lib/package_alternatives.c: prune obsolete alternatives groups

In the edge case when an updated package has different (or no)
alternatives groups, make sure to prune those that are in pkgdb
but not in the newly installed package.

A potentially common case of this is when a package that formerly
had alternatives gets removed and a transitional metapackage
takes its place (which has no alternatives).

When the new package has no dependencies, oldest next possible
alternatives group will be used. This is because that indicates
a removed package. When there are dependencies, the newest one
will be used; as this indicates a transitional package.

tests/xbps/xbps-alternatives/main_test.sh

@@ -674,6 +674,98 @@ respect_current_provider_body() {
 	atf_check_equal $rv 0
 }
 
+atf_test_case prune_leftover_groups
+
+prune_leftover_groups_head() {
+	atf_set "descr" "xbps-alternatives: prune leftover groups on upgrades"
+}
+prune_leftover_groups_body() {
+	mkdir -p repo pkg_A/usr/bin pkg_B/usr/bin
+	touch pkg_A/usr/bin/fileA pkg_B/usr/bin/fileB
+	cd repo
+	xbps-create -A noarch -n A-1.1_1 -s "A pkg" --alternatives "file:/usr/bin/file:/usr/bin/fileA" ../pkg_A
+	atf_check_equal $? 0
+	xbps-create -A noarch -n B-1.1_1 -s "B pkg" --alternatives "file:/usr/bin/file:/usr/bin/fileB" ../pkg_B
+	atf_check_equal $? 0
+	xbps-rindex -d -a $PWD/*.xbps
+	atf_check_equal $? 0
+	cd ..
+
+	# A is the current provider now
+	xbps-install -r root --repository=repo -ydv A
+	atf_check_equal $? 0
+
+	out=$(xbps-query -r root -p pkgver A)
+	atf_check_equal $out A-1.1_1
+
+	# C will replace it via a transitional package
+	mkdir -p pkg_C/usr/bin
+	touch pkg_C/usr/bin/fileC
+	rm pkg_A/usr/bin/fileA
+	cd repo
+	xbps-create -A noarch -n C-1.2_1 -s "C pkg" --alternatives "file:/usr/bin/file:/usr/bin/fileC" ../pkg_C
+	atf_check_equal $? 0
+	xbps-create -A noarch -n A-1.2_1 -s "A pkg" --dependencies "C>=1.2_1" ../pkg_A
+	atf_check_equal $? 0
+	xbps-rindex -d -a $PWD/*.xbps
+	atf_check_equal $? 0
+	cd ..
+
+	# C is now the current provider, via upgraded A
+	# also install B, to make sure it doesn't get that first
+	xbps-install -r root --repository=repo -ydv B A
+
+	out=$(xbps-query -r root -p pkgver A)
+	atf_check_equal $out A-1.2_1
+	out=$(xbps-query -r root -p pkgver B)
+	atf_check_equal $out B-1.1_1
+	out=$(xbps-query -r root -p pkgver C)
+	atf_check_equal $out C-1.2_1
+
+	lnk=$(readlink -f root/usr/bin/file)
+	rv=1
+	if [ "$lnk" = "$PWD/root/usr/bin/fileC" ]; then
+		rv=0
+	fi
+	echo "lnk: $lnk"
+	atf_check_equal $rv 0
+
+	# Create a new provider, D; then make C a removed package
+	mkdir -p pkg_D/usr/bin
+	touch pkg_D/usr/bin/fileD
+	rm pkg_C/usr/bin/fileC
+	cd repo
+	xbps-create -A noarch -n D-1.4_1 -s "D pkg" --alternatives "file:/usr/bin/file:/usr/bin/fileD" ../pkg_D
+	atf_check_equal $? 0
+	xbps-create -A noarch -n C-1.3_1 -s "C pkg" ../pkg_C
+	atf_check_equal $? 0
+	xbps-rindex -d -a $PWD/*.xbps
+	atf_check_equal $? 0
+	cd ..
+
+	# B is now the current provider, as it's the first group available after
+	# pruning C; the system special cases packages without dependencies as
+	# removed packages, so it will not assume a renamed replacement
+	xbps-install -r root --repository=repo -ydv C D
+
+	out=$(xbps-query -r root -p pkgver A)
+	atf_check_equal $out A-1.2_1
+	out=$(xbps-query -r root -p pkgver B)
+	atf_check_equal $out B-1.1_1
+	out=$(xbps-query -r root -p pkgver C)
+	atf_check_equal $out C-1.3_1
+	out=$(xbps-query -r root -p pkgver D)
+	atf_check_equal $out D-1.4_1
+
+	lnk=$(readlink -f root/usr/bin/file)
+	rv=1
+	if [ "$lnk" = "$PWD/root/usr/bin/fileB" ]; then
+		rv=0
+	fi
+	echo "lnk: $lnk"
+	atf_check_equal $rv 0
+}
+
 atf_init_test_cases() {
 	atf_add_test_case register_one
 	atf_add_test_case register_one_dangling
@@ -692,4 +784,5 @@ atf_init_test_cases() {
 	atf_add_test_case useless_switch
 	atf_add_test_case remove_current_provider
 	atf_add_test_case respect_current_provider
+	atf_add_test_case prune_leftover_groups
 }