rules: suppress a dep-rule in special case

Release justification: fixed a release blocker bug.

Previously, in a mixed version state (v22.1 and v22.2), if a old node
drops a rowLevelTTL table and the new shcema changer job was adopted
by a new node, then there is a dep rule that cannot satisfied and hence
causes forward incompatibility. This PR fixes this by suppressing this
dep rule if this particular case happens (namely, it suppress the rule
if `from` is Table element, `to` is a RowLevelTTL element, and there is
no `PUBLIC` status of the table element anywhere in the graph).

Fixes: cockroachdb#86672

Release note: None

pkg/sql/schemachanger/rel/schema_rules.go

@@ -95,6 +95,11 @@ func (sc *Schema) Def3(name string, a, b, c Var, def func(a, b, c Var) Clauses)
 	return sc.rule(name, regular, def, a, b, c).(Rule3)
 }
 
+// DefNotJoin3 defines a not-join rule with three bound variable arguments.
+func (sc *Schema) DefNotJoin3(name string, a, b, c Var, def func(a, b, c Var) Clauses) Rule3 {
+	return sc.rule(name, notJoin, def, a, b, c).(Rule3)
+}
+
 // Def4 defines a Rule4.
 func (sc *Schema) Def4(name string, a, b, c, d Var, def func(a, b, c, d Var) Clauses) Rule4 {
 	return sc.rule(name, regular, def, a, b, c, d).(Rule4)

pkg/sql/schemachanger/scplan/internal/rules/dep_drop_object.go

@@ -67,6 +67,26 @@ func init() {
 				to.typeFilter(isSimpleDependent),
 				joinOnDescID(from, to, "desc-id"),
 				statusesToAbsent(from, scpb.Status_DROPPED, to, scpb.Status_ABSENT),
+				// The following clause is added to suppress this rule for the special
+				// case where we drop a rowLevelTTL table in mixed version state for
+				// forward compatibility (issue #86672).
+				screl.Schema.DefNotJoin3("suppress rule if dropping rowLevelTTL tables in mixed version state",
+					"fromTarget", "fromEl", "toEl", func(fromTarget, fromEl, toEl rel.Var) rel.Clauses {
+						n := rel.Var("n")
+						return rel.Clauses{
+							fromEl.Type((*scpb.Table)(nil)),
+							toEl.Type((*scpb.RowLevelTTL)(nil)),
+							n.Type((*screl.Node)(nil)),
+							n.AttrEqVar(screl.Target, fromTarget),
+							screl.Schema.DefNotJoin1("node does not have a PUBLIC status", "n", func(n rel.Var) rel.Clauses {
+								public := rel.Var("public")
+								return rel.Clauses{
+									public.Eq(scpb.Status_PUBLIC),
+									n.AttrEqVar(screl.CurrentStatus, public),
+								}
+							})(n),
+						}
+					})(from.target, from.el, to.el),
 			}
 		})