Comment on alternatives removal in preun and RPM scriptlet idiom

- Comment on alternatives removal in preun and RPM scriptlet idiom
- Related: RHEL-68848

java-21-openjdk.spec

@@ -533,6 +533,18 @@ fi
 exit 0
 }
 
+# Perform alternatives removals in preun instead of postun so that we
+# are removing live symbolic links instead of dangling symbolic links,
+# even though the alternatives command does not seem to care.  The
+# documentation uses preun or postun without providing a rationale for
+# using one over the other:
+# https://docs.fedoraproject.org/en-US/packaging-guidelines/Alternatives/
+#
+# The [ $1 -eq 0 ] is an RPM scriptlet idiom meaning "only do the
+# following if this scriptlet is being run during a straight package
+# removal; in other words, do NOT do the following if this scriptlet
+# is being run as part of an upgrade transaction".
+# https://docs.fedoraproject.org/en-US/packaging-guidelines/Scriptlets/#_syntax
 %define preun_headless() %{expand:
 if [ "x$debug"  == "xtrue" ] ; then
   set -x
@@ -2389,6 +2401,7 @@ end
 - Use compatiblename not name in uniquejavadocdir and uniquesuffix
 - Do not overwrite slowdebug __provides_exclude_from and __requires_exclude_from regexps
 - Use RPM global macro for man page file extension and unwrap --slave lines
+- Comment on alternatives removal in preun and RPM scriptlet idiom
 - Resolves: RHEL-71920
 - Resolves: RHEL-71954
 - Resolves: RHEL-69321