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Add comprehension nesting validator.
PiperOrigin-RevId: 814924866
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‎validator/src/main/java/dev/cel/validator/validators/BUILD.bazel‎

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@@ -84,6 +84,23 @@ java_library(
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],
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)
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java_library(
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name = "comprehension_nesting_limit_validator",
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srcs = [
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"ComprehensionNestingLimitValidator.java",
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],
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tags = [
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],
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deps = [
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"//bundle:cel",
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"//common/ast",
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"//common/navigation",
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"//common/navigation:common",
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"//validator:ast_validator",
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"@maven//:com_google_guava_guava",
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],
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)
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java_library(
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name = "literal_validator",
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srcs = [

‎validator/src/main/java/dev/cel/validator/validators/ComprehensionNestingLimitValidator.java‎

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// Copyright 2025 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package dev.cel.validator.validators;
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import static com.google.common.base.Preconditions.checkArgument;
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import dev.cel.bundle.Cel;
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import dev.cel.common.ast.CelExpr.ExprKind;
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import dev.cel.common.navigation.CelNavigableAst;
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import dev.cel.common.navigation.CelNavigableExpr;
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import dev.cel.common.navigation.TraversalOrder;
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import dev.cel.validator.CelAstValidator;
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/**
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* Checks that the nesting depth of comprehensions does not exceed the configured limit. Nesting
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* occurs when a comprehension is used in the range expression or the body of a comprehension.
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*
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* <p>Trivial comprehensions (comprehensions over an empty range) do not count towards the limit.
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*/
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public final class ComprehensionNestingLimitValidator implements CelAstValidator {
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private final int nestingLimit;
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/**
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* Constructs a new instance of {@link ComprehensionNestingLimitValidator} with the configured
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* maxNesting as its limit. A limit of 0 means no comprehensions are allowed.
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*/
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public static ComprehensionNestingLimitValidator newInstance(int maxNesting) {
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checkArgument(maxNesting >= 0);
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return new ComprehensionNestingLimitValidator(maxNesting);
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}
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@Override
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public void validate(CelNavigableAst navigableAst, Cel cel, IssuesFactory issuesFactory) {
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navigableAst
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.getRoot()
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.allNodes(TraversalOrder.PRE_ORDER)
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.filter(node -> node.getKind() == ExprKind.Kind.COMPREHENSION)
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.filter(node -> nestingLevel(node) > nestingLimit)
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.forEach(
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node ->
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issuesFactory.addError(
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node.id(),
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String.format(
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"comprehension nesting exceeds the configured limit: %s.", nestingLimit)));
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}
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private static boolean isTrivialComprehension(CelNavigableExpr node) {
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return (node.expr().comprehension().iterRange().getKind() == ExprKind.Kind.LIST
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&& node.expr().comprehension().iterRange().list().elements().isEmpty())
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|| (node.expr().comprehension().iterRange().getKind() == ExprKind.Kind.MAP
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&& node.expr().comprehension().iterRange().map().entries().isEmpty());
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}
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private static int nestingLevel(CelNavigableExpr node) {
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if (isTrivialComprehension(node)) {
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return 0;
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}
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int count = 1;
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while (node.parent().isPresent()) {
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CelNavigableExpr parent = node.parent().get();
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if (parent.getKind() == ExprKind.Kind.COMPREHENSION && !isTrivialComprehension(parent)) {
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count += 1;
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}
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node = parent;
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}
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return count;
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}
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private ComprehensionNestingLimitValidator(int maxNesting) {
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this.nestingLimit = maxNesting;
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}
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}

‎validator/src/test/java/dev/cel/validator/validators/BUILD.bazel‎

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@@ -16,12 +16,15 @@ java_library(
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"//common:proto_ast",
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"//common/internal:proto_time_utils",
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"//common/types",
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"//extensions",
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"//extensions:optional_library",
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"//parser:macro",
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"//runtime",
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"//runtime:function_binding",
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"//validator",
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"//validator:validator_builder",
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"//validator/validators:ast_depth_limit_validator",
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"//validator/validators:comprehension_nesting_limit_validator",
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"//validator/validators:duration",
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"//validator/validators:homogeneous_literal",
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"//validator/validators:regex",

‎validator/src/test/java/dev/cel/validator/validators/ComprehensionNestingLimitValidatorTest.java‎

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// Copyright 2025 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package dev.cel.validator.validators;
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import static com.google.common.truth.Truth.assertThat;
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import static org.junit.Assert.assertThrows;
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import com.google.testing.junit.testparameterinjector.TestParameter;
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import com.google.testing.junit.testparameterinjector.TestParameterInjector;
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import dev.cel.bundle.Cel;
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import dev.cel.bundle.CelFactory;
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import dev.cel.common.CelAbstractSyntaxTree;
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import dev.cel.common.CelIssue.Severity;
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import dev.cel.common.CelValidationException;
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import dev.cel.common.CelValidationResult;
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import dev.cel.common.types.SimpleType;
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import dev.cel.extensions.CelExtensions;
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import dev.cel.parser.CelStandardMacro;
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import dev.cel.validator.CelValidator;
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import dev.cel.validator.CelValidatorFactory;
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import org.junit.Test;
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import org.junit.runner.RunWith;
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@RunWith(TestParameterInjector.class)
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public class ComprehensionNestingLimitValidatorTest {
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private static final Cel CEL =
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CelFactory.standardCelBuilder()
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.addCompilerLibraries(
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CelExtensions.optional(), CelExtensions.comprehensions(), CelExtensions.bindings())
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.addRuntimeLibraries(CelExtensions.optional(), CelExtensions.comprehensions())
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.setStandardMacros(CelStandardMacro.STANDARD_MACROS)
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.addVar("x", SimpleType.DYN)
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.build();
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private static final CelValidator CEL_VALIDATOR =
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CelValidatorFactory.standardCelValidatorBuilder(CEL)
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.addAstValidators(ComprehensionNestingLimitValidator.newInstance(1))
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.build();
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@Test
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public void comprehensionNestingLimit_populatesErrors(
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@TestParameter({
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"[1, 2, 3].map(x, [1, 2, 3].map(y, x + y))",
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"[1, 2, 3].map(x, [1, 2, 3].map(y, x + y).size() > 0, x)",
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"[1, 2, 3].all(x, [1, 2, 3].exists(y, x + y > 0))",
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"[1, 2, 3].map(x, {x: [1, 2, 3].map(y, x + y)})",
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"[1, 2, 3].exists(i, v, i < 3 && [1, 2, 3].all(j, v2, j < 3 && v2 > 0))",
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"{1: 2}.all(k, {2: 3}.all(k2, k != k2))"
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})
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String expr)
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throws Exception {
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CelAbstractSyntaxTree ast = CEL.compile(expr).getAst();
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CelValidationResult result = CEL_VALIDATOR.validate(ast);
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assertThat(result.hasError()).isTrue();
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assertThat(result.getAllIssues()).hasSize(1);
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assertThat(result.getAllIssues().get(0).getSeverity()).isEqualTo(Severity.ERROR);
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assertThat(result.getAllIssues().get(0).toDisplayString(ast.getSource()))
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.contains("comprehension nesting exceeds the configured limit: 1.");
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}
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@Test
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public void comprehensionNestingLimit_accumulatesErrors(
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@TestParameter({
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"[1, 2, 3].map(x, [1, 2, 3].map(y, [1, 2, 3].map(z, x + y + z)))",
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})
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String expr)
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throws Exception {
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CelAbstractSyntaxTree ast = CEL.compile(expr).getAst();
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CelValidationResult result = CEL_VALIDATOR.validate(ast);
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assertThat(result.hasError()).isTrue();
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assertThat(result.getAllIssues()).hasSize(2);
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}
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@Test
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public void comprehensionNestingLimit_limitConfigurable(
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@TestParameter({
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"[1, 2, 3].map(x, [1, 2, 3].map(y, x + y))",
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"[1, 2, 3].map(x, [1, 2, 3].map(y, x + y).size() > 0, x)",
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"[1, 2, 3].all(x, [1, 2, 3].exists(y, x + y > 0))",
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"[1, 2, 3].map(x, {x: [1, 2, 3].map(y, x + y)})",
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"[1, 2, 3].exists(i, v, i < 3 && [1, 2, 3].all(j, v2, j < 3 && v2 > 0))",
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"{1: 2}.all(k, {2: 3}.all(k2, k != k2))"
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})
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String expr)
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throws Exception {
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CelAbstractSyntaxTree ast = CEL.compile(expr).getAst();
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CelValidator celValidator =
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CelValidatorFactory.standardCelValidatorBuilder(CEL)
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.addAstValidators(ComprehensionNestingLimitValidator.newInstance(2))
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.build();
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CelValidationResult result = celValidator.validate(ast);
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assertThat(result.hasError()).isFalse();
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}
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@Test
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public void comprehensionNestingLimit_trivialLoopsDontCount(
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@TestParameter({
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"cel.bind(x, [1, 2].map(x, x + 1), x + [1, 2].map(x, x + 1))",
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"optional.of(1).optMap(x, [1, 2, 3].exists(y, y == x))",
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"[].map(x, [1, 2, 3].map(y, x + y))",
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"{}.map(k1, {1: 2, 3: 4}.map(k2, k1 + k2))",
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"[1, 2, 3].map(x, cel.bind(y, 2, x + y))",
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"[1, 2, 3].map(x, optional.of(1).optMap(y, x + y).orValue(0))",
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})
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String expr)
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throws Exception {
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CelAbstractSyntaxTree ast = CEL.compile(expr).getAst();
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CelValidationResult result = CEL_VALIDATOR.validate(ast);
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assertThat(result.hasError()).isFalse();
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}
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@Test
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public void comprehensionNestingLimit_zeroLimitAcceptedComprehenions(
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@TestParameter({
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"cel.bind(x, 1, x + 1)",
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"optional.of(1).optMap(x, x + 1)",
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"[].map(x, int(x))",
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"cel.bind(x, 1 + [].map(x, int(x)).size(), x + 1)"
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})
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String expr)
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throws Exception {
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CelAbstractSyntaxTree ast = CEL.compile(expr).getAst();
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CelValidator celValidator =
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CelValidatorFactory.standardCelValidatorBuilder(CEL)
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.addAstValidators(ComprehensionNestingLimitValidator.newInstance(0))
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.build();
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CelValidationResult result = celValidator.validate(ast);
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assertThat(result.hasError()).isFalse();
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}
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@Test
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public void comprehensionNestingLimit_zeroLimitRejectedComprehensions(
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@TestParameter({
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"[1].map(x, x)",
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"[1].exists(x, x > 0)",
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"[].exists(x, [1].all(y, y > 0))",
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})
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String expr)
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throws Exception {
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CelAbstractSyntaxTree ast = CEL.compile(expr).getAst();
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CelValidator celValidator =
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CelValidatorFactory.standardCelValidatorBuilder(CEL)
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.addAstValidators(ComprehensionNestingLimitValidator.newInstance(0))
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.build();
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CelValidationException e =
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assertThrows(CelValidationException.class, () -> celValidator.validate(ast).getAst());
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assertThat(e.getMessage()).contains("comprehension nesting exceeds the configured limit: 0.");
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}
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}

‎validator/validators/BUILD.bazel‎

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name = "ast_depth_limit_validator",
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exports = ["//validator/src/main/java/dev/cel/validator/validators:ast_depth_limit_validator"],
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)
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java_library(
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name = "comprehension_nesting_limit_validator",
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exports = ["//validator/src/main/java/dev/cel/validator/validators:comprehension_nesting_limit_validator"],
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)

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