files.
+	 */
+	const char *their_label;
+
+	/** The file to favor in region conflicts. */
+	git_merge_file_favor_t favor;
+
+	/** Merge file flags. */
+	git_merge_file_flags_t flags;
+} git_merge_file_options;
+
+#define GIT_MERGE_FILE_OPTIONS_VERSION 1
+#define GIT_MERGE_FILE_OPTIONS_INIT {GIT_MERGE_FILE_OPTIONS_VERSION}
+
+/**
+ * Initializes a `git_merge_file_options` with default values. Equivalent to
+ * creating an instance with GIT_MERGE_FILE_OPTIONS_INIT.
+ *
+ * @param opts the `git_merge_file_options` instance to initialize.
+ * @param version the version of the struct; you should pass
+ *        `GIT_MERGE_FILE_OPTIONS_VERSION` here.
+ * @return Zero on success; -1 on failure.
+ */
+GIT_EXTERN(int) git_merge_file_init_options(
+	git_merge_file_options *opts,
+	int version);
+
+typedef struct {
+	/**
+	 * True if the output was automerged, false if the output contains
+	 * conflict markers.
+	 */
+	unsigned int automergeable;
+
+	/**
+	 * The path that the resultant merge file should use, or NULL if a
+	 * filename conflict would occur.
+	 */
+	char *path;
+
+	/** The mode that the resultant merge file should use.  */
+	unsigned int mode;
+
+	/** The contents of the merge. */
+	unsigned char *ptr;
+
+	/** The length of the merge contents. */
+	size_t len;
+} git_merge_file_result;
 
 typedef struct {
 	unsigned int version;
@@ -269,6 +386,58 @@ GIT_EXTERN(void) git_merge_head_free(
 	git_merge_head *head);
 
 /**
+ * Merge two files as they exist in the in-memory data structures, using
+ * the given common ancestor as the baseline, producing a
+ * `git_merge_file_result` that reflects the merge result.  The
+ * `git_merge_file_result` must be freed with `git_merge_file_result_free`.
+ *
+ * Note that this function does not reference a repository and any
+ * configuration must be passed as `git_merge_file_options`.
+ *
+ * @param out The git_merge_file_result to be filled in
+ * @param ancestor The contents of the ancestor file
+ * @param ours The contents of the file in "our" side
+ * @param theirs The contents of the file in "their" side
+ * @param opts The merge file options or `NULL` for defaults
+ * @return 0 on success or error code
+ */
+GIT_EXTERN(int) git_merge_file(
+	git_merge_file_result *out,
+	const git_merge_file_input *ancestor,
+	const git_merge_file_input *ours,
+	const git_merge_file_input *theirs,
+	const git_merge_file_options *opts);
+
+/**
+ * Merge two files as they exist in the index, using the given common
+ * ancestor as the baseline, producing a `git_merge_file_result` that
+ * reflects the merge result.  The `git_merge_file_result` must be freed with
+ * `git_merge_file_result_free`.
+ *
+ * @param out The git_merge_file_result to be filled in
+ * @param repo The repository
+ * @param ancestor The index entry for the ancestor file (stage level 1)
+ * @param our_path The index entry for our file (stage level 2)
+ * @param their_path The index entry for their file (stage level 3)
+ * @param opts The merge file options or NULL
+ * @return 0 on success or error code
+ */
+GIT_EXTERN(int) git_merge_file_from_index(
+	git_merge_file_result *out,
+	git_repository *repo,
+	const git_index_entry *ancestor,
+	const git_index_entry *ours,
+	const git_index_entry *theirs,
+	const git_merge_file_options *opts);
+
+/**
+ * Frees a `git_merge_file_result`.
+ *
+ * @param result The result to free or `NULL`
+ */
+GIT_EXTERN(void) git_merge_file_result_free(git_merge_file_result *result);
+
+/**
  * Merge two trees, producing a `git_index` that reflects the result of
  * the merge.  The index may be written as-is to the working directory
  * or checked out.  If the index is to be converted to a tree, the caller
diff --git a/src/checkout.c b/src/checkout.c
index 5dd4ec7..f882f35 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -1681,29 +1681,20 @@ static int checkout_write_merge(
 {
 	git_buf our_label = GIT_BUF_INIT, their_label = GIT_BUF_INIT,
 		path_suffixed = GIT_BUF_INIT, path_workdir = GIT_BUF_INIT;
-	git_merge_file_options merge_file_opts = GIT_MERGE_FILE_OPTIONS_INIT;
-	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
-		ours = GIT_MERGE_FILE_INPUT_INIT,
-		theirs = GIT_MERGE_FILE_INPUT_INIT;
-	git_merge_file_result result = GIT_MERGE_FILE_RESULT_INIT;
+	git_merge_file_options opts = GIT_MERGE_FILE_OPTIONS_INIT;
+	git_merge_file_result result = {0};
 	git_filebuf output = GIT_FILEBUF_INIT;
 	int error = 0;
 
 	if (data->opts.checkout_strategy & GIT_CHECKOUT_CONFLICT_STYLE_DIFF3)
-		merge_file_opts.style = GIT_MERGE_FILE_STYLE_DIFF3;
-
-	if ((conflict->ancestor &&
-		(error = git_merge_file_input_from_index_entry(
-		&ancestor, data->repo, conflict->ancestor)) < 0) ||
-		(error = git_merge_file_input_from_index_entry(
-		&ours, data->repo, conflict->ours)) < 0 ||
-		(error = git_merge_file_input_from_index_entry(
-		&theirs, data->repo, conflict->theirs)) < 0)
-		goto done;
+		opts.flags |= GIT_MERGE_FILE_STYLE_DIFF3;
 
-	ancestor.label = data->opts.ancestor_label ? data->opts.ancestor_label : "ancestor";
-	ours.label = data->opts.our_label ? data->opts.our_label : "ours";
-	theirs.label = data->opts.their_label ? data->opts.their_label : "theirs";
+	opts.ancestor_label = data->opts.ancestor_label ?
+		data->opts.ancestor_label : "ancestor";
+	opts.our_label = data->opts.our_label ?
+		data->opts.our_label : "ours";
+	opts.their_label = data->opts.their_label ?
+		data->opts.their_label : "theirs";
 
 	/* If all the paths are identical, decorate the diff3 file with the branch
 	 * names.  Otherwise, append branch_name:path.
@@ -1712,16 +1703,17 @@ static int checkout_write_merge(
 		strcmp(conflict->ours->path, conflict->theirs->path) != 0) {
 
 		if ((error = conflict_entry_name(
-			&our_label, ours.label, conflict->ours->path)) < 0 ||
+			&our_label, opts.our_label, conflict->ours->path)) < 0 ||
 			(error = conflict_entry_name(
-			&their_label, theirs.label, conflict->theirs->path)) < 0)
+			&their_label, opts.their_label, conflict->theirs->path)) < 0)
 			goto done;
 
-		ours.label = git_buf_cstr(&our_label);
-		theirs.label = git_buf_cstr(&their_label);
+		opts.our_label = git_buf_cstr(&our_label);
+		opts.their_label = git_buf_cstr(&their_label);
 	}
 
-	if ((error = git_merge_files(&result, &ancestor, &ours, &theirs, &merge_file_opts)) < 0)
+	if ((error = git_merge_file_from_index(&result, data->repo,
+		conflict->ancestor, conflict->ours, conflict->theirs, &opts)) < 0)
 		goto done;
 
 	if (result.path == NULL || result.mode == 0) {
@@ -1739,7 +1731,7 @@ static int checkout_write_merge(
 
 	if ((error = git_futils_mkpath2file(path_workdir.ptr, 0755)) < 0 ||
 		(error = git_filebuf_open(&output, path_workdir.ptr, GIT_FILEBUF_DO_NOT_BUFFER, result.mode)) < 0 ||
-		(error = git_filebuf_write(&output, result.data, result.len)) < 0 ||
+		(error = git_filebuf_write(&output, result.ptr, result.len)) < 0 ||
 		(error = git_filebuf_commit(&output)) < 0)
 		goto done;
 
@@ -1747,9 +1739,6 @@ done:
 	git_buf_free(&our_label);
 	git_buf_free(&their_label);
 
-	git_merge_file_input_free(&ancestor);
-	git_merge_file_input_free(&ours);
-	git_merge_file_input_free(&theirs);
 	git_merge_file_result_free(&result);
 	git_buf_free(&path_workdir);
 	git_buf_free(&path_suffixed);
diff --git a/src/index.c b/src/index.c
index 0d7d506..ea0815e 100644
--- a/src/index.c
+++ b/src/index.c
@@ -300,7 +300,7 @@ static void index_entry_free(git_index_entry *entry)
 	git__free(entry);
 }
 
-static unsigned int index_create_mode(unsigned int mode)
+unsigned int git_index__create_mode(unsigned int mode)
 {
 	if (S_ISLNK(mode))
 		return S_IFLNK;
@@ -320,9 +320,9 @@ static unsigned int index_merge_mode(
 
 	if (index->distrust_filemode && S_ISREG(mode))
 		return (existing && S_ISREG(existing->mode)) ?
-			existing->mode : index_create_mode(0666);
+			existing->mode : git_index__create_mode(0666);
 
-	return index_create_mode(mode);
+	return git_index__create_mode(mode);
 }
 
 void git_index__set_ignore_case(git_index *index, bool ignore_case)
@@ -619,7 +619,7 @@ void git_index_entry__init_from_stat(
 	entry->dev  = st->st_rdev;
 	entry->ino  = st->st_ino;
 	entry->mode = (!trust_mode && S_ISREG(st->st_mode)) ?
-		index_create_mode(0666) : index_create_mode(st->st_mode);
+		git_index__create_mode(0666) : git_index__create_mode(st->st_mode);
 	entry->uid  = st->st_uid;
 	entry->gid  = st->st_gid;
 	entry->file_size = st->st_size;
diff --git a/src/index.h b/src/index.h
index f88d110..259a314 100644
--- a/src/index.h
+++ b/src/index.h
@@ -60,4 +60,6 @@ extern int git_index__find(
 
 extern void git_index__set_ignore_case(git_index *index, bool ignore_case);
 
+extern unsigned int git_index__create_mode(unsigned int mode);
+
 #endif
diff --git a/src/merge.c b/src/merge.c
index 0b11c0d..8a33edb 100644
--- a/src/merge.c
+++ b/src/merge.c
@@ -539,11 +539,9 @@ static int merge_conflict_resolve_automerge(
 	const git_merge_diff *conflict,
 	unsigned int merge_file_favor)
 {
-	git_merge_file_options merge_file_opts = GIT_MERGE_FILE_OPTIONS_INIT;
-	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
-		ours = GIT_MERGE_FILE_INPUT_INIT,
-		theirs = GIT_MERGE_FILE_INPUT_INIT;
-	git_merge_file_result result = GIT_MERGE_FILE_RESULT_INIT;
+	const git_index_entry *ancestor = NULL, *ours = NULL, *theirs = NULL;
+	git_merge_file_options opts = GIT_MERGE_FILE_OPTIONS_INIT;
+	git_merge_file_result result = {0};
 	git_index_entry *index_entry;
 	git_odb *odb = NULL;
 	git_oid automerge_oid;
@@ -553,7 +551,9 @@ static int merge_conflict_resolve_automerge(
 
 	*resolved = 0;
 
-	merge_file_opts.favor = merge_file_favor;
+	if (!GIT_MERGE_INDEX_ENTRY_EXISTS(conflict->our_entry) ||
+		!GIT_MERGE_INDEX_ENTRY_EXISTS(conflict->their_entry))
+		return 0;
 
 	/* Reject D/F conflicts */
 	if (conflict->type == GIT_MERGE_DIFF_DIRECTORY_FILE)
@@ -584,13 +584,19 @@ static int merge_conflict_resolve_automerge(
 	if (conflict->binary)
 		return 0;
 
+	ancestor = GIT_MERGE_INDEX_ENTRY_EXISTS(conflict->ancestor_entry) ?
+		&conflict->ancestor_entry : NULL;
+	ours = GIT_MERGE_INDEX_ENTRY_EXISTS(conflict->our_entry) ?
+		&conflict->our_entry : NULL;
+	theirs = GIT_MERGE_INDEX_ENTRY_EXISTS(conflict->their_entry) ?
+		&conflict->their_entry : NULL;
+
+	opts.favor = merge_file_favor;
+
 	if ((error = git_repository_odb(&odb, diff_list->repo)) < 0 ||
-		(error = git_merge_file_input_from_index_entry(&ancestor, diff_list->repo, &conflict->ancestor_entry)) < 0 ||
-		(error = git_merge_file_input_from_index_entry(&ours, diff_list->repo, &conflict->our_entry)) < 0 ||
-		(error = git_merge_file_input_from_index_entry(&theirs, diff_list->repo, &conflict->their_entry)) < 0 ||
-		(error = git_merge_files(&result, &ancestor, &ours, &theirs, &merge_file_opts)) < 0 ||
+		(error = git_merge_file_from_index(&result, diff_list->repo, ancestor, ours, theirs, &opts)) < 0 ||
 		!result.automergeable ||
-		(error = git_odb_write(&automerge_oid, odb, result.data, result.len, GIT_OBJ_BLOB)) < 0)
+		(error = git_odb_write(&automerge_oid, odb, result.ptr, result.len, GIT_OBJ_BLOB)) < 0)
 		goto done;
 
 	if ((index_entry = git_pool_malloc(&diff_list->pool, sizeof(git_index_entry))) == NULL)
@@ -609,9 +615,6 @@ static int merge_conflict_resolve_automerge(
 	*resolved = 1;
 
 done:
-	git_merge_file_input_free(&ancestor);
-	git_merge_file_input_free(&ours);
-	git_merge_file_input_free(&theirs);
 	git_merge_file_result_free(&result);
 	git_odb_free(odb);
 
@@ -2793,3 +2796,27 @@ int git_merge_tree_init_opts(git_merge_tree_opts* opts, int version)
 		return 0;
 	}
 }
+
+int git_merge_file_init_input(git_merge_file_input *input, int version)
+{
+	if (version != GIT_MERGE_FILE_INPUT_VERSION) {
+		giterr_set(GITERR_INVALID, "Invalid version %d for git_merge_file_input", version);
+		return -1;
+	} else {
+		git_merge_file_input i = GIT_MERGE_FILE_INPUT_INIT;
+		memcpy(input, &i, sizeof(i));
+		return 0;
+	}
+}
+
+int git_merge_file_init_options(git_merge_file_options *opts, int version)
+{
+	if (version != GIT_MERGE_FILE_OPTIONS_VERSION) {
+		giterr_set(GITERR_INVALID, "Invalid version %d for git_merge_file_options", version);
+		return -1;
+	} else {
+		git_merge_file_options o = GIT_MERGE_FILE_OPTIONS_INIT;
+		memcpy(opts, &o, sizeof(o));
+		return 0;
+	}
+}
diff --git a/src/merge_file.c b/src/merge_file.c
index 986fbf9..fc45cbf 100644
--- a/src/merge_file.c
+++ b/src/merge_file.c
@@ -8,6 +8,9 @@
 #include "common.h"
 #include "repository.h"
 #include "merge_file.h"
+#include "posix.h"
+#include "fileops.h"
+#include "index.h"
 
 #include "git2/repository.h"
 #include "git2/object.h"
@@ -22,17 +25,17 @@ GIT_INLINE(const char *) merge_file_best_path(
 	const git_merge_file_input *ours,
 	const git_merge_file_input *theirs)
 {
-	if (!GIT_MERGE_FILE_SIDE_EXISTS(ancestor)) {
-		if (strcmp(ours->path, theirs->path) == 0)
+	if (!ancestor) {
+		if (ours && theirs && strcmp(ours->path, theirs->path) == 0)
 			return ours->path;
 
 		return NULL;
 	}
 
-	if (strcmp(ancestor->path, ours->path) == 0)
-		return theirs->path;
-	else if(strcmp(ancestor->path, theirs->path) == 0)
-		return ours->path;
+	if (ours && strcmp(ancestor->path, ours->path) == 0)
+		return theirs ? theirs->path : NULL;
+	else if(theirs && strcmp(ancestor->path, theirs->path) == 0)
+		return ours ? ours->path : NULL;
 
 	return NULL;
 }
@@ -47,136 +50,230 @@ GIT_INLINE(int) merge_file_best_mode(
 	 * assume executable.  Otherwise, if any mode changed from the ancestor,
 	 * use that one.
 	 */
-	if (!GIT_MERGE_FILE_SIDE_EXISTS(ancestor)) {
-		if (ours->mode == GIT_FILEMODE_BLOB_EXECUTABLE ||
-			theirs->mode == GIT_FILEMODE_BLOB_EXECUTABLE)
+	if (!ancestor) {
+		if ((ours && ours->mode == GIT_FILEMODE_BLOB_EXECUTABLE) ||
+			(theirs && theirs->mode == GIT_FILEMODE_BLOB_EXECUTABLE))
 			return GIT_FILEMODE_BLOB_EXECUTABLE;
 
 		return GIT_FILEMODE_BLOB;
-	}
+	} else if (ours && theirs) {
+		if (ancestor->mode == ours->mode)
+			return theirs->mode;
 
-	if (ancestor->mode == ours->mode)
-		return theirs->mode;
-	else if(ancestor->mode == theirs->mode)
 		return ours->mode;
+	}
 
 	return 0;
 }
 
-int git_merge_file_input_from_index_entry(
-	git_merge_file_input *input,
-	git_repository *repo,
+int git_merge_file__input_from_index(
+	git_merge_file_input *input_out,
+	git_odb_object **odb_object_out,
+	git_odb *odb,
 	const git_index_entry *entry)
 {
-	git_odb *odb = NULL;
 	int error = 0;
 
-	assert(input && repo && entry);
-
-	if (entry->mode == 0)
-		return 0;
+	assert(input_out && odb_object_out && odb && entry);
 
-	if ((error = git_repository_odb(&odb, repo)) < 0 ||
-		(error = git_odb_read(&input->odb_object, odb, &entry->id)) < 0)
+	if ((error = git_odb_read(odb_object_out, odb, &entry->id)) < 0)
 		goto done;
 
-	input->mode = entry->mode;
-	input->path = git__strdup(entry->path);
-	input->mmfile.size = git_odb_object_size(input->odb_object);
-	input->mmfile.ptr = (char *)git_odb_object_data(input->odb_object);
-
-	if (input->label == NULL)
-		input->label = entry->path;
+	input_out->path = entry->path;
+	input_out->mode = entry->mode;
+	input_out->ptr = (char *)git_odb_object_data(*odb_object_out);
+	input_out->size = git_odb_object_size(*odb_object_out);
 
 done:
-	git_odb_free(odb);
-
 	return error;
 }
 
-int git_merge_file_input_from_diff_file(
-	git_merge_file_input *input,
-	git_repository *repo,
-	const git_diff_file *file)
+static void merge_file_normalize_opts(
+	git_merge_file_options *out,
+	const git_merge_file_options *given_opts)
 {
-	git_odb *odb = NULL;
-	int error = 0;
-
-	assert(input && repo && file);
-
-	if (file->mode == 0)
-		return 0;
-
-	if ((error = git_repository_odb(&odb, repo)) < 0 ||
-		(error = git_odb_read(&input->odb_object, odb, &file->id)) < 0)
-		goto done;
-
-	input->mode = file->mode;
-	input->path = git__strdup(file->path);
-	input->mmfile.size = git_odb_object_size(input->odb_object);
-	input->mmfile.ptr = (char *)git_odb_object_data(input->odb_object);
-
-	if (input->label == NULL)
-		input->label = file->path;
-
-done:
-	git_odb_free(odb);
-
-	return error;
+	if (given_opts)
+		memcpy(out, given_opts, sizeof(git_merge_file_options));
+	else {
+		git_merge_file_options default_opts = GIT_MERGE_FILE_OPTIONS_INIT;
+		memcpy(out, &default_opts, sizeof(git_merge_file_options));
+	}
 }
 
-int git_merge_files(
+static int git_merge_file__from_inputs(
 	git_merge_file_result *out,
-	git_merge_file_input *ancestor,
-	git_merge_file_input *ours,
-	git_merge_file_input *theirs,
-	git_merge_file_options *opts)
+	const git_merge_file_input *ancestor,
+	const git_merge_file_input *ours,
+	const git_merge_file_input *theirs,
+	const git_merge_file_options *given_opts)
 {
 	xmparam_t xmparam;
+	mmfile_t ancestor_mmfile = {0}, our_mmfile = {0}, their_mmfile = {0};
 	mmbuffer_t mmbuffer;
+	git_merge_file_options options = GIT_MERGE_FILE_OPTIONS_INIT;
+	const char *path;
 	int xdl_result;
 	int error = 0;
 
-	assert(out && ancestor && ours && theirs);
-
 	memset(out, 0x0, sizeof(git_merge_file_result));
 
-	if (!GIT_MERGE_FILE_SIDE_EXISTS(ours) || !GIT_MERGE_FILE_SIDE_EXISTS(theirs))
-		return 0;
+	merge_file_normalize_opts(&options, given_opts);		
 
 	memset(&xmparam, 0x0, sizeof(xmparam_t));
-	xmparam.ancestor = ancestor->label;
-	xmparam.file1 = ours->label;
-	xmparam.file2 = theirs->label;
 
-	out->path = merge_file_best_path(ancestor, ours, theirs);
-	out->mode = merge_file_best_mode(ancestor, ours, theirs);
+	if (ancestor) {
+		xmparam.ancestor = (options.ancestor_label) ?
+			options.ancestor_label : ancestor->path;
+		ancestor_mmfile.ptr = (char *)ancestor->ptr;
+		ancestor_mmfile.size = ancestor->size;
+	}
 
-	if (opts && opts->favor == GIT_MERGE_FILE_FAVOR_OURS)
+	xmparam.file1 = (options.our_label) ?
+		options.our_label : ours->path;
+	our_mmfile.ptr = (char *)ours->ptr;
+	our_mmfile.size = ours->size;
+
+	xmparam.file2 = (options.their_label) ?
+		options.their_label : theirs->path;
+	their_mmfile.ptr = (char *)theirs->ptr;
+	their_mmfile.size = theirs->size;
+
+	if (options.favor == GIT_MERGE_FILE_FAVOR_OURS)
 		xmparam.favor = XDL_MERGE_FAVOR_OURS;
-	else if (opts && opts->favor == GIT_MERGE_FILE_FAVOR_THEIRS)
+	else if (options.favor == GIT_MERGE_FILE_FAVOR_THEIRS)
 		xmparam.favor = XDL_MERGE_FAVOR_THEIRS;
-	else if (opts && opts->favor == GIT_MERGE_FILE_FAVOR_UNION)
+	else if (options.favor == GIT_MERGE_FILE_FAVOR_UNION)
 		xmparam.favor = XDL_MERGE_FAVOR_UNION;
 
-	xmparam.level = 
-		(opts && (opts->flags & GIT_MERGE_FILE_SIMPLIFY_ALNUM)) ?
+	xmparam.level = (options.flags & GIT_MERGE_FILE_SIMPLIFY_ALNUM) ?
 		XDL_MERGE_ZEALOUS_ALNUM : XDL_MERGE_ZEALOUS;
 
-	if (opts && opts->style == GIT_MERGE_FILE_STYLE_DIFF3)
+	if (options.flags & GIT_MERGE_FILE_STYLE_DIFF3)
 		xmparam.style = XDL_MERGE_DIFF3;
 
-	if ((xdl_result = xdl_merge(&ancestor->mmfile, &ours->mmfile,
-		&theirs->mmfile, &xmparam, &mmbuffer)) < 0) {
+	if ((xdl_result = xdl_merge(&ancestor_mmfile, &our_mmfile,
+		&their_mmfile, &xmparam, &mmbuffer)) < 0) {
 		giterr_set(GITERR_MERGE, "Failed to merge files.");
 		error = -1;
 		goto done;
 	}
 
+	if ((path = merge_file_best_path(ancestor, ours, theirs)) != NULL &&
+		(out->path = strdup(path)) == NULL) {
+		error = -1;
+		goto done;
+	}
+
 	out->automergeable = (xdl_result == 0);
-	out->data = (unsigned char *)mmbuffer.ptr;
+	out->ptr = (unsigned char *)mmbuffer.ptr;
 	out->len = mmbuffer.size;
+	out->mode = merge_file_best_mode(ancestor, ours, theirs);
 
 done:
+	if (error < 0)
+		git_merge_file_result_free(out);
+
 	return error;
 }
+
+static git_merge_file_input *git_merge_file__normalize_inputs(
+	git_merge_file_input *out,
+	const git_merge_file_input *given)
+{
+	memcpy(out, given, sizeof(git_merge_file_input));
+
+	if (!out->path)
+		out->path = "file.txt";
+
+	if (!out->mode)
+		out->mode = 0100644;
+
+	return out;
+}
+
+int git_merge_file(
+	git_merge_file_result *out,
+	const git_merge_file_input *ancestor,
+	const git_merge_file_input *ours,
+	const git_merge_file_input *theirs,
+	const git_merge_file_options *options)
+{
+	git_merge_file_input inputs[3] = { {0} };
+
+	assert(out && ours && theirs);
+
+	memset(out, 0x0, sizeof(git_merge_file_result));
+
+	if (ancestor)
+		ancestor = git_merge_file__normalize_inputs(&inputs[0], ancestor);
+
+	ours = git_merge_file__normalize_inputs(&inputs[1], ours);
+	theirs = git_merge_file__normalize_inputs(&inputs[2], theirs);
+
+	return git_merge_file__from_inputs(out, ancestor, ours, theirs, options);
+}
+
+int git_merge_file_from_index(
+	git_merge_file_result *out,
+	git_repository *repo,
+	const git_index_entry *ancestor,
+	const git_index_entry *ours,
+	const git_index_entry *theirs,
+	const git_merge_file_options *options)
+{
+	git_merge_file_input inputs[3] = { {0} },
+		*ancestor_input = NULL, *our_input = NULL, *their_input = NULL;
+	git_odb *odb = NULL;
+	git_odb_object *odb_object[3] = { 0 };
+	int error = 0;
+
+	assert(out && repo && ours && theirs);
+
+	memset(out, 0x0, sizeof(git_merge_file_result));
+
+	if ((error = git_repository_odb(&odb, repo)) < 0)
+		goto done;
+
+	if (ancestor) {
+		if ((error = git_merge_file__input_from_index(
+			&inputs[0], &odb_object[0], odb, ancestor)) < 0)
+			goto done;
+
+		ancestor_input = &inputs[0];
+	}
+
+	if ((error = git_merge_file__input_from_index(
+		&inputs[1], &odb_object[1], odb, ours)) < 0)
+		goto done;
+
+	our_input = &inputs[1];
+
+	if ((error = git_merge_file__input_from_index(
+		&inputs[2], &odb_object[2], odb, theirs)) < 0)
+		goto done;
+
+	their_input = &inputs[2];
+
+	if ((error = git_merge_file__from_inputs(out,
+		ancestor_input, our_input, their_input, options)) < 0)
+		goto done;
+
+done:
+	git_odb_object_free(odb_object[0]);
+	git_odb_object_free(odb_object[1]);
+	git_odb_object_free(odb_object[2]);
+	git_odb_free(odb);
+
+	return error;
+}
+
+void git_merge_file_result_free(git_merge_file_result *result)
+{
+	if (result == NULL)
+		return;
+
+	git__free(result->path);
+
+	/* xdiff uses malloc() not git_malloc, so we use free(), not git_free() */
+	free(result->ptr);
+}
diff --git a/src/merge_file.h b/src/merge_file.h
index 332be49..263391e 100644
--- a/src/merge_file.h
+++ b/src/merge_file.h
@@ -11,82 +11,4 @@
 
 #include "git2/merge.h"
 
-typedef struct {
-	const char *label;
-	char *path;
-	unsigned int mode;
-	mmfile_t mmfile;
-
-	git_odb_object *odb_object;
-} git_merge_file_input;
-
-#define GIT_MERGE_FILE_INPUT_INIT	{0}
-
-typedef struct {
-	bool automergeable;
-
-	const char *path;
-	int mode;
-
-	unsigned char *data;
-	size_t len;
-} git_merge_file_result;
-
-#define GIT_MERGE_FILE_RESULT_INIT	{0}
-
-typedef enum {
-	/* Condense non-alphanumeric regions for simplified diff file */
-	GIT_MERGE_FILE_SIMPLIFY_ALNUM = (1 << 0),
-} git_merge_file_flags_t;
-
-typedef enum {
-	/* Create standard conflicted merge files */
-	GIT_MERGE_FILE_STYLE_MERGE = 0,
-
-	/* Create diff3-style files */
-	GIT_MERGE_FILE_STYLE_DIFF3 = 1,
-} git_merge_file_style_t;
-
-typedef struct {
-	git_merge_file_favor_t favor;
-	git_merge_file_flags_t flags;
-	git_merge_file_style_t style;
-} git_merge_file_options;
-
-#define GIT_MERGE_FILE_OPTIONS_INIT	{0}
-
-int git_merge_file_input_from_index_entry(
-	git_merge_file_input *input,
-	git_repository *repo,
-	const git_index_entry *entry);
-
-int git_merge_file_input_from_diff_file(
-	git_merge_file_input *input,
-	git_repository *repo,
-	const git_diff_file *file);
-
-int git_merge_files(
-	git_merge_file_result *out,
-	git_merge_file_input *ancestor,
-	git_merge_file_input *ours,
-	git_merge_file_input *theirs,
-	git_merge_file_options *opts);
-
-GIT_INLINE(void) git_merge_file_input_free(git_merge_file_input *input)
-{
-	assert(input);
-	git__free(input->path);
-	git_odb_object_free(input->odb_object);
-}
-
-GIT_INLINE(void) git_merge_file_result_free(git_merge_file_result *filediff)
-{
-	if (filediff == NULL)
-		return;
-
-	/* xdiff uses malloc() not git_malloc, so we use free(), not git_free() */
-	if (filediff->data != NULL)
-		free(filediff->data);
-}
-
 #endif
diff --git a/tests/merge/files.c b/tests/merge/files.c
new file mode 100644
index 0000000..c377471
--- /dev/null
+++ b/tests/merge/files.c
@@ -0,0 +1,175 @@
+#include "clar_libgit2.h"
+#include "git2/repository.h"
+#include "git2/merge.h"
+#include "buffer.h"
+#include "merge.h"
+#include "merge_helpers.h"
+#include "refs.h"
+#include "fileops.h"
+
+#define TEST_REPO_PATH "merge-resolve"
+#define TEST_INDEX_PATH TEST_REPO_PATH "/.git/index"
+
+static git_repository *repo;
+static git_index *repo_index;
+
+// Fixture setup and teardown
+void test_merge_files__initialize(void)
+{
+	git_config *cfg;
+
+	repo = cl_git_sandbox_init(TEST_REPO_PATH);
+	git_repository_index(&repo_index, repo);
+
+	/* Ensure that the user's merge.conflictstyle doesn't interfere */
+	cl_git_pass(git_repository_config(&cfg, repo));
+	cl_git_pass(git_config_set_string(cfg, "merge.conflictstyle", "merge"));
+	git_config_free(cfg);
+}
+
+void test_merge_files__cleanup(void)
+{
+	git_index_free(repo_index);
+	cl_git_sandbox_cleanup();
+}
+
+void test_merge_files__automerge_from_bufs(void)
+{
+	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
+		ours = GIT_MERGE_FILE_INPUT_INIT,
+		theirs = GIT_MERGE_FILE_INPUT_INIT;
+	git_merge_file_result result = {0};
+	const char *expected = "Zero\n1\n2\n3\n4\n5\n6\n7\n8\n9\nTen\n";
+
+	ancestor.ptr = "0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n";
+	ancestor.size = strlen(ancestor.ptr);
+	ancestor.path = "testfile.txt";
+	ancestor.mode = 0100755;
+
+	ours.ptr = "Zero\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n";
+	ours.size = strlen(ours.ptr);
+	ours.path = "testfile.txt";
+	ours.mode = 0100755;
+
+	theirs.ptr = "0\n1\n2\n3\n4\n5\n6\n7\n8\n9\nTen\n";
+	theirs.size = strlen(theirs.ptr);
+	theirs.path = "testfile.txt";
+	theirs.mode = 0100755;
+
+	cl_git_pass(git_merge_file(&result, &ancestor, &ours, &theirs, 0));
+
+	cl_assert_equal_i(1, result.automergeable);
+
+	cl_assert_equal_s("testfile.txt", result.path);
+	cl_assert_equal_i(0100755, result.mode);
+
+	cl_assert_equal_i(strlen(expected), result.len);
+	cl_assert_equal_strn(expected, result.ptr, result.len);
+
+	git_merge_file_result_free(&result);
+}
+
+void test_merge_files__automerge_use_best_path_and_mode(void)
+{
+	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
+		ours = GIT_MERGE_FILE_INPUT_INIT,
+		theirs = GIT_MERGE_FILE_INPUT_INIT;
+	git_merge_file_result result = {0};
+	const char *expected = "Zero\n1\n2\n3\n4\n5\n6\n7\n8\n9\nTen\n";
+
+	ancestor.ptr = "0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n";
+	ancestor.size = strlen(ancestor.ptr);
+	ancestor.path = "testfile.txt";
+	ancestor.mode = 0100755;
+
+	ours.ptr = "Zero\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n";
+	ours.size = strlen(ours.ptr);
+	ours.path = "testfile.txt";
+	ours.mode = 0100644;
+
+	theirs.ptr = "0\n1\n2\n3\n4\n5\n6\n7\n8\n9\nTen\n";
+	theirs.size = strlen(theirs.ptr);
+	theirs.path = "theirs.txt";
+	theirs.mode = 0100755;
+
+	cl_git_pass(git_merge_file(&result, &ancestor, &ours, &theirs, 0));
+
+	cl_assert_equal_i(1, result.automergeable);
+
+	cl_assert_equal_s("theirs.txt", result.path);
+	cl_assert_equal_i(0100644, result.mode);
+
+	cl_assert_equal_i(strlen(expected), result.len);
+	cl_assert_equal_strn(expected, result.ptr, result.len);
+
+	git_merge_file_result_free(&result);
+}
+
+void test_merge_files__conflict_from_bufs(void)
+{
+	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
+		ours = GIT_MERGE_FILE_INPUT_INIT,
+		theirs = GIT_MERGE_FILE_INPUT_INIT;
+	git_merge_file_result result = {0};
+
+	const char *expected = "<<<<<<< testfile.txt\nAloha!\nOurs.\n=======\nHi!\nTheirs.\n>>>>>>> theirs.txt\n";
+	size_t expected_len = strlen(expected);
+
+	ancestor.ptr = "Hello!\nAncestor!\n";
+	ancestor.size = strlen(ancestor.ptr);
+	ancestor.path = "testfile.txt";
+	ancestor.mode = 0100755;
+
+	ours.ptr =  "Aloha!\nOurs.\n";
+	ours.size = strlen(ours.ptr);
+	ours.path = "testfile.txt";
+	ours.mode = 0100644;
+
+	theirs.ptr = "Hi!\nTheirs.\n";
+	theirs.size = strlen(theirs.ptr);
+	theirs.path = "theirs.txt";
+	theirs.mode = 0100755;
+
+	cl_git_pass(git_merge_file(&result, &ancestor, &ours, &theirs, NULL));
+
+	cl_assert_equal_i(0, result.automergeable);
+
+	cl_assert_equal_s("theirs.txt", result.path);
+	cl_assert_equal_i(0100644, result.mode);
+
+	cl_assert_equal_i(expected_len, result.len);
+	cl_assert_equal_strn(expected, result.ptr, expected_len);
+
+	git_merge_file_result_free(&result);
+}
+
+void test_merge_files__automerge_from_index(void)
+{
+	git_merge_file_result result = {0};
+	git_index_entry ancestor, ours, theirs;
+
+	git_oid_fromstr(&ancestor.id, "6212c31dab5e482247d7977e4f0dd3601decf13b");
+	ancestor.path = "automergeable.txt";
+	ancestor.mode = 0100644;
+
+	git_oid_fromstr(&ours.id, "ee3fa1b8c00aff7fe02065fdb50864bb0d932ccf");
+	ours.path = "automergeable.txt";
+	ours.mode = 0100755;
+
+	git_oid_fromstr(&theirs.id, "058541fc37114bfc1dddf6bd6bffc7fae5c2e6fe");
+	theirs.path = "newname.txt";
+	theirs.mode = 0100644;
+
+	cl_git_pass(git_merge_file_from_index(&result, repo,
+		&ancestor, &ours, &theirs, 0));
+
+	cl_assert_equal_i(1, result.automergeable);
+
+	cl_assert_equal_s("newname.txt", result.path);
+	cl_assert_equal_i(0100755, result.mode);
+
+	cl_assert_equal_i(strlen(AUTOMERGEABLE_MERGED_FILE), result.len);
+	cl_assert_equal_strn(AUTOMERGEABLE_MERGED_FILE, result.ptr, result.len);
+
+	git_merge_file_result_free(&result);
+}
diff --git a/tests/merge/merge_helpers.h b/tests/merge/merge_helpers.h
index 3f53abc..63d1cb7 100644
--- a/tests/merge/merge_helpers.h
+++ b/tests/merge/merge_helpers.h
@@ -4,6 +4,49 @@
 #include "merge.h"
 #include "git2/merge.h"
 
+#define AUTOMERGEABLE_MERGED_FILE \
+	"this file is changed in master\n" \
+	"this file is automergeable\n" \
+	"this file is automergeable\n" \
+	"this file is automergeable\n" \
+	"this file is automergeable\n" \
+	"this file is automergeable\n" \
+	"this file is automergeable\n" \
+	"this file is automergeable\n" \
+	"this file is changed in branch\n"
+
+#define AUTOMERGEABLE_MERGED_FILE_CRLF \
+	"this file is changed in master\r\n" \
+	"this file is automergeable\r\n" \
+	"this file is automergeable\r\n" \
+	"this file is automergeable\r\n" \
+	"this file is automergeable\r\n" \
+	"this file is automergeable\r\n" \
+	"this file is automergeable\r\n" \
+	"this file is automergeable\r\n" \
+	"this file is changed in branch\r\n"
+
+#define CONFLICTING_MERGE_FILE \
+	"<<<<<<< HEAD\n" \
+	"this file is changed in master and branch\n" \
+	"=======\n" \
+	"this file is changed in branch and master\n" \
+	">>>>>>> 7cb63eed597130ba4abb87b3e544b85021905520\n"
+
+#define CONFLICTING_DIFF3_FILE \
+	"<<<<<<< HEAD\n" \
+	"this file is changed in master and branch\n" \
+	"||||||| initial\n" \
+	"this file is a conflict\n" \
+	"=======\n" \
+	"this file is changed in branch and master\n" \
+	">>>>>>> 7cb63eed597130ba4abb87b3e544b85021905520\n"
+
+#define CONFLICTING_UNION_FILE \
+	"this file is changed in master and branch\n" \
+	"this file is changed in branch and master\n"
+
+
 struct merge_index_entry {
 	uint16_t mode;
 	char oid_str[41];
diff --git a/tests/merge/trees/automerge.c b/tests/merge/trees/automerge.c
index bd710e6..79069d8 100644
--- a/tests/merge/trees/automerge.c
+++ b/tests/merge/trees/automerge.c
@@ -54,28 +54,6 @@ static git_repository *repo;
 	  "", \
 	  "5c3b68a71fc4fa5d362fd3875e53137c6a5ab7a5" }
 
-#define AUTOMERGEABLE_MERGED_FILE \
-	"this file is changed in master\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is changed in branch\n"
-
-#define AUTOMERGEABLE_MERGED_FILE_CRLF \
-	"this file is changed in master\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is changed in branch\r\n"
-
 // Fixture setup and teardown
 void test_merge_trees_automerge__initialize(void)
 {
diff --git a/tests/merge/trees/commits.c b/tests/merge/trees/commits.c
index eeb30da..08caf80 100644
--- a/tests/merge/trees/commits.c
+++ b/tests/merge/trees/commits.c
@@ -8,17 +8,6 @@ static git_repository *repo;
 
 #define TEST_REPO_PATH "merge-resolve"
 
-#define AUTOMERGEABLE_MERGED_FILE \
-	"this file is changed in master\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is changed in branch\n"
-
 void test_merge_trees_commits__initialize(void)
 {
 	repo = cl_git_sandbox_init(TEST_REPO_PATH);
diff --git a/tests/merge/workdir/simple.c b/tests/merge/workdir/simple.c
index a9a6365..07c60c5 100644
--- a/tests/merge/workdir/simple.c
+++ b/tests/merge/workdir/simple.c
@@ -71,47 +71,6 @@ static git_index *repo_index;
 	  "", \
 	  "5c3b68a71fc4fa5d362fd3875e53137c6a5ab7a5" }
 
-#define AUTOMERGEABLE_MERGED_FILE \
-	"this file is changed in master\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is automergeable\n" \
-	"this file is changed in branch\n"
-
-#define AUTOMERGEABLE_MERGED_FILE_CRLF \
-	"this file is changed in master\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is automergeable\r\n" \
-	"this file is changed in branch\r\n"
-
-#define CONFLICTING_MERGE_FILE \
-	"<<<<<<< HEAD\n" \
-	"this file is changed in master and branch\n" \
-	"=======\n" \
-	"this file is changed in branch and master\n" \
-	">>>>>>> 7cb63eed597130ba4abb87b3e544b85021905520\n"
-
-#define CONFLICTING_DIFF3_FILE \
-	"<<<<<<< HEAD\n" \
-	"this file is changed in master and branch\n" \
-	"||||||| initial\n" \
-	"this file is a conflict\n" \
-	"=======\n" \
-	"this file is changed in branch and master\n" \
-	">>>>>>> 7cb63eed597130ba4abb87b3e544b85021905520\n"
-
-#define CONFLICTING_UNION_FILE \
-	"this file is changed in master and branch\n" \
-	"this file is changed in branch and master\n"
 
 // Fixture setup and teardown
 void test_merge_workdir_simple__initialize(void)
diff --git a/tests/structinit/structinit.c b/tests/structinit/structinit.c
index 1df970d..61fe8c7 100644
--- a/tests/structinit/structinit.c
+++ b/tests/structinit/structinit.c
@@ -65,6 +65,16 @@ void test_structinit_structinit__compare(void)
 		git_diff_find_options, GIT_DIFF_FIND_OPTIONS_VERSION, \
 		GIT_DIFF_FIND_OPTIONS_INIT, git_diff_find_init_options);
 
+	/* merge_file_input */
+	CHECK_MACRO_FUNC_INIT_EQUAL( \
+		git_merge_file_input, GIT_MERGE_FILE_INPUT_VERSION, \
+		GIT_MERGE_FILE_INPUT_INIT, git_merge_file_init_input);
+
+	/* merge_file */
+	CHECK_MACRO_FUNC_INIT_EQUAL( \
+		git_merge_file_options, GIT_MERGE_FILE_OPTIONS_VERSION, \
+		GIT_MERGE_FILE_OPTIONS_INIT, git_merge_file_init_options);
+
 	/* merge_tree */
 	CHECK_MACRO_FUNC_INIT_EQUAL( \
 		git_merge_tree_opts, GIT_MERGE_TREE_OPTS_VERSION, \