merge-ort: step 2 of tree writing -- function to create tree object

Create a new function, write_tree(), which will take a list of
basenames, modes, and oids for a single directory and create a tree
object in the object-store.  We do not yet have just basenames, modes,
and oids for just a single directory (we have a mixture of entries from
all directory levels in the hierarchy) so we still die() before the
current call to write_tree(), but the next patch will rectify that.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-ort.c

@@ -19,6 +19,7 @@
 
 #include "diff.h"
 #include "diffcore.h"
+#include "object-store.h"
 #include "strmap.h"
 #include "tree.h"
 #include "xdiff-interface.h"
@@ -523,6 +524,62 @@ struct directory_versions {
 	struct string_list versions;
 };
 
+static int tree_entry_order(const void *a_, const void *b_)
+{
+	const struct string_list_item *a = a_;
+	const struct string_list_item *b = b_;
+
+	const struct merged_info *ami = a->util;
+	const struct merged_info *bmi = b->util;
+	return base_name_compare(a->string, strlen(a->string), ami->result.mode,
+				 b->string, strlen(b->string), bmi->result.mode);
+}
+
+static void write_tree(struct object_id *result_oid,
+		       struct string_list *versions,
+		       unsigned int offset,
+		       size_t hash_size)
+{
+	size_t maxlen = 0, extra;
+	unsigned int nr = versions->nr - offset;
+	struct strbuf buf = STRBUF_INIT;
+	struct string_list relevant_entries = STRING_LIST_INIT_NODUP;
+	int i;
+
+	/*
+	 * We want to sort the last (versions->nr-offset) entries in versions.
+	 * Do so by abusing the string_list API a bit: make another string_list
+	 * that contains just those entries and then sort them.
+	 *
+	 * We won't use relevant_entries again and will let it just pop off the
+	 * stack, so there won't be allocation worries or anything.
+	 */
+	relevant_entries.items = versions->items + offset;
+	relevant_entries.nr = versions->nr - offset;
+	QSORT(relevant_entries.items, relevant_entries.nr, tree_entry_order);
+
+	/* Pre-allocate some space in buf */
+	extra = hash_size + 8; /* 8: 6 for mode, 1 for space, 1 for NUL char */
+	for (i = 0; i < nr; i++) {
+		maxlen += strlen(versions->items[offset+i].string) + extra;
+	}
+	strbuf_grow(&buf, maxlen);
+
+	/* Write each entry out to buf */
+	for (i = 0; i < nr; i++) {
+		struct merged_info *mi = versions->items[offset+i].util;
+		struct version_info *ri = &mi->result;
+		strbuf_addf(&buf, "%o %s%c",
+			    ri->mode,
+			    versions->items[offset+i].string, '\0');
+		strbuf_add(&buf, ri->oid.hash, hash_size);
+	}
+
+	/* Write this object file out, and record in result_oid */
+	write_object_file(buf.buf, buf.len, tree_type, result_oid);
+	strbuf_release(&buf);
+}
+
 static void record_entry_for_tree(struct directory_versions *dir_metadata,
 				  const char *path,
 				  struct merged_info *mi)
@@ -675,9 +732,17 @@ static void process_entries(struct merge_options *opt,
 		}
 	}
 
+	/*
+	 * TODO: We can't actually write a tree yet, because dir_metadata just
+	 * contains all basenames of all files throughout the tree with their
+	 * mode and hash.  Not only is that a nonsensical tree, it will have
+	 * lots of duplicates for paths such as "Makefile" or ".gitignore".
+	 */
+	die("Not yet implemented; need to process subtrees separately");
+	write_tree(result_oid, &dir_metadata.versions, 0,
+		   opt->repo->hash_algo->rawsz);
 	string_list_clear(&plist, 0);
 	string_list_clear(&dir_metadata.versions, 0);
-	die("Tree creation not yet implemented");
 }
 
 void merge_switch_to_result(struct merge_options *opt,