ci: add workflow to check downgrade versions

Tarantool has hardcoded list of versions it can downgrade to. This list
should consist of all the released versions less than Tarantool version.
This workflow helps to make sure we update the list before release.

When run on the commit with release tag it check the list and fail
if it misses some released version less than current. In this case
we are supposed to update downgrade list (with required downgrade code)
and update the release tag.

Closes tarantool#8319

NO_TEST=ci
NO_CHANGELOG=ci
NO_DOC=ci

.github/workflows/tree.yml

@@ -46,6 +46,9 @@ jobs:
       - name: Check entrypoint tag
         run: ./tools/check-entrypoint-tag.sh
 
+      - name: Check downgrade versions
+        run: ./tools/check-downgrade-versions.sh
+
       - name: Send VK Teams message on failure
         if: failure()
         uses: ./.github/actions/report-job-status

src/box/lua/upgrade.lua

@@ -2092,6 +2092,7 @@ end
 
 -- List of all Tarantool releases we can downgrade to.
 local downgrade_versions = {
+    -- DOWNGRADE VERSIONS BEGIN
     "2.8.2",
     "2.8.3",
     "2.8.4",
@@ -2105,6 +2106,7 @@ local downgrade_versions = {
     "2.11.1",
     "3.0.0",
     "3.1.0",
+    -- DOWNGRADE VERSIONS END
 }
 
 -- Downgrade or list downgrade issues depending of dry_run argument value.

tools/check-downgrade-versions.sh

@@ -0,0 +1,79 @@
+#!/bin/bash
+#
+# This script checks that we can downgrade to all the released versions
+# less then being released. For example when releasing version 2.11.4
+# we check that we can downgrade to 2.11.3, 2.11.2, ..., 2.10.8, 2.10.7, ...
+# 2.8.2.
+#
+# The versions we can downgrade to are those mentioned in downgrade_versions
+# list in src/box/lua/upgrade.lua. For the sake of parsing simplicity
+# the versions should be between begin and end marks:
+# -- DOWNGRADE VERSIONS BEGIN
+# -- DOWNGRADE VERSIONS END
+#
+# The check is only done for the commit tagged as release version
+# (annotated tag with name like 2.11.4).
+
+set -eo pipefail
+
+error() {
+   echo "$@" 1>&2
+   exit 1
+}
+
+# Tags that should not be considered.
+tag_exceptions=`mktemp`
+echo 2.9.0 > $tag_exceptions
+
+this_tag=`git describe --exact-match 2>/dev/null || true`
+tag_pattern='^[[:digit:]]+\.[[:digit:]]+\.[[:digit:]]+$'
+# Make downgrade check only for the release tags.
+if [[ $this_tag =~ $tag_pattern ]]; then
+    # File with expected versions.
+    expected_versions=`mktemp`
+    # Sorted (in version order) list of release tags.
+    tags=`git tag | grep -E $tag_pattern | sort -V`
+    skip=1
+    # Cut tags below 2.8.2 and above $this_tag
+    for tag in $tags; do
+        if [[ $tag = '2.8.2' ]]; then
+            skip=0
+        fi
+        if [[ $skip -eq 0 ]]; then
+            echo $tag >> $expected_versions
+        fi
+        if [[ $tag = $this_tag ]]; then
+            skip=1
+        fi
+    done
+
+    # File of versions we can downgrade to.
+    actual_versions=`mktemp`
+    begin_mark='DOWNGRADE VERSIONS BEGIN'
+    end_mark='DOWNGRADE VERSIONS END'
+    upgrade_file='src/box/lua/upgrade.lua'
+    grep -q "$begin_mark" $upgrade_file ||
+        error "Cannot find start mark in $upgrade_file"
+    grep -q "$end_mark" $upgrade_file ||
+        error "Cannot find end mark in $upgrade_file"
+
+    # Cut part of $upgrade_file between $begin_mark and $end_mark
+    # and for every line strip everything except version.
+    awk "/$begin_mark/{flag=1; next}
+         /$end_mark/{flag=0} flag" $upgrade_file |
+         sed -E 's/.*"(.*)".*/\1/' > $actual_versions
+
+    cat $tag_exceptions >> $actual_versions
+    # Sort is usual order before using `comm`.
+    sort -o $expected_versions $expected_versions
+    sort -o $actual_versions $actual_versions
+    diff=`comm -23 $expected_versions $actual_versions`
+    if [ -n "$diff" ]; then
+        echo "Some versions are missing in downgrade list:" 1>&2
+        echo "$diff"
+        exit 1
+    fi
+fi
+
+echo OK
+exit 0