config API users: test for *_get_value_multi() segfaults

As we'll discuss in the subsequent commit these tests all
show *_get_value_multi() API users unable to handle there being a
value-less key in the config, which is represented with a "NULL" for
that entry in the "string" member of the returned "struct
string_list", causing a segfault.

These added tests exhaustively test for that issue, as we'll see in a
subsequent commit we'll need to change all of the API users
of *_get_value_multi(). These cases were discovered by triggering each
one individually, and then adding these tests.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4202-log.sh

@@ -835,6 +835,17 @@ test_expect_success 'log.decorate configuration' '
 
 '
 
+test_expect_failure 'parse log.excludeDecoration with no value' '
+	cp .git/config .git/config.orig &&
+	test_when_finished mv .git/config.orig .git/config &&
+
+	cat >>.git/config <<-\EOF &&
+	[log]
+		excludeDecoration
+	EOF
+	git log --decorate=short
+'
+
 test_expect_success 'decorate-refs with glob' '
 	cat >expect.decorate <<-\EOF &&
 	Merge-tag-reach

t/t5310-pack-bitmaps.sh

@@ -404,6 +404,22 @@ test_bitmap_cases () {
 		)
 	'
 
+	test_expect_failure 'pack.preferBitmapTips' '
+		git init repo &&
+		test_when_finished "rm -rf repo" &&
+		(
+			cd repo &&
+			git config pack.writeBitmapLookupTable '"$writeLookupTable"' &&
+			test_commit_bulk --message="%s" 103 &&
+
+			cat >>.git/config <<-\EOF &&
+			[pack]
+				preferBitmapTips
+			EOF
+			git repack -adb
+		)
+	'
+
 	test_expect_success 'complains about multiple pack bitmaps' '
 		rm -fr repo &&
 		git init repo &&

t/t7004-tag.sh

@@ -1843,6 +1843,18 @@ test_expect_success 'invalid sort parameter in configuratoin' '
 	test_must_fail git tag -l "foo*"
 '
 
+test_expect_failure 'version sort handles empty value for versionsort.{prereleaseSuffix,suffix}' '
+	cp .git/config .git/config.orig &&
+	test_when_finished mv .git/config.orig .git/config &&
+
+	cat >>.git/config <<-\EOF &&
+	[versionsort]
+		prereleaseSuffix
+		suffix
+	EOF
+	git tag -l --sort=version:refname
+'
+
 test_expect_success 'version sort with prerelease reordering' '
 	test_config versionsort.prereleaseSuffix -rc &&
 	git tag foo1.6-rc1 &&

t/t7413-submodule-is-active.sh

@@ -51,6 +51,18 @@ test_expect_success 'is-active works with submodule.<name>.active config' '
 	test-tool -C super submodule is-active sub1
 '
 
+test_expect_failure 'is-active handles submodule.active config missing a value' '
+	cp super/.git/config super/.git/config.orig &&
+	test_when_finished mv super/.git/config.orig super/.git/config &&
+
+	cat >>super/.git/config <<-\EOF &&
+	[submodule]
+		active
+	EOF
+
+	test-tool -C super submodule is-active sub1
+'
+
 test_expect_success 'is-active works with basic submodule.active config' '
 	test_when_finished "git -C super config submodule.sub1.URL ../sub" &&
 	test_when_finished "git -C super config --unset-all submodule.active" &&

t/t7900-maintenance.sh

@@ -524,6 +524,29 @@ test_expect_success 'register and unregister' '
 	git maintenance unregister --config-file ./other --force
 '
 
+test_expect_failure 'register with no value for maintenance.repo' '
+	cp .git/config .git/config.orig &&
+	test_when_finished mv .git/config.orig .git/config &&
+
+	cat >>.git/config <<-\EOF &&
+	[maintenance]
+		repo
+	EOF
+	git maintenance register
+'
+
+test_expect_failure 'unregister with no value for maintenance.repo' '
+	cp .git/config .git/config.orig &&
+	test_when_finished mv .git/config.orig .git/config &&
+
+	cat >>.git/config <<-\EOF &&
+	[maintenance]
+		repo
+	EOF
+	git maintenance unregister &&
+	git maintenance unregister --force
+'
+
 test_expect_success !MINGW 'register and unregister with regex metacharacters' '
 	META="a+b*c" &&
 	git init "$META" &&