Add highly-branching MerkleProofTest

Author: Lucas MT

src/tests/integration/test-data/foundry-prove-all

@@ -139,6 +139,7 @@ LoopsTest.test_sum_100()
 LoopsTest.test_sum_1000()
 LoopsTest.testSumToN(uint256)
 LoopsTest.testSumToNBroken(uint256)
+MerkleProofTest.testValidateMerkleProof(bytes32,uint256,bytes32,bytes32,bytes32,bytes32)
 MethodDisambiguateTest.test_method_call()
 MockCallTest.testMockCall()
 MockCallTest.testMockCalls()

src/tests/integration/test-data/foundry-prove-skip

@@ -84,6 +84,7 @@ LoopsTest.test_sum_100()
 LoopsTest.test_sum_1000()
 LoopsTest.testSumToN(uint256)
 LoopsTest.testSumToNBroken(uint256)
+MerkleProofTest.testValidateMerkleProof(bytes32,uint256,bytes32,bytes32,bytes32,bytes32)
 MockCallTest.testMockCall()
 MockCallTest.testMockCalls()
 MockCallTest.testMockCallValue()

src/tests/integration/test-data/foundry/test/MerkleProofTest.t.sol

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity =0.8.13;
+
+import "forge-std/Test.sol";
+
+contract MerkleProofTest is Test {
+
+    /**
+     * The purpose of this test is to evaluate how well we handle branching.
+     * When we assume that _validateMerkleProof holds, the execution splits
+     * into 2 ** proof.length (in this case, 8) branches. We want to be able
+     * to handle this amount of branching without losing information, so we
+     * can still prove that it holds in the final assertTrue.
+     *
+     * Increase the length of the proof to evaluate scalability.
+     */
+    function testValidateMerkleProof(
+        bytes32 leaf,
+        uint256 index,
+        bytes32 root,
+        bytes32 proofElement0,
+        bytes32 proofElement1,
+        bytes32 proofElement2
+    ) external {
+        uint256 proofLength = 3;
+
+        bytes32[] memory proof = new bytes32[](proofLength);
+        proof[0] = proofElement0;
+        proof[1] = proofElement1;
+        proof[2] = proofElement2;
+
+        vm.assume(index < 2 ** proof.length);
+
+        vm.assume(_validateMerkleProof(leaf, index, root, proof));
+
+        assertTrue(_validateMerkleProof(leaf, index, root, proof));
+    }
+
+    /**
+     * Checks that the proof is valid for a Merkle tree with the given root
+     * where the given leaf is at the given index.
+     */
+    function _validateMerkleProof(
+        bytes32 leaf,
+        uint256 index,
+        bytes32 root,
+        bytes32[] memory proof
+    ) internal pure returns (bool) {
+        // Number of leaves is exponential on the tree depth
+        require(index < 2 ** proof.length);
+
+        bytes32 hash = leaf;
+
+        for (uint256 i; i < proof.length; i++) {
+            if (index % 2 == 0) {
+                // If index is even, proof element is to the right
+                hash = keccak256(abi.encodePacked(hash, proof[i]));
+            } else {
+                // If index is odd, proof element is to the left
+                hash = keccak256(abi.encodePacked(proof[i], hash));
+            }
+
+            // Go up one level in the tree
+            index = index / 2;
+        }
+
+        return hash == root;
+    }
+}