test-reach: create new test tool for ref_newer

As we prepare to change the behavior of the algorithms in
commit-reach.c, create a new test-tool subcommand 'reach' to test these
methods on interesting commit-graph shapes.

To use the new test-tool, use 'test-tool reach <method>' and provide
input to stdin that describes the inputs to the method. Currently, we
only implement the ref_newer method, which requires two commits. Use
lines "A:<committish>" and "B:<committish>" for the two inputs. We will
expand this input later to accommodate methods that take lists of
commits.

The test t6600-test-reach.sh creates a repo whose commits form a
two-dimensional grid. This grid makes it easy for us to determine
reachability because commit-A-B can reach commit-X-Y if and only if A is
at least X and B is at least Y. This helps create interesting test cases
for each result of the methods in commit-reach.c.

We test all methods in three different states of the commit-graph file:
Non-existent (no generation numbers), fully computed, and mixed (some
commits have generation numbers and others do not).

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -716,6 +716,7 @@ TEST_BUILTINS_OBJS += test-mktemp.o
 TEST_BUILTINS_OBJS += test-online-cpus.o
 TEST_BUILTINS_OBJS += test-path-utils.o
 TEST_BUILTINS_OBJS += test-prio-queue.o
+TEST_BUILTINS_OBJS += test-reach.o
 TEST_BUILTINS_OBJS += test-read-cache.o
 TEST_BUILTINS_OBJS += test-ref-store.o
 TEST_BUILTINS_OBJS += test-regex.o

t/helper/test-reach.c

@@ -0,0 +1,63 @@
+#include "test-tool.h"
+#include "cache.h"
+#include "commit.h"
+#include "commit-reach.h"
+#include "config.h"
+#include "parse-options.h"
+#include "tag.h"
+
+int cmd__reach(int ac, const char **av)
+{
+	struct object_id oid_A, oid_B;
+	struct strbuf buf = STRBUF_INIT;
+	struct repository *r = the_repository;
+
+	setup_git_directory();
+
+	if (ac < 2)
+		exit(1);
+
+
+	while (strbuf_getline(&buf, stdin) != EOF) {
+		struct object_id oid;
+		struct object *o;
+		struct commit *c;
+		if (buf.len < 3)
+			continue;
+
+		if (get_oid_committish(buf.buf + 2, &oid))
+			die("failed to resolve %s", buf.buf + 2);
+
+		o = parse_object(r, &oid);
+		o = deref_tag_noverify(o);
+
+		if (!o)
+			die("failed to load commit for input %s resulting in oid %s\n",
+			    buf.buf, oid_to_hex(&oid));
+
+		c = object_as_type(r, o, OBJ_COMMIT, 0);
+
+		if (!c)
+			die("failed to load commit for input %s resulting in oid %s\n",
+			    buf.buf, oid_to_hex(&oid));
+
+		switch (buf.buf[0]) {
+			case 'A':
+				oidcpy(&oid_A, &oid);
+				break;
+
+			case 'B':
+				oidcpy(&oid_B, &oid);
+				break;
+
+			default:
+				die("unexpected start of line: %c", buf.buf[0]);
+		}
+	}
+	strbuf_release(&buf);
+
+	if (!strcmp(av[1], "ref_newer"))
+		printf("%s(A,B):%d\n", av[1], ref_newer(&oid_A, &oid_B));
+
+	exit(0);
+}

t/helper/test-tool.c

@@ -26,6 +26,7 @@ static struct test_cmd cmds[] = {
 	{ "online-cpus", cmd__online_cpus },
 	{ "path-utils", cmd__path_utils },
 	{ "prio-queue", cmd__prio_queue },
+	{ "reach", cmd__reach },
 	{ "read-cache", cmd__read_cache },
 	{ "ref-store", cmd__ref_store },
 	{ "regex", cmd__regex },

t/helper/test-tool.h

@@ -20,6 +20,7 @@ int cmd__mktemp(int argc, const char **argv);
 int cmd__online_cpus(int argc, const char **argv);
 int cmd__path_utils(int argc, const char **argv);
 int cmd__prio_queue(int argc, const char **argv);
+int cmd__reach(int argc, const char **argv);
 int cmd__read_cache(int argc, const char **argv);
 int cmd__ref_store(int argc, const char **argv);
 int cmd__regex(int argc, const char **argv);

t/t6600-test-reach.sh

@@ -0,0 +1,86 @@
+#!/bin/sh
+
+test_description='basic commit reachability tests'
+
+. ./test-lib.sh
+
+# Construct a grid-like commit graph with points (x,y)
+# with 1 <= x <= 10, 1 <= y <= 10, where (x,y) has
+# parents (x-1, y) and (x, y-1), keeping in mind that
+# we drop a parent if a coordinate is nonpositive.
+#
+#             (10,10)
+#            /       \
+#         (10,9)    (9,10)
+#        /     \   /      \
+#    (10,8)    (9,9)      (8,10)
+#   /     \    /   \      /    \
+#         ( continued...)
+#   \     /    \   /      \    /
+#    (3,1)     (2,2)      (1,3)
+#        \     /    \     /
+#         (2,1)      (2,1)
+#              \    /
+#              (1,1)
+#
+# We use branch 'commit-x-y' to refer to (x,y).
+# This grid allows interesting reachability and
+# non-reachability queries: (x,y) can reach (x',y')
+# if and only if x' <= x and y' <= y.
+test_expect_success 'setup' '
+	for i in $(test_seq 1 10)
+	do
+		test_commit "1-$i" &&
+		git branch -f commit-1-$i
+	done &&
+	for j in $(test_seq 1 9)
+	do
+		git reset --hard commit-$j-1 &&
+		x=$(($j + 1)) &&
+		test_commit "$x-1" &&
+		git branch -f commit-$x-1 &&
+
+		for i in $(test_seq 2 10)
+		do
+			git merge commit-$j-$i -m "$x-$i" &&
+			git branch -f commit-$x-$i
+		done
+	done &&
+	git commit-graph write --reachable &&
+	mv .git/objects/info/commit-graph commit-graph-full &&
+	git show-ref -s commit-5-5 | git commit-graph write --stdin-commits &&
+	mv .git/objects/info/commit-graph commit-graph-half &&
+	git config core.commitGraph true
+'
+
+test_three_modes () {
+	test_when_finished rm -rf .git/objects/info/commit-graph &&
+	test-tool reach $1 <input >actual &&
+	test_cmp expect actual &&
+	cp commit-graph-full .git/objects/info/commit-graph &&
+	test-tool reach $1 <input >actual &&
+	test_cmp expect actual &&
+	cp commit-graph-half .git/objects/info/commit-graph &&
+	test-tool reach $1 <input >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'ref_newer:miss' '
+	cat >input <<-\EOF &&
+	A:commit-5-7
+	B:commit-4-9
+	EOF
+	echo "ref_newer(A,B):0" >expect &&
+	test_three_modes ref_newer
+'
+
+test_expect_success 'ref_newer:hit' '
+	cat >input <<-\EOF &&
+	A:commit-5-7
+	B:commit-2-3
+	EOF
+	echo "ref_newer(A,B):1" >expect &&
+	test_three_modes ref_newer
+'
+
+test_done