Which merge_file() function do you mean?

There are two different static functions and one global function,
all of them called "merge_file()", with different signatures and
purposes.  Rename them all to reduce confusion in "git grep" output:

 * Rename the static one in merge-index to "merge_one_path(const char
   *path)" as that function is about asking an external command to
   resolve conflicts in one path.

 * Rename the global one in merge-file.c that is only used by
   merge-tree to "merge_blobs()", as the function takes three blobs and
   returns the merged result only in-core, without doing anything to
   the filesystem.

 * Rename the one in merge-recursive to "merge_one_file()", just to be
   fair.

Also rename merge-file.[ch] to merge-blobs.[ch].

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge-index.c

@@ -42,7 +42,7 @@ static int merge_entry(int pos, const char *path)
 	return found;
 }
 
-static void merge_file(const char *path)
+static void merge_one_path(const char *path)
 {
 	int pos = cache_name_pos(path, strlen(path));
 
@@ -102,7 +102,7 @@ int cmd_merge_index(int argc, const char **argv, const char *prefix)
 			}
 			die("git merge-index: unknown option %s", arg);
 		}
-		merge_file(arg);
+		merge_one_path(arg);
 	}
 	if (err && !quiet)
 		die("merge program failed");