diff --follow: do call diffcore_std() as necessary

Usually, diff frontends populate the output queue with filepairs without
any rename information and call diffcore_std() to sort the renames out.
When --follow is in effect, however, diff-tree family of frontend has a
hack that looks like this:

    diff-tree frontend
    -> diff_tree_sha1()
       . populate diff_queued_diff
       . if --follow is in effect and there is only one change that
         creates the target path, then
       -> try_to_follow_renames()
	  -> diff_tree_sha1() with no pathspec but with -C
	  -> diffcore_std() to find renames
	  . if rename is found, tweak diff_queued_diff and put a
	    single filepair that records the found rename there
    -> diffcore_std()
       . tweak elements on diff_queued_diff by
       - rename detection
       - path ordering
       - pickaxe filtering

We need to skip parts of the second call to diffcore_std() that is related
to rename detection, and do so only when try_to_follow_renames() did find
a rename.  Earlier 1da6175 (Make diffcore_std only can run once before a
diff_flush, 2010-05-06) tried to deal with this issue incorrectly; it
unconditionally disabled any second call to diffcore_std().

This hopefully fixes the breakage.

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

1 files changed, 11 insertions, 0 deletions

diff --git a/tree-diff.c b/tree-diff.c
index 5b68c0864c..cd659c6fe4 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -359,6 +359,7 @@ static void try_to_follow_renames(struct tree_desc *t1, struct tree_desc *t2, co
 	diff_tree_release_paths(&diff_opts);
 
 	/* Go through the new set of filepairing, and see if we find a more interesting one */
+	opt->found_follow = 0;
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];
 
@@ -376,6 +377,16 @@ static void try_to_follow_renames(struct tree_desc *t1, struct tree_desc *t2, co
 			diff_tree_release_paths(opt);
 			opt->paths[0] = xstrdup(p->one->path);
 			diff_tree_setup_paths(opt->paths, opt);
+
+			/*
+			 * The caller expects us to return a set of vanilla
+			 * filepairs to let a later call to diffcore_std()
+			 * it makes to sort the renames out (among other
+			 * things), but we already have found renames
+			 * ourselves; signal diffcore_std() not to muck with
+			 * rename information.
+			 */
+			opt->found_follow = 1;
 			break;
 		}
 	}