Fix panic when using a repeated field as a predefined rule (#149)

Using a repeated field as a predefined rule value results in a panic, as
CEL cannot convert a `protoreflect.List` value into a valid CEL type.
This results in an error value standing in for the list's value in the
expression. When attempting to optimize the expression via computing
residuals, a type assertion without the guard boolean (i.e., `typed :=
unknown.(T)` instead of `typed, ok := unknown.(T)`) triggers the panic
on this non-list error value.

This patch adds a new helper to the celext package to compute an
appropriate value for any `protoreflect.Value` given its field
descriptor.

Fixes #148

buf.lock

@@ -2,11 +2,11 @@
 version: v2
 deps:
   - name: buf.build/bufbuild/protovalidate
-    commit: a6c49f84cc0f4e038680d390392e2ab0
-    digest: b5:e968392e88ff7915adcbd1635d670b45bff8836ec2415d81fc559ca5470a695dbdc30030bad8bc5764647c731079e9e7bba0023ea25c4e4a1672a7d2561d4a19
+    commit: 5a7b106cbb87462d9a8c9ffecdbd2e38
+    digest: b5:0f2dc6c9453e9cc9e9f36807aaa5f94022e837d91fef4dcaeed79a35c0843cc64eba28ff077aab24da3b2cb12639ad256246f9f9a36c033b99d5754b19996b7e
   - name: buf.build/bufbuild/protovalidate-testing
-    commit: 7c0e0340f14c4d6580c200dcaa9b00d0
-    digest: b5:f0dacc3a02e3fcd277c3516cd0089e69478374b5ad15fe1032853789668d1d660cac4c6e1776799a66b251b9583ddc320e9db91acf6e8681e31d76ccc1f22ea3
+    commit: 165ebb0f38244fc2a5b23a82cabe812f
+    digest: b5:4e3e21cabc93277d9069f7ded53c17659fefe47dd8daf9bc534387590feabe971b2d51b88b324835385650f3fa227e8a793a99ca9814cba76ee678f20ba9b4ef
   - name: buf.build/envoyproxy/protoc-gen-validate
     commit: daf171c6cdb54629b5f51e345a79e4dd
     digest: b5:c745e1521879f43740230b1df673d0729f55704efefdcfc489d4a0a2d40c92a26cacfeab62813403040a8b180142d53b398c7ca784a065e43823605ee49681de

celext/lookups.go

@@ -16,6 +16,8 @@ package celext
 
 import (
 	"github.com/google/cel-go/cel"
+	"github.com/google/cel-go/common/types"
+	"github.com/google/cel-go/common/types/ref"
 	"google.golang.org/protobuf/reflect/protoreflect"
 )
 
@@ -58,6 +60,15 @@ func ProtoFieldToCELType(fieldDesc protoreflect.FieldDescriptor, generic, forIte
 	return protoKindToCELType(fieldDesc.Kind())
 }
 
+func ProtoFieldToCELValue(fieldDesc protoreflect.FieldDescriptor, value protoreflect.Value, forItems bool) ref.Val {
+	switch {
+	case fieldDesc.IsList() && !forItems:
+		return types.NewProtoList(types.DefaultTypeAdapter, value.List())
+	default:
+		return types.DefaultTypeAdapter.NativeToValue(value.Interface())
+	}
+}
+
 // protoKindToCELType maps a protoreflect.Kind to a compatible cel.Type.
 func protoKindToCELType(kind protoreflect.Kind) *cel.Type {
 	switch kind {

internal/constraints/cache.go

@@ -21,7 +21,6 @@ import (
 	"github.com/bufbuild/protovalidate-go/internal/expression"
 	"github.com/bufbuild/protovalidate-go/internal/extensions"
 	"github.com/google/cel-go/cel"
-	"github.com/google/cel-go/common/types"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/reflect/protoregistry"
@@ -77,7 +76,7 @@ func (c *Cache) Build(
 			cel.Constant(
 				"rule",
 				celext.ProtoFieldToCELType(desc, true, forItems),
-				types.DefaultTypeAdapter.NativeToValue(rule.Interface()),
+				celext.ProtoFieldToCELValue(desc, rule, forItems),
 			),
 		)
 		if compileErr != nil {

proto/tests/example/v1/predefined.proto

@@ -0,0 +1,35 @@
+// Copyright 2023-2024 Buf Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto2";
+
+package tests.example.v1;
+
+import "buf/validate/validate.proto";
+
+// https://github.com/bufbuild/protovalidate-go/issues/148
+message Issue148 {
+  optional int32 test = 1 [
+    (buf.validate.field).int32.(abs_not_in) = 1,
+    (buf.validate.field).int32.(abs_not_in) = -2
+  ];
+}
+
+extend buf.validate.Int32Rules {
+  repeated int32 abs_not_in = 1800 [(buf.validate.predefined).cel = {
+    id: "int32.abs_not_in"
+    expression: "this in rule || this in rule.map(n, -n)"
+    message: "value must not be in absolute value of list"
+  }];
+}

validator_test.go

@@ -20,6 +20,7 @@ import (
 	pb "github.com/bufbuild/protovalidate-go/internal/gen/tests/example/v1"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/anypb"
 	"google.golang.org/protobuf/types/known/apipb"
 	"google.golang.org/protobuf/types/known/fieldmaskpb"
@@ -240,3 +241,12 @@ func TestValidator_Validate_Issue141(t *testing.T) {
 		require.ErrorAs(t, err, &valErr)
 	})
 }
+
+func TestValidator_Validate_Issue148(t *testing.T) {
+	t.Parallel()
+	val, err := New()
+	require.NoError(t, err)
+	msg := &pb.Issue148{Test: proto.Int32(1)}
+	err = val.Validate(msg)
+	require.NoError(t, err)
+}