merge-ort: have ll_merge() use a special attr_index for renormalization

ll_merge() needs an index when renormalization is requested.  Create one
specifically for just this purpose with just the one needed entry.  This
fixes t6418.4 and t6418.5 under GIT_TEST_MERGE_ALGORITHM=ort.

NOTE 1: Even if the user has a working copy or a real index (which is
not a given as merge-ort can be used in bare repositories), we
explicitly ignore any .gitattributes file from either of these
locations.  merge-ort can be used to merge two branches that are
unrelated to HEAD, so .gitattributes from the working copy and current
index should not be considered relevant.

NOTE 2: Since we are in the middle of merging, there is a risk that
.gitattributes itself is conflicted...leaving us with an ill-defined
situation about how to perform the rest of the merge.  It could be that
the .gitattributes file does not even exist on one of the sides of the
merge, or that it has been modified on both sides.  If it's been
modified on both sides, it's possible that it could itself be merged
cleanly, though it's also possible that it only merges cleanly if you
use the right version of the .gitattributes file to drive the merge.  It
gets kind of complicated.  The only test we ever had that attempted to
test behavior in this area was seemingly unaware of the undefined
behavior, but knew the test wouldn't work for lack of attribute handling
support, marked it as test_expect_failure from the beginning, but
managed to fail for several reasons unrelated to attribute handling.
See commit 6f6e7cf ("t6038: remove problematic test", 2020-08-03) for
details.  So there are probably various ways to improve what
initialize_attr_index() picks in the case of a conflicted .gitattributes
but for now I just implemented something simple -- look for whatever
.gitattributes file we can find in any of the higher order stages and
use it.

Signed-off-by: Elijah Newren <[email protected]>
Reviewed-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: newren

merge-ort.c

@@ -410,7 +410,7 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
 	string_list_clear(&opti->paths_to_free, 0);
 	opti->paths_to_free.strdup_strings = 0;
 
-	if (opti->attr_index.cache_nr)
+	if (opti->attr_index.cache_nr) /* true iff opt->renormalize */
 		discard_index(&opti->attr_index);
 
 	/* Free memory used by various renames maps */
@@ -1201,6 +1201,63 @@ static int merge_submodule(struct merge_options *opt,
 	return 0;
 }
 
+static void initialize_attr_index(struct merge_options *opt)
+{
+	/*
+	 * The renormalize_buffer() functions require attributes, and
+	 * annoyingly those can only be read from the working tree or from
+	 * an index_state.  merge-ort doesn't have an index_state, so we
+	 * generate a fake one containing only attribute information.
+	 */
+	struct merged_info *mi;
+	struct index_state *attr_index = &opt->priv->attr_index;
+	struct cache_entry *ce;
+
+	attr_index->initialized = 1;
+
+	if (!opt->renormalize)
+		return;
+
+	mi = strmap_get(&opt->priv->paths, GITATTRIBUTES_FILE);
+	if (!mi)
+		return;
+
+	if (mi->clean) {
+		int len = strlen(GITATTRIBUTES_FILE);
+		ce = make_empty_cache_entry(attr_index, len);
+		ce->ce_mode = create_ce_mode(mi->result.mode);
+		ce->ce_flags = create_ce_flags(0);
+		ce->ce_namelen = len;
+		oidcpy(&ce->oid, &mi->result.oid);
+		memcpy(ce->name, GITATTRIBUTES_FILE, len);
+		add_index_entry(attr_index, ce,
+				ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
+		get_stream_filter(attr_index, GITATTRIBUTES_FILE, &ce->oid);
+	} else {
+		int stage, len;
+		struct conflict_info *ci;
+
+		ASSIGN_AND_VERIFY_CI(ci, mi);
+		for (stage = 0; stage < 3; stage++) {
+			unsigned stage_mask = (1 << stage);
+
+			if (!(ci->filemask & stage_mask))
+				continue;
+			len = strlen(GITATTRIBUTES_FILE);
+			ce = make_empty_cache_entry(attr_index, len);
+			ce->ce_mode = create_ce_mode(ci->stages[stage].mode);
+			ce->ce_flags = create_ce_flags(stage);
+			ce->ce_namelen = len;
+			oidcpy(&ce->oid, &ci->stages[stage].oid);
+			memcpy(ce->name, GITATTRIBUTES_FILE, len);
+			add_index_entry(attr_index, ce,
+					ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
+			get_stream_filter(attr_index, GITATTRIBUTES_FILE,
+					  &ce->oid);
+		}
+	}
+}
+
 static int merge_3way(struct merge_options *opt,
 		      const char *path,
 		      const struct object_id *o,
@@ -1215,6 +1272,9 @@ static int merge_3way(struct merge_options *opt,
 	char *base, *name1, *name2;
 	int merge_status;
 
+	if (!opt->priv->attr_index.initialized)
+		initialize_attr_index(opt);
+
 	ll_opts.renormalize = opt->renormalize;
 	ll_opts.extra_marker_size = extra_marker_size;
 	ll_opts.xdl_opts = opt->xdl_opts;
@@ -1253,7 +1313,7 @@ static int merge_3way(struct merge_options *opt,
 
 	merge_status = ll_merge(result_buf, path, &orig, base,
 				&src1, name1, &src2, name2,
-				opt->repo->index, &ll_opts);
+				&opt->priv->attr_index, &ll_opts);
 
 	free(base);
 	free(name1);