GSN compatibility (#1880)

* switch to using Context internally

* add context import

* Add smoke test to make sure enabling GSN support works

* Update test/GSN/ERC721GSNRecipientMock.test.js

Co-Authored-By: Francisco Giordano <frangio.1@gmail.com>

* Upgrade truffle

* add missing awaits

* Revert "Upgrade truffle"

This reverts commit f9b0ba9019.

contracts/token/ERC721/ERC721.sol

@@ -1,5 +1,6 @@
 pragma solidity ^0.5.0;
 
+import "../../GSN/Context.sol";
 import "./IERC721.sol";
 import "./IERC721Receiver.sol";
 import "../../math/SafeMath.sol";
@@ -11,7 +12,7 @@ import "../../introspection/ERC165.sol";
  * @title ERC721 Non-Fungible Token Standard basic implementation
  * @dev see https://eips.ethereum.org/EIPS/eip-721
  */
-contract ERC721 is ERC165, IERC721 {
+contract ERC721 is Context, ERC165, IERC721 {
     using SafeMath for uint256;
     using Address for address;
     using Counters for Counters.Counter;
@@ -88,7 +89,7 @@ contract ERC721 is ERC165, IERC721 {
         address owner = ownerOf(tokenId);
         require(to != owner, "ERC721: approval to current owner");
 
-        require(msg.sender == owner || isApprovedForAll(owner, msg.sender),
+        require(_msgSender() == owner || isApprovedForAll(owner, _msgSender()),
             "ERC721: approve caller is not owner nor approved for all"
         );
 
@@ -115,10 +116,10 @@ contract ERC721 is ERC165, IERC721 {
      * @param approved representing the status of the approval to be set
      */
     function setApprovalForAll(address to, bool approved) public {
-        require(to != msg.sender, "ERC721: approve to caller");
+        require(to != _msgSender(), "ERC721: approve to caller");
 
-        _operatorApprovals[msg.sender][to] = approved;
-        emit ApprovalForAll(msg.sender, to, approved);
+        _operatorApprovals[_msgSender()][to] = approved;
+        emit ApprovalForAll(_msgSender(), to, approved);
     }
 
     /**
@@ -141,7 +142,7 @@ contract ERC721 is ERC165, IERC721 {
      */
     function transferFrom(address from, address to, uint256 tokenId) public {
         //solhint-disable-next-line max-line-length
-        require(_isApprovedOrOwner(msg.sender, tokenId), "ERC721: transfer caller is not owner nor approved");
+        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
 
         _transferFrom(from, to, tokenId);
     }
@@ -167,14 +168,14 @@ contract ERC721 is ERC165, IERC721 {
      * which is called upon a safe transfer, and return the magic value
      * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
      * the transfer is reverted.
-     * Requires the msg.sender to be the owner, approved, or operator
+     * Requires the _msgSender() to be the owner, approved, or operator
      * @param from current owner of the token
      * @param to address to receive the ownership of the given token ID
      * @param tokenId uint256 ID of the token to be transferred
      * @param _data bytes data to send along with a safe transfer check
      */
     function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public {
-        require(_isApprovedOrOwner(msg.sender, tokenId), "ERC721: transfer caller is not owner nor approved");
+        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
         _safeTransferFrom(from, to, tokenId, _data);
     }
 
@@ -330,7 +331,7 @@ contract ERC721 is ERC165, IERC721 {
             return true;
         }
 
-        bytes4 retval = IERC721Receiver(to).onERC721Received(msg.sender, from, tokenId, _data);
+        bytes4 retval = IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, _data);
         return (retval == _ERC721_RECEIVED);
     }
 

contracts/token/ERC721/ERC721Burnable.sol

@@ -1,19 +1,20 @@
 pragma solidity ^0.5.0;
 
+import "../../GSN/Context.sol";
 import "./ERC721.sol";
 
 /**
  * @title ERC721 Burnable Token
  * @dev ERC721 Token that can be irreversibly burned (destroyed).
  */
-contract ERC721Burnable is ERC721 {
+contract ERC721Burnable is Context, ERC721 {
     /**
      * @dev Burns a specific ERC721 token.
      * @param tokenId uint256 id of the ERC721 token to be burned.
      */
     function burn(uint256 tokenId) public {
         //solhint-disable-next-line max-line-length
-        require(_isApprovedOrOwner(msg.sender, tokenId), "ERC721Burnable: caller is not owner nor approved");
+        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721Burnable: caller is not owner nor approved");
         _burn(tokenId);
     }
 }

contracts/token/ERC721/ERC721Enumerable.sol

@@ -1,5 +1,6 @@
 pragma solidity ^0.5.0;
 
+import "../../GSN/Context.sol";
 import "./IERC721Enumerable.sol";
 import "./ERC721.sol";
 import "../../introspection/ERC165.sol";
@@ -8,7 +9,7 @@ import "../../introspection/ERC165.sol";
  * @title ERC-721 Non-Fungible Token with optional enumeration extension logic
  * @dev See https://eips.ethereum.org/EIPS/eip-721
  */
-contract ERC721Enumerable is ERC165, ERC721, IERC721Enumerable {
+contract ERC721Enumerable is Context, ERC165, ERC721, IERC721Enumerable {
     // Mapping from owner to list of owned token IDs
     mapping(address => uint256[]) private _ownedTokens;
 

contracts/token/ERC721/ERC721Metadata.sol

@@ -1,10 +1,11 @@
 pragma solidity ^0.5.0;
 
+import "../../GSN/Context.sol";
 import "./ERC721.sol";
 import "./IERC721Metadata.sol";
 import "../../introspection/ERC165.sol";
 
-contract ERC721Metadata is ERC165, ERC721, IERC721Metadata {
+contract ERC721Metadata is Context, ERC165, ERC721, IERC721Metadata {
     // Token name
     string private _name;