update-index: use unmerge_index_entry() to support removal

"update-index --unresolve" uses the unmerge_index_entry_at() that
assumes that the path to be unresolved must be in the index, which
makes it impossible to unresolve a path that was resolved as removal.

Rewrite unresolve_one() to use the unmerge_index_entry() to support
unresolving such a path.

Existing tests for "update-index --unresolve" forgot to check one
thing that tests for "checkout --merge -- paths" tested, which is to
make sure that resolve-undo record that has already been used to
recreate higher-stage index entries is removed.  Add new invocations
of "ls-files --resolve-undo" after running "update-index --unresolve"
to make sure that unresolving with update-index does remove the used
resolve-undo records.

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

builtin/update-index.c

@@ -660,25 +660,30 @@ static int unresolve_one(const char *path)
 	int pos;
 	int ret = 0;
 	struct cache_entry *ce_2 = NULL, *ce_3 = NULL;
+	struct resolve_undo_info *ru = NULL;
+
+	if (the_index.resolve_undo) {
+		struct string_list_item *item;
+		item = string_list_lookup(the_index.resolve_undo, path);
+		if (item) {
+			ru = item->util;
+			item->util = NULL;
+		}
+	}
+
+	/* resolve-undo record exists for the path */
+	if (ru) {
+		ret = unmerge_index_entry(&the_index, path, ru);
+		free(ru);
+		return ret;
+	}
 
 	/* See if there is such entry in the index. */
 	pos = index_name_pos(&the_index, path, namelen);
 	if (0 <= pos) {
-		/* already merged */
+		; /* resolve-undo record was used already -- fall back */
-		pos = unmerge_index_entry_at(&the_index, pos);
-		if (pos < the_index.cache_nr) {
-			const struct cache_entry *ce = the_index.cache[pos];
-			if (ce_stage(ce) &&
-			    ce_namelen(ce) == namelen &&
-			    !memcmp(ce->name, path, namelen))
-				return 0;
-		}
-		/* no resolve-undo information; fall back */
 	} else {
-		/* If there isn't, either it is unmerged, or
+		/* Is it unmerged? */
-		 * resolved as "removed" by mistake.  We do not
-		 * want to do anything in the former case.
-		 */
 		pos = -pos - 1;
 		if (pos < the_index.cache_nr) {
 			const struct cache_entry *ce = the_index.cache[pos];
@@ -687,9 +692,10 @@ static int unresolve_one(const char *path)
 				fprintf(stderr,
 					"%s: skipping still unmerged path.\n",
 					path);
+			}
 			goto free_return;
 		}
-		}
+		/* No, such a path does not exist -- removed */
 	}
 
 	/*

t/t2030-unresolve-info.sh

@@ -37,11 +37,17 @@ prime_resolve_undo () {
 	git checkout second^0 &&
 	test_tick &&
 	test_must_fail git merge third^0 &&
-	echo merge does not leave anything &&
 	check_resolve_undo empty &&
-	echo different >fi/le &&
+
-	git add fi/le &&
+	# how should the conflict be resolved?
-	echo resolving records &&
+	case "$1" in
+	remove)
+		rm -f file/le && git rm fi/le
+		;;
+	*) # modify
+		echo different >fi/le && git add fi/le
+		;;
+	esac
 	check_resolve_undo recorded fi/le initial:fi/le second:fi/le third:fi/le
 }
 
@@ -122,6 +128,8 @@ test_expect_success 'add records checkout -m undoes' '
 test_expect_success 'unmerge with plumbing' '
 	prime_resolve_undo &&
 	git update-index --unresolve fi/le &&
+	git ls-files --resolve-undo fi/le >actual &&
+	test_must_be_empty actual &&
 	git ls-files -u >actual &&
 	test_line_count = 3 actual
 '
@@ -130,6 +138,27 @@ test_expect_success 'unmerge can be done even after committing' '
 	prime_resolve_undo &&
 	git commit -m "record to nuke MERGE_HEAD" &&
 	git update-index --unresolve fi/le &&
+	git ls-files --resolve-undo fi/le >actual &&
+	test_must_be_empty actual &&
+	git ls-files -u >actual &&
+	test_line_count = 3 actual
+'
+
+test_expect_success 'unmerge removal' '
+	prime_resolve_undo remove &&
+	git update-index --unresolve fi/le &&
+	git ls-files --resolve-undo fi/le >actual &&
+	test_must_be_empty actual &&
+	git ls-files -u >actual &&
+	test_line_count = 3 actual
+'
+
+test_expect_success 'unmerge removal after committing' '
+	prime_resolve_undo remove &&
+	git commit -m "record to nuke MERGE_HEAD" &&
+	git update-index --unresolve fi/le &&
+	git ls-files --resolve-undo fi/le >actual &&
+	test_must_be_empty actual &&
 	git ls-files -u >actual &&
 	test_line_count = 3 actual
 '