Fix stipend-limited fallback bug

lib/parse.js

@@ -105,9 +105,15 @@ parse.ForStatement = function(contract, expression) {
 parse.FunctionDefinition = function(contract, expression) {
   parse.Modifiers(contract, expression.modifiers);
   if (expression.body) {
-    register.functionDeclaration(contract, expression);
+    // Skip fn & statement instrumentation for `receive` methods to
+    // minimize gas distortion
+    (expression.name === null && expression.isReceiveEther)
+      ? register.trackStatements = false
+      : register.functionDeclaration(contract, expression);
+
     parse[expression.body.type] &&
     parse[expression.body.type](contract, expression.body);
+    register.trackStatements = true;
   }
 };
 

lib/registrar.js

@@ -5,7 +5,11 @@
  */
 class Registrar {
 
-  constructor(){}
+  constructor(){
+    // Sometimes we don't want to inject statements
+    // because they're an unnecessary expense. ex: `receive`
+    this.trackStatements = true;
+  }
 
   /**
    * Adds injection point to injection points map
@@ -27,6 +31,8 @@ class Registrar {
    * @param  {Object} expression AST node
    */
   statement(contract, expression) {
+    if (!this.trackStatements) return;
+
     const startContract = contract.instrumented.slice(0, expression.range[0]);
     const startline = ( startContract.match(/\n/g) || [] ).length + 1;
     const startcol = expression.range[0] - startContract.lastIndexOf('\n') - 1;

test/integration/projects/solc-6/contracts/B_Wallet.sol

@@ -0,0 +1,24 @@
+pragma solidity ^0.6.0;
+
+contract B_Wallet {
+
+    event Deposit(address indexed _sender, uint _value, bytes data);
+
+    receive() external payable
+    {
+        if (msg.value > 0)
+            emit Deposit(msg.sender, msg.value, msg.data);
+    }
+
+    function transferPayment(uint payment, address payable recipient) public {
+        recipient.transfer(payment);
+    }
+
+    function sendPayment(uint payment, address payable recipient) public {
+        require(recipient.send(payment), 'sendPayment failed');
+    }
+
+    function getBalance() public view returns(uint){
+        return address(this).balance;
+    }
+}

test/integration/projects/solc-6/test/b_wallet.js

@@ -0,0 +1,30 @@
+const Wallet = artifacts.require('B_Wallet');
+
+contract('B_Wallet', accounts => {
+  it('should should allow transfers and sends', async () => {
+    const walletA = await Wallet.new();
+    const walletB = await Wallet.new();
+
+    await walletA.sendTransaction({
+      value: web3.utils.toBN(500), from: accounts[0],
+    });
+
+    await walletA.sendPayment(50, walletB.address, {
+      from: accounts[0],
+    });
+
+    await walletA.transferPayment(50, walletB.address, {
+      from: accounts[0],
+    });
+
+    // Also try transferring 0, for branch hit
+    await walletA.transferPayment(0, walletB.address, {
+      from: accounts[0],
+    });
+
+    // Throws invalid opcode if compiled w/ solc >= 0.5.14 & default EVM version
+    const balance = await walletB.getBalance();
+    assert.equal(balance.toNumber(), 100);
+  });
+});
+

test/units/buidler/standard.js

@@ -289,7 +289,12 @@ describe('Buidler Plugin: standard use cases', function() {
       {
         file: mock.pathToContract(buidlerConfig, 'ContractB.sol'),
         pct: 0,
-      }
+      },
+      {
+        file: mock.pathToContract(buidlerConfig, 'B_Wallet.sol'),
+        pct: 100,
+      },
+
     ];
 
     verify.lineCoverage(expected);