planner: address ref head issue

When planning rules like these:

```
package authz

allow[action][resource] if { action := "list"; "resource": "fruit"}

allow.eat.veggies if true
```

and referencing them in a ref like

```
resp := allow[input.action][input.resource]
```

we ended up with a broken CallDynamic statement. Since the first ref
rule is planned as `g0.data.authz.allow` and builds an object return
value, and the second rule is planned as
`g0.data.authz.allow.eat.veggies` with a boolean return value, we cannot
dynamically dispatch their calls.

With this change, the previously exising "unbalanced ruletrie" check now
also hits before reaching the end of the ref. It'll catch this situation
and avoid optimizing the dispatch. We'll end up with a longer, less
efficient, but correct plan.

Signed-off-by: Stephan Renatus <[email protected]>

Author: srenatus

internal/planner/planner.go

@@ -2491,11 +2491,9 @@ outer:
 
 	for _, node := range nodes {
 		// we're done with ref, check if there's only ruleset leaves; collect rules
-		if index == len(ref)-1 {
-			if len(node.Rules()) == 0 && node.ChildrenCount() > 0 {
-				p.debugf("no optimization of %s: unbalanced ruletrie", ref)
-				return dont()
-			}
+		if len(node.Rules()) == 0 && node.ChildrenCount() > 0 {
+			p.debugf("no optimization of %s: unbalanced ruletrie", ref)
+			return dont()
 		}
 		if rules := node.Rules(); len(rules) > 0 {
 			res = append(res, rules)

internal/planner/planner_test.go

@@ -1088,18 +1088,11 @@ func TestOptimizeLookup(t *testing.T) {
 
 		p := planner()
 		p.vars.Put(ast.Var("x"), p.newLocal())
-		rulesets, _, _, opt := p.optimizeLookup(r, ast.MustParseRef("data[x].allow.see.something_else"))
+		_, _, _, opt := p.optimizeLookup(r, ast.MustParseRef("data[x].allow.see.something_else"))
 
-		if exp, act := true, opt; exp != act {
+		if exp, act := false, opt; exp != act {
 			t.Errorf("expected 'optimize' %v, got %v\n", exp, act)
 		}
-		if exp, act := 1, len(rulesets); exp != act {
-			t.Fatalf("expected %d rulesets, got %d\n", exp, act)
-		}
-
-		if exp, act := 2, len(rulesets[0]); exp != act {
-			t.Fatalf("expected %d rules in ruleset[0], got %d\n", exp, act)
-		}
 	})
 }