git-merge-tree: generalize the "traverse <n> trees in sync" functionality

It's actually very useful for other things too. Notably, we could do the
combined diff a lot more efficiently with this.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/merge-tree.c b/merge-tree.c
index 6381118..768d83a 100644 (file)
--- a/merge-tree.c
+++ b/merge-tree.c
@@ -125,44 +125,19 @@ static void unresolved(const char *base, struct name_entry n[3])
                printf("3 %06o %s %s%s\n", n[2].mode, sha1_to_hex(n[2].sha1), base, n[2].path);
 }
 
-/*
- * Merge two trees together (t[1] and t[2]), using a common base (t[0])
- * as the origin.
- *
- * This walks the (sorted) trees in lock-step, checking every possible
- * name. Note that directories automatically sort differently from other
- * files (see "base_name_compare"), so you'll never see file/directory
- * conflicts, because they won't ever compare the same.
- *
- * IOW, if a directory changes to a filename, it will automatically be
- * seen as the directory going away, and the filename being created.
- *
- * Think of this as a three-way diff.
- *
- * The output will be either:
- *  - successful merge
- *      "0 mode sha1 filename"
- *    NOTE NOTE NOTE! FIXME! We really really need to walk the index
- *    in parallel with this too!
- * 
- *  - conflict:
- *     "1 mode sha1 filename"
- *     "2 mode sha1 filename"
- *     "3 mode sha1 filename"
- *    where not all of the 1/2/3 lines may exist, of course.
- *
- * The successful merge rules are the same as for the three-way merge
- * in git-read-tree.
- */
-static void merge_trees(struct tree_desc t[3], const char *base)
+typedef void (*traverse_callback_t)(int n, unsigned long mask, struct name_entry *entry, const char *base);
+
+static void traverse_trees(int n, struct tree_desc *t, const char *base, traverse_callback_t callback)
 {
+       struct name_entry *entry = xmalloc(n*sizeof(*entry));
+
        for (;;) {
                struct name_entry entry[3];
-               unsigned int mask = 0;
+               unsigned long mask = 0;
                int i, last;
 
                last = -1;
-               for (i = 0; i < 3; i++) {
+               for (i = 0; i < n; i++) {
                        if (!t[i].size)
                                continue;
                        entry_extract(t+i, entry+i);
@@ -182,7 +157,7 @@ static void merge_trees(struct tree_desc t[3], const char *base)
                                if (cmp < 0)
                                        mask = 0;
                        }
-                       mask |= 1u << i;
+                       mask |= 1ul << i;
                        last = i;
                }
                if (!mask)
@@ -192,38 +167,77 @@ static void merge_trees(struct tree_desc t[3], const char *base)
                 * Update the tree entries we've walked, and clear
                 * all the unused name-entries.
                 */
-               for (i = 0; i < 3; i++) {
-                       if (mask & (1u << i)) {
+               for (i = 0; i < n; i++) {
+                       if (mask & (1ul << i)) {
                                update_tree_entry(t+i);
                                continue;
                        }
                        entry_clear(entry + i);
                }
+               callback(n, mask, entry, base);
+       }
+       free(entry);
+}
 
-               /* Same in both? */
-               if (same_entry(entry+1, entry+2)) {
-                       if (entry[0].sha1) {
-                               resolve(base, NULL, entry+1);
-                               continue;
-                       }
+/*
+ * Merge two trees together (t[1] and t[2]), using a common base (t[0])
+ * as the origin.
+ *
+ * This walks the (sorted) trees in lock-step, checking every possible
+ * name. Note that directories automatically sort differently from other
+ * files (see "base_name_compare"), so you'll never see file/directory
+ * conflicts, because they won't ever compare the same.
+ *
+ * IOW, if a directory changes to a filename, it will automatically be
+ * seen as the directory going away, and the filename being created.
+ *
+ * Think of this as a three-way diff.
+ *
+ * The output will be either:
+ *  - successful merge
+ *      "0 mode sha1 filename"
+ *    NOTE NOTE NOTE! FIXME! We really really need to walk the index
+ *    in parallel with this too!
+ *
+ *  - conflict:
+ *     "1 mode sha1 filename"
+ *     "2 mode sha1 filename"
+ *     "3 mode sha1 filename"
+ *    where not all of the 1/2/3 lines may exist, of course.
+ *
+ * The successful merge rules are the same as for the three-way merge
+ * in git-read-tree.
+ */
+static void threeway_callback(int n, unsigned long mask, struct name_entry *entry, const char *base)
+{
+       /* Same in both? */
+       if (same_entry(entry+1, entry+2)) {
+               if (entry[0].sha1) {
+                       resolve(base, NULL, entry+1);
+                       return;
                }
+       }
 
-               if (same_entry(entry+0, entry+1)) {
-                       if (entry[2].sha1 && !S_ISDIR(entry[2].mode)) {
-                               resolve(base, entry+1, entry+2);
-                               continue;
-                       }
+       if (same_entry(entry+0, entry+1)) {
+               if (entry[2].sha1 && !S_ISDIR(entry[2].mode)) {
+                       resolve(base, entry+1, entry+2);
+                       return;
                }
+       }
 
-               if (same_entry(entry+0, entry+2)) {
-                       if (entry[1].sha1 && !S_ISDIR(entry[1].mode)) {
-                               resolve(base, NULL, entry+1);
-                               continue;
-                       }
+       if (same_entry(entry+0, entry+2)) {
+               if (entry[1].sha1 && !S_ISDIR(entry[1].mode)) {
+                       resolve(base, NULL, entry+1);
+                       return;
                }
-
-               unresolved(base, entry);
        }
+
+       unresolved(base, entry);
+}
+
+static void merge_trees(struct tree_desc t[3], const char *base)
+{
+       traverse_trees(3, t, base, threeway_callback);
 }
 
 static void *get_tree_descriptor(struct tree_desc *desc, const char *rev)