Register string extension functions to match pv-go (#439)

Currently, protovalidate-java doesn't register the same string extension
functions at protovalidate-go, making custom CEL rules not supported
across platforms.

Register the CEL string extension functions available in cel-java. These
are identical to the ones available in protovalidate-go except it is
missing a `quote` and `reverse` function. We could implement custom
versions but it would be better to get this addressed upstream for
consistency across CEL runtimes.

Fixes #438.

Author: pkwarren

src/main/java/build/buf/protovalidate/ValidatorImpl.java

@@ -21,6 +21,7 @@
 import dev.cel.bundle.Cel;
 import dev.cel.bundle.CelFactory;
 import dev.cel.common.CelOptions;
+import dev.cel.extensions.CelExtensions;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -35,29 +36,13 @@ final class ValidatorImpl implements Validator {
   private final boolean failFast;
 
   ValidatorImpl(Config config) {
-    ValidateLibrary validateLibrary = new ValidateLibrary();
-    Cel cel =
-        CelFactory.standardCelBuilder()
-            .addCompilerLibraries(validateLibrary)
-            .addRuntimeLibraries(validateLibrary)
-            .setOptions(
-                CelOptions.DEFAULT.toBuilder().evaluateCanonicalTypesToNativeValues(true).build())
-            .build();
-    this.evaluatorBuilder = new EvaluatorBuilder(cel, config);
+    this.evaluatorBuilder = new EvaluatorBuilder(newCel(), config);
     this.failFast = config.isFailFast();
   }
 
   ValidatorImpl(Config config, List<Descriptor> descriptors, boolean disableLazy)
       throws CompilationException {
-    ValidateLibrary validateLibrary = new ValidateLibrary();
-    Cel cel =
-        CelFactory.standardCelBuilder()
-            .addCompilerLibraries(validateLibrary)
-            .addRuntimeLibraries(validateLibrary)
-            .setOptions(
-                CelOptions.DEFAULT.toBuilder().evaluateCanonicalTypesToNativeValues(true).build())
-            .build();
-    this.evaluatorBuilder = new EvaluatorBuilder(cel, config, descriptors, disableLazy);
+    this.evaluatorBuilder = new EvaluatorBuilder(newCel(), config, descriptors, disableLazy);
     this.failFast = config.isFailFast();
   }
 
@@ -78,4 +63,16 @@ public ValidationResult validate(Message msg) throws ValidationException {
     }
     return new ValidationResult(violations);
   }
+
+  private static Cel newCel() {
+    ValidateLibrary validateLibrary = new ValidateLibrary();
+    // NOTE: CelExtensions.strings() does not implement string.reverse() or strings.quote() which
+    // are available in protovalidate-go.
+    return CelFactory.standardCelBuilder()
+        .addCompilerLibraries(validateLibrary, CelExtensions.strings())
+        .addRuntimeLibraries(validateLibrary, CelExtensions.strings())
+        .setOptions(
+            CelOptions.DEFAULT.toBuilder().evaluateCanonicalTypesToNativeValues(true).build())
+        .build();
+  }
 }

src/test/java/build/buf/protovalidate/ValidatorStringExtensionsTest.java

@@ -0,0 +1,46 @@
+// Copyright 2023-2025 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.
+
+package build.buf.protovalidate;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import build.buf.protovalidate.exceptions.ValidationException;
+import build.buf.validate.Violation;
+import com.example.noimports.validationtest.ExampleStringExtensions;
+import org.junit.jupiter.api.Test;
+
+public class ValidatorStringExtensionsTest {
+  @Test
+  public void testStringExtensionsPathMatchesParent() throws ValidationException {
+    // Test for https://github.com/bufbuild/protovalidate-java/issues/438.
+    Validator validator = ValidatorFactory.newBuilder().build();
+
+    ExampleStringExtensions validMsg =
+        ExampleStringExtensions.newBuilder().setParent("foo/bar").setPath("foo/bar/baz").build();
+    ValidationResult result = validator.validate(validMsg);
+    assertThat(result.isSuccess()).isTrue();
+
+    ExampleStringExtensions invalidMsg =
+        ExampleStringExtensions.newBuilder().setParent("foo/bar").setPath("foo/other/baz").build();
+    result = validator.validate(invalidMsg);
+    assertThat(result.isSuccess()).isFalse();
+    Violation expectedViolation =
+        Violation.newBuilder()
+            .setRuleId("path_matches_parent")
+            .setMessage("path must be a child of parent")
+            .build();
+    assertThat(result.toProto().getViolationsList()).containsExactly(expectedViolation);
+  }
+}

src/test/resources/proto/validationtest/validationtest.proto

@@ -109,6 +109,19 @@ message ExampleImportMessageInMap {
   map<int64, ExampleImportedMessage> imported_submessage = 1;
 }
 
+message ExampleStringExtensions {
+  string parent = 1;
+  string path = 2;
+
+  option (buf.validate.message).cel = {
+    id: "path_matches_parent"
+    message: "path must be a child of parent"
+    expression:
+      "this.path.lastIndexOf('/') >= 0 && "
+      "this.path.substring(0, this.path.lastIndexOf('/')) == this.parent"
+  };
+}
+
 message ExampleImportMessageInMapFieldRule {
   ExampleImportMessageInMap message_with_import = 1 [
     (buf.validate.field).cel = {