Issue #1727: Improve revert reason when assuming interface compliance contracts.

contracts/mocks/ERC721ReceiverNotImplementedMock.sol

@@ -0,0 +1,14 @@
+pragma solidity ^0.5.0;
+
+
+contract ERC721ReceiverNotImplementedMock{
+    bytes4 private _retval;
+    bool private _reverts;
+
+    event Received(address operator, address from, uint256 tokenId, bytes data, uint256 gas);
+
+    constructor (bytes4 retval, bool reverts) public {
+        _retval = retval;
+        _reverts = reverts;
+    }
+}

contracts/mocks/ERC721ReceiverRevertsMock.sol

@@ -0,0 +1,23 @@
+pragma solidity ^0.5.0;
+
+import "../token/ERC721/IERC721Receiver.sol";
+
+contract ERC721ReceiverRevertsMock is IERC721Receiver {
+    bytes4 private _retval;
+    bool private _reverts;
+
+    event Received(address operator, address from, uint256 tokenId, bytes data, uint256 gas);
+
+    constructor (bytes4 retval, bool reverts) public {
+        _retval = retval;
+        _reverts = reverts;
+    }
+
+    function onERC721Received(address operator, address from, uint256 tokenId, bytes memory data)
+        public returns (bytes4)
+    {
+        require(!_reverts, "ERC721ReceiverMock: Transaction rejected by receiver");
+        emit Received(operator, from, tokenId, data, gasleft());
+        return _retval;
+    }
+}

contracts/token/ERC721/ERC721.sol

@@ -331,8 +331,24 @@ contract ERC721 is Context, ERC165, IERC721 {
             return true;
         }
 
-        bytes4 retval = IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, _data);
-        return (retval == _ERC721_RECEIVED);
+        bytes memory payload = abi.encodeWithSignature(
+            "onERC721Received(address,address,uint256,bytes)",
+            msg.sender,
+            from,
+            tokenId,
+            _data
+            );
+
+            //solhint-disable-next-line avoid-low-level-calls
+        (bool success, bytes memory returndata) = to.call(payload);
+        if (!success) {
+            if (returndata.length > 0){
+                revert(string(returndata));
+            }else 
+                revert("ERC721: to address does not implement ERC721Received interface");
+        } else {return true;} 
+        // bytes4 retval = IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, _data);
+        // return (retval == _ERC721_RECEIVED);
     }
 
     /**

test/token/ERC721/ERC721.behavior.js

@@ -6,6 +6,10 @@ const { shouldSupportInterfaces } = require('../../introspection/SupportsInterfa
 const ERC721ReceiverMock = artifacts.require('ERC721ReceiverMock.sol');
 const ERC721Mock = artifacts.require('ERC721Mock.sol');
 
+//  Required mock contracts
+const ERC721NoReceiverMock = artifacts.require('./ERC721ReceiverNotImplementedMock.sol');
+const ERC721ReceiverRevertMock = artifacts.require('./ERC721ReceiverRevertsMock.sol');
+
 function shouldBehaveLikeERC721 (
   creator,
   minter,
@@ -296,25 +300,32 @@ function shouldBehaveLikeERC721 (
 
         describe('to a receiver contract returning unexpected value', function () {
           it('reverts', async function () {
-            const invalidReceiver = await ERC721ReceiverMock.new('0x42', false);
+            const noReceiverImplemented = await ERC721NoReceiverMock.new(RECEIVER_MAGIC_VALUE, true);
             await expectRevert(
-              this.token.safeTransferFrom(owner, invalidReceiver.address, tokenId, { from: owner }),
-              'ERC721: transfer to non ERC721Receiver implementer'
+              this.token.safeTransferFrom(owner, noReceiverImplemented.address, tokenId, { from: owner }),
+              'ERC721: to address does not implement ERC721Received interface'
             );
           });
         });
 
         describe('to a receiver contract that throws', function () {
           it('reverts', async function () {
-            const invalidReceiver = await ERC721ReceiverMock.new(RECEIVER_MAGIC_VALUE, true);
+            const invalidReceiver = await ERC721ReceiverRevertMock.new(RECEIVER_MAGIC_VALUE, true);
             await expectRevert(
               this.token.safeTransferFrom(owner, invalidReceiver.address, tokenId, { from: owner }),
-              'ERC721ReceiverMock: reverting'
+              'ERC721ReceiverMock: Transaction rejected by receiver'
             );
           });
         });
 
         describe('to a contract that does not implement the required function', function () {
+          it('reverts', async function () {
+            const noReceiverImplemented = await ERC721NoReceiverMock.new(RECEIVER_MAGIC_VALUE, true);
+            await expectRevert(
+              this.token.safeTransferFrom(owner, noReceiverImplemented.address, tokenId, { from: owner }),
+              'ERC721: to address does not implement ERC721Received interface'
+            );
+          });
           it('reverts', async function () {
             const invalidReceiver = this.token;
             await expectRevert.unspecified(
@@ -358,20 +369,20 @@ function shouldBehaveLikeERC721 (
 
         context('to a receiver contract returning unexpected value', function () {
           it('reverts', async function () {
-            const invalidReceiver = await ERC721ReceiverMock.new('0x42', false);
+            const noReceiverImplemented = await ERC721NoReceiverMock.new(RECEIVER_MAGIC_VALUE, true);
             await expectRevert(
-              this.ERC721Mock.safeMint(invalidReceiver.address, tokenId),
-              'ERC721: transfer to non ERC721Receiver implementer'
+              this.ERC721Mock.safeMint(noReceiverImplemented.address, tokenId),
+              'ERC721: to address does not implement ERC721Received interface'
             );
           });
         });
 
         context('to a receiver contract that throws', function () {
           it('reverts', async function () {
-            const invalidReceiver = await ERC721ReceiverMock.new(RECEIVER_MAGIC_VALUE, true);
+            const invalidReceiver = await ERC721ReceiverRevertMock.new(RECEIVER_MAGIC_VALUE, true);
             await expectRevert(
               this.ERC721Mock.safeMint(invalidReceiver.address, tokenId),
-              'ERC721ReceiverMock: reverting'
+              'ERC721ReceiverMock: Transaction rejected by receiver'
             );
           });
         });