Fix logical operator folding that only involve literals (#833)

Author: l46kok

cel/folding.go

@@ -206,6 +206,11 @@ func maybeShortcircuitLogic(ctx *OptimizerContext, function string, args []ast.E
 			return true
 		}
 	}
+	if len(newArgs) == 0 {
+		newArgs = append(newArgs, args[0])
+		expr.SetKindCase(newArgs[0])
+		return true
+	}
 	if len(newArgs) == 1 {
 		expr.SetKindCase(newArgs[0])
 		return true

cel/folding_test.go

@@ -197,6 +197,30 @@ func TestConstantFoldingOptimizer(t *testing.T) {
 			expr:   `false || x || false || x`,
 			folded: `x || x`,
 		},
+		{
+			expr:   `true && true`,
+			folded: `true`,
+		},
+		{
+			expr:   `true && false`,
+			folded: `false`,
+		},
+		{
+			expr:   `true || false`,
+			folded: `true`,
+		},
+		{
+			expr:   `false || false`,
+			folded: `false`,
+		},
+		{
+			expr:   `true && false || true`,
+			folded: `true`,
+		},
+		{
+			expr:   `false && true || false`,
+			folded: `false`,
+		},
 		{
 			expr:   `null`,
 			folded: `null`,