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| 1 | +// Copyright 2026 Google LLC |
| 2 | +// |
| 3 | +// Licensed under the Apache License, Version 2.0 (the "License"); |
| 4 | +// you may not use this file except in compliance with the License. |
| 5 | +// You may obtain a copy of the License at |
| 6 | +// |
| 7 | +// https://www.apache.org/licenses/LICENSE-2.0 |
| 8 | +// |
| 9 | +// Unless required by applicable law or agreed to in writing, software |
| 10 | +// distributed under the License is distributed on an "AS IS" BASIS, |
| 11 | +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 12 | +// See the License for the specific language governing permissions and |
| 13 | +// limitations under the License. |
| 14 | + |
| 15 | +package dev.cel.common.ast; |
| 16 | + |
| 17 | +import com.google.common.base.Preconditions; |
| 18 | +import com.google.common.collect.ImmutableList; |
| 19 | +import dev.cel.common.CelAbstractSyntaxTree; |
| 20 | +import dev.cel.common.annotations.Internal; |
| 21 | +import dev.cel.common.navigation.CelNavigableExpr; |
| 22 | +import java.util.Optional; |
| 23 | + |
| 24 | +/** |
| 25 | + * Represents a {@code cel.@block} expression. |
| 26 | + * |
| 27 | + * <p>CEL Block is used by the CSE (Common Subexpression Elimination) optimizer to hoist common |
| 28 | + * subexpressions into an evaluated block. |
| 29 | + */ |
| 30 | +@Internal |
| 31 | +public final class CelBlock { |
| 32 | + public static final String FUNCTION_NAME = "cel.@block"; |
| 33 | + public static final String INDEX_PREFIX = "@index"; |
| 34 | + |
| 35 | + private final CelExpr blockExpr; |
| 36 | + |
| 37 | + private CelBlock(CelExpr blockExpr) { |
| 38 | + this.blockExpr = blockExpr; |
| 39 | + } |
| 40 | + |
| 41 | + public ImmutableList<CelExpr> indices() { |
| 42 | + return blockExpr.call().args().get(0).list().elements(); |
| 43 | + } |
| 44 | + |
| 45 | + public CelExpr result() { |
| 46 | + return blockExpr.call().args().get(1); |
| 47 | + } |
| 48 | + |
| 49 | + public CelExpr expr() { |
| 50 | + return blockExpr; |
| 51 | + } |
| 52 | + |
| 53 | + /** |
| 54 | + * Extracts a {@link CelBlock} from the given AST. |
| 55 | + * |
| 56 | + * <p>Enforces the contract that {@code cel.@block} must only appear exactly once and at the root |
| 57 | + * of the AST. |
| 58 | + * |
| 59 | + * @throws IllegalArgumentException if the block is malformed or its indices are invalid. |
| 60 | + */ |
| 61 | + public static Optional<CelBlock> extract(CelAbstractSyntaxTree ast) { |
| 62 | + CelNavigableExpr celNavigableExpr = CelNavigableExpr.fromExpr(ast.getExpr()); |
| 63 | + |
| 64 | + ImmutableList<CelExpr> allCelBlocks = |
| 65 | + celNavigableExpr |
| 66 | + .allNodes() |
| 67 | + .map(CelNavigableExpr::expr) |
| 68 | + .filter(expr -> expr.callOrDefault().function().equals(FUNCTION_NAME)) |
| 69 | + .collect(ImmutableList.toImmutableList()); |
| 70 | + if (allCelBlocks.isEmpty()) { |
| 71 | + return Optional.empty(); |
| 72 | + } |
| 73 | + |
| 74 | + Preconditions.checkArgument( |
| 75 | + allCelBlocks.size() == 1, |
| 76 | + "Expected 1 cel.block function to be present but found %s", |
| 77 | + allCelBlocks.size()); |
| 78 | + Preconditions.checkArgument( |
| 79 | + celNavigableExpr.expr().equals(allCelBlocks.get(0)), |
| 80 | + "Expected cel.block to be present at root"); |
| 81 | + |
| 82 | + return Optional.of(fromExpr(allCelBlocks.get(0))); |
| 83 | + } |
| 84 | + |
| 85 | + /** |
| 86 | + * Constructs a {@link CelBlock} from a {@link CelExpr}. |
| 87 | + * |
| 88 | + * @throws IllegalArgumentException if the expression is not a valid block. |
| 89 | + */ |
| 90 | + public static CelBlock fromExpr(CelExpr expr) { |
| 91 | + Preconditions.checkArgument( |
| 92 | + expr.exprKind().getKind() == CelExpr.ExprKind.Kind.CALL, |
| 93 | + "Expected cel.@block to be a call expression"); |
| 94 | + Preconditions.checkArgument( |
| 95 | + expr.call().function().equals(FUNCTION_NAME), "Expected function to be cel.@block"); |
| 96 | + Preconditions.checkArgument( |
| 97 | + expr.call().args().size() == 2, "Expected exactly 2 arguments for cel.@block"); |
| 98 | + Preconditions.checkArgument( |
| 99 | + expr.call().args().get(0).exprKind().getKind() == CelExpr.ExprKind.Kind.LIST, |
| 100 | + "Expected first argument of cel.@block to be a list"); |
| 101 | + |
| 102 | + CelBlock block = new CelBlock(expr); |
| 103 | + |
| 104 | + // Assert correctness on block indices used in subexpressions |
| 105 | + ImmutableList<CelExpr> subexprs = block.indices(); |
| 106 | + for (int i = 0; i < subexprs.size(); i++) { |
| 107 | + verifyBlockIndex(subexprs.get(i), i, expr); |
| 108 | + } |
| 109 | + |
| 110 | + // Assert correctness on block indices used in block result |
| 111 | + CelExpr blockResult = block.result(); |
| 112 | + verifyBlockIndex(blockResult, subexprs.size(), expr); |
| 113 | + boolean resultHasAtLeastOneBlockIndex = |
| 114 | + CelNavigableExpr.fromExpr(blockResult) |
| 115 | + .allNodes() |
| 116 | + .map(CelNavigableExpr::expr) |
| 117 | + .anyMatch(e -> e.identOrDefault().name().startsWith(INDEX_PREFIX)); |
| 118 | + Preconditions.checkArgument( |
| 119 | + resultHasAtLeastOneBlockIndex, |
| 120 | + "Expected at least one reference of index in cel.block result"); |
| 121 | + |
| 122 | + return block; |
| 123 | + } |
| 124 | + |
| 125 | + private static void verifyBlockIndex(CelExpr celExpr, int maxIndexValue, CelExpr rootBlock) { |
| 126 | + boolean areAllIndicesValid = |
| 127 | + CelNavigableExpr.fromExpr(celExpr) |
| 128 | + .allNodes() |
| 129 | + .map(CelNavigableExpr::expr) |
| 130 | + .filter(expr -> expr.identOrDefault().name().startsWith(INDEX_PREFIX)) |
| 131 | + .map(CelExpr::ident) |
| 132 | + .allMatch( |
| 133 | + blockIdent -> |
| 134 | + Integer.parseInt(blockIdent.name().substring(INDEX_PREFIX.length())) |
| 135 | + < maxIndexValue); |
| 136 | + Preconditions.checkArgument( |
| 137 | + areAllIndicesValid, |
| 138 | + "Illegal block index found. The index value must be less than %s. Expr: %s", |
| 139 | + maxIndexValue, |
| 140 | + rootBlock); |
| 141 | + } |
| 142 | +} |
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