tools: add additional version checks to changelog validation

Signed-off-by: Dhwani Serai <dhwanise@amazon.com>

Author: dhwaniserai

tools/validate-changelog.sh

@@ -4,9 +4,22 @@
 # this should be sufficient to validate the CHANGELOG for our CI, provided that
 # every new tag has a corresponding CHANGELOG update, as we always parse the
 # CHANGELOG between two headers with a tagged version.
-if diff <(grep -ne '^# ' CHANGELOG.md) <(grep -ne '^# v[0-9]\+\.[0-9]\+\.[0-9]\+' CHANGELOG.md); then
-  echo "CHANGELOG validation PASSED!"
-else
+if ! diff <(grep -ne '^# ' CHANGELOG.md) <(grep -ne '^# v[0-9]\+\.[0-9]\+\.[0-9]\+' CHANGELOG.md); then
   echo "CHANGELOG validation FAILED! Headers must match the regex '^# v[0-9]\+\.[0-9]\+\.[0-9]\+.'"
   exit 1
 fi
+
+# check that all versions are unique
+versions=$(grep -o '^# v[0-9]\+\.[0-9]\+\.[0-9]\+' CHANGELOG.md)
+if [[ $(echo "${versions}" | sort | uniq -d | wc -l) -gt 0 ]]; then
+  echo "CHANGELOG validation FAILED! Duplicate versions found."
+  exit 1
+fi
+
+# check that versions are in descending order
+if ! echo "${versions}" | sort -V -r | diff - <(echo "${versions}"); then
+  echo "CHANGELOG validation FAILED! Versions must be in descending order."
+  exit 1
+else
+  echo "CHANGELOG validation PASSED!"
+fi